Article

Effect of technique variations on knee biomechanics during the squat and leg press

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Abstract

The specific aim of this project was to quantify knee forces and muscle activity while performing squat and leg press exercises with technique variations. Ten experienced male lifters performed the squat, a high foot placement leg press (LPH), and a low foot placement leg press (LPL) employing a wide stance (WS), narrow stance (NS), and two foot angle positions (feet straight and feet turned out 30 degrees ). No differences were found in muscle activity or knee forces between foot angle variations. The squat generated greater quadriceps and hamstrings activity than the LPH and LPL, the WS-LPH generated greater hamstrings activity than the NS-LPH, whereas the NS squat produced greater gastrocnemius activity than the WS squat. No ACL forces were produced for any exercise variation. Tibiofemoral (TF) compressive forces, PCL tensile forces, and patellofemoral (PF) compressive forces were generally greater in the squat than the LPH and LPL, and there were no differences in knee forces between the LPH and LPL. For all exercises, the WS generated greater PCL tensile forces than the NS, the NS produced greater TF and PF compressive forces than the WS during the LPH and LPL, whereas the WS generated greater TF and PF compressive forces than the NS during the squat. For all exercises, muscle activity and knee forces were generally greater in the knee extending phase than the knee flexing phase. The greater muscle activity and knee forces in the squat compared with the LPL and LPH implies the squat may be more effective in muscle development but should be used cautiously in those with PCL and PF disorders, especially at greater knee flexion angles. Because all forces increased with knee flexion, training within the functional 0-50 degrees range may be efficacious for those whose goal is to minimize knee forces. The lack of ACL forces implies that all exercises may be effective during ACL rehabilitation.

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... Specifically, the stance width has received relatively limited research attention, although recent publications in this area indicate that it is becoming a more prominent aspect of discussion in the strength and conditioning literature. Varying squat stance widths are utilized according to the athlete's morphology and preferences [7], although the effects and efficacy of one stance over another is not well established. McCaw & Melrose [8] examined lower extremity muscle activation when performing the barbell back squat, with low and high barbell loads using stance widths of 75 and 140% shoulder distance. ...
... In addition, the analysis of the joint moments showed that the knee extensor and ankle plantar flexor moments were significantly larger in the medium and wide conditions compared to the narrow. Escamilla et al. [7] investigated the effects of the stance width on the electromyographic activity of eight superficial thigh muscles during the leg press and barbell back squat exercises. Their findings show that the hamstring and gastrocnemius muscle activation was significantly greater in the wide squat compared to the narrow position. ...
... When also taking into account the observations from both experiments relating them to the joint energy production, this study indicates that the NARROW condition appears to arbitrate a knee-dominant squat strategy that targets the anterior chain musculature, whereas the WIDE condition produced a hip-dominant strategy [16] and targets the posterior chain musculature more effectively. This observation concurs with the electromyographic investigations of Escamilla et al. [7], McCaw & Melrose [8] and Paoli et al. [9], who found that wide-stance squat positions recruited the posterior chain musculature to a significantly greater extent. Furthermore, our observations in relation to the joint dominance are also supported by the examination of the joint moments by Lahti et al. [11], who showed that the hip-to-knee joint extension moment ratio was significantly greater when adopting a wide stance. ...
Article
This two-experiment study aimed to explore habitual and manipulated stance widths on squat biomechanics. In experiment one, 70 lifters completed back squats at 70%, 1 repetition maximum (1RM), and were split into groups (NARROW < 1.06 * greater trochanter width (GTW), MID 1.06–1.18 * GTW and WIDE > 1.37 * GTW) according to their self-selected stance width. In experiment two, 20 lifters performed squats at 70%, 1RM, in three conditions (NARROW, MID and WIDE, 1.0, 1.25 and 1.5 * GTW). The three-dimensional kinematics were measured using a motion capture system, ground reaction forces (GRF) using a force platform, and the muscle forces using musculoskeletal modelling. In experiment two, the peak power was significantly greater in the NARROW condition, whereas both experiments showed the medial GRF impulse was significantly greater in the WIDE stance. Experiment two showed the NARROW condition significantly increased the quadriceps forces, whereas both experiments showed that the WIDE stance width significantly enhanced the posterior-chain muscle forces. The NARROW condition may improve the high mechanical power movement performance and promote the quadriceps muscle development. Greater stance widths may improve sprint and rapid change-of-direction performance and promote posterior-chain muscle hypertrophy. Whilst it appears that there is not an optimal stance width, these observations can be utilized by strength and conditioning practitioners seeking to maximize training adaptations.
... Of the 4 heads that make up the quadriceps (vastus medialis, vastus lateralis, vastus intermedius, and rectus femoris), the 3 vastii often present considerably greater muscle excitation than the rectus femoris during the squat (10,11,14,39). This is due to the biarticular nature of the rectus femoris, which, in addition to crossing the knee joint, also crosses the hip joint. ...
... Regarding the quadriceps, studies indicate that the greatest excitation in the squat occurs at angles close to 908-1008 of knee flexion, that is, between the half and parallel ROMs (7,14,44). Although there are several studies verifying muscle activity with sEMG comparing different ROMs (7,14,44), only 2 studies have compared different squat amplitudes on hypertrophy of lower-limb muscles (4,21). ...
... Regarding the quadriceps, studies indicate that the greatest excitation in the squat occurs at angles close to 908-1008 of knee flexion, that is, between the half and parallel ROMs (7,14,44). Although there are several studies verifying muscle activity with sEMG comparing different ROMs (7,14,44), only 2 studies have compared different squat amplitudes on hypertrophy of lower-limb muscles (4,21). Bloomquist et al. (4) analyzed 2 groups of untrained young men who performed "deep" (parallel; 08-1208 of knee flexion ROM) or "shallow" (quarter; 08-608 of knee flexion ROM) free barbell back squats for 12 weeks. ...
Article
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The squat is one of the most widely used exercises in resistance-training programs. The aim of the present narrative review was to analyze the effect of the squat on lower-limb muscle hypertrophy. Briefly, the available literature indicates that the squat is an effective exercise for inducing hypertrophy of the quadriceps, mainly the vastii, but also the rectus femoris, although to a reduced magnitude. Multiple lines of evidence suggest little to no hamstring hypertrophy from the back squat. While the gluteus maximus clearly participates mechanically in the back squat, few longitudinal studies exist on the topic. The limited evidence available on this topic suggests deeper squats may be more hypertrophic for the gluteus maximus, and that squat depth beyond 90 degrees of knee flexion may not provide further hypertrophy of the knee flexors. Despite the popularity of the many squat variations, there are still controversies surrounding their hypertrophic potential for lower-limb musculature. Further studies are needed to investigate the hypertrophic effects of different squat variations, as well as differences in hypertrophy due to squat depth, stance, barbell position, and different squat apparatuses/machines.
... 21,45,50 The widespread applicability offered by this exercise is explained by the simplicity of its technique since it is a guided movement, 8 along with its transference to functional movements such as walking, squatting, running, or jumping. 6,8,13,17 This means that the exercise can be included in any training program regardless of the participants' age 10,19,32 or training goal, whether it be for rehabilitation, 2,6,8,43 injury prevention and return to play, 17,26 health, 2,52 or athletic performance. 13,17 Given the leg press exercise's versatility, it is essential that trainers and athletes understand the muscle activation elicited during its use, as a key factor in the concomitant development of muscle mass and strength. ...
... 6,8,13,17 This means that the exercise can be included in any training program regardless of the participants' age 10,19,32 or training goal, whether it be for rehabilitation, 2,6,8,43 injury prevention and return to play, 17,26 health, 2,52 or athletic performance. 13,17 Given the leg press exercise's versatility, it is essential that trainers and athletes understand the muscle activation elicited during its use, as a key factor in the concomitant development of muscle mass and strength. 31,38,45 Surface electromyography (sEMG) has been widely used in research 5 as a noninvasive method for assessing muscle activation and neuromuscular function. ...
... 11,26 The muscles most frequently assessed using sEMG during the leg press exercise are the vastus medialis oblique (VMO), vastus lateralis (VL), rectus femoris (RF), and biceps femoris. 13,26,28,50,52 In addition, some other studies have evaluated the leg press exercise using different feet stances (conditions) over the footplate. For instance, a low feet position over the footplate resulted in greater quadriceps muscle activation, 11 whereas there were no differences in overall muscle activation between the 30° forefoot external rotation condition and wide and narrow feet stances. ...
