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Gender differences in active musculoskeletal stiffness. Part II. Quantification of leg stiffness during functional hopping tasks
Abstract
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.
... Most authors have proposed various factors, including the influence of hormones and menstrual cycles, as well as anatomical, genetic, and neuromuscular differences between male and female athletes [8][9][10]. However, as the cause of ACL injury may be attributed to a complex interplay of risk factors, several studies have suggested that biomechanical factors may partially explain the gender difference in the incidence of ACL injury [11], and it is believed that stiffness of the musculoskeletal system is one of the biomechanical factors that may contribute to the sex differences in ACL injury rates [12]. ...
... Leg stiffness has been shown to be an important indicator of the risk of sports injury. Through numerous studies, an increasing amount of evidence indicates that both excessively high and excessively low stiffness can significantly contribute to a higher incidence of musculoskeletal injuries [7,12,25]. Previous studies have shown that excessive leg stiffness may increase peak forces and reduce the lower limb range of motion, the combination of which usually increases loading rates [26]. The combination of increased peak forces, loading rates, and impact forces can make people more susceptible to skeletal injuries [27]. ...
... Ward, Rachel E et al. compared the stiffness of male and female dancers and male and female athletes during jumping and landing tasks and they also found that female athletes had less leg stiffness than male athletes [33]. A previous study by Padua et al. also found that, compared to males, female athletes had significantly less stiffness in the lower limbs during jumping compared to males [12]. However, the mean leg stiffness values for the male and female athletes in this study were higher than in previous studies, which may be due to differences in our single-leg landing task. ...
In general, at the same level of exercise, female athletes are three to six times more likely to injure an anterior cruciate ligament (ACL) than male athletes. Female athletes also had higher rates of ACL injury than males in a single-leg landing task after a backcourt backhand side overhead stroke in badminton. In many previous studies, stiffness of the musculoskeletal system in the lower limbs has been reported as a potential factor contributing to differences in ACL injury rates between genders. The purpose of this study was to describe the differences between genders in leg and knee stiffness in male and female athletes during a single-leg landing action after the backhand side overhead shot in the backcourt. Eight male athletes and eight female athletes participated in this test. Leg stiffness and knee stiffness were calculated separately for male and female athletes during the landing phase. The results showed that both absolute and normalized leg stiffness were lower in female athletes than in male athletes (p < 0.05). And both absolute and normalized knee stiffness were also lower than male athletes (p < 0.05). The low leg stiffness and knee stiffness demonstrated by females in this single-leg drop task compared to male athletes may indicate that females have lower dynamic leg stability than males during the drop, which may lead to hypermobility of the knee joint and may put females at a higher risk of injury in this high-risk maneuver for non-contact cruciate ligament injuries.
... How the test is performed will have a direct influence on the stiffness values obtained. For example, Farley et al. (1991) and Granata, Padua, & Wilson (2001) reported that vertical stiffness increased with hopping frequency (Farley et al., 1991;Granata, et al., 2002). However, researchers have suggested that sub-maximal hopping (in which self-selected or metronome-controlled frequencies are typically employed) may demonstrate greater correspondence to submaximal performance tasks whilst maximal tasks may demonstrate greater correspondence to maximal performance tasks (Maloney, Fletcher, & Richards, 2016;J. ...
... Five acceptable consecutive hops were used for analysis (from 6th to 10th) (Chelly & Denis, 2001;Hobara et al., 2013). Those trials where the correlation between vertical GRF and vertical displacement of COM during ground contact phase was less than r = 0.8 were eliminated (Granata et al., 2002). In control strategy, the participants hopping frequency must have been within 5% of designated metronome frequency to be accepted for data analysis (Granata et al., 2002). ...
... Those trials where the correlation between vertical GRF and vertical displacement of COM during ground contact phase was less than r = 0.8 were eliminated (Granata et al., 2002). In control strategy, the participants hopping frequency must have been within 5% of designated metronome frequency to be accepted for data analysis (Granata et al., 2002). The spring-mass model assumes that the lower extremity behaves like a linear spring during the ground contact phase of hopping, so vertical stiffness can be calculated as the ratio of peak ground reaction force ( ) to maximum vertical displacement of the center of mass (∆y) which occurs at the midpoint of the ground contact phase (T. A. McMahon & Cheng, 1990). ...
Vertical stiffness has been highlighted as a potential determinant of performance and may be estimated across a range of different performance tasks. The aim of the current study was to investigate the relationship between vertical stiffness determined during 9 different hopping tests and performance of vertical jumps. Twenty healthy, active males performed vertical hopping tests with three different strategies (self‐selected, maximal, and controlled) and three different limb configurations (bilateral, unilateral preferred, and unilateral non‐preferred), resulting in nine different variations, during which vertical stiffness was determined. In addition, participants performed squat jump (SQJ) and countermovement jump (CMJ) during which jump height, CMJ stiffness, and eccentric utilization ratio (EUR) were determined. Vertical stiffness in bilateral and unilateral preferred tasks performed with a self‐selected and maximal, but not controlled, strategy was associated with stiffness in the CMJ ( r = 0.61–0.64; p < 0.05). However, stiffness obtained during unilateral preferred and non‐preferred hopping with self‐selected strategy was negatively associated with performance in SQJ and CMJ tasks ( r = −0.50 to −0.57; p < 0.05). These findings suggest that high levels of vertical stiffness may be disadvantageous to static vertical jumping performance. In addition, unilateral hopping with a self‐selected strategy may be the most appropriate task variation if seeking to determine relationships with vertical jumping performance.
Highlights
Stiffness obtained during unilateral hopping with a preferred strategy was negatively associated with vertical jumping performances
Stiffness obtained during hopping with preferred and maximal strategies was associated with stiffness obtained during a countermovement jump
In this population, hopping stiffness may therefore be reflective of an individual's countermovement jump strategy
High levels of stiffness may be disadvantageous to static‐start vertical jumping
... Injuries to the Anterior Cruciate Ligament (ACL) are particularly common during landing [6]. Granata et al. [7] found that women showed smaller joint stiffness than men at landing, which was an important cause of non-contact ACL rupture. At the same time, the valgus torque of the knee joint increased at or near exhaustion, indicating a decrease in the ability of the musculoskeletal system to maintain joint stability. ...
... This study also has certain limitations, first of all, Our experiment was based on laboratory environment collection, and there was a gap with the real competition, the subjects of this study group were limited to male table tennis players, and on the surface of previous research, women than men in landing showed smaller joint stiffness, which is the important cause leading to the non-contact ACL rupture [7]. Secondly, since the chasse-step method is the most common in table tennis, but the one-step method and the cross-step method are also often used in mixed movement, this study only uses the chasse-step method to explore the mechanism of knee joint injury in the landing process before and after fatigue, and whether other steps are also different needs further discussion and explanation. ...
This study investigated the relationship between lower extremity biomechanics and anterior cruciate ligament (ACL) injury in table tennis players before and after fatigue. We compared the biomechanical changes in the lower limbs of table tennis players during landing after completing a chasse-step while stroking, both before and after fatigue. A further aim was to examine ACL injury and provide a reference for training table tennis players. Ten national Level I table tennis players underwent lower extremity neuromuscular fatigue by running at a constant speed. Biomechanical data of the athletes were collected before and after fatigue. The effects of movement and characteristic time before and after fatigue on biomechanics were determined using a paired sample t-test. After fatigue, the angle of the ankle joint and the range of motion of the knee joint were significantly reduced (p < 0.001), while the angle of motion of the hip joint did not change considerably (p = 0.747). The angular velocity of the ankle and knee joints increased significantly after fatigue (p < 0.001), but the angular velocity of the hip joint decreased significantly (p = 0.013). Additionally, the ankle plantar flexion moment (p = 0.003), knee flexion moment (p < 0.001), and hip flexion moment (p < 0.001) increased significantly after fatigue. The ankle power (p = 0.023), knee power (p = 0.009), and hip power (p < 0.001) were significantly reduced throughout the landing cycle after fatigue. Fatigue in table tennis athletes reduces the sagittal plane buckling angle of the knee and ankle joints during landing. This change increases ground reaction and knee joint forces, significantly elevating the risk of knee injuries, including ACL tears. The reduced flexion angle exposes the knee to greater torque and diminishes its shock absorption capacity, heightening the risk of lower limb injuries. These findings underscore the need to address the impact of fatigue on landing mechanics in sports training and rehabilitation, emphasizing preventive measures.
... To address this gap and provide scientific evidence regarding leg stiffness and R P , our study took a new methodological approach. A higher level of leg stiffness is believed to enhance the dynamic mechanism's ability to generate rebound movements during the stretch-shortening cycle [23,24] and reduce the risk of excessive load on passive knee structures [25]. Plyometric training is known to enhance these characteristics, and by using the mini trampoline as a training tool, we aimed to gain valuable insights beyond what traditional vertical jumps, countermovement jumps, and repetitive jumps can offer. ...
... However, Granata et al. [23] stated in their work that it is not clear whether the cause of the sex difference in leg stiffness is due to the physical characteristics (i.e., height and weight) of male and female subjects. Furthermore, hopping involves the storage and utilization of strain energy and, therefore, the maintenance of leg stiffness; landing involves the dissipation of strain energy and, therefore, a rapid reduction in leg stiffness following the initial impact phase. ...
The purpose of this study was to evaluate the acute effects of a mini trampoline training session (SuperJump®) on leg stiffness and reactive power (RP) while examining its relation to participants’ sex. A total of 20 participants (11 females, age: 24.4 ± 1.0 yrs; 9 males, age: 27.3 ± 2.9 yrs) performed continuous jump repetitions (RJs), measured on a force plate, before (PRE) and after (POST) a 30 min Superjump® session. Linear repeated measures mixed models were used to examine the effects of the Superjump® session on the leg stiffness mean (KMEAN), mean of the best RJs (KBEST), and RP in relation to sex. Before and after the mini trampoline training session, females showed lower KMEAN and KBEST values compared with males. Despite the significant (p < 0.002) decreases in RP after the Superjump® session in both males (PRE: 23.1 ± 6.5 W/kg; POST: 21.2 ± 6.1 W/kg) and females (PRE: 23.6 ± 5.5 W/kg; POST: 21.9 ± 5.3 W/kg), leg stiffness remained unchanged, suggesting a potential protective effect of mini trampoline training on leg stiffness during acute adaptations. These findings suggest that Superjump® training might exert a protective effect on leg stiffness, which prevents acute decreases that are commonly observed in other training modalities. The sex-related differences emerging from the present study emphasize the need for personalized approaches when integrating this innovative training tool into athletes’ regimens.
... Then, the take-off phase begins, which ends when the feet lose contact with the ground and the value of the ground reaction forces drop to zero. Leg stiffness was estimated in parts of the countermovement (between the lowest ground reaction force and the lowest height above the ground of the greater trochanter of the femur) and take-off phases (between the local maximum of ground reaction force from which ground reaction forces only decreased and the moment when the value of ground reaction forces drops to zero), where F(∆l) profile was nearly linear (Figure 2) [28] i.e., when the value of the coefficient of determination R 2 was over 0.6 [29]. The slope coefficient for the analyzed parts of the F(∆l) curve is the numerical value of stiffness in these ranges. ...
... Then, the take-off phase begins, which ends when the feet lose contact with the ground and the value of the ground reaction forces drop to zero. Leg stiffness was estimated in parts of the countermovement (between the lowest ground reaction force and the lowest height above the ground of the greater trochanter of the femur) and take-off phases (between the local maximum of ground reaction force from which ground reaction forces only decreased and the moment when the value of ground reaction forces drops to zero), where F(Δl) profile was nearly linear (Figure 2) [28] i.e., when the value of the coefficient of determination R 2 was over 0.6 [29]. The slope coefficient for the analyzed parts of the F(Δl) curve is the numerical value of stiffness in these ranges. ...
Assessment of the inter-limb asymmetry of leg stiffness is carried out using one-legged jumping tasks. However, the level of asymmetry may vary depending on the performance on one or both lower limbs. Therefore, the purpose of this study was to identify the differences in leg stiffness between the dominant and non-dominant lower limb during a two-legged countermovement jump. The research was conducted on 35 s-league basketball players (body height: 1.90 ± 0.08 m, body mass: 81.9 ± 10 kg, age: 19.5 ± 1.7 years). Each participant performed three countermovement jumps with arm swing to the maximum height. Measurements employed a BTS SMART motion analysis system and two Kistler force plates. Statistically significant differences were found during the comparison of leg stiffness in the dominant and non-dominant lower limbs. Inter-limb asymmetry of leg stiffness reached 22.0% in the countermovement phase and 8.9% in the take-off phase. Significant inter-limb asymmetry of leg stiffness might lead to injury or considerably reduce the performance of athletes. Therefore, an important role is to conduct strength and speed-strength trainings with proper loads to both body sides. Coaches should pay more attention to similar lower limbs movement patterns during two-legged exercises and bilateral strength development.
... Covariates were assessed in separate ANCOVAs to determine significant factors contributing to muscle changes. Due to previously reported differences in male and female muscle characteristics (Granata et al., 2002;Owens et al., 2007), the sex variable was investigated further with independent t-tests and Pearson correlations, as well as within the ANCOVA analysis. All statistical analysis was carried out using SPSS (version 23) with the alpha level set at 0.05. ...
