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Lower extremity stiffness: Implications for performance and injury
Abstract
Lower extremity stiffness is thought to be an important factor in musculoskeletal performance. However, too little or too much stiffness is believed to increase the risk of musculoskeletal injury.
To provide a current update of the lower extremity stiffness literature as it pertains to both performance and injury.
It appears that increased stiffness is beneficial to performance. As well it appears that there may be an optimal amount of stiffness that allows for injury-free performance. There is some evidence that increased stiffness may be related to bony injuries and decreased stiffness may be associated with soft tissue injuries. Further investigations should evaluate the relationship between stiffness and injury prospectively. Initial reports suggest that stiffness can be modified in response to the external environment or verbal cues.
A greater understanding of the role of stiffness in both performance and injury will provide a stronger foundation for the development of optimal training intervention programs.
... Stiffness and spatiotemporal variables were selected for this study as they result from complex interactions by the central nervous system and the musculoskeletal system, represent the response of the musculoskeletal system to the external environment and encompass the kinematic, kinetic and motor strategies for absorbing GRFs (Farley & González, 1996;Ferris & Farley, 1997;McMahon & Cheng, 1990). Greater knee stiffness has been associated with running-related injuries (Messier et al., 2018), possibly due to increased musculoskeletal loading on bony structures (Butler et al., 2003). However, insufficient stiffness may lead to excessive joint motion and a greater risk of soft tissue injuries (Butler et al., 2003). ...
... Greater knee stiffness has been associated with running-related injuries (Messier et al., 2018), possibly due to increased musculoskeletal loading on bony structures (Butler et al., 2003). However, insufficient stiffness may lead to excessive joint motion and a greater risk of soft tissue injuries (Butler et al., 2003). The potential for this non-linear relationship with stiffness and injury was observed in a previous study, but only weak or non-significant associations with injury were found (Davis & Gruber, 2021). ...
... For example, runners alter leg and joint stiffness when running at different speeds (Arampatzis et al., 1999;Brughelli & Cronin, 2008;Kuzmeski et al., 2021), on different surfaces (Ferris et al., 1998(Ferris et al., , 1999, when barefoot (Sinclair et al., 2016), or with minimalist, traditional or maximalist shoes (Borgia & Becker, 2019;Gruber et al., 2021). Changes in stiffness under various conditions may influence both performance and injury (Butler et al., 2003;Messier et al., 2018). The ability to adjust stiffness under various conditions may only develop with sufficient exposure to different running conditions, thus stiffness may be less adaptable in non-and less-experienced runners than more-experienced runners. ...
... Increased mechanical stiffness is believed to be a determinant element in athletic performances (Brughelli & Cronin, 2008a). This is observed in human movements such as running and jumping, where economical movements are advantageous to performance (Butler et al., 2003;Chelly & Denis, 2001;McMahon & Cheng, 1990). For example, having higher mechanical stiffness in the lower extremities can help create a more responsive and elastic stride. ...
... This enhanced mechanical stiffness reduces the energy requirement by minimising energy loss during the ground contact phase, thereby improving propulsion and running speed. Similarly, increased stiffness helps generate and transfer force quickly, enabling athletes to jump higher and further with minimal energy expenditure, thereby reducing the overall energy demand (Struzik et al., 2021) Mechanical stiffness can be measured and reported in three distinct ways: (i) vertical stiffness (Kvert), (ii) leg stiffness (Kleg) and (iii) joint stiffness (Kjoint) (Brughelli & Cronin, 2008a;Butler et al., 2003). Kvert describes the linear movement of the wholebody centre of mass (COM) in the vertical direction. ...
... Kjoint describes the resistance to change at the individual joint segments (hip, knee and ankle). However, within the literature, there are a range of approaches that have been used to quantify Kvert (four approaches), Kleg (three approaches) and Kjoint (two approaches) (Brughelli & Cronin, 2008a;Butler et al., 2003). In general, Kvert is defined as the ratio between peak vertical ground reaction force (GRF) and the displacement of the COM. ...
Mechanical stiffness, including vertical (Kvert), leg (Kleg), and joint (Kjoint) stiffness, is an important mechanical determinant associated with neuromuscular and athletic performances that influences force production and energy transformation. Strength and conditioning (S&C) coaches employ diverse training methods to improve athletes' mechanical stiffness. This systematic review and meta-analysis examined the effect of S&C interventions on mechanical stiffness. A comprehensive search across six electronic databases, including CINAHL, COCHRANE LIBRARY, MEDLINE, SCOPUS, SPORT DISCUSS, and WEB OF SCIENCE, identified 23 studies (40 intervention groups, 632 subjects) for the systematic review, with 12 studies (20 intervention groups, 420 subjects) included in the pre-post or/and control-intervention random effects meta-analysis. Plyometric or jump-related training had a significant and small effect on Kleg (SMD = 0.38; Z = 2.61, p = 0.009). When plyometrics training was combined with balance training, a significant and large effect on Kleg occurred (SMD = 0.80; Z = 2.93, p = 0.003). Resisted sprint training had a significant and large effect on Kleg (SMD = 0.80; Z = 6.07, p < 0.0001). These findings provide initial guidance for S&C coaches in designing programs to enhance mechanical stiffness. Future research directions are suggested to further explore the impact of S&C interventions on stiffness.
... This movement can be described within the framework of the stretch-shortening cycle (SSC), which is essential for developing sufficient lower-limb stiffness to store elastic energy and generate force during SSC activities (Komi, 2000;Brazier et al., 2019). Stiffness can be described as the resistance to deformation of an object in response to an applied force (Butler et al., 2003;Pruyn et al., 2014;Brazier et al., 2019). It arises from the interplay of muscles, tendons, ligaments, cartilage, and bones (Butler et al., 2003;Brughelli and Cronin, 2008). ...
... Stiffness can be described as the resistance to deformation of an object in response to an applied force (Butler et al., 2003;Pruyn et al., 2014;Brazier et al., 2019). It arises from the interplay of muscles, tendons, ligaments, cartilage, and bones (Butler et al., 2003;Brughelli and Cronin, 2008). Previous badminton research on stiffness has predominantly focused on footwear (Oleson et al., 2005;Luo et al., 2009;Park et al., 2017;Yu et al., 2023), leaving joint stiffness during lunging movements relatively underexplored. ...
... The lunge can be described within the framework of the stretchshortening cycle (SSC), which is essential for developing sufficient lower-limb stiffness to store elastic energy and generate force during SSC activities (Komi, 2000;Brazier et al., 2019). Stiffness can be described as the resistance to deformation of an object in response to an applied force (Butler et al., 2003;Pruyn et al., 2014;Brazier et al., 2019). The ability to generate higher stiffness in the lower limb benefits movements (Maloney and Fletcher, 2021), like maximumvelocity running (Bret et al., 2002) or changes in direction (Serpell et al., 2014). ...
Background
Forehand and backhand forward lunges are frequently performed in badminton, placing significant demands on the lower limbs. The purpose of this study was to examine the differences in lower limb biomechanics between these two lunge types in female amateur players.
Methods
This study involved 17 female amateur badminton players performing forehand and backhand forward lunges. Lower limb kinematics and dynamics were recorded using an eight-camera Vicon motion capture system and two AMTI force plates. Variables such as joint angle, range of motion, stiffness, and ground reaction forces measured during the stance phase were analyzed using paired t-tests. To account for the one-dimensional nature of joint angles, moments, and ground reaction forces, the analysis was performed using paired sample t-tests in Statistical Parametric Mapping 1D.
Results
The forehand lunge exhibited a smaller hip flexion angle, greater hip internal rotation angle, and increased hip stiffness compared to the backhand lunge. The backhand lunge, in contrast, demonstrated a higher ankle varus angle and greater transverse plane hip range of motion. SPM1D analysis revealed significant differences in both the early (0%–10%) and late (80%–100%) phases of the stance phase. In the early phase, the backhand lunge showed a larger internal rotation moment at the hip, an external rotation moment at the knee, and a smaller knee extension moment. In the late phase, the forehand lunge revealed greater internal rotation moments at the hip, external rotation moments at the knee, ankle valgus moments, and smaller knee flexion moments.
Conclusion
The backhand lunge requires greater hip internal rotation than the forehand lunge. Additionally, it is associated with higher ankle varus angles, which may increase the risk of ankle injuries. In contrast, the forehand lunge demonstrates greater hip stiffness, potentially reflecting an adaptation of the lower limb to varying directional demands. These findings emphasize the importance of incorporating targeted ankle and hip training exercises into conditioning programs.
... Stiffness pertains to both injury and performance (Butler et al., 2003). It is defined as the relationship between an applied load and the elastic deformation of a biological structure (Ditroilo et al., 2012). ...
... It is defined as the relationship between an applied load and the elastic deformation of a biological structure (Ditroilo et al., 2012). When it comes to the human body, stiffness can be described from the level of a single muscle fibre to the entire body, which is modelled as a mass and spring (Farley and Gonzalez, 1996;Butler et al., 2003). Muscular contraction adds complexity to stiffness characteristics as it creates a link between neuromuscular function and the mechanical properties of the structures (Latash and Zatsiorsky, 1993). ...
... Stiffness is essential in sports performance and injury prevention. Within a certain range, high levels of lower-limb stiffness have been positively correlated with performance metrics like jump height, sprint speed, and efficient force transfer due to reduced ground contact time and greater force output (Butler, et al., 2003). These adaptations contribute to greater movement economy and faster response in high-intensity sports settings, potentially enhancing an athlete's velocity and explosiveness (Brazier et al., 2019). ...
Purpose
Higher stiffenss is expected to augment performance by increasing the utilisation of elastic energy. However, excessive lower extremity stiffness increases the risk of bony injuries; while insufficient stiffness is associated with a higher likelihood of soft tissue injuries. Thus, there might be an ‘optimal’ stiffness value or range that allows for maximising athletic performance while simultaneously minimising risk of sports injury. Basketball players can be classified by position as centres, guards and forwards, with each position characterised by specific injury risks and exercise patterns. Therefore, this study aims to establish normative data for lower extremity stiffness characteristics of players in the Women’s Chinese Basketball Association (WCBA) and compare the characteristics based on position.
Methods
A total of 124 WCBA athletes (over 70% of the WCBA teams) were recruited for this study, including 63 forwards, 22 centres and 39 guards. Stiffness was evaluated before and during the 2020–2021 WCBA season, which was averaged for data analysis. Quasi-static stiffness measurements of muscles and tendons were collected via a handheld myometer on seven sites of each leg. Vertical stiffness was also evaluated by OptoGait system.
Results
Descriptive statistics were used to establish the normative values of stiffness for forwards, centres and guards. The Kruskal Wallis test and post hoc Bonferroni pairwise comparisons found significant higher stiffness of the left patellar tendon (PT) in guards than centres (p = 0.004) and in guards than forwards (p = 0.012), right PT stiffness in guards than centres (p = 0.016) and in guards than forwards (p = 0.017), mean PT stiffness in guards than centres (p = 0.003) and in guards than forwards (p = 0.008); stiffness of the right soleus (SOL) in guards than forwards (p = 0.033), stiffness of the left biceps femoris (BF) in forwards than centres (p = 0.049) and in guards than centres (p = 0.038); and stiffness of the left vertical stiffness (hopping) in forwards than centres (p = 0.041).
Conclusion
Forwards, centres and guards were characterised by significantly different stiffness values, which could be utilised for improvement of athletic performance and injury prevention.
... Stiffness is commonly used as a variable to explain differences in neuromuscular function and performance (Butler et al., 2003;Latash & Zatsiorsky, 1993;Maloney & Fletcher, 2021). Stiffness describes a material´s ability to resist deformation in response to loading (Latash & Zatsiorsky, 1993) and in human biomechanical studies is a result of the combined stiffness in different tissues (muscles, tendon, ligaments, cartilage and bones) loaded during a specific movement (Latash & Zatsiorsky, 1993). ...
... Although high stiffness facilitates greater energy return and increased performance, sufficient shock absorption is needed to avoid injury. Therefore, high stiffness may also increase the risk of injury (Butler et al., 2003) and some authors have also suggested that stiffness can be used to assess neuromuscular readiness for return to sport after injury (Jordan et al., 2015(Jordan et al., , 2018. Quantifying stiffness therefore appears relevant in an athletic population due to its importance for performance and potential for injury prevention. ...
... Lower limb stiffness (k LLS ) (also called vertical stiffness) is derived by calculating the vertical displacement of the COM in response to a vertical ground reaction force (GRF z ) during tasks performed in the sagittal plane (Latash & Zatsiorsky, 1993), Joint stiffness (k JOINT ) is derived from the change in angular displacement (θ) in response to the moment (τ) acting about the joint , Leg stiffness (k LEG ) is derived from the compression of a leg (L LEG ) modelled as a spring response to a force (F) (T. A. McMahon & Cheng, 1990), Further details describing different methods of measuring stiffness are provided in two review articles investigating the topic (Butler et al., 2003;Maloney & Fletcher, 2021). Beyond the aforementioned approaches, alternative methodologies accounting for the three-dimensional complexity of human motion have been introduced. ...
Introduction: Stiffness (k) describes a material’s resistance to deformation and is useful for understanding neuromuscular function, performance, and injury risk. The aim of this study is to compare the lower limb stiffness method (kLLS), which uses only force plate data, with methods combining force plate and motion capture data to calculate stiffness during the eccentric phase of a countermovement. Material and Methods: Twelve resistance-trained males: age 24.9 (4.4) years, height 1.81 (0.05) m, weight 88.2 (14) kg) performed three maximal effort countermovement jumps (CMJ). Data were collected synchronously using three-dimensional (3D) kinematic and kinetic data (dual force plate setup). Lower limb stiffness (z), joint stiffness (x, y, and z), and leg stiffness (linear, sagittal plane, and 3D) were calculated for the eccentric phase of all CMs. Results: kLLS showed high concurrent validity with strong correlations to kinetic-kinematic methods (r = 0.90-0.97, p < 0.05). A linear mixed model revealed no significant differences in k-values between kLLS and leg stiffness, indicating high concurrent validity. Discussion: kLLS offers valid and valuable information affecting performance, injury risk, and return-to-sport decisions. Conclusion: The findings suggest that kLLS is a valid method for calculating stiffness in CMJs and equal to 3D leg stiffness.
... Whereas lower extremity stiffness is considered to be a key factor in optimizing running, jumping, and hopping activities, too much stiffness has been associated with reduced joint motion, a decreased ability to absorb forces, and bony injury. 4,15,17,72 On the other side of the continuum, too much compliance has been linked to an increased risk for soft tissue injury and muscle strain. 11,12,71 Therefore, there appears to be an optimal level of muscle stiffness for athletes that allows them to maximize performance and minimize injury. ...
... 49,50,53,54,61 Of specific interest are measures that have been identified as risk factors in athletes and clinical patterns that have been identified by experienced practitioners. 15,24,46,64,70 Lower extremity mobility and flexibility in basketball athletes influences performance and risk of lower quarter injury. These factors may be related to a less-than-optimal degree of stiffness and/or compliance. ...