Article
Background: The leg press is one of the most typical exercises for strengthening the lower limbs. The objectives of this study were to compare 5 inclined leg press exercise conditions, varying the feet width stance (100% or 150% hip width), the feet rotation (0° or 45° external rotation) on the footplate and using 2 different movement velocities (MVs; maximum intended, and 2:2 seconds steady-paced velocities) to determine their effect on muscle activation as well as on the kinematic parameters between trained men and trained women. Hypotheses: There will be no significant differences in muscle activation with regard to the feet position. The higher the MV, the greater the muscle activation. Study design: A cross-sectional cohort study. Level of evidence: Level 3. Methods: A repeated-measures between-group design was performed to examine muscle activation and kinematic parameters for the different conditions between gender groups. The level of significance was set at alpha = 0.05 for all statistical analyses. Results: Muscle activation presented no differences between conditions regarding feet width stance or feet rotation. Furthermore, muscle activation was greater during positive phases than negative phases of the exercise for all conditions and was also greater under maximum intended velocity conditions compared with steady-paced conditions. Otherwise, the muscle activation pattern presented slight differences by gender. In men, the greatest muscle activation was for the vastus medialis, followed by the vastus lateralis (VL), rectus femoris (RF), and gluteus medialis (GMED), while in women, the greatest muscle activation was for the vastus medialis, followed by the RF, VL, and GMED. Finally, greater mean propulsive velocity, maximum velocity, maximum power, and footplate displacement values were reported for men than for women under all the conditions. Conclusion: The inclined leg press exercise produces the highest muscle activation in the vastus medialis, regardless of the velocity, feet stance, or gender. Clinical relevance: Given that there are no differences in muscle activation regarding the feet stance, a participant's preferred feet stance should be encouraged during the inclined leg press exercise. Furthermore, the MV would preferably depend on the session objective (a training or a rehabilitation program), being aware that there is greater muscle activation at higher speeds. The inclined leg press exercise could be performed as a closed kinetic chain exercise when the main objective is to activate the vastus medialis.
... The risk factors are related to changes in the movement kinetics of the tibiofemoral joint, caused by changes in the force exerted on the knee and hip joints. The risk of injury occurs when there is muscle imbalance of the trunk and hip or alteration of the kinetic movement of the feet and ankles [16,[22][23][24][25][26] Studies in rehabilitation have shown that bodybuilding physical activity, with protocols of exercises to strengthen the hips and quadriceps muscles, together with work tasks, are protective factors in decreasing PFPS incidence [17,19,27,28]. In the sports area, it is possible to find some studies with which it is possible to establish a direct relationship between the act of squatting and the occurrence of PFPS [28][29][30]. ...
... The first one is based on the knowledge about the degrees of knee flexion, considering its anterior translational movement over the anterior tibial line as the main factor of PFPS worsening [22,40,45,49,53,54,65]. ...
... Finally, as a third point, considering the posed research question, the tension overloads on the knees are compared following the evaluation models applied in different types of squats. In these cases, it is observed that there is an overload of the patellofemoral ligament in diverse degrees of knee flexion, mainly between 60 • and 90 • degrees [22,24,33,49,53,57,62]. ...
Article
Full-text available
Patellofemoral pain syndrome (PFPS) is highly prevalent; it can cause severe pain and evolve into progressive functional loss, leading to difficulties performing daily tasks such as climbing and descending stairs and squatting. This systematic review aimed to find evidence, in the literature, of squat movements that can cause or worsen PFPS. This work was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement, and its protocol was registered in PROSPERO (CRD42019128711). From the 6570 collected records, 37 were included. From these 37 articles, 27 present a causal relationship between knee flexion and PFPS, 8 describe a relationship, considering the greater existence of muscle contractions, and one article did not describe this relationship in its results. The main limitations stem from the fact that different studies used different evaluation parameters to compare the force exerted on the patellofemoral joint. Furthermore, most studies are focused on sports populations. After analysing the included works, it was concluded that all squat exercises can cause tension overload in the knee, especially with a knee flexion between 60° and 90° degrees. The main causal/worsening factors of PFPS symptoms are the knee translocation forward the toes (on the same body side) when flexing the knee, and the muscle imbalance between the thigh muscles.
... The ACL provides 86% of the total resistance to anterior translation of the tibia relative to the femur [285]. When ACL, peak load to failure [307] 2160 Weight bearing Barbell squat [278,279] 0 Leg press [278,279] 0 Forward lunge (both with and without a stride, using 12-repetition maximum load and through 90° of knee flexion) [280,316] 0 Side lunge (both with and without a stride, using 12-repetition maximum load and through 90° of knee flexion) [316] 0 Dynamic squat to stand [288] 25°20 Single-leg squat [289] < 50°~ 100 Double foot drop landing (stepping off a 60-cm platform) [291] 30°-50°250 Level ground walking [317] 15°-20°303 Single-leg landing from running to a stop [295] 25°-30°1294 Non-weight bearing Dynamic seated knee extension (using 12-repetition maximum load and through 90° of knee flexion) [278] 15°158 Isokinetic knee extension (0°-90° of knee flexion) at 180°/s [289] 35°-40°254 Isokinetic knee extension (0°-90° of knee flexion) at 120°/s [289] 35°-40°325 Isokinetic knee extension (0°-90° of knee flexion) at 60°/s [289] 35°-40°349 Isometric seated knee extension [289] 35°-40°396 Isometric or isokinetic knee flexion [289] 0 the knee is between 0° and 60° of flexion, the contracted quadriceps creates force across the patellar tendon to create an anterior force on the proximal tibia, loading the ACL [285,286]. However, the contracting quadriceps create posteriorly directed forces, in knee flexion angles greater than 60°, acting to unload the ACL [285,286]. ...
... The ACL provides 86% of the total resistance to anterior translation of the tibia relative to the femur [285]. When ACL, peak load to failure [307] 2160 Weight bearing Barbell squat [278,279] 0 Leg press [278,279] 0 Forward lunge (both with and without a stride, using 12-repetition maximum load and through 90° of knee flexion) [280,316] 0 Side lunge (both with and without a stride, using 12-repetition maximum load and through 90° of knee flexion) [316] 0 Dynamic squat to stand [288] 25°20 Single-leg squat [289] < 50°~ 100 Double foot drop landing (stepping off a 60-cm platform) [291] 30°-50°250 Level ground walking [317] 15°-20°303 Single-leg landing from running to a stop [295] 25°-30°1294 Non-weight bearing Dynamic seated knee extension (using 12-repetition maximum load and through 90° of knee flexion) [278] 15°158 Isokinetic knee extension (0°-90° of knee flexion) at 180°/s [289] 35°-40°254 Isokinetic knee extension (0°-90° of knee flexion) at 120°/s [289] 35°-40°325 Isokinetic knee extension (0°-90° of knee flexion) at 60°/s [289] 35°-40°349 Isometric seated knee extension [289] 35°-40°396 Isometric or isokinetic knee flexion [289] 0 the knee is between 0° and 60° of flexion, the contracted quadriceps creates force across the patellar tendon to create an anterior force on the proximal tibia, loading the ACL [285,286]. However, the contracting quadriceps create posteriorly directed forces, in knee flexion angles greater than 60°, acting to unload the ACL [285,286]. ...
... Trunk flexion while performing a seated knee extension can be achieved by putting a wedge behind the person's back, while also placing the hamstrings at an advantage to unload the ACL. PCL, peak strain to failure [78,401,402] 739-4000 Weight bearing Squat and leg press (using 12-repetition maximum loading, and through 90° of knee flexion) [278,279] 60°-90°1500-2000 ...