... Sex did not account for the variance in stiffness within the ANCOVA model and suggests that initial stiffness values have greater influence than sex on stiffness response, supported by similar correlation trends for males and females (Table 3). This could be further investigated in a sex comparison study, given the known difference between male and female muscle composition (Granata et al., 2002;Nair et al., 2016;Owens et al., 2007). It is important to note that, while ODI, BMI, waist or height measurements do not contribute to stiffness response, they could still influence the initial stiffness values. ...
Background
Despite the lack of objective evidence, spinal manual therapies have been common practice for many years, particularly for treatment of lower back pain (LBP). This exploratory study measured and analysed the effect of a spinal mobilisation intervention on muscle tissue quality in LBP sufferers.
Methods
40 people with LBP participated in a within-subject repeated measures cross-over study with intervention and control conditions. A myometer was used to assess the change in para-spinal muscle tissue quality before and after the intervention. Analysis considered the magnitude of muscle response together with individual covariates as potential contributors.
Results
A significant post intervention reduction was observed in muscle stiffness (p = 0.012, η 2 partial = 0.15), tone (p = 0.001, η 2 partial = 0.25) and elasticity (p = 0.001, η 2 partial = 0.24). Significant increases were seen in 2 variables post control: stiffness (p = 0.004, η 2 partial = 0.19), tone (p = 0.006, η 2 partial = 0.18) and a significant decrease in elasticity (p ˂ 0.000, η 2 partial = 0.3). Significant contributing covariates include baseline stiffness, BMI, waist circumference and sex. Baseline stiffness and tone were significantly correlated to their response levels.
Conclusions
The significant reduction in all muscle tissue qualities following the intervention provide preliminary data for an evidence-based LBP therapeutic. Baseline stiffness, BMI, waist circumference and sex could act as significant contributors to magnitude of response. The results warrant further investigation into spinal mobilisation therapies to further build the objective evidence base.
... Previous biomechanical studies on typically developed participants (Beerse & Wu, 2017;Farley et al., 1991;Granata, Padua, & Wilson, 2002) showed that hopping frequency is associated with vertical stiffness. Our results confirmed this association in DS participants, as evidenced by the significant correlation observed between these two variables (ρ = 0.68). ...
... Moreover, recent evidence using a pendulum test to evaluate knee joint stiffness supports the notion of higher passive joint stiffness in DS individuals (Ferreira, Liang, & Wu, 2020) compared to a control group; but see also Casabona, Valle, Pisasale, Pantò, and Cioni (2012) for opposite results. In typically developed individuals, it has been shown that an increased muscle stiffness may be promoted by muscle reflex response (Granata et al., 2002;Jones & Watt, 1971), although studies focusing on muscle reflex response in individuals with DS failed to show significant differences in early reflex response (Rigoldi et al., 2016;Shumway-Cook & Woollacott, 1985) or showed even delayed long latency response in this population (Shumway-Cook & Woollacott, 1985) compared to a control group. Overall, these evidences show that the higher joint stiffness observed in DS may not be accounted solely by muscle reflex response and that also supra-spinal structures shall be considered. ...
Introduction
Individuals with Down syndrome (DS) show a delayed acquisition of gross motor skills. Among gross motor skills, hopping is a particular form of jumping that can be performed using one leg. Despite its large use during play and physical activity, this skill in adults with DS has not received much attention so far. Here, we aim at investigating hopping skill in adults with DS both from a quantitative and qualitative point of view.
Methods
Center of mass and dominant leg kinematics during hopping over distance were recorded from 24 adult individuals with DS and from 21 typically developed adults (TD) using two inertial measurement units positioned on the posterior aspect of the lower back and on the lateral malleolus of the hopping leg. From linear acceleration and angular velocity signals, hopping frequency (HF), cycle, stance and flight duration (CD, SD, FD), vertical stiffness (KV) and peak to peak linear acceleration and angular velocities about the cranio-caudal, antero-posterior and medio-lateral axes were extracted. A qualitative process assessment of the hopping skill was carried out using the performance criteria of the test for gross motor development (TGMD-3). The extracted parameters were submitted to analysis of covariance, with stature as a covariate to rule-out possible confounding effects.
Results
The qualitative assessment highlighted a poorer hopping performance in the DS group compared to the TD group. DS participants showed higher HF and KV, shorter CD, SD, FD and lower angular velocity about the cranio-caudal axis compared to the TD group. Significant correlations between the temporal parameters of the quantitative assessment and the results of the qualitative assessment were observed.
Discussion
The poorer motor competence in hopping in individuals with DS compared to TD peers may be related to the shorter flight time and higher vertical stiffness observed in TD peers. The adopted instrumental approach, overcoming the limitations of subjective evaluations, represents a promising opportunity to quantify motor competence in hopping.
... 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.
... A) Natural Variability in Hopping: The results shown in Fig. 2 reveal variations in average normalized GRF among participants at their self-selected frequencies (without metronome). This affirms the intrinsic variability in human hopping patterns, influenced by physiological and neuromuscular factors [14], [22]. However, the hop-to-hop variance in GRF peaks (less than 10% of the peak) is not significantly different among subjects. ...
... It plays a key role in supporting loads and stabilizing the body during dynamic tasks. Abnormal joint stiffness can increase the risk of injury-insufficient stiffness may result in excessive joint mobility, while excessive stiffness can raise the risk of bone injuries [25][26][27][28]. Previous studies have highlighted the importance of exploring the relationship between joint stiffness and leg stiffness across various motor tasks and speeds, especially in high-impact activities like jumping and running [29]. ...
This study investigates the impact of quadriceps fatigue on lower limb biomechanics during the landing phase of a single-leg vertical jump (SLJ) in 25 amateur male basketball players from Ningbo University. Fatigue was induced through single-leg knee flexion and extension exercises until task failure. Kinematic and dynamic data were collected pre-fatigue (PRF) and post-fatigue (POF) using the Vicon motion capture system and the AMTI force platform and analyzed using an OpenSim musculoskeletal model. Paired sample t-tests revealed significant changes in knee and hip biomechanics under different fatigue conditions, with knee joint angle (p < 0.001), velocity (p = 0.006), moment (p = 0.006), and power (p = 0.036) showing significant alterations. Hip joint angle (p = 0.002), moment (p = 0.033), and power (p < 0.001) also exhibited significant changes. Muscle activation and joint power were significantly higher in the POF condition, while joint stiffness was lower. These findings suggest that quadriceps fatigue leads to biomechanical adjustments in the knee and hip joints, which may increase the risk of injury despite aiding in landing stability.
... These results suggest that the impairments in the generation of elastic energy during the eccentric phase were independent of quadriceps weakness and may be due to a disruption in stretch-shortening cycle function. The function of the lower extremity during a CMJ has often been described as that of a spring, which stores elastic energy during the eccentric phase and releases it during the concentric phase (9,12). The ability to rapidly unweight oneself and then to eccentrically control the descent into the countermovement is essential to producing large amounts of force during the concentric phase of the CMJ (17,18). ...
... A free oscillation technique [16,[25][26][27] was used to assess the unilateral musculoarticular (MA) stiffness of the quadriceps. The free oscillation technique models the human body as a damped, single-degree-of-freedom "spring-mass" system. ...
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.
... The values [32] of 15-16-year-old (30.8 ± 10.3 kN/m) and 19-20-year-old female groups (39.4 ± 10.9 kN/m) were significantly higher than in our study. In male rugby players, studies have shown similar values: 34.9 [33] or 33.9 ± 8.7 kN/m [34]. Similarly, RSI values of a 19-20-year-old female group (mean 1.67) were significantly higher, with male values even higher (2.22) in the same age group [32]. ...
Background: Most specific rugby movements require an efficient stretch-shortening cycle (SSC). Reactive strength index (RSI) and leg stiffness have been considered a reliable measure of SSC capability and an indicator of ACL injury risk. The aim of this study was to assess and compare absolute leg stiffness (ALS) and RSI in amateur female rugby players from different countries.Methods: Players of three female rugby teams participated in the study: the female Czech team, the junior female Czech team, and the female university English team. Twenty repetitions of the submaximal bilateral hopping test were used for the calculation of ALS. RSI was obtained from 5 repetitions of the maximum hop test. Results: The values of the basic statistics were as follows: the female Czech team (median, mean SD): ALS, 25.3 kNm–1, 25.4 3.6 kNm–1; RSI, 0.53, 0.60 0.24; the junior female Czech team (median, mean SD): ALS, 22.7 kNm–1, 23.1 4.6 kNm–1; RSI, 0.37, 0.42 0.19, and the female university English team (median, mean SD): ALS, 22.7 kNm–1, 24.0 3.5 kNm–1; RSI, 0.61, 0.59 0.20. Only a between-group comparison of RSI of the female Czech team and the junior female Czech team (p = 0.04, r = 0.37, medium effect) showed significant differences. Conclusion: No significant differences between groups were found, except for Czech teams of different ages in RSI. The lower values of ALS and RSI compared to other studies can potentially be associated with a higher risk of ACL injury.
... Carmichael 2017). Factors such as body weight, joint stress, and hormonal environment (particular sex hormones) have been proposed as potential contributors to the capsule thickness variations between anatomical regions (Bey et al. 2005;Ticker et al. 1996;Voycheck et al. 2010;Granata et al. 2002;Fuss and Bacher 1991;McFarland et al. 1996). Studies conducted in humans have demonstrated that the joint capsule thickness exhibits differing properties between sexes (Araújo et al. 2004;Bey et al. 2005;McFarland et al. 1996;Borsa et al. 2002;Brown and Aaron 2001;Brown et al. 2000;Chandrashekar et al. 2006;Kubo et al. 2003;Moore et al. 2004;Pollard et al. 2006). ...
Differences between serum C-reactive protein (SCRP) and synovial fluid C-reactive protein (SFCRP) concentrations in healthy animals may be influenced by the sex of the individual and associated with various factors. The objective of this study was to evaluate the disparities in SCRP and SFCRP concentrations between females and males, as well as within each sex. Sixty healthy dogs (N = 60), comprising both sexes, were enrolled in the study. Peripheral blood and knee synovial fluid samples were collected for SCRP and SFCRP analysis, respectively. Serum C-reactive protein (SCRP) and SFCRP concentrations were measured, with mean of 9.61 ± 4.96 mg/L for SCRP and 1.28 ± 3.05 mg/L for SFCRP. Notably, SFCRP concentrations were consistently lower than SCRP concentrations in both sexes. Statistically significant differences were observed between sexes for both SCRP (P = 0.021) and SFCRP (P = 0.007). Further analysis within females revealed statistically significant differences between SCRP and SFCRP concentrations (P = 0.002), whereas in males, such differences were not significant (P = 0.175). Additionally, weak correlations were found between SCRP and SFCRP concentrations for both sexes (females r = 0.07; males r = 0.29). Joint capsule thickness was assessed using ultrasonography, revealing thicker joint capsules in males. A robust positive association was noted between joint capsule thickness and the SFCRP concentration in both sexes. These findings offer valuable insights into the dynamics of CRP in the context of joint health in male and female patients, elucidating the underlying pathological mechanisms of joint disease and inflammation. Overall, this underscores the importance of considering sex-specific factors in the assessment and management of joint health, as well as in the design and interpretation of studies involving SFCRP concentrations.
... Impaired EMD performance (18.1%) immediately following match-play suggests that game-related exercise stress disrupted post-synaptic processes such as the transmission of force through the series elastic component and alterations within the excitation-contraction coupling process (Howatson, 2010). Comparable research evidence in elite male soccer players is lacking, but arduous soccer-activities increased EMD latencies by 58.4% (De Ste Croix et al., 2015) in female players, who have previously demonstrated prolonged EMD latencies (Blackburn et al., 2009;Granata et al., 2002;Zhou et al., 1995). ...
Purpose: The purpose of this study was to assess sensorimotor and neuromuscular performance capabilities over an in-season microcycle in early-career professional soccer players and to examine the relationship with training and match-play workload. Methods: Sensorimotor and neuromuscular performance capabilities (isometric knee extensor: force replication error, peak force, electromechanical delay, rate of force development) of 12 professional soccer players were assessed over a 7-day period. Training and match-play workload was also recorded over the same period for each player (high-intensity running distance). Fluctuations in sensorimotor and neuromuscular performance and workload variables were analysed. Results: There was evidence of fluctuations in sensorimotor and neuromuscular performance capability over the microcycle that reached statistical (p < .005) and practical (18.1% [baseline-to-peak]) significance alongside heterogeneity in training and match workload (264% [coefficient of variation], p < .0005). Some temporal congruence among fluctuating patterns of intra-microcycle training and match-play load and concomitant electromechanical delay performance was noted (p < .005). Asynchronous responses were observed for peak force, but rate of force development and force replication error capabilities were unchanged during the microcycle. Conclusion: While some neuromuscular performance capabilities fluctuate over an in-season microcycle and are influenced partially by high-intensity running workload, sensorimotor performance capabilities were unchanged during the microcycle.
... When performing bounces or jumps, the literature states that the shorter the contact time of the lower extremities on the support surface, the higher the stiffness. 17, 28 In this case an increase occurs in stretch-reflex activity reliance due to the decrement in the ground contact time. 29 It is speculated that this neural adjustment of the extensor muscles of lower limbs that is a strong predictor of leg stiffness in boys, may apply in adults' Cross Fit athletes. ...