... Stiffness has been described as the resistance of a structure to deform in response to an applied force. 15,37,52 Athletic performance in tasks associated with sports, such as hopping, jumping, running, and change of direction, have been shown to be influenced by global stiffness characteristics of the lower extremity. Compliance is viewed as the inverse of stiffness and is found on the other end of the structural deformity continuum. ...
Background
Musculoskeletal injuries are prevalent in the NBA and are associated with a significant number of games missed. There is a lack of reference data for clinical measures in NBA players, making it difficult for sports medicine professionals to set goals and develop programs.
Hypothesis
Values for clinical measures in NBA players will differ from those of the general population but will not differ between dominant (D) and nondominant (ND) limbs.
Study Design
Descriptive laboratory study.
Level of Evidence
Level 3.
Methods
Clinical measures were taken on 325 players invited to NBA training camp (2008-2022). Measures included range of motion for great toe extension, hip rotation, weightbearing ankle dorsiflexion, flexibility, arch height (AH) indices, and tibial varum.
Results
Clinical values for NBA players differ from reference norms of the general population. Results for NBA players include great toe extension (D, 40.4°; ND, 39.3°), 90/90 hamstring (D, 41.5°; ND, 40.9°), hip internal rotation (D, 29.0°; ND, 28.8°), hip external rotation (D, 29.7°; ND, 30.9°), total hip rotation (D, 60.2°; ND, 60.4°), Ely (D, 109.9°; ND, 108.8°), AH difference (D, 0.5 mm; ND, 0.5 mm), AH index (D, 0.310; ND, 0.307), arch stiffness (D, 0.024; ND, 0.024), arch rigidity (D, 0.924; ND, 0.925), tibial varum (D, 4.6°; ND, 4.5°), and weightbearing ankle dorsiflexion (D, 35.4°; ND, 35.6°). Descriptive statistics are presented; 2-tailed paired t tests show that, whereas most measures demonstrated differences between sides, the results were not statistically significant.
Conclusion
Clinical measures of NBA players differ from those reported for the general population and athletes of other sports although there were no statistically significant differences between D and ND limbs.
Clinical Relevance
Establishing a reference database may help clinicians develop more sensitive and more effective preseason and return-to-play screening processes, aiding the management of player orthopaedic care and reducing injury risk.
... An increase in passive stiffness of the quadriceps, characterised by reduced compliance [11], may contribute to a high level of sagittal knee dynamic knee stiffness (DJS) [12,13]. It reflects the collective biomechanical effects of active and passive knee structures on dynamic knee angular-joint stiffness and is identified as knee joint "quasi-stiffness" [12,14], representing the collective resistance applied onto the knee joint during dynamic motions [15]. Whether quadriceps strength and stiffness would be associated with DJS have not been established. ...
... In addition, a prospective study from Chang et al. (2017) found that higher sagittal knee DJS during the loading response phase of gait was associated with the worsening of cartilage damage over a period of 2 years in knee OA patients [13]. Greater sagittal knee DJS may restrict sagittal knee motion concentrating load to a smaller knee joint surface [14,15], thus may contribute to the development of knee OA. Hence, it is important to investigate whether DJS would predict the incidence of knee OA, and its potential mediation role in the relationship between quadriceps properties and knee OA onset. ...
... An elevated DJS reflects increased collective resistance from muscles and soft tissues for dynamic knee motions (a "quasi-stiffer" knee joint) during dynamic motions [15]. Greater sagittal knee DJS could potentially limit the range of motion in the knee, thereby concentrating stress on a reduced surface area of the joint [14,15], potentially contributing to the development of knee OA. ...
Background
Decreased strength and increased stiffness of the quadriceps have been associated with a higher risk of developing knee osteoarthritis (OA) in elders. Dynamic joint stiffness (DJS) represents collective resistance from active and passive knee structures for dynamic knee motions. Elevated sagittal knee DJS has been associated with worsening of cartilage loss in knee OA patients. Altered quadriceps properties may affect DJS, which could be a mediator for associations between quadriceps properties and knee OA. Hence, this study aimed to examine whether DJS and quadriceps properties would be associated with the development of clinical knee OA over 24 months, and to explore the mediation role of DJS in associations between quadriceps properties and knee OA.
Methods
This was a prospective cohort study with 162 healthy community-dwelling elders. Gait analysis was conducted to compute DJS during the loading response phase. Quadriceps strength and stiffness were evaluated using a Cybex dynamometer and shear-wave ultrasound elastography, respectively. Knee OA was defined based on clinical criteria 24 months later. Logistic regression with generalized estimating equations was used to examine the association between quadriceps properties and DJS and incident knee OA. Mediation analysis was performed to explore the mediation role of DJS in associations between quadriceps properties and the incidence of knee OA.
Results
A total of 125 participants (65.6 ± 4.0 years, 58.4% females) completed the 24-month follow-up, with 36 out of 250 knees identified as clinical knee OA. Higher DJS (OR = 1.86, 95%CI: 1.33–2.62), lower quadriceps strength (1.85, 1.05–3.23), and greater quadriceps stiffness (1.56, 1.10–2.21) were significantly associated with a higher risk of clinical knee OA. Mediation analysis showed that the DJS was not a significant mediator for the associations between quadriceps properties and knee OA.
Conclusions
Higher sagittal knee dynamic joint stiffness, lower quadriceps strength, and greater quadriceps stiffness are potential risk factors for developing clinical knee OA in asymptomatic elders. Associations between quadriceps properties and knee OA may not be mediated by dynamic joint stiffness. Interventions for reducing increased passive properties of the quadriceps and knee joint stiffness may be beneficial for maintaining healthy knees in the aging population.
... Typically, alterations in lower limb joint kinematics influence kinetic data during single-leg landings. Lower limb stiffness, a crucial kinetic parameter, is usually classified into joint stiffness, vertical stiffness, and leg stiffness based on various classification and calculation methods [31]. Joint stiffness parameters integrate kinematic and kinetic data to illustrate how applied forces impact changes in joint movement patterns. ...
... In this research, the increased neuromuscular control of the lower limb in CAIBP coincided with increased peak knee and ankle moments and stiffness. Lower extremity joint stiffness is highly correlated with athletic performance and sports injuries and is an expression of dynamic outcomes [31,75]. Players utilize changes in the lower extremity joints to meet the demands of their sport in order to regulate the loads on the lower extremity joints caused by ground reaction forces. ...
Background: Ankle sprains are very common in badminton, and chronic ankle instability (CAI) often develops in players after these injuries. CAI badminton players (CAIBP) are more susceptible to injuries during high-intensity tasks, such as jumping landings, due to decreased ankle stability. This study aims to explore the variations in lower limb biomechanics between CAIBP and normal badminton players (NBP) during single-leg medial landing tasks. Methods: Sixteen CAIBP and sixteen NBP university badminton players volunteered to participate in this experiment. The study used OpenSim open-source software to simulate and calculate lower limb joint angles, moments, and joint stiffness for the CAI group and healthy controls during a single-leg medial landing task, and utilized Delsys EMG to assess muscle pre-activation and activation levels. Independent samples t-tests and one-dimensional statistical parametric mapping were used to analyze the experimental results. Results: In terms of kinematics, before and after initial contact (IC) during landing, CAIBP showed significantly greater hip adduction and flexion angles than NBP (p < 0.001). Pre-IC, CAIBP exhibited less knee flexion (p = 0.004). Both pre- and post-IC, CAIBP exhibited significantly greater dorsiflexion angles (p = 0.045) and inversion angles (p < 0.001). In terms of muscle activation and dynamics, pre-IC, CAIBP had significantly less pre-activation of the peroneus longus than NBP (p = 0.007), and significantly more gastrocnemius lateral (p = 0.021) and gastrocnemius medial (p < 0.001) pre-activation. Post-IC, CAIBP had significantly greater muscle activation of the tibialis anterior (p < 0.001). Post-IC, peak knee extension moments (p = 0.012) and peak ankle plantarflexion moments (p = 0.001) were significantly greater in CAIBP than in NBP. In addition, CAIBP reported significantly higher knee stiffness (p = 0.001) and ankle stiffness (p < 0.001). Conclusions: During the medial landing task, CAIBP exhibited increased hip adduction and flexion, altered sagittal plane motion of the ankle, and increased activation of certain lower extremity muscles compared to NBP. Although these altered landing mechanisms contribute to enhanced stability during landing to some extent, they may also increase the potential risk of knee injury.
... As shown in Figure 1, data analysis was conducted using the first five successful serves [32]. This study selected kinematic and dynamic indicators for the three joints of the lower limb in the sagittal, coronal, and horizontal planes [33], including ROM in degrees ( • ), moment and peak moment in Nm/kg, and stiffness in Nm/kg • , which was calculated using the formula shown below [20]: had completed a full dynamic warm-up (DWU) [31], consisting of 4-5 min of self-directed general warm-up, 6-8 min of dynamic stretching, 10 min of tennis-specific high-intensity exercises, and 3 rounds of explosive movements with a 15 s rest between each round, a platform-style serve was simulated on the force platform, ensuring that the subject applied the same magnitude of force for each serve as they had for the first one. As shown in Figure 1, data analysis was conducted using the first five successful serves [32]. ...
... As shown in Figure 1, data analysis was conducted using the first five successful serves [32]. This study selected kinematic and dynamic indicators for the three joints of the lower limb in the sagittal, coronal, and horizontal planes [33], including ROM in degrees (°), moment and peak moment in Nm/kg, and stiffness in Nm/kg°, which was calculated using the formula shown below [20]: ...
The kinematic and kinetic performance of tennis players differs across skill levels, with joint range of motion (ROM), moments, and stiffness being strongly linked to injury risk. Focusing on the biomechanical characteristics of lower-limb joints throughout the landing stage, especially among athletes of different skill levels, aids in understanding the link between injury risk and performance level. This study recruited 15 male campus tennis enthusiasts and 15 male professional tennis players. The kinematic and kinetic differences between amateur and professional players during the landing phase of the tennis serve were analyzed using SPM1D 0.4.11 and SPSS 27.0.1, with independent-sample t-tests applied in both cases. Throughout the tennis serve’s landing stage, the professional group exhibited significantly greater sagittal plane hip-joint stiffness (p < 0.001), horizontal plane moment (59~91%; p = 0.036), and a significantly higher peak moment (p = 0.029) in comparison with the amateur group. For the knee joint, the professional group exhibited significantly larger ROM in flexion–extension (0~82%; p = 0.003); along with greater ROM (0~29%; p = 0.042), moment (12~100%; p < 0.001), peak moment (p < 0.001) in adduction-abduction; and internal–external rotational moments (19~100%; p < 0.001) were markedly higher. The professional group showed significantly higher ankle joint ROM (p < 0.001) and moments (6~74%; p = 0.004) in the sagittal plane, as well as greater horizontal-plane ROM (27~67%; p = 0.041) and peak moments (p < 0.001). Compared with amateur tennis players, professional tennis players exhibit greater ROM, joint moments, and stiffness in specific planes, potentially increasing their risk of injury during the landing phase.
... IMUs are wearable devices integrating accelerometers, gyroscopes, and magnetic sensors to measure motion-related parameters, such as angular velocity, linear acceleration, and orientation, through sensor fusion algorithms [1]. These devices provide a real-time, comprehensive view of training loads and physiological responses in ecological environments [2]. The use of IMUs, combined with other wearable sensors (e.g., Global Positioning System, GPS), is increasingly becoming a staple in athlete monitoring [3], particularly for elite team sports such as football, where maintaining peak performance and minimizing injuries is critical. ...
... Among these metrics, vertical stiffness (K vert ) is a key biomechanical parameter reflecting the body's ability to store and release elastic energy during dynamic activities. Adequate vertical stiffness is associated with running efficiency [22], minimizing energy expenditure [23] while maximizing elastic energy return, which ultimately supports improved athletic performance [2,[24][25][26]. Conversely, reduced stiffness can indicate fatigue, suboptimal running mechanics, or increased injury risk. ...
Featured Application
This work investigates the relationship between the acute:chronic workload ratio (ACWR) and specific running parameters in elite football players.
Abstract
In contemporary sports science, the integration of wearable inertial measurement units (IMUs) has revolutionized athlete performance monitoring, offering insights into training load management and injury risk mitigation. The acute:chronic workload ratio (ACWR) has emerged as a pivotal metric, indicating the balance between acute training stress and chronic adaptation. This study investigates the relationship between ACWR and running parameters, i.e., contact time (CT), flight time (FT), and vertical stiffness (Kvert). Data from thirty-five elite male soccer players were analyzed using the WIMU Pro system. Statistical analyses showed that CT increased with workload, with significant differences observed between athletes in the sweet spot and others in the danger zone (p < 0.05), and effect sizes (Cohen’s d) ranging from 0.28 to 0.37. Kvert values were consistently lower in athletes in the danger zone across all workload indicators (p < 0.001), with large effect sizes going up to 0.94. Conversely, FT showed no significant variation between ACWR groups. These findings suggest that elevated ACWRs may be linked to reductions in vertical stiffness, highlighting a potential increase in risk of injury. Coaches and practitioners can utilize these insights to tailor training programs, integrating load monitoring with tactical considerations to optimize athlete performance. Understanding the nuanced interplay between workload ratios and biomechanical parameters provides valuable insights for performance optimization for elite football athletes.
... In physics and engineering, stiffness is defined as the ratio between the applied force and the strain induced in a structure. In biomechanics, the term "elastic stiffness" is used [15]. This term differs from the sometimes-used term "elasticity" and is connected to the dampening effect of a tissue, such as the elasticity of the skin [15]. ...
... In biomechanics, the term "elastic stiffness" is used [15]. This term differs from the sometimes-used term "elasticity" and is connected to the dampening effect of a tissue, such as the elasticity of the skin [15]. Passive stiffness is related to myofascial tissue-muscles, fascias, and tendons. ...
Objectives: This study aimed to evaluate the immediate effect of Game Ready (GR) heat–cold compression contrast therapy (HCCT) on changes in the biomechanical parameters of the quadriceps femoris muscles and tissue perfusion. Methods: Fifteen male MMA fighters were subjected to HCCT on the dominant leg’s thigh and control sham therapy on the other. The experimental intervention used a pressure cuff with the following parameters: time—20 min; pressure—25–75 mmHg; and temp.—3–45°C, changing every 2 min. For the control group, the temp. of sham therapy was 15–36 °C, and pressure was 15–25 mmHg, changing every 2 min. Measurements were taken on the head of the rectus femoris muscle (RF) 5 min before therapy, 5 min after, and 1 h after therapy in the same order in all participants: microcirculatory response (PU), muscle tension (MT), stiffness (S), flexibility (E), tissue temperature (°C), and pressure pain threshold (PPT). Results: The analysis revealed significant differences between the HCCT and sham therapy groups and the measurement time (rest vs. post 5 min and post 1 h) for PU, MT, E, and °C (p < 0.00001) (a significant effect of time was found) in response to GR therapy. No significant differences were found for the PPT. Conclusions: The results of this study prove that GR HCCT evokes changes in the biomechanical parameters of the RF muscles and perfusion in professional MMA fighters.