Article
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Mechanical loading to the knee joint results in a differential response based on the local capacity of the tissues (ligament, tendon, meniscus, cartilage, and bone) and how those tissues subsequently adapt to that load at the molecular and cellular level. Participation in cutting, pivoting, and jumping sports predisposes the knee to the risk of injury. In this narrative review, we describe different mechanisms of loading that can result in excessive loads to the knee, leading to ligamentous, muscu-lotendinous, meniscal, and chondral injuries or maladaptations. Following injury (or surgery) to structures around the knee, the primary goal of rehabilitation is to maximize the patient's response to exercise at the current level of function, while minimizing the risk of re-injury to the healing tissue. Clinicians should have a clear understanding of the specific injured tissue(s), and rehabilitation should be driven by knowledge of tissue-healing constraints, knee complex and lower extremity biomechanics, neuromuscular physiology, task-specific activities involving weight-bearing and non-weight-bearing conditions , and training principles. We provide a practical application for prescribing loading progressions of exercises, functional activities, and mobility tasks based on their mechanical load profile to knee-specific structures during the rehabilitation process. Various loading interventions can be used by clinicians to produce physical stress to address body function, physical impairments, activity limitations, and participation restrictions. By modifying the mechanical load elements, clinicians can alter the tissue adaptations, facilitate motor learning, and resolve corresponding physical impairments. Providing different loads that create variable tensile, compressive, and shear deformation on the tissue through mechanotransduction and speci-ficity can promote the appropriate stress adaptations to increase tissue capacity and injury tolerance. Tools for monitoring rehabilitation training loads to the knee are proposed to assess the reactivity of the knee joint to mechanical loading to monitor excessive mechanical loads and facilitate optimal rehabilitation. Key Points Mechanical loads encountered during high-risk cutting, pivoting, and jumping sports predispose the structures of the knee to risk of injury. Individual tissues of the knee respond and adapt differently to various mechanical load stimuli. Appropriate selection of exercises, functional activities , and mobility tasks based on their mechanical load profile can be utilized during rehabilitation to systematically and progressively load the structure of the knee to promote tissue healing and repair.
... Nonetheless, some conditions have been evaluated in the male population. For instance, Escamilla et al. [11] reported no differences in thigh muscle activation under different conditions (stance width and feet rotation modifications) during the leg press. Peng et al. [12], on the other hand, reported higher medial thigh muscle activation in a male population during the leg press with hip adduction resistance, compared to the conventional leg press. ...
... The present study results are consistent with other studies in the male population. For example, Escamilla et al. [11] affirmed that varying the foot external rotation (0-30 • ) during the flat leg press did not affect VMO, VL or RF muscle activation in a young male population. Peng et al. [12], on the other hand, analyzed VM, VL and hip adductor longus muscle activation during the leg press with isometric hip adduction resistance in a young male population. ...
... In addition, in their systematic review, Smith et al. [5] stated that the VMO muscle could not be preferentially activated by modifying the lower limb position during quadriceps exercises. However, they did not analyze leg press exercises in their review, thus highlighting the need to expand our knowledge on this issue [8,11]. ...
Article
Full-text available
Knee joint muscle activation imbalances, especially weakness in the vastus medialis oblique, are related to patellofemoral pain within the female population. The available literature presents the leg press as an exercise which potentially targets vastus medialis oblique activation, thus reducing imbalances in the quadriceps muscles. The main aim of the present study was to compare thigh muscle activation and kinematic parameters under different conditions during the inclined leg press exercise in a young female population. A cross-sectional study was conducted on 10 young, trained females. Muscle activation of the vastus medialis oblique, vastus lateralis, rectus femoris and gluteus medialis was analyzed under five different inclined leg press conditions, modifying the feet rotation (0-45 • external rotation) and the stance width (100-150% hip width) on the footplate. All the conditions were performed at two different movement velocities: controlled velocity (2" eccentric-2" concentric) and maximal intended velocity. Mean propulsive velocity, maximum velocity and maximum power were also assessed. The results show that both controlled velocity conditions and maximal intended velocity conditions elicited a similar muscle activation pattern with greater activation during the concentric phase (p < 0.001, ηp 2 = 0.96). The maximal intended velocity conditions showed greater overall muscle activation (p < 0.001, ηp 2 = 0.91). The vastus medialis oblique presented the greatest muscle activation, followed by the rectus femoris, vastus lateralis and, the gluteus medialis. Furthermore, the inclined leg press condition with 0º feet rotation, 100% hip width distance and the maximal intended velocity generated the greatest kinematic parameter outputs. In conclusion, the inclined leg press exercise might be an optimal exercise to target vastus medialis activation regardless of the feet rotation and stance width conditions.
... Inverse dynamics combined with musculoskeletal modelling have proven powerful tools to evaluate muscle effort and joint loading, especially for complex multi-joint exercises with muscle activations that are difficult to predict (Chiu, 2018). This method has been used to study conventional barbell squat (Wretenberg et al., 1993;Escamilla, 2001;Schoenfeld, 2010;Bryanton et al., 2012), and to a lesser degree, leg press (Wilk et al., 1996;Escamilla et al., 2001;Kolditz et al., 2015). Comparisons of joint loads between these two exercises have, however, almost exclusively focused on the knee joint (Wilk et al., 1996;Escamilla et al., 1998Escamilla et al., , 2001. ...
... This method has been used to study conventional barbell squat (Wretenberg et al., 1993;Escamilla, 2001;Schoenfeld, 2010;Bryanton et al., 2012), and to a lesser degree, leg press (Wilk et al., 1996;Escamilla et al., 2001;Kolditz et al., 2015). Comparisons of joint loads between these two exercises have, however, almost exclusively focused on the knee joint (Wilk et al., 1996;Escamilla et al., 1998Escamilla et al., , 2001. To date, only two studies have investigated joint biomechanics during flywheel resistance exercise: Chiu and Salem (2006) compared joint kinetics between flywheel and barbell front squats, and recently our group published a study comparing joint loads during submaximal flywheel squat and leg press (Sjöberg et al., 2020). ...
Article
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The aim was to compare the musculoskeletal load distribution and muscle activity in two types of maximal flywheel leg-extension resistance exercises: horizontal leg press, during which the entire load is external, and squat, during which part of the load comprises the body weight. Nine healthy adult habitually strength-training individuals were investigated. Motion analysis and inverse dynamics-based musculoskeletal modelling were used to compute joint loads, muscle forces, and muscle activities. Total exercise load (resultant ground reaction force; rGRF) and the knee-extension net joint moment (NJM) were slightly and considerably greater, respectively, in squat than in leg press ( p ≤ 0.04), whereas the hip-extension NJM was moderately greater in leg press than in squat ( p = 0.03). Leg press was performed at 11° deeper knee-flexion angle than squat ( p = 0.01). Quadriceps muscle activity was similar in squat and leg press. Both exercise modalities showed slightly to moderately greater force in the vastii muscles during the eccentric than concentric phase of a repetition ( p ≤ 0.05), indicating eccentric overload. That the quadriceps muscle activity was similar in squat and leg press, while rGRF and NJM about the knee were greater in squat than leg press, may, together with the finding of a propensity to perform leg press at deeper knee angle than squat, suggest that leg press is the preferable leg-extension resistance exercise, both from a training efficacy and injury risk perspective.
... Full squats (F-SQ) may enhance flexibility and improve athletic performance [12]. Squats are usually performed at a shallow depth (knee flexion 0-60 • ) during rehabilitation training, because the injury risk to the soft tissue in the knee joint may increase during high flexion [5,9,18]. In addition, the increase of squat depth will lead to the rise in the moment of the hip joint, knee joint, and ankle joint [12,19,20], which may lead to related sports injuries. ...
... OpenSim is an open-source platform for generating and executing dynamic simulation and analysis, which provides tools for solving inverse kinematics and inverse dynamics [27,28,34]. The model was adjusted based on the open-source squat model to prevent the muscles from passing through the bones and allow higher joint mobility (ROM) [13,18] The muscle-tendon slake employed Hill's muscle model and followed the relationships between muscle force and strain. OpenSim can match marker trajectories collected in the motion capture system to the virtual makers in the model, enabling authentic and reliable musculoskeletal model [13,31]. ...