... Así, dos conceptos contradictorios nos llevan a una sola conclusión, que para un buen rendimiento deportivo en deportes que se basan en constantes ciclos de estiramiento-acortamiento una extensibilidad y un stiffness óptimo es requerido, y que ninguno debe exceder en demasía en desmedro del otro si es que se entrenan en forma separada. Varios estudios han examinado la relación entre stiffness y rendimiento deportivo, algunos de ellos reportando que el stiffness de la pierna aumenta con la frecuencia del salto cuando los sujetos saltan en el mismo lugar [148][149][150] . En otro estudio se estableció una correlación entre el incremento de la velocidad y el incremento del stiffness durante el rebote post aterrizaje de un salto 151 . ...
... In terms of leg stiffness comparison of players from these studies, it should also be considered that both groups of rugby players in the current study were heterogenous with a large age range. Comparable results were found in a healthy population aged from 21 to 31 years [58] with ALS values of 26.30 ± 6.50 kN·m -1 . However, it has to be considered that although a similar test protocol as in the current study was applied, a different measurement device was used. ...
This randomized control study aimed to assess 12 weeks of a novel neuromuscular training program (KneeRugbyWomen) on jump-related biomechanical variables in amateur female rugby players. Twenty-four participants were randomly allocated to either an experimental group (EG; n = 12, age: 20.05 ± 4.43 yrs., height: 166.54 ± 4.46 cm, weight: 64.65 ± 6.44 kg) or a control group (CG; n = 12, age: 20.04 ± 4.88 yrs., height: 166.83 ± 7.30 cm, weight: 69.83 ± 12.84 kg). Participants were tested before and after a 12-week intervention for jump-related biomechanical variables (leg stiffness, Reactive Strength Index (RSI), and landing mechanics using the Landing Error Scoring System (LESS)). A significant increase in RSI was found in EG (p = 0.012, r = 0.70, large effect). At post-testing, players in EG had significantly greater RSI scores compared to CG at post-intervention (p = 0.007, r = 0.55, large effect). LESS scores of CG were significantly greater compared to EG at pre-intervention (p = 0.008, r = 0.55, large effect) and post-intervention (p = 0.003, r = 0.60, large effect). Results of this study demonstrate a positive effect of the KneeRugbyWomen training program on RSI, which has been previously associated with increased ACL injury risk in female players.
... Of the many injury predictors for running, lower extremity stiffness has garnered much attention (Brazier et al., 2019;Butler et al., 2003;Cannon et al., 2019;Davis & Gruber, 2021;DuBose et al., 2017;Flanagan et al., 2008;Hamill et al., 2009;Lorimer et al., 2018;Maquirriain, 2012;Padua et al., 2006;Pruyn et al., 2012;Wang, 2009;Williams et al., 2003), predominately with the notion too much or too little stiffness leads to an increase in injury risk (Butler et al., 2003). Although a direct correlation between lower extremity joint stiffness and injury have yet to be formally established, research has supported that too much stiffness can increase injury bony risk due to high levels of peak force and loading rates, while too little stiffness can increase soft-tissue injury risk due to the increase in joint range of motion (Brazier et al., 2014;Granata et al., 2001;Pruyn et al., 2012;Williams et al., 2001). ...
Running is one of the most common forms of physical activity for autistic adolescents. However, research examining their lower extremity dynamics is sparse. In particular, no information exists regarding lower extremity joint stiffness in autistic adolescents. This study compared knee and ankle joint stiffness during the absorption phase of running between autistic adolescents and non-autistic controls. Motion capture and ground reaction forces were recorded for 22 autistic adolescents and 17 non-autistic age, sex, and BMI matched peers who ran at self-selected and standardized (3.0 m/s) speeds. Group × speed knee and ankle joint stiffness, change in moment, and range of motion were compared using mixed-model ANOVAs. There were no group × speed interactions for any variable. Autistic adolescents presented with significant (12 % and 19 %) reduced knee and ankle joint stiffness, respectively. In addition, autistic adolescents had significant reduced changes in knee and ankle joint moments by 11 % and 21 %, respectively, compared to their non-autistic peers. Only knee joint stiffness and knee joint moments were sensitive to running speed, each significantly increasing with speed by 6 %. Current literature suggests joint stiffness is an important mechanism for stability and usage of the stretch shortening cycle (or elastic recoil); as such, it is possible that the reduced ankle plantar flexor and knee extensor stiffness found in autistic adolescents in this study could be indicative of reduced efficiency during running. As group differences existed across both speeds, autistic adolescents may benefit from therapeutic and/or educational interventions targeting efficient running mechanics.
... Reports show that female team sport athletes are 3-6 times more likely to obtain an anterior cruciate ligament (ACL) injury than their male counterparts (113). However, there is disagreement about the influence of sex hormones on female ACL injury rates (55). Recently, Martin et al. (106), reported that injury rates were 47 and 32% greater in the late follicular phase than in the early follicular and luteal phases. ...
Ladies Gaelic football (LGF) is a traditional , amateur Gaelic sport played by female athletes. LGF is an invasion-based field sport involving high-intensity, intermittent match play. There is currently a paucity of research on intercounty (elite level) LGF despite a growing interest in the male version of the game. This article aims to provide strength and conditioning recommendations for LGF with particular focus on the intercounty level of play. Recommendations within this article include a needs analysis, female injury epidemiology , physical and physiological demands, female physiology, strength training, and specific conditioning guidelines based on the sport. Additional recommendations include an LGF-specific testing battery, a proposed periodization cycle, and sports-specific speed and agility development.
... Stiffness is defined as the resistance offered by muscle tissue to deformation against an external force that tries to modify its initial shape [1]. The importance of myotendinous stiffness lies in its influence on the joint stability [2,3] and its relationship to explosive force production [4] and to stretching-shortening cycle activity performance [5]. Furthermore, the assessment of small changes in stiffness can be a method of early identification of the development of muscle fatigue, muscle damage or muscle injury [6,7], adaptations to sport practice [8,9] and even age-related changes in myotendinous properties [10]. ...
The aim of the study was to describe the applicability of shear wave elastography to assess muscular and tendinous stiffness of the lower limbs during an incremental isometric strength test and to differentiate the stiffness evolution between superficial and deep muscle regions. Dominant rectus femoris and patellar tendons of 30 physically active people (28.3 ± 9.2 years, 173.2 ± 7.7 cm, 76.2 ± 12.6 kg) were measured in different isometric strength conditions (relaxed muscle, and at 10%, 20%, 30%, 40%, 50% and 60% of maximal voluntary contraction (MVC)). The percentage of success was >85% at all muscle contraction intensities for rectus femoris muscles but only in a relaxed condition for patellar tendons. Rectus femoris stiffness significantly increased compared to the relaxed condition from 30% to 60% MVC (p ≤ 0.011) in superficial muscle regions, and from 10% to 60% MVC(p≤0.002)indeepmuscle regions. Deep muscle regions showed higher stiffness values than superficial muscle regions at 30% MVC (51.46 ± 38.17 vs. 31.83 ± 17.05 kPa; p = 0.019), 40% MVC(75.21 ± 42.27 vs. 51.25 ± 28.90 kPa; p = 0.018), 50% MCV (85.34 ± 45.05 vs. 61.16 ± 37.03 kPa; p =0.034) and 60% MVC(109.29 ± 40.04 vs. 76.67 ± 36.07 kPa; p = 0.002). Rectus femoris stiffness increased during the incremental isometric contraction test, and inter-region differences were found at 30% MVC.
... Sex differences may be present in, but not limited to, joint laxity, muscle-tendon unit properties, and muscle architecture. There is evidence that females have greater ankle and knee joint laxity than males, which would impact the dynamics of joint torque production (Gabriel et al., 2008;Granata et al., 2002aGranata et al., , 2002bKomi and Karlsson, 2008) and the occurrence of injury (Hewett et al., 2008;Rosene and Fogarty, 1999;Rozzi et al., 1999). Sex differences in joint laxity were reported across all ages (Jansson et al., 2007;Oatis, 1993;Wright and Johns, 1961) and may be a result of fluctuations in estrogen concentrations throughout the menstrual cycle (Park et al., 2009b;Park et al., 2009a;Park et al., 2009c) and potential structural changes to the ligaments stabilizing the joint (Konopka et al., 2016). ...
The lack of systematic investigations on sex-related differences in motor unit behaviour poses a challenge in understanding and optimizing health and performance in males and females. Limited investigations revealed that sex differences in motor unit behaviour might be present in human muscles. This review summarizes the current knowledge on sex differences in motor unit behaviour and potential factors that may contribute to these differences. We show significant under-representation of female participants in motor unit studies and a limited number of studies investigating sex differences in motor unit behaviour. We place the current insights within the context of methodological limitations and outline several recommendations and future directions to improve female representation in this research area. We conclude that there is an urgent need to gather more data in females and investigate sex differences in motor unit behaviour. The knowledge gained could be used to develop sex-specific approaches to improve neuromuscular performance and rehabilitation.
... Athletes' lower limb injuries may occur if mechanical stiffness is too low or too high [21]. Stiffness that is too low may produce excessive joint mobility and injury to the related soft tissue [22][23][24]. Furthermore, excessive stiffness may raise the risk of lower extremity bone damage [25]. Vertical stiffness is widely used to explain the stiffness of the lower limb [26]. ...
The aim of this study was to assess the stiffness of each lower limb joint in healthy persons walking at varying speeds when fatigued. The study included 24 subjects (all male; age: 28.16 ± 7.10 years; height: 1.75 ± 0.04 m; weight: 70.62 ± 4.70 kg). A Vicon three-dimensional analysis system and a force plate were used to collect lower extremity kinematic and kinetic data from the participants before and after walking training under various walking situations. Least-squares linear regression equations were utilized to evaluate joint stiffness during single-leg support. Three velocities significantly affected the stiffness of the knee and hip joint (p < 0.001), with a positive correlation. However, ankle joint stiffness was significantly lower only at maximum speed (p < 0.001). Hip stiffness was significantly higher after walking training than that before training (p < 0.001). In contrast, knee stiffness after training was significantly lower than pre-training stiffness in the same walking condition (p < 0.001). Ankle stiffness differed only at maximum speed, and it was significantly higher than pre-training stiffness (p < 0.001). Walking fatigue appeared to change the mechanical properties of the joint. Remarkably, at the maximum walking velocity in exhaustion, when the load on the hip joint was significantly increased, the knee joint’s stiffness decreased, possibly leading to joint instability that results in exercise injury.
... Hewett et al. (18) found that runners with increased leg stiffness had higher loading rates during the stance phase of running, and a higher incidence of stress fractures due to reduced ground reaction force impact attenuation, compared to runners with lower leg stiffness (8,18). However, it has also been reported that runners with lower leg stiffness expend more metabolic energy during running, and have a higher incidence of soft tissue injury, such as ligament damage, due to greater joint motion (19,20). Thus, there likely exists an optimal leg stiffness during running that mitigates injury risk while improving performance through reductions in metabolic cost. ...
People with lower limb impairment can participate in activities such as running with the use of a passive-dynamic ankle-foot orthosis (PD-AFO). Specifically, the Intrepid Dynamic Exoskeletal Orthosis (IDEO) is a PD-AFO design that includes a carbon-fiber strut, which attaches posteriorly to a custom-fabricated tibial cuff and foot plate and acts in parallel with the impaired biological ankle joint to control sagittal and mediolateral motion, while allowing elastic energy storage and return during the stance phase of running. The strut stiffness affects the extent to which the orthosis keeps the impaired biological ankle in a neutral position by controling sagittal and mediolateral motion. The struts are currently manufactured to a thickness that corresponds with one of five stiffness categories (1 = least stiff, 5 = most stiff) and are prescribed to patients based on their body mass and activity level. However, the stiffness values of IDEO carbon-fiber struts have not been systematically determined, and these values can inform dynamic function and biomimetic PD-AFO prescription and design. The PD-AFO strut primarily deflects in the anterior direction (ankle dorsiflexion), and resists deflection in the posterior direction (ankle plantarflexion) during the stance phase of running. Thus, we constructed a custom apparatus and measured strut stiffness for 0.18 radians (10°) of anterior deflection and 0.09 radians (5°) of posterior deflection. We measured the applied moment and strut deflection to compute angular stiffness, the quotient of moment and angle. The strut moment-angle curves for anterior and posterior deflection were well characterized by a linear relationship. The strut stiffness values for categories 1–5 at 0.18 radians (10°) of anterior deflection were 0.73–1.74 kN·m/rad and at 0.09 radians (5°) of posterior deflection were 0.86–2.73 kN·m/rad. Since a PD-AFO strut acts in parallel with the impaired biological ankle, the strut and impaired biological ankle angular stiffness sum to equal total stiffness. Thus, strut stiffness directly affects total ankle joint stiffness, which in turn affects ankle motion and energy storage and return during running. Future research is planned to better understand how use of a running-specific PD-AFO with different strut stiffness affects the biomechanics and metabolic costs of running in people with lower limb impairment.