... It is well known that muscle stiffness can follow musculoskeletal injury and can also affect athletic performance. For example, it has been shown that there is an optimal level of stiffness that improves running performance (Butler et al., 2003). However, high levels of muscle stiffness increases the likelihood of soft tissue injury (Butler et al., 2003;Kawai et al., 2021) and musculoskeletal pain disorders (Dieterich et al., 2020;Heredia-Rizo et al., 2020;Lo et al., 2019;Rätsep and Asser, 2017;Taş et al., 2018). ...
... For example, it has been shown that there is an optimal level of stiffness that improves running performance (Butler et al., 2003). However, high levels of muscle stiffness increases the likelihood of soft tissue injury (Butler et al., 2003;Kawai et al., 2021) and musculoskeletal pain disorders (Dieterich et al., 2020;Heredia-Rizo et al., 2020;Lo et al., 2019;Rätsep and Asser, 2017;Taş et al., 2018). Studies have also shown that increased muscle stiffness reduces the pain pressure threshold in a muscle (De Meulemeester et al., 2017;Sánchez-Infante et al., 2021); that is, a person with greater muscle stiffness reports more pain when manual pressure is applied directly to the muscle. ...
... 17 In the human body, stiffness can be described from the level of a single muscle fiber to the entire body, which has been modeled as mass and spring. 18 Common measurements of stiffness in the active population include muscle stiffness, tendon stiffness, and vertical stiffness (K vert ). 19,20 The stiffness of the muscles and tendons is typically measured using handheld dynamometers (MyotonPRO, Myoton AS, Tallinn, Estonia). ...
... The athletes jogged 6.1 m, then they started Exercise 1 in the next 6.1 m, and jogged the rest 6.1 m. Thereafter, the athletes completed the rest of the warm-up exercises (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) consecutively. Exercises 20-22 were performed in the badminton half-court with a loaded vest (Load Vest, PROIRON, Shanghai, China) (See below figure). ...
This study investigated whether lower extremity stiffness plays a role in the enhancement of change of direction speed (CODS) and the duration of this enhancement after dynamic loaded warm-up (DLWU). Fifteen badminton athletes underwent DLWU, and CODS, individual muscle and tendon stiffness, and vertical stiffness were measured before DLWU and 6, 12, and 18 min after DLWU. The data were analyzed using ANOVA and covariance analysis. Significant improvements in CODS were found at 6, 12, and 18 min post-DLWU compared to pre-DLWU (p < 0.05). The Achilles tendon stiffness of the dominant leg increased at 6 min (p = 0.039) and 18 min (p = 0.024) post-DLWU compared to pre-DLWU. Achilles tendon stiffness of the dominant leg had a significant effect on improving CODS (p > 0.05). CODS improvement lasted up to 18 min after DLWU in badminton athletes, potentially related to increased Achilles tendon stiffness of the dominant leg.
... The concept of stiffness is derived from Hooke's law, which can be described as the ability of objects to resist deformation under external forces (1,2). Higher stiffness results in lower strain, while lower stiffness results in higher strain. ...
... While optimal stiffness may be necessary for performance, injury may result from either too high or too low stiffness (1). Higher stiffness leads to an increased risk of injury, which may be due to increased impulse and peak forces during exercise as well as reduced joint movement in the lower limbs (11). ...
Background
Vertical stiffness (Kvert) can be used to evaluate sports performance and injury risk in players. The My Jump 2 smartphone application (App), is increasingly being used by researchers, coaches, and players in the competitive sports field. We aimed to analyze the reliability and concurrent validity of the My Jump 2 app for measuring Kvert in male college players.
Methods
Twenty male college players (10 soccer players, 10 basketball players; age, 20.2 ± 1.3 years old; weight, 76.4 ± 6.0 kg; height, 178.3 ± 4.7 cm) volunteered to take part in this study. Three drop jumps were performed by participants from 30 cm to 40 cm on a force platform and retested after three days. All the jumps were recorded by both the Force platform and the My Jump 2 app. Data obtained from the above two devices were compared using the paired t tests, intraclass correlation coefficient (ICC), coefficient of variation (CV), Pearson product moment correlation coefficient (r), Bland-Altman plots, and one-way regression.
Results
There was almost perfect agreement between measurement instruments for the Kvert value (ICC > 0.972, 95% CI = 0.954–0.992, P < 0.01). Almost perfect agreement was observed between evaluators (ICC > 0.989, 95% CI = 0.981–0.997, P < 0.05). Also, the My Jump 2 app showed excellent intra-rater reliability in all participants (ICC = 1.000, 95% CI = 1.000–1.000, P < 0.001). The My Jump 2 showed good variability when measuring Kvert at T1 30 cm (CV = 5.4%), T1 40 cm (CV = 6.7%), T2 30 cm (CV = 5.0%), and T2 40 cm (CV = 10.3%). The test-retest reliability of My Jump 2 was moderate to good at 30 cm (ICC = 0.708, 95% CI = 0.509–0.827); however, it was lower to moderate at 40 cm (ICC = 0.445, 95% CI = 0.222–0.625). Very large correlations were observed between the force platform and the My Jump 2 for Kvert (r > 0.9655, P < 0.001).
Conclusion
The My Jump 2 smartphone application showed excellent reliability and intra-rater consistency in measuring Kvert in male college players. While demonstrating excellent intra-rater consistency and strong agreement with force platform measurements, it showed slightly lower reliability at higher jump heights. Overall, the My Jump 2 app is a valid tool for evaluating Kvert in college players with careful consideration of its limitations, particularly at higher jump heights.
... 17 In the human body, stiffness can be described from the level of a single muscle fiber to the entire body, which has been modeled as mass and spring. 18 Common measurements of stiffness in the active population include muscle stiffness, tendon stiffness, and vertical stiffness (K vert ). 19,20 The stiffness of the muscles and tendons is typically measured using handheld dynamometers (MyotonPRO, Myoton AS, Tallinn, Estonia). ...
... The athletes jogged 6.1 m, then they started Exercise 1 in the next 6.1 m, and jogged the rest 6.1 m. Thereafter, the athletes completed the rest of the warm-up exercises (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) consecutively. Exercises 20-22 were performed in the badminton half-court with a loaded vest (Load Vest, PROIRON, Shanghai, China) (See below figure). ...
... Additionally, no previous work has focused on the effects of an external focus of attention on measures of lower extremity stiffness. Stiffness is a measure of how compliant the lower extremities are, which serves to absorb external forces during running [25]. Several studies have demonstrated that a runner's leg and knee stiffness are closely associated with their vertical force characteristics [26][27][28]. ...
... Secondary GRF variables of interest were vertical stiffness during initial loading ("stiffness") and peak vertical force. Vertical stiffness was calculated as described previously [25,30], as the change in vertical force divided by the vertical change in center of mass position. Additionally, from the accelerometer sensor in the IMU, peak vertical tibial accelerations (TAs) were extracted as described previously [35]. ...
... In fact, the mechanical properties of the treadmill deck have an important effect on physiological response. It has been reported that athletes adjust leg stiffness and dynamics when running on surfaces with different mechanical properties [6,7]. During running, the body is continuously subjected to repetitive impact forces that are caused by GRF during the stance phase. ...
In previous research on treadmills, the main focus has been on comparing the physiological differences induced by running on treadmill decks and other exercise surfaces, with relatively little research on the mechanical properties of treadmill decks. Reducing sports injuries is a common desire of runners, which may be closely related to muscle activity. Obviously, the mechanical properties of the treadmill play an important role in this process. Muscle activity was evaluated based on a mass-spring-damper (MSD) model that provides a simulated signal of the ground reaction forces (GRF) and vibration of the lower-limb soft tissues (LLST) during the landing of the human body during running. We improved the original human motion model by considering the stiffness and damping effect of the treadmill deck. In addition, based on the theory of muscle activity regulation, the dimensionless objective function is established, and the particle swarm optimization algorithm is used to find the best range of treadmill deck parameters under pre- and post-fatigue conditions. The results show that the hardness of the treadmill deck can affect the regulation of muscle activity. Based on this, the parameters of the specific safe area of the treadmill deck are obtained, and the size of the safe area after fatigue is significantly reduced compared to that before fatigue. By studying the physiological effects of the mechanical properties of the treadmill deck on runners, the research results are expected to provide references for the design of treadmill deck parameters and reduce the risk of runners’ sports injuries, which has practical application value for treadmill design and runners’ health.
... 2,3 The theories of spinal stability can be dated back to Knutsson and Barr in 1940s and 50s 6 and progressed through Panjabi's multi-system approach to stability, of which the neutral zone function of the spine relies on the passive (inert spinal tissue), active (spinal musculature), and control subsystems (neural recruitment) where "ideal" stability is contingent upon interdependence between all. 4 Musculoskeletal instability consists of excessive joint motion without inert and/or muscular protective control. Various scales have been proposed to identify a balance of tissue stiffness and compliance for maintaining health, 7 which would be similar for a stability-instability continuum. Despite the broad spectrum of spine pathology classified as discogenic, spondylitic, facet-related, and non-specific low back pain, some have proposed the overarching relationship to the absence of spinal stability, otherwise known as spinal instability, as the causative agent to injury. ...
Exercise targeting the trunk and hip (core) musculature is common practice in rehabilitation and performance training. Historical underpinnings of core exercise focus on providing stability to the spine, thus improving the function of the spine and extremities, while instability has been postulated to result in pathology and impaired performance. Mechanistic studies on the topic are often conflicting and indeterminate, suggesting the theoretical underpinnings of targeted core exercise may be over assumed in common practice. The best modes of intervention also remain undefined, with combined methods having potential to optimize outcomes. This includes moving beyond isolated exercise camps and being inclusive of both targeted exercise and progressive multi-joint movements. The purpose of this clinical commentary is to describe the historical mechanisms of the stability-instability continuum and the role of exercise intervention. A spectrum of ideologies related to core exercise are examined, while appreciating positive outcomes of exercise interventions across healthy and pathological populations. Finally, exercise summaries were compiled to improve critical reasoning within current practice and inspire future investigations.
Level of Evidence
5
... To further understand human running performance, the spring-mass model was widely Sensors 2024, 24, 8087 2 of 13 adopted in research [3][4][5][6]. This model posits that the body's potential elastic energy is influenced by vertical stiffness (K vert ), a key parameter for optimizing locomotion [7,8]. It is a quantitative measure of the body's ability to absorb and restore potential elastic energy, largely governed by musculotendinous structures [3]. ...
Temporal parameters are crucial for understanding running performance, especially in elite sports environments. Traditional measurement methods are often labor-intensive and not suitable for field conditions. This study seeks to provide greater clarity in parameter estimation using a single device by comparing it to the gold standard. Specifically, this study aims to investigate how the temporal parameters and vertical stiffness (Kvert) of running stride exerted by IMU sensors are related to the parameters of the smart insole for outdoor acquisition. Ten healthy male subjects performed four 60-meter high-speed runs. Data were collected using the WIMU PRO™ device and smart insoles. Contact time (CT) and flight time (FT) were identified, and Kvert was calculated using Morin’s method. Statistical analyses assessed data normality, correlations, and reliability. WIMU measured longer CT, with differences ranging from 26.3% to 38.5%, and shorter FT, with differences ranging from 27.3% to 54.5%, compared to smart insoles, across different running speeds. Kvert values were lower with WIMU, with differences ranging from 23.96% to 45.01% depending on the running activity, indicating significant differences (p < 0.001). Using these results, a multiple linear regression model was developed for the correction of WIMU’s Kvert values, improving the accuracy. The improved accuracy of Kvert measurements has significant implications for athletic performance. It provides sports scientists with a more reliable metric to estimate player fatigue, potentially leading to more effective training regimens and injury prevention strategies. This advancement is particularly valuable in team sports settings, where easy-to-use and accurate biomechanical assessments of multiple athletes are essential.
... Foure [38] and Kubo [39,40] indicated that the stiffness of the muscle-tendon complex increased after long-term plyometric, isometric, and weight training. However, high levels of stiffness may be associated with increased peak forces, impact forces, and reduced joint motion, increasing the risk of bony injuries [19,41]. ...
Propulsive power is one of the factors that determine the performance of sprint cycling. Pedaling rate is related to power output, and stiffness is associated with improving performance in athletic tasks. Purpose: to investigate the relationship between musculoarticular stiffness and pedaling rate. Methods: twenty-two healthy, untrained male volunteers (19 ± 2 years, 175 ± 6 cm, 74 ± 16 kg) were divided into two groups after their musculoarticular (MA) stiffness was tested, and these groups were the stiffness group (SG) and compliant group (CG). A 6-s maximal cycling test was conducted in four cycling modes, which were levels 5 and 10 air-resistance, and levels 3 and 7 magnetic-resistance. Peak and average cadence, peak power output (POpeak), crank force (CFpeak), peak rate of crank force development (RCFD), and the angle of peak crank force were collected. The significance of differences between the two groups for these variables was assessed using an independent samples t-test. Pearson product–moment correlations were calculated to analyze the relationship between MA stiffness and each performance variable. Results: the SG had significantly higher peak cadence and average cadence at level 3 magnetic-resistance, peak crank force, and peak power output at level 10 air-resistance, peak rate of crank force development at levels 5 air-resistance, 10 air-resistance, and 3 magnetic-resistance (p < 0.05). MA stiffness was significantly correlated with average cadence at levels 5 and 10 air-resistance, peak crank force in all 4 modes, and RCFD and peak power output at level 10 air-resistance. There were no significant relationships between MA stiffness and the angle of peak crank force in each cycling mode. Conclusion: results indicate that participants with relatively higher MA stiffness seemed to have a higher pedaling rate during a 6-s sprint cycling in these conditions. They also performed a superior crank force and rate of crank force development, producing greater power output when sprint cycling. Optimizing cycling resistance or gear ratio to enhance both RCFD and musculotendinous stiffness may be crucial for improving sprint cycling performance.
... p = 0.194; I 2 = 63%). Previous studies reported that too much stiffness of the muscle-tendon unit might lead to various lower body injuries including soft-tissue, joint, and bone injuries, occurring in noncontact situations [16,17,[42][43][44]. The mechanisms by which stiffness of the muscle-tendon unit is related to the occurrence of muscle-tendon injuries are not completely clear but may involve a reduction in a cushioning effect. ...
Purpose
Previous meta-analysis studies concluded that static stretching intervention cannot decrease all-cause injury in healthy active individuals. On the other hand, static stretching intervention may decrease muscle injury, but the evidence has not been integrated. The aim of this study was to systematically review the papers and analyze the preventative effects of static stretching intervention on muscle and tendon injuries in healthy active participants.
Methods
A computerized search of PubMed, Web of Science, and EBSCO was performed in June 2023. Randomized controlled trials with static stretching investigations to prevent muscle and tendon injuries were included.