Article
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Background: Females with different practice experience may show different body postures and movement patterns while squatting in different depths, which may lead to changes of biomechanical loadings and increase the risks of injuries. Methods: Sixteen novice female participants without squat training experience participated in this study. A 3D motion capture system was used to collect the marker trajectory and ground reaction force data during bodyweight squatting in different depths. The participants' kinematic data and joint moment were calculated using OpenSim's inverse kinematics and inverse dynamics algorithm. In this study, authors adapted a model especially developed for squatting and customized the knee joint with extra Degree-of-Freedom (DoF) in the coronal and horizontal plane with adduction/abduction and internal/external rotation. A paired-sample t-test was used to analyze the difference of joint range of motions (ROM) and peak moments between full-squat (F-SQ) and half-squat (H-SQ). One-Dimensional Statistical Parametric Mapping (SPM1D) is used to analyze the difference of joint angle and moment between the process of squatting F-SQ and H-SQ. Results: (1) Compared with H-SQ, F-SQ showed larger ROM in sagittal, coronal, and transverse planes (p < 0.05). (2) SPM1D found that the difference in joint angles and joint moments between F-SQ and H-SQ was mainly concentrated in the mid-stance during squatting, which suggested the difference is greatly pronounced during deeper squat. (3) Peak hip extension moment, knee extension moment, hip adduction moment, and plantar flexion moment of F-SQ were significantly higher than H-SQ (p < 0.05). (4) Difference of hip and knee extension moments and rotation moments between the F-SQ and H-SQ were exhibited during descending and ascending. Conclusions: The study found that novice women had larger range of joint motion during the F-SQ than H-SQ group, and knee valgus was observed during squatting to the deepest point. Greater joint moment was found during F-SQ and reached a peak during ascending after squatting to the deepest point. Novice women may have better movement control during H-SQ. The findings may provide implications for the selection of lower limb strength training programs, assist the scientific development of training movements, and provide reference for squat movement correction, thus reducing the risk of injury for novice women in squatting practice.
... Moreover, activities like squatting and cross-leg sitting may strain the newly-reconstructed ACL. Escamilla et al. 17 found that, in early squatting between 0°and 60°, the shear forces were low and primarily restricted by the ACL. With near-maximum knee flexion, the shear forces also peak, putting a lot of stress on the new ACL. ...
... With near-maximum knee flexion, the shear forces also peak, putting a lot of stress on the new ACL. 17 Andersson et al. 18 performed a systematic review of four randomized studies. They found that in ACL-R with BPTB graft, early CKC exercises generate lower levels of pain, lower risk of increased laxity, and better self-reported knee function than OKC quadriceps exercises. ...
Article
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Resumo Objetivo Comparar a eficácia dos protocolos de reabilitação acelerada precoce e de reabilitação conservadora retardada após reconstrução artroscópica do ligamento cruzado anterior, em termos da escala do International Knee Documentation Committee (IKDC), da dor (segundo a Escala Visual Analógica), da frouxidão e da rigidez no pós-operatório de um ano para determinar o melhor desfecho. Materiais e Métodos Um total de 80 participantes foram divididos em dois grupos (grupo da acelerada precoce e grupo da conservadora retardada), que foram analisados pelos testes do Qui-quadrado de Pearson e da soma dos postos de Wilcoxon. Resultados A frouxidão do joelho no pós-operatório de 1 ano foi significativamente mais alta ( p = 0,039) no grupo da acelerada precoce do que no grupo da conservadora retardada. Em termos de dor pós-operatória (pela Escala Visual Analógica) e pontuações no IKDC, ambos os grupos apresentaram resultados similares. A amplitude de movimento pós-operatória foi melhor no grupo da acelerada precoce, mas isso não foi estatisticamente significativo ( p = 0,36). Conclusão O protocolo de reabilitação acelerada precoce foi associado com uma frouxidão significativa do joelho em um ano de pós-operatório em comparação com o protocolo de reabilitação conservadora retardada.
... Mechanical models [9], electromyographic techniques [10], magnetic resonance [11], and computed tomography [12] are used to check chronic or acute adaptations of muscles in the LP exercise, to more accurately identify the muscle functions. Several muscles participate in the execution of the exercise LP (quadriceps and gluteus maximus), hamstrings (biceps femoris, semimembranosus, and semitendinosus), triceps sural, among others, with different functions [13]. ...
... However, some authors [14,15] suggest that for there to be increases in protein synthesis of muscle fibers, it is necessary that, in addition to being recruited, they must be subjected to a certain level of functional stress or mechanical load. Data from Escamilla, et al. [10], using the electromyography technique, are divergent about variations in the position of the feet in the LP and the muscular action of the hamstrings and quadriceps. Probably, due to the types of equipment used and the limitation of the technique for this type of inference. ...
... Moreover, activities like squatting and cross-leg sitting may strain the newly-reconstructed ACL. Escamilla et al. 17 found that, in early squatting between 0°and 60°, the shear forces were low and primarily restricted by the ACL. With near-maximum knee flexion, the shear forces also peak, putting a lot of stress on the new ACL. ...
... With near-maximum knee flexion, the shear forces also peak, putting a lot of stress on the new ACL. 17 Andersson et al. 18 performed a systematic review of four randomized studies. They found that in ACL-R with BPTB graft, early CKC exercises generate lower levels of pain, lower risk of increased laxity, and better self-reported knee function than OKC quadriceps exercises. ...
... These findings can be partially explained by the different activation patterns of the leg muscles during squat. Escamilla et al. (2001) measured EMG patterns of different muscle groups in 10 subjects and found that the peak quadriceps activity occurs at 80-90°knee flexion and that the activity is 25-50% greater in the knee extension phase. Conversely, knee flexor muscles are more active at smaller flexion angles during squat. ...
Article
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Understanding the sources of error is critical before models of the musculoskeletal system can be usefully translated. Using in vivo measured tibiofemoral forces, the impact of uncertainty in muscle-tendon parameters on the accuracy of knee contact force estimates of a generic musculoskeletal model was investigated following a probabilistic approach. Population variability was introduced to the routine musculoskeletal modeling framework by perturbing input parameters of the lower limb muscles around their baseline values. Using ground reaction force and skin marker trajectory data collected from six subjects performing bodyweight squat, the knee contact force was calculated for the perturbed models. The combined impact of input uncertainties resulted in a considerable variation in the knee contact force estimates (up to 2.1 BW change in the predicted force), especially at larger knee flexion angles, hence explaining up to 70% of the simulation error. Although individual muscle groups exhibited different contributions to the overall error, variation in the maximum isometric force and pathway of the muscles showed the highest impacts on the model outcomes. Importantly, this study highlights parameters that should be personalized in order to achieve the best possible predictions when using generic musculoskeletal models for activities involving deep knee flexion.
... First, we did not consider the stance width in this work since our skeletal model is 2D. It has been observed that there are no significant differences in quadriceps muscles between the narrow and wide stance [62]. There may be some changes for the gluteus medius muscles, however, if the stance distance is changed. ...
Article
Objective: In this study, a novel hybrid predictive musculoskeletal model is proposed which has both motion prediction and muscular dynamics assessment capabilities. Methods: First, a two-dimensional (2D) skeletal model with 10 degrees of freedom is used to predict a symmetric lifting motion, outputting joint angle profiles, ground reaction forces (GRFs), and center of pressure (COP). These intermediate outputs are input to the scaled musculoskeletal model in OpenSim for muscle activation and joint reaction load analysis. Finally, the experimental validation is carried out. Results: Static Optimization tool is used to estimate the muscle activation data in OpenSim for the predicted lifting motion. Joint reaction forces of the lumbosacral joint (L5-S1) are generated using the OpenSim Joint Reaction analysis tool. The predicted joint angles, muscle activations, and peak joint reaction forces are compared with experimental data and data from literature to validate the hybrid model. Conclusion: The proposed hybrid model combines the skeletal models rapid motion prediction with OpenSims complex muscular dynamics assessment, and it can serve as a new generic tool for motion prediction and injury analysis in ergonomics and biomechanics.
... The first exercise was a squatting exercise, which has shown to strengthen and activate successfully the quadriceps and gluteal muscles with a relative low hamstrings co-activation (Begalle, Distefano, Blackburn, & Padua, 2012;Claiborne, Armstrong, Gandhi, & Pincivero, 2006;Lee et al., 2016;Reiman, Bolgla, & Loudon, 2012;Shields et al., 2005;Willy & Davis, 2011). If the participant experienced pain, they were instructed to lean their trunk more forward or place their feet wider (Escamilla et al., 2001;Kulas, Hortobagyi, & DeVita, 2012). ...