... Así, dos conceptos contradictorios nos llevan a una sola conclusión, que para un buen rendimiento deportivo en deportes que se basan en constantes ciclos de estiramiento-acortamiento una extensibilidad y un stiffness óptimo es requerido, y que ninguno debe exceder en demasía en desmedro del otro si es que se entrenan en forma separada. Varios estudios han examinado la relación entre stiffness y rendimiento deportivo, algunos de ellos reportando que el stiffness de la pierna aumenta con la frecuencia del salto cuando los sujetos saltan en el mismo lugar [148][149][150] . En otro estudio se estableció una correlación entre el incremento de la velocidad y el incremento del stiffness durante el rebote post aterrizaje de un salto 151 . ...
Libro que describe el qué, el cómo y el por qué se hace lo que se hace en relación a las Ciencias Aplicadas al Deporte en el Deporte de Alto Rendimiento en Chile. Estas ciencias apoyan el proceso de preparación y competencia de los atletas chilenos, con el propósito de mejorar el rendimiento deportivo a nivel internacional.
... As proven in the literature, stiffness reflects the resistance of the tissue to the force that changes its initial shape [9]. A significant disproportion of stiffness between agonists and antagonists was recognized as a risk factor that may affect injuries by reducing joint stability [11]. High muscle stiffness is considered one of the key factors limiting the proper function of agonists and antagonists function. ...
Purpose:
Myofascial stiffness is the biomechanical property that can be considered as a modifiable risk factor injury of athletes. Moreover, the level of muscle stiffness can be crucial to assessment muscle adaptation to exercise. However, stiffness of flexor muscles in rock climbers has never been investigated. The purpose of this study was to evaluate the myofascial stiffness of the flexor digitorum superficialis (FDS) in the rock climbers.
Methods:
The group of rock climbers (n = 16) has been compared to the non-climbers group (n = 16), matched in terms of anthropometric measures and an average level of physical fitness. Moreover, the impact of the one-time rock climbing training on FDS stiffness was assessed in the rock climbers group. The measurement of myotonometric myofascial stiffness of FDS muscles was performed, when the elbow was flexed and fully extended. In both positions, the measurements were taken with the hand open and closed.
Results:
It has been shown that rock climber's FDS muscle stiffness before training was significantly higher (from 15 to 20%) compared to non-climbers group. Moreover, after climbing myofascial stiffness of FDS muscles increased significantly from 25 to 40%.
Conclusions:
Rock climbers have significantly higher stiffness of FDS muscles after rock climbing training. Moreover, the increased stiffness in the FDS differentiates rock climbers from the active and healthy control group. Results may indicate that decrease of muscle stiffness of FDS can be an important factor for the improvement of the climbing effectiveness and prevention of overload in the forearm flexor muscles and their recovery.
... Como en un salto vertical Kvert y Kleg tienen el mismo valor (Brughelli & Cronin, 2008;McMahon & Cheng, 1990), en el presente estudio elegimos estimar Kvert porque su cálculo se basa directamente el movimiento del COM. Kvert se determinó como la pendiente de una línea ajustada a partir de la relación de la fuerza de reacción vertical del suelo (Fz) y posición vertical del COM como se indica en (Granata, Padua, & Wilson, 2002). ...
RESUMEN Se discute sobre la importancia de energía elástica acumulada en miembros inferiores en la performance de saltos verticales. A tales efectos, se presenta un análisis de la rigidez durante las fases de contrabalanceo y de impulso en saltos de tipo counter movement jump (CMJ). Se realizó una reconstrucción 3D de noventa CMJ de esfuerzo máximo en base a la ubicación de 49 marcadores corporales. Los datos se agruparon en resultados buenos, medios y pobres según la altura máxima del salto. Se calculó la rigidez vertical del sistema durante las fases de contrabalanceo e impulso, la fuerza vertical máxima y los tiempos de cada fase. Se realizó un ANOVA de una vía considerando la altura del salto como factor. Los valores de rigidez mostraron que el cuerpo se comporta como un sistema masa-resorte lineal durante el impuso, pero el movimiento no se corresponde tan bien con ese modelo durante el contramovimiento de los buenos CMJ, que tienen un tiempo de empuje corto y una mayor fuerza vertical. Concluimos que el aumento de la rigidez del conjunto de estructuras de miembros inferiores importa pero no es un fenómeno pasivo y que la importancia de la energía elástica es cuestionable.
... It is common practice in biomechanics to use the force measurements to evaluate the corresponding centre of mass displacement, i.e. the leg compression, for a given jumping test frequency [46][47][48]. This is performed by dividing the measured force time-history by a test subject's mass to evaluate the acceleration and double integrating. ...
An empirical nonlinear, frequency-dependant, spring-mass system is conjectured for modelling human rhythmic jumping. This model is vital for correctly estimating human-structure dynamic interactions. An experimental study was employed to evaluate the leg mechanics and dynamic loading of a human jumper. Testing was performed over a large range of prescribed jumping frequencies. Subjects performed rhythmic jumps on a force plate and they were monitored by a motion capture system from which the displacement of the centre of mass was identified. Least squares system identification was utilised to determine the parameters of the spring-mass model for human rhythmic jumping. A nonlinear stiffness, rather than a conventional linear spring, is proposed to better capture the observed behaviour during periodic jumping. Force-displacement curves of each subject, during the contact phase of rhythmic jumping, were explored. These display an array of both classical Duffing’s type nonlinear softening and hardening spring stiffnesses over the range of jumping frequencies. The coefficients of the Duffing’s type model are observed to be highly sensitive to jumping frequency. A Poincaré section (phase-space) representation is used to visualise the jumping attractor’s topology. Thus, an experimental bifurcation analysis is performed suggesting the presence of both period doubling and fold bifurcations. These describe the transition from observed period-2 to period-1 jumping and coexisting low/high amplitude jumping behaviour. This study presents a framework for characterising the nonlinear loading of a human performing rhythmic jumping from direct measurements of force and displacement.
... In their research, Abian et al. [38] showed a difference of as much as 10 cm between men and women during a vertical jump. Such a great difference results from the strength of the lower limbs [39]. The performance of the optimal vertical jump depends mainly on the vertical speed at the moment of take-off, which is correlated with the explosive power generated during this task [40]. ...
Purpose: Plyometric exercises, in the form of jumping, are extreme physical activities. The aim of the study was to determine how symmetrical-single versus asymmetrical-continued plyometric exercises differ between men and women and affect speed abilities. Methods: Twenty-two healthy females and forty-four males from different sports practices participated in the investigation. The countermovement jump (CMJ) and drop jump (DJ) of 40/60 cm box were performed on two independent and synchronized force platforms (Bilateral Tensiometric Platform S2P, Ljubljana, Slovenia). The measurement of a standing long jump (SLJ) and all continuous jumps: standing five jumps (SFJ), standing bounce triple jump (SBTJ), five double-leg jumps (FD-LJ), and a 10 m horizontal single leg jump (HSLJ-10mL/R) were performed using OptoJump–Next Microgate (OptoJump, Bolzano, Italy). Results: Statistically significant differences were noted in all jump kinematic and somatic parameters, in favor of the men. The correlations between values of height of symmetrical jumps (bilateral) and distance (SLJ) were stronger in women despite the shorter jumps than the men. When an alpha-level of 0.01 was set, this study demonstrated a stronger correlation between symmetrical-single and asymmetrical-continuous plyometrics exercises and sprints, both men and women. This relationship is due to their similar kinematic and dynamic structures with sprinting steps. Conclusions: The results showed a large dispersion of the relationship (p < 0.05) between jumps and sprints divided into 10, 20 and 30 m, both in men and women. Both types of exercises implemented as a plyometric training regime are an extremely important tool for sprint speed development.
... Several studies have reported gender differences in lower limb tissue stiffness [32,35,36] that may account for differences in sagittal plane ROM especially in pelvic and ankle during walking. ...
... As greater forces are applied to the body, greater resistance to movement is needed to produce controlled movements. 20 Although some level of dynamic joint stiffness is required for optimal utilization of the stretch-shortening cycle and maintenance of joint stability, Granata et al 23 suggested that too little dynamic joint stiffness may allow for excessive joint motion and less joint stability during gait. ...
Context:
Previous studies have reported that the incidence of patellofemoral pain in women is 2.2 times higher than that in men. Lower hip frontal dynamic joint stiffness in women may be related to the magnitude of hip adduction and internal rotation associated with patellofemoral pain.
Objective:
To identify sex differences in hip frontal dynamic joint stiffness and examine the relationship between hip frontal dynamic joint stiffness and hip adduction and internal rotation during gait.
Design:
Cross-sectional study.
Setting:
University campus.
Participants:
A total of 80 healthy volunteers (40 women and 40 men) participated in this study.
Intervention(s):
Kinematic and kinetic data during gait were collected using a motion capture system and force plates.
Main outcome measures:
Hip frontal dynamic joint stiffness, hip adduction, and hip internal rotation were calculated during gait.
Results:
Women demonstrated lower hip frontal dynamic joint stiffness than men during gait (P < .01). They also displayed decreased hip frontal dynamic joint stiffness associated with increased hip adduction (r = -.85, P < .001) and internal rotation (r = -.48, P < .001). Conversely, in men, decreased hip frontal dynamic joint stiffness was associated with increased hip adduction (r = -.74, P < .001) but not internal rotation (r = .17, P = .28).
Conclusions:
Sex differences between hip frontal dynamic joint stiffness and hip internal rotation during gait may contribute to the increased incidence of patellofemoral pain in women.
... We also hypothesize that the sex difference in ankle stiffness in the sagittal plane is significantly higher than that in the frontal plane, because the degree of ankle stiffness modulation is substantially higher in the sagittal plane than the frontal plane (Lee et al., 2014a,c;Lee and Hogan, 2015). In addition, based on previous findings of sex differences in active muscle mechanics (Granata et al., 2002a), we further hypothesized that the sex difference in ankle stiffness in the sagittal plane still persists even after normalization by body weight times height, but not in the frontal plane. ...
The purpose of this study is to quantify sex differences in 2-dimensional (2D) ankle stiffness during upright standing balance and investigate the mechanisms for the differences. A dual-axis robotic platform, capable of perturbing the ankle and measuring the corresponding ankle torques in both the sagittal and frontal planes, was used to reliably quantify the 2D ankle stiffness while healthy young human subjects perform a range of standing balance tasks, specifically, ankle muscle co-contraction tasks, weight-bearing tasks, and ankle torque generation tasks. In all task conditions and in both planes of ankle motion, ankle stiffness in males was consistently greater than that in females. Among all 26 experimental conditions, all but 2 conditions in the frontal plane showed statistically significant sex differences. Further investigation on the normalized ankle stiffness, scaled by weight times height, suggests that while sex differences in ankle stiffness in the sagittal plane could be explained by sex differences in anthropometric factors as well as neuromuscular factors, the differences in the frontal plane are mostly explained by anthropometric factors. This study also demonstrates that the sex differences in the sagittal plane were significantly higher as compared to those in the frontal plane. The results in this study will provide a foundation for not only characterizing sex differences in ankle stiffness during locomotion, but also investigating sex differences in lower body stability and risk of ankle injury.
This study determined the relationship between the shock attenuation index and joint movements of the trunk and lower extremities during single-leg landing.Fourteen healthy subjects were enrolled, including 7 males and 7 females. The angles of the trunk and lower extremities and the shock attenuation index due to the ground reaction force during the reaction force during the landing motion of one foot were measured. The measured indices were compared between the sexes. In correlation coefficients were calculated between each index. No significant gender difference was observed in the shock attenuation index. Only females showed a negative correlation between the shock attenuation index and the angular changes in knee flexion during landing. In addition, only females showed a positive correlation the angle of ankle plantarflexion during landing and the angle of knee valgus during shock attenuation.These results suggest that females absorb shock by using more joint motion at the knee than males.
The number of studies on warm-up protocols has increased in recent years. However, there are very few studies that are specific to the population of female athletes and consist of a large number of participants. This study was designed to investigate the effects of 3 different warm-up protocols on sprinting performance in young female volleyball players. A total of 62 licensed female volleyball players aged 13-17 years participated voluntarily. There were 3 sessions in the study. The participants were randomly divided into a warm-up group (GWG), a dynamic stretch group (DSG) and a static stretch group (SSG). After completing the warm-up protocols, the groups underwent a 5-minute transition period. The 20-metre sprint performance test was then performed. Data analysis was performed with the Python programming language and IBM SPSS 26 software. Shapiro-Wilk and Kolmogorov-Smirnov tests and kurtosis and skewness checks were performed. The data were indicated to be normally distributed (p> 0,05). Repeated Measures Anova test was used to detect the differences and the significance level was chosen as α=0,05. When the results were examined, it was found that there was no statistically significant difference between the GWG and SSG 20 meter sprint time values (p>0,05), whereas when the DSG and GWG and SSG 20 metre sprint time values were compared, it was found that the DSG group's sprint time improved statistically significantly (p
Context:
Excessive hip adduction and internal rotation are abnormal movements that may lead to the onset and progression of patellofemoral pain. Previous studies have reported that lower dynamic frontal plane hip joint stiffness in the gait of women is associated with the magnitude of hip adduction and internal rotation angles. However, the factors contributing to the lack of dynamic frontal plane hip joint stiffness in the gait of young women are unclear. This study aims to investigate the factors affecting dynamic frontal plane hip joint stiffness during the weight-acceptance phase of the gait of healthy young women.