Results
Of 5575 papers identified, 4 papers were included (three papers examined both muscle and tendon injuries, and one paper examined only tendon injuries). For muscle injuries, the result of the meta-analysis showed that the static stretching intervention group significantly decreased muscle injuries compared to the control group (odds ratio = 0.37; 95% confidence interval, 0.16–0.85; p < 0.01; I² = 63%). For tendon injuries, it was found that there was no significant difference between the static stretching intervention group and the control group (odds ratio = 0.57; 95% confidence interval, 0.25–1.33; p = 0.194; I² = 63%).
Conclusions
These data indicated that static stretching intervention can prevent muscle injuries, but not tendon injuries, in healthy active participants.
... It is thought that appropriate strength and endurance training can prevent tendon pathologies that athletes may encounter (Frankewycz et al., 2018;Couppe et al., 2009). In terms of athlete performance, too much or too little stiffness in the muscle mass of athletes can be a risk factor for injury (Butler et al., 2003). It is important for football players to know these structural differences in terms of their own performances in order to improve the situation and conditions or to avoid injury. ...
As in all performance athletes, too hard or too soft Achilles tendon (AT) affects athletic performance and increases the risk of injury in soccer players. The aim of this study was to know the tendon stiffness and mechanical properties of the tendon according to the positions and thus to apply appropriate training programs for the structural improvement of the mechanical properties of the AT according to the positions of the soccer players. In this study, 21 male professional soccer players with a mean age of 18.19±0.402 years, mean height of 180.48±6.258 cm, mean body weight of 70.71±7.823 kg, and mean BMI of 21.66±1.65 kg/m₂ were included. The mechanical and viscoelastic properties of the AT were evaluated with the highly reliable MyotonPro device (Myoton AS, Estonia). AT measurements of professional soccer players were performed 4 cm above the distal insertion of the tendon (calcaneal tubercle) after determining the distal insertion of the tendon in the prone position with the ankles hanging from the table in a neutral position. Although there was a significant result (p
... Reduced stiffness in the tendon reflects muscle characteristics. The scientific literature further acknowledges that low muscle stiffness can heighten the risk of injury and disrupt movement patterns [38]. ...
The purpose of this study was to compare the effects of dry needling (DN) intervention on the responses of muscle tone, stiffness, and elasticity, as well as power, pressure pain thresholds, and blood perfusion of the flexor carpi radialis muscle in mixed martial arts (MMA) athletes. Thirty-two trained/developmental men MMA fighters (25.5±4.5 years; 24.5±3 body mass index) participated in a randomized crossover study. Participants underwent a single intervention, receiving both DN and placebo. Laser Doppler flowmetry measured blood perfusion, while a myotonometer assessed the mechanical characteristics of muscle tone, stiffness, and elasticity of the flexor carpi radialis muscle. Pressure pain thresholds (PPT) were measured using an algometer, and maximal forearm muscle force was measured using a hand dynamometer. Outcomes were assessed at baseline, immediately after, and 24 hours and 48 hours post-intervention. A two-way repeated-measures ANOVA revealed significant Intervention*Time interaction for all outcomes: perfusion unit (p<0.001), muscle tone (p<0.001), stiffness (p<0.001), elasticity (p<0.001), PPT (p<0.001) and maximal forearm muscle force (p<0.001). The current study suggests that a single session of DN enhances muscle recovery, increases muscle strength, and improved PPT in MMA athletes. These positive adaptations appear to last up to 48 hours in some variables.
... Shorter contact times and faster step frequencies are generally associated with worse running economy and higher leg stiffness at a given speed. Higher leg stiffness has been associated with increased injury risk due to increased musculoskeletal loading on bony structures in nonamputee runners (38,39). Therefore, because the use of an RSP two categories less stiff than recommended decreased affected leg stiffness, this may contribute to improved running economy in athletes with a TTA (12) and affect running biomechanics, which have been associated with injury risk. ...
Similar to non-amputees, female athletes with unilateral transtibial amputation (TTA) using running-specific leg prostheses (RSPs) may have worse running economy and higher rates of running-related injury than male athletes. Optimizing RSP configuration for female athletes could improve running economy and minimize biomechanical asymmetry, which has been associated with running-related injury. Nine females with a TTA ran at 2.5 m/s while we measured metabolic rates and ground reaction forces. Subjects used an RSP with a manufacturer-recommended stiffness category, one category less stiff and two categories less stiff than recommended. Use of an RSP two categories less stiff resulted in 3.0% lower net metabolic power (p=0.04), 7.8% lower affected leg stiffness (p=6.01x10 ⁻⁴ ), increased contact time asymmetry (p=0.04), and decreased stance average vertical ground reaction force asymmetry (p=0.04) compared to a recommended stiffness category RSP. Lower RSP stiffness (kN/m) values were associated with lower net metabolic power (p=0.02), lower affected leg stiffness (p=1.36x10 ⁻⁴ ), longer affected leg contact time (p=1.46x10 ⁻⁴ ) and similar affected leg peak and stance-average vertical ground reaction force compared to higher RSP stiffness values. Subjects then used the RSP stiffness category that elicited the lowest net metabolic power with 100 g, 200 g and 300 g added distally. We found no significant effects of added mass on net metabolic power, biomechanics, or asymmetry. These results suggest that female runners with a TTA could decrease metabolic power during running while minimizing biomechanical asymmetries, which have been associated with running-related injury using an RSP two categories less stiff than manufacturer recommended.
... The relationship between stiffness and physical performance is complex and multifaceted, influenced by various factors, including age, sex, muscle-specific characteristics, and activity levels. The positive association between increased musculoskeletal stiffness and elite athletic performance during fast stretch-shorten cycle activities has been extensively documented in prior research 35 . In congruence, the current findings revealed that stiffness measurements collected by a myometer under passive conditions appear to be related to dynamic muscle activities in youth soccer players. ...
The aim of the present study was to investigate the variations in individual muscle stiffness across different maturation stages (i.e., peak height velocity [PHV]) in elite youth soccer players and to explore the associations between lower limb muscle stiffness and performance in sprinting (10, 20, and 40 m sprint), maneuverability (9–3-6–3-9 m sprint test), and jumping (countermovement jump [CMJ]). A total of 131 elite youth soccer players aged 12–18 years, volunteered to participate in the study and were divided into pre-PHV (n = 21), mid-PHV (n = 33), and post-PHV (n = 80). Muscle stiffness of the rectus femoris (RF) and biceps femoris (BF) muscles was assessed using a MyotonPRO. Results showed that players in the pre-PHV stage had lower stiffness in the BF and RF muscles compared to mid-PHV (p < 0.001; effect size [ES] = moderate to large) and post-PHV players (p < 0.001; ES = moderate to large). It was also observed that the mid-PHV group had lower stiffness levels in their RF muscle compared to the post-PHV group (p < 0.001; ES = small). Significant correlations were found between BF and RF stiffness and sprint (p < 0.001) and maneuverability (p < 0.001) performance. RF stiffness showed a significant positive correlation with CMJ (p < 0.05), suggesting that greater lower body stiffness is beneficial for athletic performance in youth soccer players. The findings highlighting the importance of considering training methods that increase muscular stiffness, particularly in relation to the RF muscle, to optimize athletic performance.
... Considerable research has been conducted on leg stiffness during hopping, one of the simplest SSC movements, suggesting the importance of adjusting leg stiffness to control hop frequencies (Brughelli and Cronin, 2008;Butler et al., 2003;Struzik et al., 2021). The adjustment of leg stiffness during hopping is primarily achieved by adjusting ankle stiffness rather than knee or hip stiffness (Farley and Morgenroth, 1999;Ferris et al., 1998;Hobara et al., 2011;Kuitunen et al., 2011). ...
The biomechanics underlying bouncing exercises are characterized by the spring-like behavior of the human leg. However, the mechanism underlying the mechanistic contribution of muscle dynamics to the adjustment of leg stiffness is unclear. This study aimed to elucidate the mechanisms governing the changes in leg stiffness during hopping at different frequencies by examining the dynamics of the muscle–tendon complex (MTC) of the medial gastrocnemius muscle (MG). We hypothesized that an increase in muscle stiffness would augment leg stiffness, thereby enabling hopping at higher frequencies. Kinematic and kinetic data were obtained using a motion capture system and force plates. Simultaneously, ultrasound images of the MG were acquired to quantify the muscle fascicle length and pennation angle. The results showed that the stiffness of the MTC increased with hop frequency and exhibited a strong correlation with the leg stiffness. In addition, with increasing frequency, the fascicle contractions shifted from isometric to concentric. To explain these results, an MTC model comprising a contractile component (CC) and series elastic component (SEC) was constructed. We observed a negative CC stiffness, which increased the MTC stiffness. Although this result appears to diverge from our initial hypothesis, the effect of negative CC stiffness on MTC stiffness can be understood, from the perspective of two springs in series, as an extension of the very high stiffness effect. This quantitative understanding of the dynamic interaction between the muscle and tendon offers a unified framework for interpreting various results of previous studies on fascicle dynamics during hopping.
... 9 İnsan vücudu açısından ise sertlik, tek bir kas lifi seviyesinden, tüm vücudun bir kütle ve yay olarak modellenmesine kadar tarif edilebilir. 10 Bacak sertliği (BS), performansın belirleyicilerindendir ve yer temasında kasiskelet sisteminin ortalama sertliğini temsil eden alt ekstremite eklemlerinin bir kompleksidir. 11 Bacağın sertliği, vücuttaki dokuların (örneğin kaslar, tendonlar, kemik, bağlar, kıkırdak) bireysel sertlik değerlerinin birleşimidir. ...
Amaç: Bu çalışmanın amacı, judo sporcularında bacak kas sert- liği ve anaerobik güç parametreleri arasındaki ilişkilerin incelenmesi- dir. Gereç ve Yöntemler: Araştırma grubunu 15 kadın 15 erkek olmak üzere toplam 30 judo sporcu gönüllü olarak oluşturmuştur. Ölçümler, sporcunun en az 48 saat ara ile günde tek teste gireceği şekilde organize edilmiştir. 1. test gününde sporcuların anaerobik güç ve anaerobik kap- asite ölçümleri, 2. test gününde ise bacak sertliği ölçümleri yapılmıştır. Parametrelerin ilişkisi Pearson korelasyon katsayı ile cinsiyetler arası farklar ise t-testi ile incelenmiştir. Tüm istatistiksel analizler için an- lamlılık değeri 0,05 olarak belirlenmiştir. Bulgular: Judocuların bacak sertliği ile rölatif zirve güç ve rölatif ortalama güç değerleri arasında orta düzeyde, pozitif ve anlamlı bir ilişki olduğu görülürken (p<0,05), kontak süresi ile rölatif ortalama güç arasında orta düzeyde, negatif ve anlamlı bir ilişki görülmektedir (p<0,05). Havada kalış süresi ile anae- robik parametreler arasında ise anlamlı bir ilişki görülmemektedir (p>0,05). Kadın ve erkek judocuların rölatif zirve güç, rölatif ortalama güç ve bacak sertliği değerleri arasında anlamlı bir farklılık görülürken (p<0,05), kontak süresi, havada kalış süresi ve yorgunluk yüzdesi ben- zerlik göstermektedir (p>0,05). Sonuç: Bacak sertliği ile sporcuların rölatif zirve güç ve rölatif ortalama güçleri arasında ilişki olduğu ve bacak sertliği arttıkça rölatif zirve güç ve rölatif ortalama güç değerle- rinde de artış olacağı söylenebilir.
... An optimal level of stiffness facilitates effective force generation and transmission, thereby enhancing agility and coordination (Pruyn et al., 2014). Nevertheless, excessive stiffness can impede ROM and disrupt natural movement patterns, elevating the risk of injuries (Butler et al., 2003). Consequently, grasping and regulating muscle stiffness are pivotal for musculoskeletal wellbeing and elevating the overall physical performance. ...
This study aimed to investigate the correlation between the passive muscle stiffness of the pectoralis major muscle pars clavicularis (PMc) and shoulder extension range of motion (ROM) in both male and female participants. Thirty-nine (23 male/16 female) physically active and healthy participants volunteered in this study. After a standardized warm-up, the PMc stiffness was tested via shear wave elastography at a slightly stretched position (long muscle length) and in a non-stretched position (short muscle length). Additionally, a custom-made device and 3D motion capture assessed the active shoulder extension ROM. We found a significant moderate and negative relationship between shoulder extension ROM and PMc stiffness at long muscle length (rs = −0.33; p = 0.04) but not at short muscle length (r = −0.23; p = 0.17). Additionally, there was no significant difference between male and female participants in the correlation analyses at both elbow angles. The moderate correlation between PMc stiffness at a slightly stretched position and shoulder extension ROM suggests that additionally, other structures such as nerves/fascia stiffness or even stretch tolerance might be factors that can be related to shoulder extension ROM.
... Leg stiffness values are calculated using the formula below, utilizing the best flight and ground contact times: KN = M × π (Tf + Tc) ÷ Tc 2 [(Tf + Tc ÷ π)−(Tc ÷ 4)] (Dalleau et al.,2004). ...
In reviewing the literature, it was decided to conduct this study due to the lack of studies investigating the influence of leg stiffness on performance parameters such as reactive agility, jumping power and speed in gymnasts. The aim of this study is to investigate the effects of gymnasts' leg stiffness on performance parameters such as reactive agility, jump and speed. For this purpose, 65 gymnastics athletes aged 12-22 years were included in the study. The drop jump test (with Optojump measuring device) was used to evaluate the jump, and the vertical jump test (Optojump measuring device) for the evaluation of leg stiffness, while the 20m sprint test (with Witty measuring device) was made for speed evaluation. The measurements of reactive agility were performed with the SpeedCourt™. As a result of our study, we found a moderate positive correlation between the leg stiffness values and the reactive strength index (RSI) values obtained from the gymnastics athletes' jump tests. In addition, we found a negative relationship at a low level between speed and agility with leg stiffness values. It can be concluded that increasing gymnasts' leg stiffness contributes positively to jumping power, speed and reactive agility. In this case, it is recommended to include plyometric exercises in the training programs to improve the leg stiffness of trampoline gymnasts, rhythmic gymnasts and artistic gymnasts who focus on jumping.
... Indeed, from a mechanical point of view, a small displacement of the CoM is economical because of the small amount of mechanical work performed. In agreement, several studies indicate that an increase in stiffness is associated with an increase in movement economy (Butler et al., 2003;Kerdok et al., 2002;Liu et al., 2022;McMahon & Cheng, 1990). ...
Landing from a jump is a challenging task as the downward movement of the center of mass of the body (CoM) of the participant must be decelerated quickly to allow the subject to return to a standing still position. The energy accumulated during the aerial phase of the jump must indeed be fully dissipated by the lower limbs during landing; the higher the drop jump height, the greater the amount of energy to be dissipated. Depending on the participant and the circumstances, the landing strategy, i.e. the way to dissipate the energy, can be more or less stiff. Generally, a stiff strategy is associated with a higher risk of injury such as an ACL injury (Almonroeder et al., 2020; Laughlin et al., 2011; Southard et al., 2012). To prevent such injuries, basic verbal instructions targeting the knee joint, such as “focus on bending your knees when you land”, are often used in injury prevention programs to soften the landing and reduce constraints, e.g. the peak ground reaction force (Almonroeder et al., 2020). According to others, the role of the ankle should also be considered in prevention programs (Lee et al., 2018; Tait et al., 2022). Therefore, gaining insight into the role of lower limb joints in adjusting the landing strategy can be helpful in reducing constraints and so the risk of injury.