Article
Objectives Guidelines for a comprehensive rehabilitation programme for patellofemoral pain (PFP) have been developed by international experts. The aim of this study was to analyse the effect of such a rehabilitative exercise programme on pain, function, kinesiophobia, running biomechanics, quadriceps strength and quadriceps muscle inhibition in individuals with PFP. Design Observational study. Setting Clinical environment. Participants Twenty-seven participants with PFP. Main outcome measures Symptoms [numeric pain rating scale (NPRS)and the pain subscale of the Knee Injury and Osteoarthritis Outcome Score (KOOS)], function measured by using the KUJALA scale and KOOS, kinesiophobia measured by using the Tampa scale, three-dimensional biomechanical running data, quadriceps isometric, concentric and eccentric strength and arthrogenic muscle inhibition (AMI) were acquired before and after the six-week exercise programme. Results Although pain did not significantly improve all patients were pain-free after the six-week exercise programme (NPRS: p = 0.074). Function, kinesiophobia and quadriceps AMI improved significantly after the six-week exercise programme (KUJALA: p = 0.001, KOOS: p = 0.0001, Tampa: p = 0.017, AMI: p = 0.018). Running biomechanics during stance phase did not change after the exercise intervention. Quadriceps strength was not different after the six-week exercise programme (isometric: p = 0.992, concentric: p = 0.075, eccentric: p = 0.351). Conclusion The results of this study demonstrate that the current exercise recommendations can improve function and kinesiophobia and reduce pain and AMI in individuals with PFP. There is a need for reconsideration of the current exercise guidelines in stronger individuals with PFP.
... Squats can recruit multiple muscle groups in a single movement and is related to many daily activities, such as lifting heavy objects [9]. Exercise is also included as a core in many sports to improve athletic performance [10]. The squat exercise mainly strengthens the lower body and core muscles, including the quadriceps femoris, BF, RA, and ES [5]. ...
Article
Background: Life in modern society has become convenient, but the lack of exercise due to a sedentary lifestyle has led to muscle weakness. The quadriceps femoris is essential for walking, standing, and using stairs in daily life. Muscle weakness can lead directly to impaired function. Squatting is the most representative exercise for effective muscle development and increasing the knee extensor strength. This study examined the effects of ankle angle during wall squats on the muscle activity of the vastus medialis oblique (VMO), vastus lateralis (VL), rectus femoris (RF), biceps femoris (BF), rectus abdominis (RA), and erector spinae (ES) to determine which ankle angle can better strengthen the vastus medialis oblique as a method of rehabilitation training after a knee joint injury. Methods: All subjects (n = 20) performed the following three types of wall squats randomly: (1) GWS (General Wall Squat), (2) WSD 10° (Wall Squat with dorsiflexion 10°), and (3) WSP 10° (Wall Squat with plantarflexion 10°). Each subject completed all three kinds of wall squatting exercises three different times, and the muscle activity data of the VMO, VL, RF, BL, RA, and ES were recorded. Results: Compared to GWS exercise, the VMO and RF muscle activity increased significantly under WSP 10° exercise (p < 0.05), whereas the VL, BF, RA, and ES activity did not increase significantly (p > 0.05). No significant change between WSD 10° and WSP 10° was observed (p > 0.05). Conclusions: WSP 10° can help increase the quadriceps muscle activity. Wall squat exercise with different ankle angles can be used for quadriceps muscle strengthening training for normal people and for recovery training for patellofemoral pain syndrome (PFPS) patients in the rehabilitation stage.
... O exercício agachamento também tem feito parte dos programas de treinamento esportivo, pois apresenta semelhanças biomecânicas e neuromusculares com uma ampla gama de movimentos atléticos [4]. Dessa forma, foi incluído como o exercício central em muitas rotinas esportivas. ...
Article
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Aguiar RS, Castro JBP, Santos AOB, Silva GCPSM, Scartoni FR, Nunes RAM, Vale RGS. Efeitos do exercício agachamento por trás na atividade mioelétrica de membros inferiores em homens treinados: uma revisão sistemática. Revista Brasileira de Fisiologia do Exercício. 2021;20(1):83-92. Objetivo: O objetivo deste estudo foi descrever os efeitos do exercício agachamento por trás sobre a atividade mioelétrica de membros inferiores em homens treinados. Métodos: Foi realizada uma revisão sistemática seguindo as recomendações do PRISMA. Foram pesquisadas as bases de dados Medline (Pubmed), SciELO, Scopus, SPORTDiscus e Lilacs. Os termos de pesquisa incluíram eletromiografia, exercício, treinamento de resistência e agachamento. Foram incluídos estudos experimentais que descreveram o exercício agachamento por trás por meio da eletromiografia de superfície (EMG) em homens com experiência em treinamento resistido (TR) e exercício agachamento por trás em ângulos de 60º a 90º. Resultados: Oito estudos preencheram os critérios de inclusão. As intervenções dos estudos incluídos variaram de 2 a 7 dias. Os protocolos demonstraram melhorar o sistema neuromuscular e proporcionar maior aquisição de força nos músculos envolvidos na realização do exercício agachamento por trás (p < 0,05). Foram analisados 37 músculos, com predomínio dos músculos vasto lateral, vasto medial, glúteo máximo e reto femoral. Conclusão: Os estudos investigados nesta revisão mostraram que o exercício agachamento por trás em ângulos de 60º a 90º aumentou a atividade mioelétrica de membros inferiores registrada em cargas de 30% e 100% de 1RM em homens experientes em TR. Porém, mais estudos com maior qualidade metodológica são necessários na análise do exercício agachamento para reduzir o risco de viés.
... The benefits of squat exercises have been reported in athletic training [1,2], rehabilitation [3,4], and locomotive syndrome in elderly people [5]. Squats can refer to a wide variety of exercises, comprising partial squat [6], half squat [7], parallel squat [8,9], full squat [8,9], and deep squat [7]. Furthermore, there are front [9][10][11], back [10][11][12], and overhead squats [12] with various bar positionings. ...
Article
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Isometric bodyweight squats are fundamental exercises in athletic training and rehabilitation. Previously, we measured muscle activity in a normal squat posture (NSP) and a squat posture with the center of foot pressure (COP) intentionally shifted forward as far as possible (forward-shifted posture: FSP), and the muscle activity patterns varied significantly according to the COP location. This study focused on stepwise loading as a training strategy. Ten healthy male participants performed isometric bodyweight squats in a previous study, adopting the NSP and FSP, with three knee flexion angles (30°, 60°, and 90°). The muscle activities of the vastus medialis (VM), semitendinosus, tibialis anterior (TA), and gastrocnemius muscle lateral head were measured using surface electromyogram. This study further explored the relationship between COP shifting and knee flexion angles on electromyogram changes using three-dimensional diagrams. In one-way repeated measures analysis of variance by ranks, knee flexion angles affected the muscle activities of the VM and TA in the NSP and muscle activities of the VM in the FSP. Combining these findings, stepwise loading tasks were created to train individual target muscles. The ten male participants examined all the tasks, and the feasibility was confirmed accordingly.
... Because patellar contact area is the least at 0°, greater sensitivity may be exhibited at this angle with forces from quadriceps contraction. Tibiofemoral joint compressive forces increase from 0°to 55-75°knee flexion during a squat and leg press, and forces are greater during the squat versus the leg press due to greater quadriceps and hamstring activity [59]. Patellar tendon force is lower at lower knee flexion angles when performing a squat from a horizontal and decline surface [60]. ...
Article
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Purpose of Review Anterior knee pain is a common musculoskeletal complaint among people of all ages and activity levels. Non-operative approaches with an emphasis on physical therapy management are the recommended initial course of care. The purpose of this review is to describe the current evidence for physical therapist management of anterior knee pain with consideration of biomechanical and psychosocial factors. Recent Findings The latest research suggests anterior knee pain is a combination of biomechanical, neuromuscular, behavioral, and psychological factors. Education strategies to improve the patient’s understanding of the condition and manage pain are supported by research. Strong evidence continues to support the primary role of exercise therapy and load progression to achieve long-term improvements in pain and function. Preliminary studies suggest blood flow restriction therapy and movement retraining may be useful adjunct techniques but require further well-designed studies. Summary Anterior knee pain includes multiple conditions with patellofemoral pain being the most common. An insidious onset is typical and often attributed to changes in activity and underlying neuromuscular impairments. A thorough clinical history and physical examination aim to identify the patient’s pain beliefs and behaviors, movement faults, and muscle performance that will guide treatment recommendations. Successful physical therapist management involves a combination of individualized patient education, pain management, and load control and progression, with an emphasis on exercise therapy.