Design:
Cross-sectional study.
Methods:
This study included 30 healthy women between the ages of 18 and 30 years. The pelvic width/femur length ratio was calculated by dividing the pelvic width by the femur length. Data on hip kinematics and kinetics and activation of the gluteus maximus and medius, tensor fasciae latae, and adductor longus muscles during gait were collected using a motion capture system, force plates, and surface electromyography. Stepwise multiple regression analysis was conducted to determine the extent to which each independent factor affected dynamic frontal plane hip joint stiffness.
Results:
In healthy young women, decreased dynamic frontal plane hip joint stiffness was associated with decreased muscle activity of the gluteus maximus during the gait, as well as greater pelvic width/femur length ratio.
Conclusions:
Women with a relatively great pelvic width relative to femur length may have more difficulty in producing dynamic frontal plane hip joint stiffness. However, increasing the muscle activity of the gluteus maximus may contribute to increased dynamic frontal plane hip joint stiffness.
Background:
Anterior cruciate ligament (ACL) reconstructions are associated with long-term functional impairments. Improved understanding of dynamic knee joint stiffness and work may provide insights to help address these poor outcomes. Defining the relationship between knee stiffness, work and quadriceps muscle symmetry may reveal therapeutic targets. The purposes of this study were to investigate between-limb differences in knee stiffness and work during early phase landing 6-months after an ACL reconstruction. Additionally, we investigated relationships among symmetry of knee joint stiffness and work during early-phase landing and quadriceps muscle performance symmetry.
Methods:
Twenty-nine participants (17 M, 20.0 ± 5.3 years) were tested 6-months after ACL reconstruction. Motion capture analysis was used to assess between-limb differences in knee stiffness and work during the first 60 ms of a double-limb landing. Quadriceps peak strength and rate of torque development (RTD) were assessed with isometric dynamometry. Paired t-tests and Pearson's product moment correlations were used to determine between-limb differences of knee mechanics and correlations of symmetry respectively.
Findings:
Knee joint stiffness and work were significantly reduced (p < 0.01, p < 0.01) in the surgical limb (0.021 ± 0.01 Nm*(deg*kg*m)-1, -0.085 ± 0.06 J*(kg*m) -1) compared to the uninvolved limb (0.045 ± 0.01 Nm*(deg*kg*m)-1, -0.256 ± 0.10 J*(kg*m) -1). Greater knee stiffness (51 ± 22%) and work (35 ± 21%) symmetry were significantly associated with greater RTD symmetry (44.5 ± 19.4%) (r = 0.43, p = 0.02; r = 0.45, p = 0.01) but not peak torque symmetry (62.9 ± 16.1%) (r = 0.32, p = 0.10; r = 0.34, p = 0.10).
Interpretation:
Dynamic stiffness and energy absorption are lower in the surgical knee during landing from a jump. Therapeutic interventions that target increasing quadriceps RTD may help optimize dynamic stability and energy absorption during landing.
The musculoskeletal anatomy of women and men is grossly similar yet individually distinctive. Sexual dimorphism in the human musculoskeletal system is apparent but more subtle than in other species. Some musculoskeletal sex differences in humans are present at an early age, while others tend to appear later in life. Sex differences in gross skeletal geometry and specific tissue characteristics are common. Women tend to have different characteristics of specific bones and bony features than men which have been explained by both genetic and environmental factors. Women and men appear to have several differences in collagenous, cartilage, and bone tissues, which may predispose women to certain pathologies such as osteoarthritis and osteoporosis later in life. Sexual dimorphism can manifest itself by specific differences in each joint throughout the body, possibly resulting in sex differences of clinical pathology and symptomology such as differences in shoulder impingement; laxity and idiopathic capsulitis; elbow tendinosis; carpal tunnel syndrome; hip fracture and labral tears; anterior cruciate ligament injuries; ankle sprains and Achilles tendinopathy; cervical spine macrotrauma; thoracolumbar postural changes including kyphosis, lordosis, and/or scoliosis; and sacroiliac joint conditions. Consideration of the sex differences in musculoskeletal anatomy is important for both the general public and health care professionals in order to provide a basis for understanding normal and abnormal conditions that may exist. Moreover, a thorough appreciation that men and women have differences in musculoskeletal anatomy may help in the understanding that they have distinctive health care needs.
Abstract
Background: The purpose of this short experience-based paper is to compare and discuss the state of cross-border reproductive care (CBRC) before and after the outbreak, and to point out the possible impact of the COVID-19 pandemic on women who rely on cross-border treatment. In the context of modernity, international
commercial sperm banks and CBRC have emerged as social and political solutions for single women and lesbians to overcome reproductive dilemmas and build families. However, with the spread of COVID-19 and the mobility difficulties caused by strict border control, this phase-based solution to social infertility seems to be examed again.
Method: This paper adopts a textual analysis method to analyze the social meanings of official border policy texts and artificial reproduction recommendations in various countries. And 20 members were randomly interviewed from five Facebook communities related to sperm banking and CBRC. Also, as a complete observer,
the websites of Facebook communities, sperm banks, and hospitals providing reproductive care were observed to map changes in medical mobility as a result of the COVID-19 pandemic.
Results: There is a lack of research on the impact of COVID-19 on cross-border mobility and encounters with social infertility due to medical factors. It also motivates us to reflect on the specific social conditions, regulations and cultures in different national contexts, and to think about the reasons that drive people to adopt CBRC, as well as the factors that contribute to the social infertility and reproductive resource scarcity.
Conclusion: This article believes that reproductive regulations will eventually need to be revised to make them more relevant and humane after the urgent epidemic and national security governance. During the ongoing COVID-19 pandemic, these basic and important questions reappear before our eyes, and they are testing how
individuals and the public make judgments and decisions in the face of the COVID-19.
Keywords: Border, COVID-19, Dilemma, Fertility, Reproductive care
Purpose
To determine whether average growth tempo influenced longitudinal relationships between maturity status and coordination capability using a 15-s hopping task (Aim 1). To investigate how differences in absolute growth tempo were associated with change in coordination capability within and across peak growth (Aim 2).
Methods
Participants were N1 = 110 (Aim 1) and N2 = 71 (Aim 2) Australian male competitive swimmers, aged 10–15 years, exposed to repeated-measures tracking (2-years, and 12-months respectively) of maturity status, growth tempo and movement coordination capability. Coordination capability was estimated via vertical stiffness (KV) in a hopping task, reflected by participant mean KV and between-jump coefficient of variation (CV).
Results
For Aim 1, log-linear mixed model trends identified maturity status and growth tempo were significantly associated with KV mean and KV CV. For a given maturity status, mean KV was 9% lower in the ‘High’ average growth tempo group than the ‘Low’ average tempo group. For Aim 2, mixed repeated-measures analyses of variance identified how time points of increased growth tempo were significantly associated with 7–11% reductions in mean KV, with similar mean KV decrements irrespective of growth tempo group. Meanwhile, KVCV only illustrated progressive longitudinal reductions.
Conclusions
Within maturational progression, short-term accelerations in growth tempo corresponded with short-term decreases in KV mean, suggesting temporary disruptions to movement coordination capability. Measuring growth tempo and applying hopping tasks in specific movement contexts could help consistently identify disturbances in motor coordination.
The purpose of this review study is to review the studies that have assessed the interaction between surface stiffness and lower limb stiffness. There is a general hypothesis that with the increase of surface stiffness, the lower limb stiffness decreases or vice versa. These interactions take place with the aim of maintaining the dynamics of the center of mass and reducing the energy consumption during movement. One of the mechanisms for these interactions is the change in joint stiffness and leg geometry. Some studies suggested that the stretch reflex has no role in changing the lower limb stiffness. Although interactions between lower limb stiffness and surface stiffness has been recognized, there is little evidence about neuromuscular mechanism of these interactions. More studies is needed in this filed.
Introduction
Collegiate athletes who suffer a concussion may possess prolonged impairments even after clearance for return-to-participation, which may place them at an increased risk of lower extremity injury.
Objective
To conduct a systematic review and meta-analysis of studies examining risk of lower extremity musculoskeletal injury following a concussion in collegiate athletes.
Methods
A literature search was performed using the following databases: PubMed, CINAHL, SPORTDiscus. The following search terms were used to identify relevant articles, [“concussion” OR “brain injury” OR “mild traumatic brain injury” OR “mTBI”] AND [“lower extremity injury” OR “musculoskeletal injury”]. Articles were included if they were published between January 2000 and July 2021 and examined collegiate athletes’ risk of sustaining a lower extremity musculoskeletal injury following a concussion. Methodological quality of included studies was performed with a modified Downs and Black Checklist. The primary outcome of interest was the risk of sustaining a lower extremity musculoskeletal injury following a concussion. A random effects meta-analysis was conducted in which a summative relative risk (RR) for sustaining a lower extremity injury in athletes with and without a history of concussion was calculated.
Results
Seven studies met the eligibility criteria to be included in the systematic review. There were 348 athletes in the concussion group and 482 control athletes in the included studies. Most of the studies were of good or excellent quality. Five of the seven studies were able to be included in the meta-analysis. College athletes who suffered a concussion possessed a 58% greater risk of sustaining a lower extremity musculoskeletal injury than those who did not have a history of a concussion (RR = 1.58[1.30, 1.93]).
Conclusions
Lower extremity injury risk is potentially increased in college athletes following a concussion compared to those without a history of a concussion. Further research is needed to investigate the mechanism behind this increased risk. Clinical assessments throughout the concussion return-to-play protocol may need to be improved in order to detect lingering impairments caused by concussions.
Level of Evidence
1
Leg stiffness plays a key role in the storage and release of elastic energy during stance. However, the extent to which a runner is able to reuse stored energy remains a limiting factor in determining their running effectiveness. In this study, ten habitual rearfoot strikers and ten habitual forefoot strikers were asked to run on a treadmill in three footwear conditions: traditional, neutral, and minimal running shoes. We examined the effect of habitual foot strike pattern and footwear on leg stiffness control within three task-relevant phases of stance (i.e. touch-down, loading, unloading). Control was quantified using stride-to-stride leg stiffness time-series and the coefficient of variability and detrended fluctuation analysis (DFA). The results are interpreted within a theoretical framework that blends dynamic systems theory and optimal feedback control. Results indicate that leg stiffness control is tightly regulated by an active control process during the loading period of stance. In contrast, the touch-down and unloading phases are driven mostly by passive allometric control mechanisms. The effect of footwear on leg stiffness control was inconclusive due to inconsistent trends across three shoe types. However, stiffness control was affected by landing technique. Habitual rearfoot strike runners have reduced DFA values during the touch-down and unloading phases. These sub-phases are associated with an allometric control process and suggests that rearfoot strike runners express a reduction in system complexity for leg stiffness control and hence, a less adaptable system.
In the current book, I collaborated with a kine students and the research committee of the squash federation.
This project, in the first phase, began with the search for credible scientific sources and articles related to the sport of squash. In this phase
About 350 scientific articles in English were published in credible international journals.
In the second phase, while studying and carefully reviewing all the collected sources, about 200 articles for summarizing and translating into the Persian language were selected.
In the third phase of the project, English articles were summarized. The basis of summarizing is turning articles into a direction sheet
A general description of the activity performed and a display of the results was obtained.
After summarizing the articles, the English to Persian translation phase of the articles began.
After submitting the summaries of the translated articles, the materials were reviewed .
The present edition summarizes all the above activities so far.
The purpose of the current study was to determine allometric equations for leg stiffness, the main parameter of elastic behavior of the human body. Totally, 30 young healthy men participated voluntarily in this study and performed a vertical hopping test on a force plate and in front of a high-speed camera. Leg stiffness was calculated, and its relationship with individual characteristics such as body mass, height, body mass index and age was determined by Pearson correlation test, and the allometric equations were formed by regression analysis. Positive significant correlations were observed between leg stiffness of the controlled hopping test and body mass. Allometric scaling equations were Kbilateral=190M 1.1 for bilateral leg stiffness, Kdominant=501M 0.84 for dominant leg stiffness and Knondominant=549M 0.82 for non-dominant leg stiffness. These equations can help in the correct normalization of the elastic behavior of the human body and allow the estimation of leg stiffness based on body mass.
Hamstring injuries (HSI) are common in a number of different sports and can confer a significant burden to both male and female athletes. Though research on HSIs in the female athlete population is lacking, current literature suggests male athletes are between two to four times more likely than female athletes to sustain an HSI. Despite this discrepancy, the role of intrinsic sex differences in HSI risk factors has not been previously explored. This review aims to summarize these sex-based differences in HSI risk factors and their influence on the lower rate of HSIs seen in female athletes as compared to male athletes. Women exhibit increased hamstring flexibility and decreased hamstring musculotendinous stiffness as compared to men; women are also shown to be more resistant to skeletal muscle fatigue. Sex differences in the hamstring to quadriceps ratio and certain lower limb morphologies may also contribute to the sex discrepancy in HSI rates. This remains an area for future research in order to understand the multifaceted nature of HSI injury risk factors and optimize HSI rehabilitation and prevention programs for both male and female athletes.