... The term dynamic stiffness is also used to characterize muscle tissue. This parameter concerns deformable bodies that store and return elastic energy [8]. The dynamic stiffness (S) is measured in N/m. ...
This study investigated the relationship between the stiffness of the upper trapezius muscle and the range of rotational movement of the cervical spine. A total of 60 right-handed asymptomatic students participated in the study. Participants (N = 22) characterised by asymmetry in rotational movements were selected for the experimental group. A difference of ≥10° between right and left rotation of the cervical spine was considered asymmetrical. The control group (N = 38) included participants whose rotation difference was < 10°. Belonging to the experimental or control group did not significantly differentiate trapezius muscle stiffness. The rotation side differentiated the stiffness of the right and left trapezius muscles only in the group of people with rotational movement asymmetry. There were high correlation coefficients between right cervical rotation and the stiffness of the muscle on the right side, and between rotation to the left and the stiffness of the muscle on the left side. There is a relationship between the stiffness of the right and left upper trapezius muscles and the range of right and left rotational motion of the cervical spine. Stiffness of the upper trapezius correlates more strongly with rotation to the side on which the muscle lies than to the opposite side. Increased stiffness of the upper trapezius muscle on the side of limited cervical spine rotation is likely to be determined by the muscle fibre stretching mechanism.
... • RSI: A measure to assess SSC performance and was calculated as the ratio of JH to GCT (Flanagan and Comyns, 2008). • Leg stiffness (Kleg): Lower extremity stiffness has been associated with injury risk and athletic performance (Butler et al., 2003) and ...
The purpose of this study was to compare the effects of two arm positions, akimbo and the newly introduced bent-in-front, on jump metrics in the ten-to-five repeated jump test (10/5 RJT) and to evaluate the reliability and validity of new modified bent-in-front variation. In contrast to akimbo, bent-in-front arm variation allows participants to use their arms freely by holding them with free hands, with parallel arms bent in front of chest and elbows pointing downward without swinging. This new arm position was designed to alleviate postural control difficulties and ensure smooth movement during repeated jumps on the force plate. However, the 10/5 RJT was designed to measure lower-body stretch-shortening cycle (SSC) performance, and it is unknown whether the bent-in-front arm variation would affect jump performance, such as arm swing. If the arms can be freed without interfering with jump performance, it would be possible to determine lower-body SSC performance without the contribution of the arms and have the advantage of postural control assistance. Fifty-five healthy sports science students who regularly participated in intercollegiate or recreational sports performed 10/5 RJT with arms akimbo and bent-in-front during two sessions. Four jump metrics, including the reactive strength index, and four reliability and validity statistics, including intraclass-correlation-coefficients, were estimated. The results indicated no significant differences in the jump metrics between two arm variations. Bent-in-front arm variation can be deemed as a valid and reliable test. Therefore, the newly introduced 10/5 RJT with arms bent-in-front can be used to evaluate SSC performance in this cohort.
Background and Aims: The Patellofemoral Pain Syndrome (PFPS) is a one of the most common overuse injuries and an important cause for anterior knee pain in active people that its risk factors are unknown. On the other joint stiffness is a modifiable mechanical property that may be related to overuse injury. So the aim of this study was to investigate the role the ankle and knee stiffness in the prediction of patellofemoral pain syndrome in active people. Materials and Methods: 80 physical education students (50 female, 30 male) were selected in an accessible manner. Before the start of training sessions, the ankle and knee stiffness of both legs was measured. During the sessions, injured people were examined and the type of injury registered by the orthopedic physician. At the end of the training sessions, the subjects were divided into two groups of injured and non-injured. The independent T-test was used to compare the knee and ankle stiffness between two groups of injured and non-injured. Binary logistic regression was used to investigate the role of knee and ankle stiffness in the prediction of the occurrence of this syndrome. Results: There was a significant difference between the injured and non-injured groups on ankle stiffness (p=0.01). However, no significant difference was observed in the knee stiffness (p=0.104). Logistic regression analysis revealed that subjects who injured had a significantly more ankle stiffness before the injury compared to group non-injuries. So ankle stiffness is risk factor this syndrome. Conclusion: This study showed that ankle stiffness could predict patellofemoral pain syndrome. So that high ankle stiffness may increase the risk of overuse injuries. This research provides important information to the coaches and team doctors about the management of injury and its treatment.
The aim of this study was to establish alterations in vertical and lower-limb joint stiffness following anterior cruciate ligament reconstruction (ACLR). 127 male patients 8–10 months post-ACLR and 45 non-injured controls performed unilateral and bilateral drop jumps, and cutting, while ground reaction forces (GRFs) and 3D kinematics were recorded. Stiffness and changes in vertical GRF were lower in ACLR patients during bilateral drop jumps compared to non-injured controls. ACLR patients also displayed lower knee stiffness in the bilateral drop jumps (d=-0.91, p < 0.001 and d = 0.53, p < 0.001, respectively) and cutting (d=-0.85, p < 0.001 and d = 0.19, p=0.040, respectively). In the unilateral drop jump, there were no differences in ankle, knee, or hip stiffness between groups, yet ACLR patients displayed smaller changes in knee moments (d=-0.63, p < 0.001) and decreased knee range of motion (d=0.44, p=0.013). During the bilateral drop jump, ACLR patients displayed lower ankle stiffness (d=0.46, p=0.003) and smaller ankle moment changes (d=0.48, p=0.006), compared to controls. Hence, joint level analysis provides practitioners with a more detailed insight into an athlete’s movement strategy following ACLR than whole body analysis. Range of motion, change in moment, and stiffness of the knee joint especially, can help practitioners to assess fitness for return-to-sport in ACLR patients.
Background/aim: One major problem in football practice is defining the scaling of the field size for the intended practice task design. To increase the frequency of actions under high pressure in training, practitioners tend to design training environments with reduced pitch dimensions (Owen et al., 2014). On the other side, the emergence of collective behavior depends on the ambient information that is
available in the learning environment. To facilitate the skill transfer from training to the actual game, there is a need to investigate if the interpersonal layout given in training represents the affordances of the performance environment (Sullivan et al., 2021). The present study analyzes how collective behaviors change when the area per player is reduced.
Methods: 22 male soccer players of a 5th division club in Germany were separated into two teams and competed for an 11 versus 11 in four different field conditions. Thereby the area per player changed across conditions from formal field 324m² (FF324), to medium field 218m² (MF218), to half field 162m² (HF162), and small field 101m², (SF101). Area per player was played and examined. Each condition size was played with eleven players per team. Each team played five attacks per condition (a total of 40 attacks). The two teams performed 40 trials in a crossover study design. Players’ positional data were computed using a local positioning system and processed to calculate measures
of inter-team distance, team length and width (offensive, defensive), total convex hull, team spread (offensive, defensive), dyadic distance (offensive, defensive), distance to the nearest opponent (offensive, defensive), mean pressure received and mean pressure exerted.
Conclusions: The data shows, that when downscaling the field sizes in football, the interpersonal distances are just like the total convex hull compresses. Moreover, large dimensional changes lead to different game properties on a physical and tactical level. Future studies should focus on the potential of representative fields in practice tasks, as this might allow players to get better attuned to the
ambient informational properties that specify the actions in the actual performance environment.
Anterior Cruciate Ligament (ACL) injuries rank among the most prevalent and severe types of injuries, significantly impacting both athletes and non-athletes alike. These injuries not only result in immediate physical impairment, such as intense pain, substantial swelling, and a marked loss of mobility, but also carry long-term health consequences that can alter a person’s quality of life. Chronic pain, persistent instability, and an increased risk of developing osteoarthritis are among the lasting effects that can follow an ACL injury. An in-depth understanding of the biophysics behind ACL injuries is paramount for devising effective prevention and treatment protocols. Biophysics, which combines principles from physics with biological systems, provides crucial insights into the mechanical and structural integrity of the ACL and its susceptibility to injury under various conditions. This systematic review aims to collate and synthesize the current knowledge surrounding the biophysical mechanisms that underlie ACL injuries.
Background
Women typically have a higher body fat content than men. Fat accumulation is associated with muscle weakness and alterations in mechanical properties. This study aims to determine the relationship between BMI and weight status with the mechanical properties of muscle and tendon. It was hypothesized that the stiffness and tone of the forearm muscle and Achilles tendon would be correlated with weight status and BMI.
Methods
A cross-sectional study was conducted with 136 female university students. Grip strength was assessed using a dynamometer, body composition was analyzed through bioimpedance, and countermovement jump performance was evaluated with a force platform. Stiffness and tone were measured using the MyotonPro device. ANOVA was used to compare grip strength and countermovement jump performance according to body composition. The Pearson correlation coefficient was used to examine bivariate associations.
Results
Relative grip strength decreased with an increase in fat content, while forearm muscle stiffness and tone decreased with rising weight status and BMI. Stiffness of the Achilles tendon increased with an increase in fat content and showed a significant positive correlation with BMI. Multiple regression analysis revealed a weak correlation between BMI, body composition, and stiffness of the forearm muscles.
Conclusion
The results of this study support the notion that the stiffness of the forearm muscles and Achilles tendon is correlated with BMI in young adult women. Furthermore, an increase in body fat percentage is linked to a decrease in mechanical properties and poorer muscle function.
Anterior Cruciate Ligament (ACL) injuries rank among the most prevalent and severe types of injuries, significantly impacting both athletes and non-athletes alike. These injuries not only result in immediate physical impairment, such as intense pain, substantial swelling, and a marked loss of mobility, but also carry long-term health consequences that can alter a person's quality of life. Chronic pain, persistent instability, and an increased risk of developing osteoarthritis are among the lasting effects that can follow an ACL injury. An in-depth understanding of the biophysics behind ACL injuries is paramount for devising effective prevention and treatment protocols. Biophysics, which combines principles from physics with biological systems, provides crucial insights into the mechanical and structural integrity of the ACL and its susceptibility to injury under various conditions. This systematic review aims to collate and synthesize the current knowledge surrounding the biophysical mechanisms that underlie ACL injuries. The review encompasses a range of factors, including the biomechanical forces that place stress on the ligament, anatomical structures that may predispose individuals to injury, and physiological conditions that affect ligament health and resilience. Each of these factors plays a crucial role in the incidence and severity of ACL injuries. Biomechanical forces, for example, can involve sudden changes in direction or impact during physical activity, leading to excessive stress on the ACL. Anatomical factors might include variations in bone structure or ligament alignment that inherently increase the risk of injury. Additionally, physiological conditions such as muscle strength, flexibility, and overall ligament health can influence the likelihood and extent of an ACL injury. The findings of this review underscore the necessity of adopting integrated approaches in both injury prevention and rehabilitation. Such approaches must consider the multifaceted nature of ACL injuries, involving not only mechanical and anatomical aspects but also physiological and possibly even genetic factors. By emphasizing a multi-faceted understanding, interventions can be more effectively tailored to address the complex interplay of elements that contribute to ACL injuries. This holistic approach can lead to better outcomes for those at risk of or recovering from ACL injuries, enhancing the efficacy of prevention strategies and rehabilitation protocols.
The stiffness of the supporting leg may alter the energy transfer to the trunk and lower extremities of the kicking leg, which may affect kick performance. This study aimed to clarify whether the stiffness of the supporting leg affects the trunk kinematics during kicking and kicking performance in soccer players. Twenty-two male collegiate soccer players participated in the study. The data for the stiffness properties of the supporting leg and trunk kinematics were obtained and calculated using a 3-dimensional motion analysis system. The results showed that a greater leg stiffness of the supporting leg was associated with a lower trunk rotation angle during kicking. There were no significant correlations between the maximum swing speed and the stiffness of the supporting leg ( P < .05). These results suggest that stiffness of the supporting leg may restrain trunk rotation during the kicking motion. However, the lack of a relationship with swing speed indicates the need for further investigation into its effects on kicking performance.
The aim of this research was to evaluate the reliability of the measurements of biomechanical parameters of the muscles of athletes representing different disciplines as well as untrained people. Ninety-four young, healthy male individuals participated in the study and were divided into five subgroups: footballers (n = 25), volleyballers (n = 14), handballers (n = 19), MMA fighters (n = 16), and undrained group (n = 20). All of the participants underwent measurements of stiffness (S), muscle tone (T) and elasticity (E) by two independent measurers using MyotonPro equipment. Analysis was conducted on two different parts of the quadriceps femoris: rectus femoris (RF) and vastus medialis (VM. Consequently, the comprehensive analysis comprised 564 measurements (94 participants * 3 parameters = 282 * 2 measurers = 564). The results proves high reliability of the myotonometry (Pearson's CC over 0.8208–0.8871 for different parameters, ICC from to 0.74 to 0.99 for different muscles and parameters) excluding only stiffness for the VM which was characterized withlow ICC of 0.08 and relatively highest between the examined parameters MAE% of 8.7% which still remains low value. The most significant differences between the parameters in examined groups were observed between MMA fighters and volleyballers in terms of muscle tone and elasticity of the VM (correlation of 0.14842 and 0.15083 respecitively). These results confirm the usability of myotonometry in measuring the biomechanical properties of the muscles in different sports groups and confirm the independence of the results obtained from the person performing the measurement.
CITATION Trybulski R, Kużdżał A, Wilk M, Więckowski J, Fostiak K and Muracki J (2024) Reliability of MyotonPro in measuring the biomechanical properties of the quadriceps femoris muscle in people with different levels and types of motor preparation. The aim of this research was to evaluate the reliability of the measurements of biomechanical parameters of the muscles of athletes representing different disciplines as well as untrained people. Ninety-four young, healthy male individuals participated in the study and were divided into five subgroups: footballers (n = 25), volleyballers (n = 14), handballers (n = 19), MMA fighters (n = 16), and undrained group (n = 20). All of the participants underwent measurements of stiffness (S), muscle tone (T) and elasticity (E) by two independent measurers using MyotonPro equipment. Analysis was conducted on two different parts of the quadriceps femoris: rectus femoris (RF) and vastus medialis (VM. Consequently, the comprehensive analysis comprised 564 measurements (94 participants * 3 parameters = 282 * 2 measurers = 564). The results proves high reliability of the myotonometry (Pearson's CC over 0.8208-0.8871 for different parameters, ICC from to 0.74 to 0.99 for different muscles and parameters) excluding only stiffness for the VM which was characterized withlow ICC of 0.08 and relatively highest between the examined parameters MAE% of 8.7% which still remains low value. The most significant differences between the parameters in examined groups were observed between MMA fighters and volleyballers in terms of muscle tone and elasticity of the VM (correlation of 0.14842 and 0.15083 respecitively). These results confirm the usability of myotonometry in measuring the biomechanical properties of the muscles in different sports groups and confirm the independence of the results obtained from the person performing the measurement.