... The reason for the differential findings of CE effect between muscle groups is unclear; the dose of open kinetic chain exercise during the CE intervention was the same for hamstrings and quadriceps. However, it is conceivable that the leg-press exercise is more quadriceps dominant (Escamilla et al 2001) and thus the dose was dissimilar. Given that the cross-education effect is musclespecific (Andrushko et al 2018) and that dose may play a role in determining the extent of adaptation (Papandreou et al 2013); the dose in the present study may have been insufficient to elicit detectable change of 50 N in this ACLR population. ...
Chapter
Whether we’re dealing with the high-performance professional athlete, or the recreational sports performer, injury can mean the undesirable cessation of training, or performance, or both. The aim of any subsequent sports rehabilitation programme is to enable the performer to return to sports, safely, effectively and ideally, as quickly as possible. The development and deployment of a successful rehabilitation plan often requires the rehabilitation professional to have the knowledge and command of several different disciplines from kinesiology to strength and conditioning, behavioural psychology to imagery and diagnostics. With all of these requirements, coupled with the pressures of getting the athlete back to sport in the quickest time possible, one can be forgiven for letting something drop off the list. Unfortunately, however, this can sometimes mean overlooking some of the basic principles that fundamentally drive adaptation and thus successful recovery. Outside the realms of well-funded elite sport with unlimited resources and multidisciplinary teams, competition exists for time, expertise, personnel, equipment and funding. Often rehabilitation professionals are limited to a single session per week with an athlete, yet the goals remain the same; to get the athlete back to sport ASAP. In this chapter we will introduce the concept of conditioning efficacy and a process to follow to provide best opportunity to achieve the desired outcomes from your intervention. We will address how to structure your rehabilitation plans to incorporate the fundamental principles that determine neuromuscular adaptation, and then explore how we can leverage science to optimise the efficacy of rehabilitation and end-stage conditioning. The aim is to equip you with more tools to achieve the best results even under some of the most demanding of conditions.
... Interestingly, the relative muscle effort of the plantar flexors during the squat was similar to the ones of the hip and knee extensors, suggesting that the plantar flexors have an important involvement in the exercise performance. On the other hand, Escamilla et al. [29] reported that the activation of the plantar flexors was relatively low during different variations of the squat and leg press (9-17%), when normalized to a maximal isometric contraction. In addition to the controversial findings, these previous studies only analyzed MJ exercises and did not compare MJ and SJ under similar load conditions. ...
Article
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The present study aimed to compare soleus, lateral, and medial gastrocnemius muscles activation during leg press and calf raise exercises in trained men. The study involved 22 trained men (27.1 ± 3.6 years, 82.7 ± 6.6 kg, 177.5 ± 5.2 cm, 3.6 ± 1.4 experience years) who performed one set of each exercise using a 10-repetition maximum (10RM) load in a counterbalanced randomized order and separated by 10 min of rest. The electromyographic signal was measured for the three major plantar flexors: soleus, medial, and lateral gastrocnemius. A comparison between exercises showed that the mean adjusted by peak values during the leg press were 49.20% for the gastrocnemius lateralis, 51.31% for the gastrocnemius medialis, and 50.76% for the soleus. Values for calf raise were 50.70%, 52.19%, and 51.34% for the lateral, medial gastrocnemius, and soleus, respectively. There were no significant differences between exercises for any muscle (lateral gastrocnemius (p = 0.230), medial gastrocnemius (p = 0.668), and soleus (p = 0.535)). The present findings suggest that both leg press and calf raises can be used with the purpose to recruit triceps surae muscles. This bring the suggestion that one can chose between exercises based on personal preferences and practical aspects, without any negative impact on muscle activation.
... The reason for the differential findings of CE effect between muscle groups is unclear; the dose of open kinetic chain exercise during the CE intervention was the same for hamstrings and quadriceps. However, it is conceivable that the leg-press exercise is more quadriceps dominant (Escamilla et al 2001) and thus the dose was dissimilar. Given that the cross-education effect is musclespecific (Andrushko et al 2018) and that dose may play a role in determining the extent of adaptation (Papandreou et al 2013); the dose in the present study may have been insufficient to elicit detectable change of 50 N in this ACLR population. ...
Article
Full-text available
PurposeTo investigate the effects of cross-education (CE) exercise on strength and performance at 10 and 24 weeks post anterior cruciate ligament (ACL) surgery.Methods Design: randomised controlled trial. N = 44 ACL-reconstruction patients, randomly-allocated into: CE: strength training of the non-operative limb, or CON: sham exercise of upper limb stretching. Each patient underwent standardised ACL rehabilitation, plus 8 weeks of thrice weekly CE or CON, commencing at 2 weeks post surgery. The primary outcome was quadriceps peak force (QPF) of the ACL-reconstructed limb at 10 weeks post surgery. Secondary measures were hamstrings peak force (HPF), rate of force development (RFD) and International Knee Documentation Committee score (IKDC) at 10 and 24 weeks; QPF and hop for distance (HOP) at 24 weeks post surgery.ResultsCE significantly attenuated the decline in QPF of the ACL-reconstructed limb at 10 weeks compared to CON (16.6% decrease vs. 32.0%, respectively); that advantage was not retained at 24 weeks. A training effect was observed in the trained limb for HPF and QPF, which was retained at 24 weeks. No significant differences were observed for IKDC, HOP, RFD, or HPF of the reconstructed limb. Inter-limb symmetry (ILS) ranged from 0.78 to 0.89 and was not significantly different between groups.Conclusion High-intensity CE strength training attenuated the post-operative decline in QPF and should be considered in early-phase ACL rehabilitation. ILS data showed good symmetry, but it masked significantly inferior performance between groups and should be used with caution.Trial registration numberNCT02722876.
... Knee flexion moment (KFM) is different, in that there is only a weak association with JCF at the second stance phase peak (Richards et al., 2018) and with peak medial knee JCF when combined with KAM (Creaby, 2015). Yet the effects of muscle cocontraction, an important mechanism for joint stabilisation during exercise (Escamilla et al., 2001), is not included in KFM. Internal flexion moments are essentially a measure of joint stabilisation and are calculated as such. ...
Article
Background Musculoskeletal modelling is a common means by which to non-invasively analyse movement. Such models have largely been used to observe function in both healthy and patient populations. However, utility in a clinical environment is largely unknown. The aim of this review was to explore existing uses of musculoskeletal models as a clinical intervention, or decision-making, tool. Methods A literature search was performed using PubMed and Scopus to find articles published since 2010 and relating to musculoskeletal modelling and joint and muscle forces. Findings 4662 abstracts were found, of which 39 relevant articles were reviewed. Journal articles were categorised into 5 distinct groups: non-surgical treatment, orthoses assessment, surgical decision making, surgical intervention assessment and rehabilitation regime assessment. All reviewed articles were authored by collaborations between clinicians and engineers/modellers. Current uses included insight into the development of osteoarthritis, identifying candidates for hamstring lengthening surgery, and the assessment of exercise programmes to reduce joint damage. Interpretation There is little evidence showing the use of musculoskeletal modelling as a tool for patient care, despite the ability to assess long-term joint loading and muscle overuse during functional activities, as well as clinical decision making to avoid unfavourable treatment outcomes. Continued collaboration between model developers should aim to create clinically-friendly models which can be used with minimal input and experience by healthcare professionals to determine surgical necessity and suitability for rehabilitation regimes, and in the assessment of orthotic devices.
... Additionally, the utilization of a WSBS technique most likely attributed to the strong findings. In a study done by Escamilla et al. (2001) it was shown that wide stance squats compared to narrow stance squats exhibited substantially larger hip extensor moments at the hip. Additionally, Fry et al. (2009) found that when restricting the squat and causing the shins to stay more vertical, larger torques at the hip than at the knee were detected. ...