Background: Multiple Sclerosis (MS) has many disabling symptoms due to weakened
signal propagation in the central nervous system. Manual therapeutics are often seen
to have a positive effect on these symptoms with limited information as to why. The
purpose of this project was to investigate a spinal mobilisation intervention,
objectively measuring the changes it may be causing to muscle quality and movement
patterns as a contribution to research in MS therapeutics.
Methods: A series of 3 studies were designed to investigate the effects of a spinal
mobilisation intervention on muscle quality and movement patterns. Study 1 tested
people with lower back pain (LBP) as a pilot population (n=40), testing for an
immediate effect on muscle quality. Study 2 replicated this with MS patients (n=20)
assessing muscle quality, balance, and pain. Study 3 tested the intervention in a
longer-term 4 bout study (n=20), assessing muscle quality, balance, pain, and fatigue.
Results: Significant muscle stiffness reductions were seen in the LBP population post
the intervention (p = 0.01, η2partial = 0.15). Baseline stiffness was found as a significant
contributor (p = 0.002, R2 = 0.22). These muscular results were not replicated with
the MS population. However, significant improvements in self-reported pain as a
result of the intervention were revealed (p = 0.008, η2partial = 0.33). Study 3 findings
demonstrated significant improvements from baseline in balance and fatigue
measures as a result of the intervention. High variability in the data are seen within
the MS population.
Purpose:
To examine the influence of growth and maturation in the trajectory of stretch-shortening cycle capability.
Method:
Using a mixed-longitudinal design, absolute and relative leg stiffness and reactive strength index (RSI) were measured 3 times over a 3-year period in 44 youth team-sport players. Maturation was determined as maturity offset and included within the Bayesian inference analysis as a covariate alongside chronological age.
Results:
Irrespective of age and maturation, there was no change in absolute leg stiffness, however relative leg stiffness decreased over time. Maturation and age reduced this decline, but the decline remained significant (Bayesian factor [10] = 5097, model averaged R2 = .61). The RSI increased over time and more so in older more mature youth players (Bayesian factor [10] = 9.29e8, model averaged R2 = .657).
Conclusion:
In youth players who are at/post peak height velocity, relative leg stiffness appears to decline, which could have an impact on both performance and injury risk. However, RSI increases during this period, and these data reinforce that leg stiffness and RSI reflect different components of stretch-shortening cycle capability. Practitioners should consider these differences when planning training to maximize stretch-shortening cycle capability during growth and maturation in athletes on the developmental performance pathway.
When mammals run, the overall musculoskeletal system behaves as a single linear "leg spring". We used force platform and kinematic measurements to determine whether leg spring stiffness (k(leg)) is adjusted to accommodate changes in surface stiffness (ksurf) when humans hoop in place, a good experimental model for examining adjustments to k(leg) in bouncing gaits. We found that k(leg) was greatly increased to accommodate surfaces of lower stiffnesses. The series combination of k(leg) and ksurf [total stiffness (ktot)] was independent of ksurf at a given hopping frequency. For example, when humans hopped at a frequency of 2 Hz, they tripled their k(leg) on the least stiff surface (ksurf = 26.1 kN/m; k(leg) = 53.3 kN/m) compared with the most stiff surface (ksurf = 35,000 kN/m; k(leg) = 17.8 kN/m). Values for ktot were not significantly different on the least stiff surface (16.7 kN/m) and the most stiff surface (17.8 kN/m). Because of the k(leg) adjustment, many aspects of the hopping mechanics (e.g., ground-contact time and center of mass vertical displacement) remained remarkably similar despite a > 1,000-fold change in ksurf. This study provides insight into how k(leg) adjustments can allow similar locomotion mechanics on the variety of terrains encountered by runners in the natural world.
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 short-range stiffness of smoothly but submaximally contracting isometric soleus muscles of anesthetised cats was measured by applying small fast stretches. The ratio of isometric tension to stiffness was plotted against tension over a wide range of muscle lengths and stimulus rates. The results fitted a straight line well, as predicted from crossbridge theory, showing the stiffness to be a function of tension only, independent of the combination of length and stimulus rate used to generate the tension. The major deviation from this line was attributed to incomplete fusion at low frequencies of stimulation. Values believed to be tendon compliance and crossbridge tension per unit of stiffness were found from the graph, and the tendon compliance correlated with the maximum muscle tension. Shortening the tendon by attaching nearer to the muscle changed the results in a manner consistent with the theory, provided that appropriate precautions were taken against slippage.
1. The properties of human soleus muscle were studied by systems analysis. Single stimulus pulses and random stimulus pulse trains were applied to a branch of the nerve to soleus muscle and the resultant tension fluctuations were recorded. 2. The frequency-response function between stimulus pulses and tension conforms to that of a second-order, low-pass filter. The parameters of the second-order system, low frequency gain, natural frequency, and damping ratio, varied systematically with the angle of the ankle. As the ankle was flexed (the length of the muscle was increased), the low frequency gain increased, the natural frequency decreased, and the damping ratio was unaffected or increased slightly. 3. These results are discussed in relation to the twitch responses of human soleus muscles and the responses previously observed in cat muscles.
We studied stretch reflexes of soleus muscles of intercollicularly decerebrated cats using a new technique for estimating the component of a stretch reflex that results from the purely mechanical properties of the active muscle (mechanical response). The difference between a net stretch reflex and its underlying mechanical response provided a direct measure of reflex action. 1. The relative contributions of reflex action and the mechanical response are different for stretch and release. With stretch, reflex action is generally large and the mechanical response small. The opposite is true with release. The property that remains relatively constant, when stretch and release are compared, is the net stiffness in opposition to length change. We concluded that reflex action compensates for variations in the inherent stiffness of the muscle. 2. Compensation is effective over a range of intermediate values of initial force, but it fails whenever the reflex force approaches zero or the maximal force at that length. 3. Reflex action is capable of modifying muscular force within 22 ms of the onset of length change. This indicates that even during a fast gallop, there is sufficient time for reflex action. 4. The mechanical properties of the active soleus muscle are highly nonlinear; e.g., muscular stiffness becomes negative transiently during stretch. In stable decerebrate preparations we found that reflex action resulted in a considerable improvement in linearity. 5. Our results support two complementary hypotheses: a) stiffness may be the regulated property of the stretch reflex, and b) the main function of autogenetic reflexes may be to conpensate for variations in the properties of skeletal muscle rather than to oppose changes in load.
The authors report a series of 52 cases of serious knee ligament injuries in volleyball players. The most frequent mechanism of injury was landing from a jump in the attack zone. Women were more affected than men. Injuries were more frequent during games than training. Volleyball must then be considered among high-risk sports according to the frequency and gravity of our surgical findings. Results are similar to those obtained in athletes in other sports who underwent the same surgical 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.
Twelve experienced male weight lifters performed a rebound bench press and a purely concentric bench press lift. Data were obtained pertaining to 1) the benefits to concentric motion derived from a prior stretch and 2) the movement frequency adopted during performance of the stretch-shorten cycle (SSC) portion of the rebound bench press lift. The subjects also performed a series of quasi-static muscular actions in a position specific to the bench press movement. A brief perturbation was applied to the bar while these isometric efforts were maintained, and the resulting damped oscillations provided data pertaining to each subject's series elastic component (SEC) stiffness and natural frequency of oscillation. A significant correlation (r = -0.718, P less than 0.01) between maximal SEC stiffness and augmentation to concentric motion derived from prior stretch was observed. Subjects were also observed to perform the SSC portion of the rebound bench press movement to coincide with the natural frequency of oscillation of their SEC. These results are interpreted as demonstrating that the optimal stiffness in a rebound bench press lift was a resonant-compliant SEC.
The dynamics of joint mechanics are a fundamental characteristic of the motor system. They determine the displacements evoked by perturbing forces during postural control and the forces that must be generated to perform a voluntary movement. This article reviews experimental studies of these dynamics, with an emphasis on the behavior of single joints in alert humans. Technical aspects of the experimental and analytic methods that have been used are summarized first. Major results obtained with the different methods are then reviewed, compared, and contrasted. The interpretation of these results in terms of the underlying physiological mechanisms is then considered, with an emphasis on the relative contributions of passive properties of tissue, the mechanical behavior of muscle, and stretch reflexes. Finally, important unanswered questions regarding the dynamics of joint mechanics are reviewed.
Utilizing a new testing method, the authors are reporting for the first time on the ranked order of importance of each ligament and capsular structure in resisting the clinical anterior and posterior drawer tests. The ranked importance is based on the force provided by each ligament in resisting the drawer tests. Tests were conducted with the knee at 90 and 30 degrees of flexion up to five millimeters of anterior and posterior drawer in the intact knee. A second series of tests was also performed at larger drawer displacements to determine the back-up restraints to drawer motions when the cruciate ligaments have been cut. Clinical relevance: In this report the authors introduce the concept of primary and secondary ligament restraints to the clinical examination. In anterior drawer the anterior cruciate ligament is the primary restraint. It provides an average of 86 per cent of the total resisting force. All other ligaments and capsular structures provide the remaining secondary restraint, each typically less than 3 per cent. These results explain many clinical paradoxes of function of the anterior cruciate ligament. The secondary restraints, although small, may block the clinical drawer test despite rupture of the anterior cruciate ligament. This is because the clinical drawer test is performed with small manual forces. However, with loss of the primary restraint (the anterior curciate ligament), anterior stability under higher forces of functional activity is markedly affected, although underestimated by the clinical drawer test. Over time, the weak secondary restraints stretch and the laxity increases. In the absence of the anterior cruciate ligament, the restraints to anterior drawer are the iliotibial tract and band, the middle one-third of the medial and lateral capsules, and the medial and lateral collateral ligaments. These are the structures that are tested in clinical cases of chronic laxity of the anterior cruciate ligament, assuming that they undergo no concomitant injury. For straight posterior drawer, the posterior cruciate ligament provides a mean of 95 per cent of the total restraining force. After loss of the posterior cruciate ligament, the secondary restraints to the posterior drawer test are the posterior lateral capsule and popliteus complex combined (58 per cent), the medial collateral ligament (16 per cent), and to a lesser extent many other structures. The anterior cruciate ligament did not resist posterior drawer, nor did the posterior cruciate ligament resist anterior drawer. A false-positive anterior drawer test after rupture of the posterior cruciate ligament occurs due to a posterior shift in the starting position of the tibia. The authors concluded that: (1) Knee stability and proposed surgical procedures must be analyzed in terms of all ligament restraints. However, special attention must be given to the primary restraints that cannot be substituted for by only the secondary ones. (2) Secondary restraints may block clinical laxity tests, but often stretch out and do not provide knee stability under higher functional forces of activity. (3) The anterior and posterior cruciate ligaments provide the overwhelming resistance to these respective tibial displacements. After the cruciate ligaments are torn, minimum back-up ligament support exists. This explains the high risk of altered joint function after cruciate injury, when functional stability is dependent on muscle restraints and joint geometry.
All injuries occurring over a 7-week period at a local indoor soccer arena were documented for analysis of incidence rates. All injury rates were calculated per 100 player-hours. The overall injury rates for male and female players were similar, 5.04 and 5.03, respectively. The lowest injury rate was found among the 19- to 24-year-old athletes and the highest injury rate was found among the oldest age group (> or = 25 years). Collision with another player was the most common activity at the time of injury, accounting for 31% of all injuries. The most common injury types were sprains and muscle contusions, both occurring at a rate of 1.1 injuries per 100 player-hours. Male players suffered a significantly higher rate of ankle ligament injuries compared with female players (1.24 versus 0.43, P < 0.05), while female players suffered a significantly higher rate of knee ligament injuries (0.87 versus 0.29, P < 0.01). Goalkeepers had injury rates (4.2) similar to players in nongoalkeeper positions (4.5).
Physical training-related injuries are common among army recruits and other vigorously active populations, but little is known about their causation. To identify intrinsic risk factors, we prospectively measured 391 army trainees. For 8 weeks of basic training, 124 men and 186 women (79.3%) were studied. They answered questionnaires on past activities and sports participation, and were measured for height, weight, and body fat percentage; 71% of the subjects took an initial army physical training test. Women had a significantly higher incidence of time-loss injuries than men, 44.6% compared with 29.0%. During training, more time-loss injuries occurred among the 50% of the men who were slower on the mile run, 29.0% versus 0.0%. Slower women were likewise at greater risk than faster ones, 38.2% versus 18.5%. Men with histories of inactivity and with higher body mass index were at greater injury risk than other men, as were the shortest women. We conclude that female gender and low aerobic fitness measured by run times are risk factors for training injuries in army trainees, and that other factors such as prior activity levels and stature may affect men and women differently.
The ability to balance is important to the mobility obtained by legged creatures found in nature, and may someday lead to versatile legged vehicles. In order to study the role of balance in legged locomotion and to develop appropriate control strategies, a 2D hopping machine was constructed for experimentation. The machine has one leg on which it hops and runs, making balance a prime consideration. Control of the machine's locomotion was decomposed into three separate parts: a vertical height control part, a horizontal velocity part, and an angular attitude control part. Experiments showed that the three part control scheme, while very simple to implement, was powerful enough to permit the machine to hop in place, to run at a desired rate, to translate from place to place, and to leap over obstacles. Results from modeling and computer simulation of a similar one-legged device are described by Raibert [10].