Cardiel-Sánchez, S, Rubio-Peirotén, A, Molina-Molina, A, García-Cebadera Gómez, C, Almenar-Arasanz, A, Ráfales-Perucha, A, Roche-Seruendo, LE, and Cartón-Llorente, A. Effects of plyometric training on running biomechanics and jumping ability of U14 athletes. J Strength Cond Res XX(X): 000-000, 2024-Children under the age of 14 years (U14) are particularly susceptible to musculoskeletal disorders because of growth spurts. Plyometric training has been shown to be beneficial for both injury reduction and performance enhancement. The aim of this study was to evaluate the effects of plyometric training on the jumping ability and running biomechanics of U14 track-and-field athletes. A single-blind randomized controlled trial was conducted. Thirty-five (18 female and 17 male) U14 athletes (age: 12.5 ± 1.2 years; height: 152.3 ± 7.7 cm; body mass: 47.3 ± 6.9 kg) were randomized into experimental and control groups. All subjects completed their usual training for 4 weeks, and those in the intervention group added a low-volume plyometric program twice a week. Preintervention and postintervention assessments included a countermovement jump (CMJ) to determine maximum jump height, 10-second repeated jumps to assess reactive strength index (RSI), and a 3-minute run at 12 km·h-1 to analyze running kinematics contact time, flight time, step length (SL), step frequency (SF), mean power output, vertical spring stiffness, and leg spring stiffness (LSS). The results revealed no main effect of time for any of the variables. A group-by-time interaction was found for RSI (p = 0.045) in the intervention group, whereas a significant increase in LSS was also found after the intervention (p = 0.031). However, no changes in CMJ height or other running parameters were observed. The significance level for the study was set at ρ ≤ 0.05. Plyometric-jump training may improve the stretch-shortening cycle in U14 athletes by increasing RSI and LSS. Athletes and coaches in running-related sports should be aware of these short-term effects when aiming to optimize the energy storage and release mechanism.
Anaerobic performance (vertical jumps) is an important indicator in determining athletic performance in soccer. The aim of this study was to investigate the effects of biomechanical and viscoelastic properties of lateral and medial gastrocnemius (LG&MG) muscle and achilles tendon (AT) on jumping performance of professional soccer players. A total of 21 male professional soccer players with a mean age of 18.19±0.40 years, a mean height of 180.48±6.25 cm, a mean body weight of 70.71±7.82 kg, and a mean BMI of 21.66±1.65 kg/m₂ were included in this study. LG and MG muscle, as well as AT biomechanical and viscoelastic properties were evaluated with Myoton Pro device. Measurements were performed in the prone position of the soccer players, LG and MG at 50° plantar flexion, and AT at 0° (neutral position) at an angle of 4 cm above the calcaneal tubercle. Counter movement jump (CMJ) were recorded with the high-speed camera in the validated My Jump 2 application. A significant correlation was observed between the LG (F) tension value and CMJ (P) value and between the MG (R&C) values and the CMJ (F&P) value of professional soccer players (p<0.05). There was no significant relationship between AT values and CMJ values (p>0.05). It should not be forgotten that training coaches on this subject and applying this information to soccer players by conscious coaches will bring about increases in the athletic performance of soccer players, and all these performance characteristics can be achieved with planned and programmed training.
Takeuchi, K, Nakamura, M, Matsuo, S, Samukawa, M, Yamaguchi, T, and Mizuno, T. Combined effects of static and dynamic stretching on the muscle-tendon unit stiffness and strength of the hamstrings. J Strength Cond Res 38(4): 681–686, 2024—Combined static and dynamic stretching for 30 seconds is frequently used as a part of a warm-up program. However, a stretching method that can both decrease muscle-tendon unit (MTU) stiffness and increase muscle strength has not been developed. The purpose of this study was to examine the combined effects of 30 seconds of static stretching at different intensities (normal-intensity static stretching [NS] and high-intensity static [HS]) and dynamic stretching at different speeds (low-speed dynamic [LD] and high-speed dynamic stretching [HD]) on the MTU stiffness and muscle strength of the hamstrings. Thirteen healthy subjects (9 men and 4 women, 20.9 ± 0.8 years, 169.3 ± 7.2 cm, 61.1 ± 8.2 kg) performed 4 types of interventions (HS-HD, HS-LD, NS-HD, and NS-LD). Range of motion (ROM), passive torque, MTU stiffness, and muscle strength were measured before and immediately after interventions by using an isokinetic dynamometer machine. In all interventions, the ROM and passive torque significantly increased ( p < 0.01). Muscle-tendon unit stiffness significantly decreased in HS-HD and HS-LD (both p < 0.01), but there was no significant change in NS-HD ( p = 0.30) or NS-LD ( p = 0.42). Muscle strength significantly increased after HS-HD ( p = 0.02) and NS-LD ( p = 0.03), but there was no significant change in HS-LD ( p = 0.23) or NS-LD ( p = 0.26). The results indicated that using a combination of 30 seconds of high-intensity static stretching and high-speed dynamic stretching can be beneficial for the MTU stiffness and muscle strength of the hamstrings.
The Squat Jump (SJ) test is widely recognized as a reliable test for assessing lower-limb explosive strength. However, uncertainty persists in the literature regarding the optimal starting positions for maximizing vertical jump performance. This uncertainty is exacerbated by a disproportionate focus on athletes in existing studies, with insufficient consideration being given to non-athletic women. To address this gap, this study investigated the influence of leg starting angle on explosive jump height in a homogeneous sample of non-athletic women. Thirty-two female students enrolled in a Sports Science master’s degree program at the University of Salerno participated in the study. Descriptive statistics were employed to summarize data on various variables, and Pearson’s correlations were calculated to assess the relationship between knee angle in the starting position and achieved jump height. The study revealed that different starting positions had a noteworthy impact on jump height among the participants. A strong negative correlation (−0.701) was identified between Squat Jump elevation and the knee angle in the starting position. Notably, 62.5% of the subjects opted for a starting knee position of approximately 70 degrees, with all of them consistently achieving a jump height associated with this specific angle. These findings provide valuable insights into the relationship between leg starting angle and explosive jump height in non-athletic women. The observed correlation underscores the significance of the starting position in Squat Jump performance. The prevalence of a specific knee angle choice among participants suggests potential implications for training and performance optimization in this sample.
Increased incidence of stress fracture has been reported for amenorrheic runners, while some studies have reported decreased spinal bone mass in amenorrheic runners. Based on results from these studies, one tends to associate decreased spinal bone mass with an increased risk of stress fracture. The present study compared regional bone mass and external loads during running between six female runners reporting a history of stress fracture (seven tibial and three femoral neck) and eight female runners with no history of stress fracture. Dual photon absorptiometry measures indicated significantly greater spinal (L2-L4) and femoral neck bone mineral density in stress fracture subjects (p<0.05) but no differences between groups for tibial bone density. Normalized forces recorded from Kistler force plates indicated significantly greater vertical propulsive, maximal medial, lateral, and posterior forces for stress fracture subjects during running (p<0.05).
Abstract The purpose of this study was to examine the knee and ankle joint stiffness and negative joint work during running when participants utilised their preferred and non-preferred footfall pattern. A total of 40 healthy, young runners (20 habitual forefoot (FF) and 20 habitual rearfoot (RF) runners) served as participants in this study. Three-dimensional data were obtained using a motion capture system and a force platform. The participants completed over-ground trials in each of two conditions: 1. their natural footfall pattern; and 2. their non-preferred footfall pattern. Joint stiffness was calculated by the ratio of the change in joint moment and the change in joint angle during the energy absorption phase of support. Negative joint work was calculated as the integral of the joint power-time curve during the same time interval. It was observed that joint stiffness was different between the footfall patterns but similar for both groups within a footfall pattern. A stiffer knee and a more compliant ankle were found in the FF pattern and the opposite in the RF pattern. Negative work was greater in the ankle and less in the knee in the FF pattern and the reverse in the RF pattern. We conclude that runners, in the short term, can alter their footfall pattern. However, there is a re-organisation of the control strategy of the joint when changing from a FF to a RF pattern. This re-organisation suggests that there is a possible difference in the types of injuries that may be sustained between the FF and the RF footfall patterns.
The main purpose of this study was to investigate the effects of both strike pat- tern (forefoot vs. rearfoot strike pattern) and orthotic intervention on shock to the lower extremity. Semi-rigid orthotic devices were manufactured for 15 injury- free recreational runners. Tibial accelerometry, ground reaction force, and 3D kinematic data were collected on their right leg in four conditions: forefoot strike (FFS) and rearfoot strike (RFS) with and without orthotics. Two-way repeated- measures analysis of variance tests were used to assess the effects of strike pat- tern and orthotic intervention on tibial acceleration; angular excursions of the ankle and knee; ground reaction force (GRF) vertical and anteroposterior peaks and load rates; and ankle, knee, and leg stiffness. There was a significant in- crease in tibial acceleration for the FFS pattern compared to the RFS pattern. This may be explained in part by the significantly greater peak vertical GRF, peak anteroposterior GRF, anteroposterior GRF load rates, knee stiffness, and leg stiffness found in the FFS pattern compared to the RFS pattern. Tibial accel- eration and rearfoot eversion excursions were similar between the orthotic and no-orthotic conditions. Knee flexion excursion and average GRF vertical load rates were significantly decreased while dorsiflexion excursion and knee stiffness were significantly increased in the orthotic condition. No significant interactions were found between strike pattern and orthotic condition for any variables assessed.
The notion of joint stiffness as commonly studied in biomechanics and motor control is compared with the physical definition of stiffness. The importance of elastic deformation and storage of elastic energy is stressed. Different terms are suggested in order to differentiate between experimentally observed relations between joint angle and torque that are likely to have different nature. A review of studies measuring stiffness of joint subcomponents and intact joints is presented. We suggest to either abandon the term ‘joint stiffness’ as misleading or to state up front stiffness of which of the joint components or subsystems is analyzed in each particular study. We also suggest that each study of ‘joint stiffness’ should clearly state to what extent the results are defined by the system's properties and to what extent they are reflections of the particular experimental procedure.
The storage and recovery of elastic energy in muscle-tendon springs is important in running, hopping, trotting, and galloping. We hypothesized that animals select the stride frequency at which they behave most like simple spring-mass systems. If higher or lower frequencies are used, they will not behave like simple spring-mass systems, and the storage and recovery of elastic energy will be reduced. We tested the hypothesis by having humans hop forward on a treadmill over a range of speeds and hop in place over a range of frequencies. The body was modeled as a simple spring-mass system, and the properties of the spring were measured by use of a force platform. Our subjects used nearly the same frequency (the "preferred frequency," 2.2 hops/s) when they hopped forward on a treadmill and when they hopped in place. At this frequency, the body behaved like a simple spring-mass system. Contrary to our predictions, it also behaved like a simple spring-mass system when the subjects hopped at higher frequencies, up to the maximum they could achieve. However, at the higher frequencies, the time available to apply force to the ground (the ground contact time) was shorter, perhaps resulting in a higher cost of generating muscular force. At frequencies below the preferred frequency, as predicted by the hypothesis, the body did not behave in a springlike manner, and it appeared likely that the storage and recovery of elastic energy was reduced. The combination of springlike behavior and a long ground contact time at the preferred frequency should minimize the cost of generating muscular force.
The purpose of this study was to test the effect of a jump-training program on landing mechanics and lower extremity strength in female athletes involved in jumping sports. These parameters were compared before and after training with those of male athletes. The program was designed to decrease landing forces by teaching neuromuscular control of the lower limb during landing and to increase vertical jump height. After training, peak landing forces from a volleyball block jump decreased 22%, and knee adduction and abduction moments (medially and laterally directed torques) decreased approximately 50%. Multiple regression analysis revealed that these moments were significant predictors of peak landing forces. Female athletes demonstrated lower landing forces than male athletes and lower adduction and abduction moments after training. External knee extension moments (hamstring muscle-dominant) of male athletes were threefold higher than those of female athletes. Hamstring-to-quadriceps muscle peak torque ratios increased 26% on the nondominant side and 13% on the dominant side, correcting side-to-side imbalances. Hamstring muscle power increased 44% with training on the dominant side and 21% on the nondominant. Peak torque ratios of male athletes were significantly greater than those of untrained female athletes, but similar to those of trained females. Mean vertical jump height increased approximately 10%. This training may have a significant effect on knee stabilization and prevention of serious knee injury among female athletes.
A running animal coordinates the actions of many muscles, tendons, and ligaments in its leg so that the overall leg behaves like a single mechanical spring during ground contact. Experimental observations have revealed that an animal's leg stiffness is independent of both speed and gravity level, suggesting that it is dictated by inherent musculoskeletal properties. However, if leg stiffness was invariant, the biomechanics of running (e.g. peak ground reaction force and ground contact time) would change when an animal encountered different surfaces in the natural world. We found that human runners adjust their leg stiffness to accommodate changes in surface stiffness, allowing them to maintain similar running mechanics on different surfaces. These results provide important insight into mechanics and control of animal locomotion and suggest that incorporating an adjustable leg stiffness in the design of hopping and running robots is important if they are to match the agility and speed of animals on varied terrain.
When humans hop in place or run forward, leg stiffness is increased to offset reductions in surface stiffness, allowing the global kinematics and mechanics to remain the same on all surfaces. The purpose of the present study was to determine the mechanism for adjusting leg stiffness. Seven subjects hopped in place on surfaces of different stiffnesses (23-35,000 kN/m) while force platform, kinematic, and electromyographic data were collected. Leg stiffness approximately doubled between the most stiff surface and the least stiff surface. Over the same range of surfaces, ankle torsional stiffness increased 1.75-fold, and the knee became more extended at the time of touchdown (2.81 vs. 2.65 rad). We used a computer simulation to examine the sensitivity of leg stiffness to the observed changes in ankle stiffness and touchdown knee angle. Our model consisted of four segments (foot, shank, thigh, head-arms-trunk) interconnected by three torsional springs (ankle, knee, hip). In the model, an increase in ankle stiffness 1.75-fold caused leg stiffness to increase 1.7-fold. A change in touchdown knee angle as observed in the subjects caused leg stiffness to increase 1.3-fold. Thus both joint stiffness and limb geometry adjustments are important in adjusting leg stiffness to allow similar hopping on different surfaces.
To prospectively evaluate the effect of neuromuscular training on the incidence of knee injury in female athletes, we monitored two groups of female athletes, one trained before sports participation and the other not trained, and a group of untrained male athletes throughout the high school soccer, volleyball, and basketball seasons. Weekly reports included the number of practice and competition exposures and mechanism of injury. There were 14 serious knee injuries in the 1263 athletes tracked through the study. Ten of 463 untrained female athletes sustained serious knee injuries (8 noncontact), 2 of 366 trained female athletes sustained serious knee injuries (0 noncontact), and 2 of 434 male athletes sustained serious knee injuries (1 noncontact). The knee injury incidence per 1000 athlete-exposures was 0.43 in untrained female athletes, 0.12 in trained female athletes, and 0.09 in male athletes (P = 0.02, chi-square analysis). Untrained female athletes had a 3.6 times higher incidence of knee injury than trained female athletes (P = 0.05) and 4.8 times higher than male athletes (P = 0.03). The incidence of knee injury in trained female athletes was not significantly different from that in untrained male athletes (P = 0.86). The difference in the incidence of noncontact injuries between the female groups was also significant (P = 0.01). This prospective study demonstrated a decreased incidence of knee injury in female athletes after a specific plyometric training program.