Article
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Increased involvement of the hip musculature during some movements is associated with enhanced performance and reduced injury risk. However, the impact of hip dominant weight training methods on movement strategy has seen limited attention within the literature. The aim of this study was to evaluate if a 9-week hip dominant weight training intervention promotes a more hip dominant movement strategy leading to an improvement in countermovement jump performance. Twenty-two experienced female dancers were recruited and separated into an intervention (age 24.4 ± 6.3 years, body height 165.5 ± 5.8 cm, body mass 65.9 ± 5.6 kg) and a control (age 22.9 ± 5.6 years, body height 163.3 ± 5.4 cm, body mass 57.4 ± 6.8 kg) group. The intervention group participated in a 9-week hip dominant training intervention, which consisted of a wide stance back squat, Romanian deadlift, hip thrusters, and a bent over row. Hip and knee kinematics and kinetics, and countermovement jump performance were assessed pre and post training. Significant interaction effects were found for peak hip joint moment (p = 0.030, η2 = 0.214) and countermovement jump performance (p = 0.003, η2 = 0.356), indicating an increase in peak hip joint moment and countermovement jump performance for the intervention group. Specifically, the intervention group showed a mean increase in jump height of 11.5%. The data show that the use of a hip dominant weight training strategy can improve hip contribution in the propulsion phase of the countermovement jump. Strength and conditioning specialists should incorporate hip dominant weight training exercises to increase hip strength and improve performance.
... In athletes, menisci injuries are mainly produced by a compressive force coupled with tibiofemoral external or internal rotation as the knee moves from flexion to extension during rapid change of direction (Brindle et al., 2001). While it is known that excessive loading of the menisci can lead to degenerative changes, it is not known at what magnitude compressive forces and rotation torques become injurious to cartilage (Escamilla et al., 2001). In this study, the results show that the peak of compressive knee force, the maximal knee flexion angle and the external rotation knee torque are significantly higher in DOS than in ANS. ...
Article
The open stance forehand has been hypothesized to be more traumatic for knee injuries in tennis than the neutral stance forehand. This study aims to compare kinematics and kinetics at the knee during three common forehand stroke stances (attacking neutral stance ANS, attacking open stance AOS, defensive open stance DOS) to determine if the open stance forehand induces higher knee loadings and to discuss its potential relationship with given injuries. Eight advanced tennis players performed eight repetitions of forehand strokes with each stance (ANS: forward run and stroke with feet parallel with the hitting direction, AOS: forward run and stroke with feet perpendicular to the hitting direction, DOS: lateral run and stroke with feet perpendicular to the hitting direction) at maximal effort. All the trials were recorded with an optoelectronic motion capture system. The flexion-extension, abduction-adduction, external-internal rotation angles, intersegmental forces and torques of the right knee were calculated. Ground reaction forces were measured with a forceplate. The DOS increases vertical GRF, maximum knee flexion and abduction angles, range of knee flexion-extension, peak of compressive, distractive and medial knee forces, peak of knee abduction and external rotation torques. Consequently, the DOS appears potentially more at risk for given knee injuries.
... in vertical jump, when compared to weight lifters and physically active individuals, consequently, those who presented better performance owed it to a longer phase duration [6][7][8][9]. ...
... The 1RM back squat was used as a global assessment of lower extremity strength that involves similar muscles and biomechanics to those involved in running. 30 We selected knee-and hip-extensor isometric strength tests because they are clinical assessments of strength that are often used to assess distance runners. 23 The primary finding was that greater 1RM back-squat strength was associated with a larger peak knee-flexion angle, smaller peak knee internal-rotation angle, and smaller knee internal-rotation moment after adjusting for sex, running speed, and foot-strike index. ...
Article
Context Running-related injuries are common in distance runners. Strength training is used for performance enhancement and injury prevention. However, the association between maximal strength and distance-running biomechanics is unclear. Objective To determine the relationship between maximal knee- and hip-extensor strength and running biomechanics previously associated with injury risk. Design Cross-sectional study. Setting Research laboratory. Patients or Other Participants A total of 36 collegiate distance runners (26 men, 10 women; age = 20.0 ± 1.5 years, height = 1.74 ± 0.09 m, mass = 61.97 ± 8.26 kg). Main Outcome Measure(s) Strength was assessed using the 1-repetition maximum (1RM) back squat and maximal voluntary isometric contractions of the knee extensors and hip extensors. Three-dimensional running biomechanics were assessed overground at a self-selected speed. Running variables were the peak instantaneous vertical loading rate; peak forward trunk-lean angle; knee-flexion, internal-rotation, and -abduction angles and internal moments; and hip-extension, internal-rotation, and -adduction angles and internal moments. Separate stepwise linear regression models were used to examine the associations between strength and biomechanical outcomes (ΔR2) after accounting for sex, running speed, and foot-strike index. Results Greater 1RM back-squat strength was associated with a larger peak knee-flexion angle (ΔR2 = 0.110, ΔP = .045) and smaller peak knee internal-rotation angle (ΔR2 = 0.127, ΔP = .03) and internal-rotation moment (ΔR2 = 0.129, ΔP = .03) after accounting for sex, speed, and foot-strike index. No associations were found between 1RM back-squat strength and hip kinematics or kinetics, trunk lean, or vertical loading rate. Hip- and knee-extensor maximal voluntary isometric contractions were also not associated with any biomechanical variables. Conclusions Greater 1RM back-squat strength was weakly associated with a larger peak knee-flexion angle and smaller knee internal-rotation angle and moment in collegiate distance runners. Runners who are weaker in the back-squat exercise may exhibit running biomechanics associated with the development of knee-related injuries.
... O exercício agachamento também tem feito parte dos programas de treinamento esportivo, pois apresenta semelhanças biomecânicas e neuromusculares com uma ampla gama de movimentos atléticos [4]. Dessa forma, foi incluído como o exercício central em muitas rotinas esportivas. ...
Article
Full-text available
Aguiar RS, Castro JBP, Santos AOB, Silva GCPSM, Scartoni FR, Nunes RAM, Vale RGS. Effects of the back squat exercise on lower limb myoelectric activity in trained men: a systematic review. Revista Brasileira de Fisiologia do Exercício. 2021;20(1):83-92. Aim: The aim of this study was to describe the effects of the back squat exercise on the lower limb myoelectric activity in trained men. Method: We conducted a systematic review following the recommendations of PRISMA and registered on the International Prospective Register of Systematic Reviews (PROSPERO), as number CRD42018082308. MEDLINE (PubMed), SciELO, Scopus, SPORTDiscus, and LILACS (BVS) databases were searched. The search terms included electromyography, exercise, resistance training, and squat. We included experimental studies that described the back squat exercise using surface electromyography (EMG) in men experienced in resistance training (RT) and back squat exercise at angles from 60º to 90º. Results: Eight studies met the inclusion criteria. The interventions of the included studies ranged from 2 to 7 days. The protocols demonstrated to improve the neuromuscular system and to provide greater acquisition of strength in the muscles involved in performing the back squat exercise (p<0.05). Thirty-seven muscles were analyzed, with a predominance of the vastus lateralis, vastus medialis, gluteus maximus, and rectus femoris muscles. Conclusion: The studies investigated in this review showed that the back squat exercise at angles from 60º to 90º increased the lower limb myoelectric activity recorded in loads of 30% and 100% of 1RM in men experienced in RT. However, more studies with higher methodological quality are needed in the analysis of the squat exercise to reduce the risk of bias.
... Players must strengthen the structures of the knee joints, such as muscles, ligaments, and tendons, to prevent injuries caused by external forces, with squat exercises (SE) being one of the best knee joint exercises. Squat movements are also crucial for running and jumping, and are the most important and basic movements of the lower body as they strengthen the hip muscles, quadriceps muscle, and trunk muscles, as well as the bone density along with ligaments and tendons [4]. In addition, SE can improve the muscle strength of the lower extremities by supporting weight, and is a functional exercise that stimulates multi-joint movement, functional type of muscle mobilization, and a sense of proprioception, compared with an exercise that does not support weight [5]. ...