In brief: Volleyball has rarely been studied with regard to injuries. However, recent identification of severe knee injuries incurred as a result of participation in volleyball has prompted an investigation of injuries associated with this sport. Among 7,490 persons referred to a major metropolitan outpatient sports medicine clinic for rehabilitation, 106 were treated for injuries related to volleyball. Nearly 90% of the injuries were concentrated in the lower extremities. In particular, knee injuries accounted for 59% of the injuries in both males and females, while ankle injuries accounted for 22% and 24%, respectively. The mechanism of jumping, landing, and twisting upon impact with the ground or floor was associated with 63% of all the injuries, including 61% of the knee injuries and 92% of the ankle injuries. The costs associated with these injuries indicate a significant problem. Directions for future research are identified so that the most appropriate strategies for prevention and control can be determined.
In order to explore the balance in legged locomotion, we are studying systems that hop and run on one springy leg. Pre vious work has shown that relatively simple algorithms can achieve balance on one leg for the special case of a system that is constrained mechanically to operate in a plane (Rai bert, in press; Raibert and Brown, in press). Here we general ize the approach to a three-dimensional (3D) one-legged machine that runs and balances on an open floor without physical support. We decompose control of the machine into three separate parts: one part that controls forward running velocity, one part that controls attitude of the body, and a third part that controls hopping height. Experiments with a physical 3D one-legged hopping machine showed that this control scheme, while simple to implement, is powerful enough to permit hopping in place, running at a desired rate, and travel along a simple path. These algorithms that control locomotion in 3D are direct generalizations of those in 2D, with surprisingly little additional complication.
In this study, landing strategies of gymnasts were hypothesized to change with different landing surfaces. This hypothesis was tested by comparing the kinematics and reaction force-time characteristics of two-foot competition-style drop landings performed by male and female collegiate gymnasts onto three surfaces (soft mat, stiff mat, no mat). Significantly lower peak vertical forces, longer landing phase times, and greater knee and hip flexion were observed between the no mat condition and the mat conditions. Knee flexion and peak knee flexion velocities were also observed to be significantly greater for landings on the stiff mat than those on the soft mat. These results indicate that the gymnasts in this study modulated total body stiffness in response to changes in landing surface conditions by using a multi joint solution. In addition, the presence of a mat may reduce the need for joint flexion and may alter the vertical impulse characteristics experienced during landing.
In this study, drop height and landing mat composition were hypothesized to influence the landing strategies preferred by female gymnasts. Adjustments in strategy in response to changes in drop height and mat composition were identified by comparison of mechanical variables characterizing two-foot competition-style drop landings from three heights onto two different mats varying in composition (i.e., soft vs. stiff). Force-time characteristics of the landings were quantified (1000 Hz) by a force plate fully supporting the mat. Segment kinematics were recorded simultaneously with shuttered video (60 Hz). Significant differences (ANOVA; p < .05) in peak vertical force, landing phase time, time to peak vertical force, and lower extremity kinematics were found across drop heights. Only time to vertical impact peak and minimum knee angular position produced significant differences between the soft and stiff mats. These results indicate changes in drop height and mat composition may elicit changes in landing st...
This target article addresses the role of storage and reutilization of elastic energy in stretch-shortening cycles. It is argued that for discrete movements such as the vertical jump, elastic energy does not explain the work enhancement due to the prestretch. This enhancement seems to occur because the prestretch allows muscles to develop a high level of active state and force before starting to shorten. For cyclic movements in which stretch- shortening cycles occur repetitively, some authors have claimed that elastic energy enhances mechanical efficiency. In the current article it is demonstrated that this claim is often based on disputable concepts such as the efficiency of positive work or absolute work, and it is argued that elastic energy cannot affect mechanical efficiency simply because this energy is not related to the conversion of metabolic energy into mechanical energy. A comparison of work and efficiency measures obtained at different levels of organization reveals that there is in fact no decisive evidence to either support or reject the claim that the stretch- shortening cycle enhances muscle efficiency. These explorations lead to the conclusion that the body of knowledge about the mechanisms and energetics of the stretch-shortening cycle is in fact quite lean. A major challenge is to bridge the gap between knowledge obtained at different levels of organization, with the ultimate purpose of understanding how the intrinsic properties of muscles manifest themselves under in-vivo-like conditions and how they are exploited in whole-body activities such as running. To achieve this purpose, a close cooperation is required between muscle physiologists and human movement scientists performing inverse and forward dynamic simulation studies of whole-body exercises.
The effective lumped stiffness and damping ratio of the human leg system was determined from measurements of parallel and antiparallel-mode oscillations while standing on a linear spring. Knee flexion angle was held fixed in each trial, and varied systematically from 0° to 75°. At each knee angle, subjects carried weights up to twice body weight on their shoulders to determine the effect of increasing muscle force. For small knee flexion angles (θ ≤ 30°), reflex stiffness was independent of muscle force, but rose slightly with muscle force for large flexions. The damping ratio was calculated to be 0.34, showing the underdamped character often reported for skeletomotor feflex mechanisms. Leg stiffness measured in this way is consistent with measurements taken during human running.
To separate fact from fiction regarding the susceptibility of women athletes to injury, three surveys were conducted. The initial data were collected from the athletic departments of collegiate institutions, and the final material was assembled from certified athletic trainers at these institutions, plus an extensive computer search of applicable publications. The collected statistical data were tabulated, and a written commentary was evaluated by the authors. It was established that injuries sustained by female athletes, aside from those related to different biological structures, were essentially no different than those of men, nor are well-trained women athletes more prone to injury. Ankle and knee injuries are most frequent, and women sustain many contusions, sprains, and shin splints. It is anticipated that the overall number of injuries will decrease as better coaches and trainers become available to women athletes.
Thirty-five normal cadaver knees were tested manually in six positions of the knee using apparatus designed to measure the moment-rotation responses for both varus-valgus angulation and torsion of the tibia, as well as the force-displacement responses for anterior-posterior movement of the tibia. The responses of all knees to all modes of loading were non-linear, reflecting increasing stiffness. With the knee at full extension, stiffness was maximum and laxity was minimum. Hence, it was in this position that changes in stability (laxity and stiffness) were best demonstrated when ligament structures were sectioned. Differences in laxity were observed between right and left knees of intact paired specimens. Torsional laxity and internal rotation stiffness were most affected by sectioning the medial collateral ligament, while external rotation stiffness was only affected by division of both the lateral collateral ligament and the posterior capsule. Varus-valgus laxity was relatively unaffected by removal of the menisci or section of the cruciate ligaments but increased greatly when either collateral ligament was cut. The medial collateral ligament was the main contributor to valgus stiffness, whereas the lateral collateral ligament had no measurable effect on varus stiffness. Anterior-posterior stability was affected to some extent by virtually every sectioning procedure. Isolated section of the anterior cruciate ligament produced the greatest increase in anterior-posterior laxity at full extension and section of the posterior cruciate, the greatest increase at 90 degrees of flexion. Large increases in anterior-posterior laxity were also observed when the medial collateral ligament and posterior capsule were sectioned in combination.
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.
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.
From the mechanical point of view the spinal system is highly complex, containing a multitude of components, passive and active. In fact, even if the active components (the muscles) were exchanged by passive springs, the total number of elements considerably exceeds the minimum needed to maintain static equilibrium. In other words, the system is statically highly indeterminate. The particular role of the active components at static equilibrium is to enable a virtually arbitrary choice of posture, independent of the distribution and magnitude of the outer load albeit within physiological limits. Simultaneously this implies that ordinary procedures known from the analysis of mechanical systems with passive components cannot be applied. Hence the distribution of the forces over the different elements is not uniquely determined. Consequently nervous control of the force distribution over the muscles is needed, but little is known about how this achieved. This lack of knowledge implies great difficulties at numerical simulation of equilibrium states of the spinal system. These difficulties remain even if considerable reductions are made, such as the assumption that the thoracic cage behaves like a rigid body. A particularly useful point of view about the main principles of the force distributions appears to be the distinction between a local and a global system of muscles engaged in the equilibrium of the lumbar spine. The local system consists of muscles with insertion or origin (or both) at lumbar vertebrae, whereas the global system consists of muscles with origin on the pelvis and insertions on the thoracic cage. Given the posture of the lumbar spine, the force distribution over the local system appears to be essentially independent of the outer load of the body (though the force magnitudes are, of course, dependent on the magnitude of this load). Instead different distributions of the outer load on the body are met by different distributions of the forces in the global system. Thus, roughly speaking, the global system appears to take care of different distributions of outer forces on the body, whereas the local system performs an action, which is essentially locally determined (i.e. by the posture of the lumbar spine). The present work focuses on the upright standing posture with different degree of lumbar lordosis. The outer load is assumed to consist of weights carried on the shoulders. By reduction of the number of unknown forces, which is done by using a few different principles, a unique determination of the total force distributions at static equilibrium is obtained.(ABSTRACT TRUNCATED AT 400 WORDS)
The purpose of this study was to evaluate the mechanical response to stretch in normal human ankle dorsiflexors at different levels of voluntary contraction. In an active muscle, the total mechanical response is the sum of the intrinsic response from the contractile apparatus, the response from passive tissues, and the reflex mediated response. Each of these components was investigated. The total incremental stiffness was defined as the ratio between the torque increment and the amplitude of the stretch. In 14 subjects the total stiffness increased from ~0.6 N·m/deg to 2.5 N·m/deg at 50% of MVC and remained constant (±10%) from 30 to 80% of MVC. The contribution to incremental stiffness from intrinsic muscle properties was measured during electrical stimulation of the deep peroneal nerve at 7-50 Hz. Intrinsic stiffness increased linearly with torque from ~0.5 N·m/deg to ~2.5 N·m/deg at 80% of MVC. The reflex component (total minus intrinsic stiffness) had a maximum of 0.5-1.5 N·m/deg at 30-50% of MVC and was approximately zero at no and maximal contraction. For intermediate levels of contraction the reflex increased the stiffness with 40-100% of the intrinsic stiffness in this flexor muscle. Total, intrinsic, and reflex mediated stiffness were all nearly independent of the amplitude of stretch in the range from 2 to 7°. The higher stiffness observed for 1° stretches could be due to 'short range stiffness' of the cross bridges. Stretching of a contracting muscle generates large force increments even for moderate amplitudes of stretch. Approximately half of this force increment is due to the stretch reflex, which makes the muscle stiffer than predicted from the intrinsic stiffness. These findings in human flexor muscles are surprisingly similar to previous findings in extensor muscles of the decerebrate cat.
System identification techniques have been used to track changes in dynamic stiffness of the human ankle joint over a wide range of muscle contraction levels. Subjects lay supine on an experimental table with their left foot encased in a rigid, low-inertia cast which was fixed to an electro-hydraulic actuator operating as a position servo. Subjects generated tonic plantarflexor or dorsiflexor torques of different magnitudes ranging from rest to maximum voluntary contractions (MVC) during repeated presentations of a stochastic ankle angular position perturbation. Compliance impulse response functions (IRF) were determined from every 2.5 s perturbation sequence. The gain (G), natural frequency (omega n), and damping (zeta) parameters of the second-order model providing the best fit to each IRF were determined and used to compute the corresponding inertial (I), viscous (B) and elastic (K) stiffness parameters. The behaviour of these parameters with mean torque was found to follow two simple rules. First, the elastic parameter (K) increased in proportion to mean ankle torque as it was varied from rest to MVC; these changes were considerable involving increases of more than an order of magnitude. Second, the damping parameter (zeta) remained almost invariant over the entire range of contractions despite the dramatic changes in K.
The relationships between the mean rectified EMG from two muscle groups crossing the knee joint and the rotational stiffness and laxity about the longitudinal axis of the lower leg were investigated. The EMG signals from three of the quadricep muscle group and two of the hamstring muscle group were monitored using surface electrodes. Each subject sustained self-induced muscle activity from specific muscle combinations while the foot was twisted internally and externally by the researcher. Joint rotation was measured using an electrogoniometer. Analyses of the data showed increased joint stiffness with increased numbers of active muscles. The stiffness measurements ranged from 0.16 to 2.54 Nm degree-1 depending upon the combination of active muscles. The stiffness measured in different tests were very repeatable with standard deviations ranging from 0.02 to 0.25 Nm degree-1. Increases in joint stiffness of over 400% by activation of these muscles were measured.
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.
The synergistic action of the ACL and the thigh muscles in maintaining joint stability was studied experimentally. The EMG from the quadriceps and hamstring muscle groups was recorded and analyzed in three separate experimental procedures in which the knee was stressed. The test revealed that direct stress of the ACL has a moderate inhibitory effect on the quadriceps, but simultaneously it directly excites the hamstrings. Similar responses were also obtained in patients with ACL damage during loaded knee extension with tibia subluxation, indicating that an alternative reflex arc unrelated to ACL receptors was available to maintain joint integrity.
The antagonist muscles (hamstrings) were clearly demonstrated to assume the role of joint stabilizers in the patient who has a deficient ACL. The importance of an appropriate muscle-conditioning rehabilitation program in such a patient is substantiated.