Mammals use the elastic components in their legs (principally tendons, ligaments, and muscles) to run economically, while maintaining consistent support mechanics across various surfaces. To examine how leg stiffness and metabolic cost are affected by changes in substrate stiffness, we built experimental platforms with adjustable stiffness to fit on a force-plate-fitted treadmill. Eight male subjects [mean body mass: 74.4 +/- 7.1 (SD) kg; leg length: 0.96 +/- 0.05 m] ran at 3.7 m/s over five different surface stiffnesses (75.4, 97.5, 216.8, 454.2, and 945.7 kN/m). Metabolic, ground-reaction force, and kinematic data were collected. The 12.5-fold decrease in surface stiffness resulted in a 12% decrease in the runner's metabolic rate and a 29% increase in their leg stiffness. The runner's support mechanics remained essentially unchanged. These results indicate that surface stiffness affects running economy without affecting running support mechanics. We postulate that an increased energy rebound from the compliant surfaces studied contributes to the enhanced running economy.
The goals of this study were to examine the following hypotheses: (a) there is a difference between the theoretically calculated (McMahon and Cheng, 1990. Journal of Biomechanics 23, 65-78) and the kinematically measured length changes of the spring-mass model and (b) the leg spring stiffness, the ankle spring stiffness and the knee spring stiffness are influenced by running speed. Thirteen athletes took part in this study. Force was measured using a "Kistler" force plate (1000 Hz). Kinematic data were recorded using two high-speed (120 Hz) video cameras. Each athlete completed trials running at five different velocities (approx. 2.5, 3.5, 4.5, 5.5 and 6.5 m/s). Running velocity influences the leg spring stiffness, the effective vertical spring stiffness and the spring stiffness at the knee joint. The spring stiffness at the ankle joint showed no statistical difference (p < 0.05) for the five velocities. The theoretically calculated length change of the spring-mass model significantly (p < 0.05) overestimated the actual length change. For running velocities up to 6.5 m/s the leg spring stiffness is influenced mostly by changes in stiffness at the knee joint.
The purpose of this study was to compare the moment-angle relationship of the ankle joint during running and sprinting to determine how the dynamic angular stiffness is influenced by different activities. For both running and sprinting, the results indicated that the ankle joint produced an exclusively extensor moment, absorbing energy during the first half of the stance phase and producing energy during the second half. The biphasic nature of the joint absorbing energy followed by the joint producing energy, while continually creating an extensor moment, was similar to a spring being compressed and allowed to extend. The dynamic stiffness of the ankle joint was 5.68 N · m/°for running and 7.38 N · m/δ for sprinting. It appeared that the stiffness of the ankle joint was not specialized characteristic of each individual but rather a specialized characteristic of the activity or demand placed upon it.
Active females demonstrate increased risk for musculoskeletal injuries relative to equivalently-trained males. Although gender differences in factors such as passive laxity, skeletal geometry and kinematics have been examined, the effect of gender on active muscle stiffness has not been reported. Stiffness of the active quadriceps and hamstrings musculature were recorded during isometric knee flexion and extension exertions from twelve male and eleven female subjects. A second-order biomechanical model of joint dynamics was used to quantify stiffness from the transient motion response to an angular perturbation of the lower-leg. Female subjects demonstrated reduced active stiffness relative to male subjects at all torque levels, with levels 56–73% of the males. Effective stiffness increased linearly with the torque load, with stiffness increasing at a rate of 3.3 Nm/rad per unit of knee moment in knee flexion exertions (hamstrings) and 6.6 Nm/rad per unit of knee moment extension exertions (quadriceps). To account for gender differences in applied moment associated with leg mass, regressions analyses were completed that demonstrated a gender difference in the slope of stiffness-versus-knee moment relation. Further research is necessary to identify the cause of the observed biomechanical difference and implications for controlling injury.
A modified mass-spring-damper model was used to simulate the vertical ground reaction forces of a human runner as stride length was altered. Spring stiffness values were selected by an optimizing routine that altered model parameters to match the model ground reaction force curve to a runner's actual ground reaction force curve. A mass in series with a spring was used to simulate the behavior of body structures that produce the active portion of the ground reaction force. A second mass in series with a spring-damper system was used to simulate the behavior of those components that cause the impact portion of the ground reaction force. The stiffness of the active spring showed a 51% decrease as subjects increased their stride length. The stiffness value of the impact spring showed a trend opposite that of the active spring, increasing by 20% as strides lengthened. It appears that the impact stiffness plays a role in preventing the support leg from collapsing in response to the increased contact velocities seen in the longer strides.
Using data from six male subjects, this study compared ground reaction
force and tibial acceleration parameters for running. A bone-mounted triaxial
accelerometer and a force platform were employed for data collection. Low peak
values were found for the axial acceleration, and a time shift toward the
occurrence of the first peak in the vertical force data was present. The time
to peak axial acceleration differed significantly from the time to the first
force peak, and the peak values of force and acceleration demonstrated only a
moderate correlation. However, a high negative correlation was found for the
comparison of the peak axial acceleration with the time to peak vertical force.
Employing a multiple regression analysis, the peak tibial acceleration could be
well estimated using vertical force loading rate and peak horizontal ground
reaction force as predictors.
To simulate the forces from hopping, the right foot of adult rabbits was subjected to 1 1/2 the animal's body weight 40 times a minute for 20-40 minutes per day. During these brief periods of repetitive impulsive loading the legs were held in short-leg splints to eliminate the natural shock-absorbing mechanism associated with ankle dorsiflexion and calve muscle stretching. Under these conditions subchondral bone stiffening occurred and was associated with the earliest metabolic changes of cartilage damage. When bone stiffening returned to normal the effect on the cartilage did not completely disappear, although these effects diminished. The results suggested that subchondral bone stiffening accompanies the earliest metabolic changes in osteoarthrosic chondrocytes and suggests that trabecular microfracture may occur very early in this sequence of events.
Walking and running on the level involves external mechanical work, even when speed averaged over a complete stride remains constant. This work must be performed by the muscles to accelerate and/or raise the center of mass of the body during parts of the stride, replacing energy which is lost as the body slows and/or falls during other parts of the stride. External work can be measured with fair approximation by means of a force plate, which records the horizontal and vertical components of the resultant force applied by the body to the ground over a complete stride. The horizontal force and the vertical force minus the body weight are integrated electronically to determine the instantaneous velocity in each plane. These velocities are squared and multiplied by one-half the mass to yield the instantaneous kinetic energy. The change in potential energy is calculated by integrating vertical velocity as a function of time to yield vertical displacement and multiplying this by body weight. The total mechanical energy as a function of time is obtained by adding the instantaneous kinetic and potential energies. The positive external mechanical work is obtained by adding the increments in total mechanical energy over an integral number of strides.
Ground reaction forces (GRF), joint positions, joint moments, and muscle powers in the lower extremity were compared between soft and stiff landings from a vertical fall of 59 cm. Soft and stiff landings had less than and greater than 90 degrees of knee flexion after floor contact. Ten trials of sagittal plane film and GRF data, sampled at 100 and 1000 Hz, were obtained from each of eight female athletes and two landing conditions. Inverse dynamics were performed on these data to obtain the moments and powers during descent (free fall) and floor contact phases. Angular impulse and work values were calculated from these curves, and the conditions were compared with a correlated t-test. Soft and stiff landings averaged 117 and 77 degrees of knee flexion. Larger hip extensor (0.010 vs 0.019 N.m.s.kg-1; P less than 0.01) and knee flexor (-0.010 vs -0.013 N.m.s.kg-1; P less than 0.01) moments were observed during descent in the stiff landing, which produced a more erect body posture and a flexed knee position at impact. The shapes of the GRF, moment, and power curves were identical between landings. The stiff landing had larger GRFs, but only the ankle plantarflexors produced a larger moment (0.185 vs 0.232 N.m.s.kg-1; P less than 0.01) in this condition. The hip and knee muscles absorbed more energy in the soft landing (hip, -0.60 vs -0.39 W.kg-1; P less than 0.01; knee, -0.89 vs -0.61 W.kg-1; P less than 0.01), while the ankle muscles absorbed more in the stiff landing (-0.88 vs -1.00 W.kg-1; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
A mathematical model for terrestrial running is presented, based on a leg with the properties of a simple spring. Experimental force-platform evidence is reviewed justifying the formulation of the model. The governing differential equations are given in dimensionless form to make the results representative of animals of all body sizes. The dimensionless input parameters are: U, a horizontal Froude number based on forward speed and leg length; V, a vertical Froude number based on vertical landing velocity and leg length, and KLEG, a dimensionless stiffness for the leg-spring. Results show that at high forward speed, KLEG is a nearly linear function of both U and V, while the effective vertical stiffness is a quadratic function of U. For each U, V pair, the simulation shows that the vertical force at mid-step may be minimized by the choice of a particular step length. A particularly useful specification of the theory occurs when both KLEG and V are assumed fixed. When KLEG = 15 and V = 0.18, the model makes predictions of relative stride length S and initial leg angle theta o that are in good agreement with experimental data obtained from the literature.
The investigation of impact force attenuation during landings may help identify performance strategies. The purpose of the study was to evaluate the effects of height (three), distance (three), and technique (three) on impact forces during landings. Three male volunteer subjects were filmed while performing three right foot landings onto a force platform for each combination of height, distance, and technique for a total of 81 trials per subject. Between- and within-subject three-way ANOVAs and three regression models (mechanical, biomechanical, refined biomechanical) were computed on the dependent variables of first (F1) and second (F2) maximum vertical force. Results of the between-subject ANOVAs indicated significant (P less than 0.05) height, distance, and technique main effects for F1 and a height x technique interaction for F2. The within-subject ANOVA results identified unique models for each of the three subjects. The biomechanical regression model exhibited the best predictions of F1 and F2 for S1 (81.0 and 72.0% explained variance, respectively), while the refined biomechanical model accounted for 83.4, 81.3, 80.9, and 88.0% of the F1 and F2 variances for S2 and S3, respectively. In conclusion, the within-subject results identified unique individual landing strategies that were masked by the group analyses suggesting that caution be exercised in using between-subject analysis techniques.
1. During each step of running, trotting or hopping part of the gravitational and kinetic energy of the body is absorbed and successively restored by the muscles as in an elastic rebound. In this study we analysed the vertical motion of the centre of gravity of the body during this rebound and defined the relationship between the apparent natural frequency of the bouncing system and the step frequency at the different speeds. 2. The step period and the vertical oscillation of the centre of gravity during the step were divided into two parts: a part taking place when the vertical force exerted on the ground is greater than body weight (lower part of the oscillation) and a part taking place when this force is smaller than body weight (upper part of the oscillation). This analysis was made on running humans and birds; trotting dogs, monkeys and rams; and hopping kangaroos and springhares. 3. During trotting and low-speed running the rebound is symmetric, i.e. the duration and the amplitude of the lower part of the vertical oscillation of the centre of gravity are about equal to those of the upper part. In this case, the step frequency equals the frequency of the bouncing system. 4. At high speeds of running and in hopping the rebound is asymmetric, i.e. the duration and the amplitude of the upper part of the oscillation are greater than those of the lower part, and the step frequency is lower than the frequency of the system. 5. The asymmetry is due to a relative increase in the vertical push. At a given speed, the asymmetric bounce requires a greater power to maintain the motion of the centre of gravity of the body, Wext, than the symmetric bounce. A reduction of the push would decrease Wext but the resulting greater step frequency would increase the power required to accelerate the limbs relative to the centre of gravity, Wint. It is concluded that the asymmetric rebound is adopted in order to minimize the total power, Wext + Wint.
An important determinant of the mechanics of running is the effective vertical stiffness of the body. This stiffness increases with running speed. At any one speed, the stiffness may be reduced in a controlled fashion by running with the knees bent more than usual. In a series of experiments, subjects ran in both normal and flexed postures on a treadmill. In other experiments, they ran down a runway and over a force platform. Results show that running with the knees bent reduces the effective vertical stiffness and diminishes the transmission of mechanical shock from the foot to the skull but requires an increase of as much as 50% in the rate of O2 consumption. A new dimensionless parameter (u omega 0/g) is introduced to distinguish between hard and soft running modes. Here, omega 0 is the natural frequency of a mass-spring system representing the body, g is gravity, and u is the vertical landing velocity. In normal running, this parameter is near unity, but in deep-flexed running, where the aerial phase of the stride cycle almost disappears, u omega 0/g approaches zero.
It has been suggested that osteonal remodeling is triggered by bone microdamage. The validity of this theory rests on the assumption that loading within the physiological range will produce substantial microdamage with relatively few load cycles. The object of the first experiment was to determine threshold values required to consistently produce fatigue microdamage in vivo. The left forelimb of five groups of dogs, characterized by different strain levels and different numbers of load cycles, were loaded in three point bending. The number of microscopic fields which contained some microdamage was calculated as a percentage of the total number of fields. This experiment indicated that loads producing strains as low as 1500 microstrain on the radius and 1400 microstrain on the ulna for 10,000 cycles will produce significant bone microdamage. A second experiment was performed to verify this threshold and to determine whether microcracks are associated with the initiation of bone remodeling. Procedures in this experiment were the same as those in the first, except that all dogs were loaded in such a way as to produce strains on the radius of 1500 microstrain for 10,000 cycles, and the dogs were sacrificed 1-4 days after loading. The loaded limb demonstrated significantly more microdamage than the control limb (p = 0.03). Moreover, we observed 44 times as many microcracks in association with resorption spaces as expected by chance alone. These data support the hypothesis that fatigue microdamage is a significant factor in the initiation of intracortical bone remodeling.
When humans and other mammals run, the body's complex system of muscle, tendon and ligament springs behaves like a single linear spring ('leg spring'). A simple spring-mass model, consisting of a single linear leg spring and a mass equivalent to the animal's mass, has been shown to describe the mechanics of running remarkably well. Force platform measurements from running animals, including humans, have shown that the stiffness of the leg spring remains nearly the same at all speeds and that the spring-mass system is adjusted for higher speeds by increasing the angle swept by the leg spring. The goal of the present study is to determine the relative importance of changes to the leg spring stiffness and the angle swept by the leg spring when humans alter their stride frequency at a given running speed. Human subjects ran on treadmill-mounted force platform at 2.5ms-1 while using a range of stride frequencies from 26% below to 36% above the preferred stride frequency. Force platform measurements revealed that the stiffness of the leg spring increased by 2.3-fold from 7.0 to 16.3 kNm-1 between the lowest and highest stride frequencies. The angle swept by the leg spring decreased at higher stride frequencies, partially offsetting the effect of the increased leg spring stiffness on the mechanical behavior of the spring-mass system. We conclude that the most important adjustment to the body's spring system to accommodate higher stride frequencies is that leg spring becomes stiffer.
By applying a simple, linear mass-spring model to running, the normalized leg spring stiffness (Kleg), the normalized effective vertical stiffness (Kvert), and the mass-specific mechanical power output of the spring (Psp) were determined and correlated with aerobic demand. The purpose of the study was to determine whether leg spring characteristics explain any of the interindividual variability observed in aerobic demand at a given submaximal running speed.
Recreational runners (N = 16) ran on a treadmill at 3.35 m x s(-1) for physiological measures and overground for biomechanical measures. The latter included a sagittal plane video record of the running motion and ground reaction data.
We found no relationship between the aerobic demand of running and Kleg (r = -0.18), an inverse relationship between aerobic demand and Kvert (r = -0.48), and a positive correlation between aerobic demand and Psp (r = 0.45).
The inverse relationship between Kvert and aerobic demand indicates that less economical runners possess a more compliant running style during ground contact. This running style may place greater force demands on extensor musculature.
When humans hop in place or run forward, they adjust leg stiffness to accommodate changes in stride frequency or surface stiffness. The goal of the present study was to determine the mechanisms by which humans adjust leg stiffness during hopping in place. Five subjects hopped in place at 2.2 Hz while we collected force platform and kinematic data. Each subject completed trials in which they hopped to whatever height they chose ("preferred height hopping") and trials in which they hopped as high as possible ("maximum height hopping"). Leg stiffness was approximately twice as great for maximum height hopping as for preferred height hopping. Ankle torsional stiffness was 1.9-times greater while knee torsional stiffness was 1.7-times greater in maximum height hopping than in preferred height hopping. We used a computer simulation to examine the sensitivity of leg stiffness to the observed changes in ankle and knee stiffness. Our model consisted of four segments (foot, shank, thigh, head-arms-trunk) interconnected by three torsional springs (ankle, knee, hip). In the model, increasing ankle stiffness by 1.9-fold, as observed in the subjects, caused leg stiffness to increase by 2.0-fold. Increasing knee stiffness by 1.7-fold had virtually no effect on leg stiffness. Thus, we conclude that the primary mechanism for leg stiffness adjustment is the adjustment of ankle stiffness.
The purpose of the study was to investigate changes in lower extremity joint energy absorption for different landing heights and landing techniques.
Nine healthy, active male subjects volunteered to perform step-off landings from three different heights (0.32 m, 2.5 m(-s); 0.62 m, 3.5 m(-s); and 1.03 m, 4.5 m(-s)) using three different landing techniques (soft, SFL; normal, NML; and stiff landing, STL). Each subject initially performed five NML trials at 0.62 m to serve as a baseline condition and subsequently executed five trials in each of the nine test conditions (3 heights x 3 techniques).
The results demonstrated general increases in peak ground reaction forces, peak joint moments, and powers with increases in landing height and stiffness. The mean eccentric work was 0.52, 0.74, and 0.87 J x kg(-1) by the ankle muscles, and 0.94, 1.31, and 2.15 J x kg(-1) by the hip extensors, at 0.32, 0.62, and 1.03 m, respectively. The average eccentric work performed by the knee extensors was 1.21, 1.63, and 2.26 J x kg(-1) for the same three heights.
The knee joint extensors were consistent contributors to energy dissipation. The ankle plantarflexors contributed more in the STL landings, whereas the hip extensors were greater contributors during the SFL landings. Also a shift from ankle to hip strategy was observed as landing height increased.
To prospectively evaluate the effect of neuromuscular training on the incidence of knee injury in female athletes, we monitored two groups of female athletes, one trained before sports participation and the other not trained, and a group of untrained male athletes throughout the high school soccer, volleyball, and basketball seasons. Weekly reports included the number of practice and competition exposures and mechanism of injury. There were 14 serious knee injuries in the 1263 athletes tracked through the study. Ten of 463 untrained female athletes sustained serious knee injuries (8 noncontact), 2 of 366 trained female athletes sustained serious knee injuries (0 noncontact), and 2 of 434 male athletes sustained serious knee injuries (1 noncontact). The knee injury incidence per 1000 athlete-exposures was 0.43 in untrained female athletes, 0.12 in trained female athletes, and 0.09 in male athletes (P 0.02, chi-square analysis). Untrained female athletes had a 3.6 times higher incidence of knee injury than trained female athletes (P 0.05) and 4.8 times higher than male athletes (P 0.03). The incidence of knee injury in trained female athletes was not significantly different from that in untrained male athletes (P 0.86). The difference in the incidence of noncontact injuries between the female groups was also significant (P 0.01). This prospective study demonstrated a decreased incidence of knee injury in female athletes after a specific plyometric training program.
The purpose of this study was to determine if high-arched and low-arched runners exhibit different injury patterns.
Non-randomized, two-group injury survey.
Running-related injuries are thought to be related, in part, to lower extremity structure. High-arched and low-arched runners with their different bony architecture may exhibit very different lower extremity mechanics and, consequently, different injury patterns. It was hypothesized that high-arched runners will exhibit a greater incidence of lateral injuries, skeletal injuries and knee injuries while low-arched runners will show a greater incidence of medial injuries, soft tissue injuries and foot injuries.
Twenty high-arched and 20 low-arched runners were included in this study. Running-related injuries were recorded and divided into injury patterns of medial/lateral, bony/soft tissue and knee/foot and ankle for both high-arched and low-arched runners. A chi(2) analysis was then employed in an attempt to associate injury patterns with arch structure.
High-arched runners reported a greater incidence of ankle injuries, bony injuries and lateral injuries. Low-arched runners exhibited more knee injuries, soft tissue injuries and medial injuries.
Based on these results, high and low arch structure is associated with different injury patterns in runners. Relevance. Different injury patterns are present in individuals with extreme high arches when compared to those with extremely low arches. These relationships may lead to improved treatment and intervention strategies for runners based on their predisposing foot structure.
The purposes of this study were: a) to examine the effect of verbal instructions given to the subjects on the control of lower extremity stiffness and b) to determine the effect of leg stiffness on mechanical energetic processes during drop jumps on a sprung surface.
A total of 10 female athletes performed a series of drop jumps on a sprung surface from heights of 20 and 40 cm. The instructions given to the subjects were a) "jump as high as you can" and b) "jump high a little faster than at your previous jump." The jumps were performed at each height until the athlete could not achieve a shorter ground contact time. Four jumps per subject per height were analyzed. The ground reaction forces were measured using a "Kistler" force plate (1000 Hz). The athletes' body positions were recorded using a high-speed (250 Hz) video camera. The deformation of the sprung surface was determined by another high-speed camera operating at 500 Hz. Surface EMG was used to measure muscle activity in five leg muscles.
The contact time showed high correlation with leg stiffness as well as with ankle and knee stiffness. The change in leg stiffness was not due to the duration of the preactivation but rather to the level of activation during this phase. An increase in leg stiffness caused an increase in the energy stored and recovered in and by the sprung surface and a decrease of the energy produced by the subjects.
By influencing contact time through verbal instructions, it is possible to control leg stiffness. Maximal vertical take-off velocity of the center of mass and maximal take-off body energy can be achieved having different levels of leg stiffness. The maximization of mechanical power is achieved by optimal leg stiffness values and leg muscle preactivation levels.
The purposes of this study are: a) to examine the possibility of influencing the leg stiffness through instructions given to the subjects and b) to determine the effect of the leg stiffness on the mechanical power and take-off velocity during the drop jumps. A total of 15 athletes performed a series of drop jumps from heights of 20, 40 and 60 cm. The instructions given to the subjects were a) "jump as high as you can" and b) "jump high a little faster than your previous jump". The jumps were performed at each height until the athlete could not achieve a shorter ground contact time. The ground reaction forces were measured using a "Kistler" force plate (1000 Hz). The athletes body positions were recorded using a high speed (250 Hz) video camera. EMG was used to measure muscle activity in five leg muscles. The data was divided into 5 groups where group 1 was made up of the longest ground contact times of each athlete and group 5 the shortest. The leg and ankle stiffness values were higher when the contact times were shorter. This means that by influencing contact time through verbal instructions it is possible to control leg stiffness. Maximum center of mass take-off velocity the can be achieved with different levels of leg stiffness. The mechanical power acting on the human body during the positive phase of the drop jumps had the highest values in group 3. This means that there is an optimum stiffness value for the lower extremities to maximize mechanical power.
Stiffness has often been considered as a regulated property of the neuromuscular system. The purpose of this study was to examine the ankle and knee joint stiffness regulation during sprint running.
Ten male sprinters ran at the constant relative speeds of 70, 80, 90, and 100% over a force platform, and ground reaction forces, kinematic, and EMG parameters were collected.
The results indicated that with increasing running speed the average joint stiffness (change in joint moment divided by change in joint angle) was constant (7 N x m x deg(-1)) in the ankle joint and increased from 17 to 24 N x m x deg(-1) (P < 0.01) in the knee joint.
The observed constant ankle joint stiffness may depend on (constant) tendon stiffness because of its dominating role in triceps surae muscle-tendon unit. Thus, we conclude that in sprint running the spring-like behavior of the leg might be adjusted by changing the stiffness of the knee joint. However, in complicated motor task, such as sprint running, ankle and knee joint stiffness might be controlled by the individual mechanical and neural properties.
The purposes of this study were a) to develop a model of the foot capable of describing the foot motion during dynamic movements and b) to study the influence of different mats on foot motion during landing in gymnastics.
Six female gymnasts (height: 1.63 +/- 0.04 m, weight: 58.21 +/- 3.46 kg) participated in this study. All six gymnasts carried out barefoot landings, falling from 80 and 115 cm onto three mats each with a different stiffness (hard, medium, and soft). Three synchronized digital high-speed video cameras (250 Hz) captured the motion of the left shank and foot. At the same time, the reaction forces between mat and foot at the forefoot and rearfoot were measured by two instrumented insoles (Paromed, 1000 Hz). The kinematics of the tibiotalar, talonavicular, and calcaneocuboid joints were examined. The lower leg and the foot were modeled by means of a multi-body system, comprising seven rigid bodies. For each joint, two joint coordinate systems attached on each of the connected segments were defined.
The mat stiffness did not show any influence on the maximal reaction forces or on the kinematics of the tibiotalar joint. For the soft mat, higher maximal eversion angles at the talonavicular and the calcaneocuboid joints were measured.
The relative motion between forefoot and rearfoot was influenced by changing mat stiffness. Therefore, the construction of the mat influenced the motion of the foot. The observation of only the tibiotalar joint is not enough when studying the influence of different mats on foot motion. The functional benefit of the mechanical advantages of a soft mat (higher energy absorption) includes a decrease in stability. The surface of the landing mat should, therefore, be reinforced by a stabilizing mechanism.
Leg stiffness was compared between age-matched males and females during hopping at preferred and controlled frequencies. Stiffness was defined as the linear regression slope between the vertical center of mass (COM) displacement and ground-reaction forces recorded from a force plate during the stance phase of the hopping task. Results demonstrate that subjects modulated the vertical displacement of the COM during ground contact in relation to the square of hopping frequency. This supports the accuracy of the spring-mass oscillator as a representative model of hopping. It also maintained peak vertical ground-reaction load at approximately three times body weight. Leg stiffness values in males (33.9+/-8.7 kN/m) were significantly (p<0.01) greater than in females (26.3+/-6.5 kN/m) at each of three hopping frequencies, 3.0, 2.5 Hz, and a preferred hopping rate. In the spring-mass oscillator model leg stiffness and body mass are related to the frequency of motion. Thus male subjects necessarily recruited greater leg stiffness to drive their heavier body mass at the same frequency as the lighter female subjects during the controlled frequency trials. However, in the preferred hopping condition the stiffness was not constrained by the task because frequency was self-selected. Nonetheless, both male and female subjects hopped at statistically similar preferred frequencies (2.34+/-0.22 Hz), therefore, the females continued to demonstrate less leg stiffness. Recognizing the active muscle stiffness contributes to biomechanical stability as well as leg stiffness, these results may provide insight into the gender bias in risk of musculoskeletal knee injury.
The adjustment of the leg during running was addressed using a spring-mass model with a fixed landing angle of attack. The objective was to obtain periodic movement patterns. Spring-like running was monitored by a one-dimensional stride-to-stride mapping of the apex height to identify mechanically stable fixed points. We found that for certain angles of attack, the system becomes self-stabilized if the leg stiffness was properly adjusted and a minimum running speed was exceeded. At a given speed, running techniques fulfilling a stable movement pattern are characterized by an almost constant maximum leg force. With increasing speed, the leg adjustment becomes less critical. The techniques predicted for stable running are in agreement with experimental studies. Mechanically self-stabilized running requires a spring-like leg operation, a minimum running speed and a proper adjustment of leg stiffness and angle of attack. These conditions can be considered as a movement criterion for running.
To determine whether the stiffness characteristics of the leg change during a treadmill run to voluntary exhaustion.
Fifteen runners performed a test run at a constant speed that elicited approximately 80% of their .VO(2peak). The run was performed on a treadmill instrumented to measure vertical ground reaction forces; vertical stiffness and leg stiffness were calculated from these forces. Force data were sampled for 15 s every 5 min and immediately before the end of the test. From the force data, average stiffness characteristics were determined for each sample period. An ANOVA with repeated measures (alpha = 0.01) was performed for the group on both vertical and leg stiffness. A single-subject, case-series analysis was also performed on each subject by using ANOVA (alpha = 0.01).
Group analysis revealed significant decreases (P < 0.01) in both vertical (23.9 to 23.1 kN.m(-1)) and leg (9.3 to 9.0 kN.m(-1)) stiffness over the run. Based on single-subject ANOVA, 14 of the 15 runners experienced significant (P < or = 0.01) changes in k(vert) over the run. A significant correlation between changes in stride rate and vertical stiffness was found (r = 0.85). Changes in the stiffness properties of the leg, as determined via the spring-mass model, resulted in changes in vertical displacement of the center of mass and leg length (distance from ankle to hip) during stance, as opposed to changes in peak force during ground contact.
Observed changes in stride rate possibly result from changes in the stiffness characteristics of the leg during a run to fatigue.
Joint stiffness during running with different footfall patterns Conference Proceedings: XIth Congress of the Canadian Society for BiomechanicsLeg spring'' characteristics and the aerobic demand of running
- J Hamill
- T R Derrick
- I Mcclay
Hamill, J., Derrick, T.R., McClay, I., 2000. Joint stiffness during running with different footfall patterns. Conference Proceedings: XIth Congress of the Canadian Society for Biomechanics, Mon-treal, Que., Canada, p. 47. Heise, G.D., Martin, P.E., 1998. ''Leg spring'' characteristics and the aerobic demand of running. Med. Sci. Sports 30, 750–754.
Lower extremity stiffness in runners with different foot types
- D S Williams
- I Davis
- J P Scholz
- J Hamill
- T S Buchanan