Injuries treated at the University of Rochester Section of Sports Medicine over a 7 year period were surveyed. Patients were drawn from professional, intercollegiate (Division III), high school, intramural, and unorganized athletics at the University and the surrounding community. Data on injury diagnosis was available for 4,551 cases, with data on age, gender, and sport of injury available for 3,431 of the cases. The average patient age was 21.6 years, with a peak in the 16 to 19 age group. Patients with fractures had an average age below the overall mean, while those with internal derangement of the knee, patellofemoral pain syndrome, and inflammatory injuries were significantly older than average. Males accounted for 80.3% of all injuries. For both sexes the most common areas injured were the knee and ankle, with sprains/strains the most common injuries. Injuries involving the patellofemoral articulation were significantly more frequent among females. The most common sport of injury was football, with greater than 12 times the number of injuries seen in the next most common sport.
1. The presence of a form of stretch reflex, previously described in the arm by other authors, has been confirmed in the gastrocnemius muscle of the human leg. The electromyographic (e.m.g.) manifestation of this reflex occurred 120 msec ( S.E. of mean = 3·5 msec) following a sharply applied, and maintained, dorsiflexing force to the foot. This form of response is referred to in this article as the Functional Stretch Reflex (FSR).
2. To determine the contribution of the FSR to the control of normal leg movement, the e.m.g. activity in the above muscle was monitored during single downward steps of 12·7, 25·4 and 38·1 cm and during repetitive, rhythmic, hopping movements on one foot.
3. It was found that e.m.g. activity associated with steps to the ground began 141 msec ( S.E. of mean = 8·5 msec) before contact with the ground and ended 131 msec ( S.E. of mean = 7·6 msec) after contact, when the e.m.g. usually became temporarily inactive.
4. It is inferred from these results that the muscular deceleration associated with landing was brought about by the release of a pre‐programmed pattern of neuromuscular activity which was inaccessible to reflex activity resulting from the mechanical event of landing, rather than by a stretch reflex.
5. It was found that subjects chose their preferred frequency of hopping with great accuracy and consistency. The mean value obtained was 2·06 Hz ( S.E. of mean = 0·02 Hz).
6. At the preferred frequency, e.m.g. activity began 84 msec ( S.E. of mean = 9·6 msec) before and terminated 263 msec ( S.E. of mean = 10 msec) after contact with the ground.
7. It is inferred that in rhythmical hopping and perhaps also in running, each landing is effected, as in single steps, by a predetermined pattern of neuromuscular activity. However, when hopping at the preferred frequency, the take‐off phase of muscular activity is timed to make maximal use of the FSR, i.e. between 120 and 260 msec after initial contact.
8. The results emphasize the importance of pre‐programming complex muscular contractions suitable for opposing sudden passive stretching forces, and of initiating them prior to the onset of these forces.
This study reports the disability of 103 patients with symptomatic chronic laxity of the anterior cruciate ligament that was uncomplicated by other associated major ligament deficiency or prior ligament reconstructive procedures. All of the patients were evaluated at an average of 5.5 years after injury but a subgroup of thirty-nine patients was evaluated at an average of 11.2 years after injury. All had been active in sports, with two-thirds, participating in high-school or college athletics. The diagnosis of a tear of the anterior cruciate ligament was made by the original treating physician in only seven (6.8 per cent) of the 103 knees. Sixty-four patients (62 per cent) stated that the pain that followed the injury restricted normal activities for longer than three weeks. Eighty-five patients (82 per cent) had returned to some form of sports activity. This gave a false initial impression that the injury was not eventually disabling for sports, as a significant reinjury occurred in thirty-six patients (35 per cent) within six months and in fifty-three patients (51 per cent) within one year after the original injury. At follow-up five years later, only thirty-six patients (35 per cent) were participating in strenuous sports. A significant number of patients with longer follow-up had knee symptoms that affected their routine daily and recreational activities. A subjective moderate to severe over-all disability was reported by thirty-two patients (31 per cent) for walking activities alone, by forty-five patients (44 per cent) for over-all routine activities of daily living, and by seventy-seven patients (74 per cent) for turning or twisting sports activities. Pain occurred in thirty-one patients (30 per cent) during walking activities, in fofty-eight patients (47 per cent) during recreational activities, and in seventy-one patients (69 per cent) during strenuous sports activities. Twenty-two patients (21 per cent) complained of giving-way during walking acivities; thirty-four patients (33 per cent), during recreational sports; and sixty-six patients (65 per cent), during strenuous sports. Joint swelling occurred four to five times as frequently in the patients who had had the injury for the longest time (average, 11.2 years). If the patient had had a meniscectomy, there was a statistically significant twofold to fourfold increase in symptoms of pain and swelling related to activity. Giving-way was not affected, as this is related to instability of the anterior cruciate ligament. Significant roentgenographic changes of arthritis were noted in nineteen (21 per cent) of ninety-one patients starting at an average of 109 months after injury. Seventeen patients (44 per cent) in the subset with the longest follow-up had significant roentgenographic changes. Thse changes correlated statistically with participation in strenuous sports activities, with running activities, and with giving-way. Important qualifications to this retrospective study are: (1) the patients studied were limited to those with tears of the anterior cruciate ligament who sought treatment for relief of their symptoms, (2) these patients continued to be active athletically and thus continued to abuse their knees, and (3) none of the patients had had proper initial treatment, rehabilitation, or counseling which might have prevented joint deterioration. As a whole, the results show the significant functional disability found in the patient with a symptomatic anterior cruciate-deficient knee, initially for sports activities but later, following reinjury, for meniscal damage, joint arthritis, and the activities of daily living.
Static and dynamic components of mechanical impedance of human forearm were evaluated by applying two kinds of perturbations: 1) large viscoelastic loads, and 2) small pseudo-random perturbations. When the task involved the active resistance of the perturbations, both stiffness and viscosity increased relatively to their values in the passive task, the increment in stiffness being larger than that in viscosity. The time course of such changes was investigated during the transition between the two operating points defined by the instructions "do not resist" and "resist" the applied perturbations. The changes in stiffness and viscosity were relatively slow, those in the latter lagging behind those in the former.
The left foot of five human subjects was rotated in a fixed stochastic pattern about a constant ankle angle and the forces opposing these perturbations were measured. The dynamic stiffness transfer functions relating ankle angular position to ankle torque were calculated. Stiffness gain was flat at low frequencies, had a resonant valley at intermediate frequencies and rose at about 40 dB/decade at high frequencies. The low frequency gain and resonant frequency increased progressively with increases in tonic muscular activity. The dynamic stiffness of the ankle was well described by a linear, under-damped, second-order transfer function having inertial, viscous and elastic terms. Estimates of the inertial parameter were independent of the level of muscle activity whereas the viscous and elastic parameters increased with increases in mean torque level.
Female athletes are at increased risk for certain sports-related injuries, particularly those involving the knee. Factors that contribute to this increased risk are the differences in sports undertaken and in gender anatomy and structure. Gender differences include baseline level of conditioning, lower extremity alignment, physiological laxity, pelvis width, tibial rotation and foot alignment. Sports like gymnastics and cheerleading create a noncontact environment, but can result in significant knee injuries. In quick stopping and cutting sports, females have an increased incidence of anterior cruciate ligament (ACL) injury by noncontact mechanisms. Patellofemoral (PF) disorders are also very common in female athletes.
Awareness of these facts helps the sports medicine professional make an accurate diagnosis and institute earlier treatment-focused rehabilitation with or without surgery. Further prospective and retrospective research is needed in areas of epidemiology, mechanisms, severity and types of knee injuries. The goal is to lessen the severity of certain knee injuries and to prevent others.
With detailed information concerning the role of the anterior cruciate ligament in the overall kinematic response of the knee during external loading, current clinical management of the orthopedic injuries to this joint may be improved upon and refined. Among the largest challenges to be met will be elucidation of the effects of various levels and types of muscular stabilization concurrent with a precise determination of the roles of passive knee restraints.
A total of 675 male soldiers of the same age (17 years) and on the same physical exertion regimen were studied in order to determine the incidence of joint laxity and its potential relationship to the appearance of musculoligamentous lesions. They were investigated during their 2-month military training period, which involved the same heavy physical exertion for all the individuals.
The degree of joint laxity was determined on the basis of five criteria involving the hand, elbow, knee and spine.
The overall population was divided into three groups according to the number of criteria met, namely: (1) normal or non-lax individuals, with none or only one criterion (67% of the studied population); (2) lax individuals, with two or three criteria (25.5%); and (3) hyperlax indivuduals, with four or five criteria (7.5%).
The occurrence of musculoligamentous lesions during the 2-month study, particuarly those involving the ankle and knee, was significantly more frequent in hyperlax and lax individuals than it was in their counterparts with normal joint mobility. These results confirm that joint hyperlaxity predisposes individuals to musculoligamentous lesions.
Women's participation in intercollegiate athletics has increased dramatically in recent years. Greater participation has increased awareness of health and medical issues specific to the female athlete. Some reports have noted a higher susceptibility to knee injury, specifically injuries to the anterior cruciate ligament, in female athletes as compared with their male counterparts. We performed a 5-year evaluation of anterior cruciate ligament injuries in collegiate men's and women's soccer and basketball programs using the National College Athletic Association Injury Surveillance System. Results showed significantly higher anterior cruciate ligament injury rates in both female sports compared with the male sports. Noncontact mechanisms were the primary cause of anterior cruciate ligament injury in both female sports. Possible causative factors for this increase in anterior cruciate ligament injuries among women may be extrinsic (body movement, muscular strength, shoe-surface interface, and skill level) or intrinsic (joint laxity, limb alignment, notch dimensions, and ligament size).
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.
This study examined the coactivation of trunk flexor and extensor muscles in healthy individuals. The experimental electromyographic data and the theoretical calculations were analyzed in the context of mechanical stability of the lumbar spine.
To test a set of hypotheses pertaining to healthy individuals: 1) that the trunk flexor-extensor muscle coactivation is present around a neutral spine posture, 2) that the coactivation is increased when the subject carries a load; and 3) that the coactivation provides the needed mechanical stability to the lumbar spine.
Theoretically, antagonistic trunk muscle coactivation is necessary to provide mechanical stability to the human lumbar spine around its neutral posture. No experimental evidence exists, however, to support this hypothesis.
Ten individuals executed slow trunk flexion-extension tasks, while six muscles on the right side were monitored with surface electromyography: external oblique, internal oblique, rectus abdominis, multifidus, lumbar erector spinae, and thoracic erector spinae. Simple, but realistic, calculations of spine stability also were performed and compared with experimental results.
Average antagonistic flexor-extensor muscle coactivation levels around the neutral spine posture as detected with electromyography were 1.7 +/- 0.8% of maximum voluntary contraction for no external load trials and 2.9 +/- 1.4% of maximum voluntary contraction for the trials with added 32-kg mass to the torso. The inverted pendulum model based on static moment equilibrium criteria predicted no antagonistic coactivation. The same model based on the mechanical stability criteria predicted 1.0% of maximum voluntary contraction coactivation of flexors and extensors with zero load and 3.1% of maximum voluntary contraction with a 32-kg mass. The stability model also was run with zero passive spine stiffness to simulate an injury. Under such conditions, the model predicted 3.4% and 5.5% of maximum voluntary contraction of antagonistic muscle coactivation for no extra load and the added 32 kg, respectively.
This study demonstrated that antagonistic trunk flexor-extensor muscle coactivation was present around the neutral spine posture in healthy individuals. This coactivation increased with added mass to the torso. Using a biomechanical model, the coactivation was explained entirely on the basis of the need for the neuromuscular system to provide the mechanical stability to the lumbar spine.
While military parachuting injuries have been well studied, the relationship between gender and risk of injury has not. Injuries among women may be different due to anatomic and physiologic differences, or due to exposure to different jump conditions. Training methods and equipment developed for men may not be as effective in preventing injuries among women.
We hypothesize that the nature and distribution of parachute injuries will vary by gender.
This descriptive retrospective study used 10 yr of parachute injury data reported to the U.S. Army Safety Center at Fort Rucker, AL, and exposure data obtained from the Defense Manpower Data Center, Monterey, CA.
Women appear to jump under less hazardous conditions (jump more often than men in daylight and in static-line, non-tactical environments), yet appear to be at greater risk of serious injury, particularly lower extremity fractures. Injured male parachutists are more likely to experience upper extremity injury. Women's injuries are more likely to be the result of an improper parachute landing fall or parachute malfunction, while men are more likely to be injured due to ground hazards.
There are some provocative gender differences in patterns of injury. Further research is indicated starting with a comprehensive, prospective study, controlling for physical fitness and exposure differences, as well as for potential reporting bias, in order to better understand the apparent differences in reported injuries.
We report on a conceptual two degrees of freedom (2 DOF) human gait model, which incorporates nonlinear joint stiffness as a stabilizing agent. Specifically, muscle spring-like property provides inherent stability during gait movement using a nonlinear angular spring and dash pot at each joint. The instability problem of the gait model in direct dynamic analysis is overcome by simulating the human co-contraction muscle function. By developing dynamic system stability requirements and hypothesizing a minimum joint stiffness criterion, we determine time-varying joint stiffness. Optimum joint stiffnesses are present for varying gait pattern, stride lengths and cadences. We conclude that nonlinear joint stiffness can be incorporated into gait models to overcome stability problems inherent in such linkage models.