Article
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Background and purpose: Knee injuries are common among female softball players, and the stability of the lower extremities and the strength of the knee are essential factors for them. The purpose of this study was to investigate the effect of Kinesio taping with squat exercise (KTSE) on lower extremity muscle activity, muscle strength, muscle tone, and dynamic stability of softball players. Methods: In this study, 40 softball players were randomly assigned to the KTSE group and sham taping with squat exercise (SKTSE) group. All subjects were tested three times a week for 6 weeks, i.e., for a total of 18 times. To evaluate the lower-extremity muscle activity, muscle strength, and muscle tone of the lower extremities, as well as dynamic stability, we used Noraxon Mini DTS, a digital muscular meter from JTech Medical, MyotonPRO, and the side hop test (a clinical evaluation method), respectively. These items were measured before the experiment and 6 weeks after the start of the experiment. Results: Both groups showed significant differences in lower-extremity muscle activity, muscle strength, muscle tone, and dynamic stability (p < 0.05). After the experiment, significant effects on lower-extremity muscle activity, muscle strength, muscle tone, and dynamic stability were observed in the KTSE group compared with in the SKTSE group (p < 0.05). Conclusions: KTSE did not have a negative effect on all items of the functional performance test. KTSE improved lower-extremity muscle activity, muscle strength, muscle tone, and dynamic stability.
... Given the benefits and translation across activities, weight lifting programs implement one-repetition-maximum (1RM) and submaximum (to failure) back squat tests to track progress of athletes' strength, muscle hypertrophy, and sport readiness [5]. The back squat requires participation of every lower extremity muscle in some capacity (isometric, concentric, or eccentric) [6][7][8][9][10][11]. In general, the loads for the hip and knee joints comprise 80-90%, whereas the ankle contributes 0-20% of the total lower extremity moment to lift the system mass during the upward portion of back squats [6,[12][13][14][15][16][17][18]. ...
Article
Previous literature suggests the sticking region, the transition period between an early peak concentric velocity to a local minimum, in barbell movements may be the reason for failing repeated submaximal and maximal squats. This study determined the effects of load on lower extremity biomechanics during back squats. Twenty participants performed the NSCA's one-repetition maximum (1RM) testing protocol, testing to supramaximum loads (failure). After completing the protocol and a 10-minute rest, 80% 1RM squats were performed. Statistical parametric mapping was used to determine vertical velocity, acceleration, ankle, knee, and hip sagittal and frontal plane biomechanics differences between 1RM, submaximum, and supramaximum squats (105% 1RM). Vertical acceleration was a better discriminative measure than velocity, exibiting differences across all conditions. Supramaximum squats emphasized knee moments, whereas 1RM emphasized hip moments during acceleration. Submaximum squats had reduced hip and knee moments compared to supramaximum squats, but similar knee moments to 1RM squats. Across all conditions, knee loads mirrored accelerations and a prominent knee (acceleration) to hip (sticking) transition existed. These results indicate that 1) submaximum squats performed at increased velocities can provide similar moments at the ankle and knee, but not hip, as maximal loads and 2) significant emphasis on hip strength is necessary for heavy back squats.
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The aim of this study was to investigate barbell, joint kinematics, joint kinetics of hip, knee, and ankle in tandem with myoelectric activity around the sticking region in three-repetition maximum (3-RM) back squats among recreationally trained lifters. Unlike previous literature, this study also investigated the event of first-peak deacceleration, which was expected to be the event with the lowest force output. Twenty-five recreationally trained lifters (body mass: 70.8 ± 10.5, age: 24.6 ± 3.4, height: 172 ± 8.5) were tested in 3-RM back squats. A repeated one-way analysis of variance showed that ground reaction force output decreased at first peak deacceleration compared with the other events. Moreover, torso forward lean, hip moment arm, and hip contribution to total moment increased, whereas the knee moment arms and moment contribution to total moment decreased in the sticking region. Also, stable moment arms and moment contributions to total moment were observed for the ankle in the sticking region. Furthermore, the knee extensors together with the soleus muscle decreased myoelectric activity in the post-sticking region, while the gluteus maximus and biceps femoris increased myoelectric activity in the post-sticking region. Our findings suggest that the large hip moment arms and hip contributions to total moment together with a lower myoelectric activity for the hip extensors contribute to a poor biomechanical region for force output and, thereby, to the sticking region among recreationally trained lifters in 3-RM back squats.
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Context: Continuous visual feedback (VF) can improve abilities to achieve desired movements and maximize rehabilitation outcomes by displaying actual versus target body positions in real time. Bandwidth VF reduces the reliance on feedback by displaying movement cues only when performance errors exceed specified thresholds. As such, bandwidth VF may better train independent movement abilities through greater development of intrinsic body control. In this study, continuous and bandwidth VF were investigated across modes of display (abstract and representative) that differed in body-discernibility. Objective: To compare the performance of the 2-legged squat during training with concurrent feedback (real-time VF) and short-term retention (immediately after training, VF removed). Design: Cross-sectional. Setting: University research laboratory. Participants: Eighteen healthy individuals. Methods: Marker-based motion capture displayed real-time position. Main outcome measures: Four VF cases (continuous-abstract, bandwidth-abstract, continuous-representative, and bandwidth-representative) were evaluated for accuracy and consistency to a target trajectory and target depth. Results: During training, both continuous VF cases showed significantly (P < .05) higher accuracy and consistency to the target trajectory compared with both bandwidth VF cases. Bandwidth VF resulted in greater potential learning (retention performance relative to a training baseline) compared with continuous-abstract. Conclusions: Continuous-representative may offer unique performance benefits in both training and retention of multisegment movement tasks. Bandwidth VF showed greater potential for learning. For long-term learning, an optimal VF paradigm should consider continuous-representative with bandwidth features.
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Background Beetroot juice (BRJ) is used as an ergogenic aid, but no previous study has analyzed the effect this supplement has on the production of explosive force and muscular endurance in physically active women. Hypothesis BRJ improves explosive force and muscular endurance in the lower limbs of physically active women. Study design Randomized double-blind crossover study. Level of evidence Level 3 Methods Fourteen physically active women performed a countermovement jump (CMJ) test, a back squat test for assessing velocity and power at 50% and 75% of one-repetition maximum (1RM), and the number of repetitions on a muscular endurance test consisting of 3 sets at 75% of 1RM in a resistance training protocol comprising 3 exercises (back squat, leg press, and leg extension). The participants performed the test in 2 sessions, 150 minutes after ingesting 70 mL of either BRJ (400 mg of nitrate) or a placebo (PLA). Results A greater maximum height was achieved in the CMJ after consuming BRJ compared with a PLA ( P = 0.04; effect size (ES) = 0.34). After a BRJ supplement at 50% 1RM, a higher mean velocity [+6.7%; P = 0.03; (ES) = 0.39 (–0.40 to 1.17)], peak velocity (+6%; P = 0.04; ES = 0.39 [−0.40 to 1.17]), mean power (+7.3%; P = 0.02; ES = 0.30 [−0.48 to 1.08]) and peak power (+6%; P = 0.04; ES = 0.20 [−0.59 to 0.98]) were attained in the back squat test. In the muscular endurance test, BRJ increased performance compared with the PLA ( P < 0.00; η p ² = 0.651). Conclusion BRJ supplements exert an ergogenic effect on the ability to produce explosive force and muscular endurance in the lower limbs in physically active women. Clinical relevance If physically active women took a BRJ supplement 120 minutes before resistance training their performance could be enhanced.
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Introduction One of the challenges confronting the coaches and sport scientist is to understand the physical factors contributing to successful performance. One common method to identify the appropriate training program for improving fitness level is the analysis of the effect of these practices on various factors of training exercises. The initial testing session can give the athletes and coach an information of current functional capability at the start of a program and can allow them to compare that capacity with reference values from appropriate peer group, so that future testing can be compared to this and any changes can be noted .Also the assessment of current status reveals strengths and relative weaknesses and can be the basis for development of an optimal training program(1) .The purpose of this study was to investigate the effect of an eight-weeks general preparation exercise on some selected biomechanical, anthropometrical and physiological parameters of the Iranian national women Taekwondo team. Methodology Nine elite member of Iranian national women Taekwondo team (age 23.22±1.98 years old, and weight 61.88±8.44 kg) participated in this study. All participants read and signed an approved informed consent form. The exercise program consist of 72 sessions (3 session reviewing and practicing techniques ,2 sessions of combat (live) taekwondo ,2 sessions strength training, ,1 session interval running and 1 session of endurance training each week). The testing was conducted twice, before and after the 8-week training period. The biomechanical, anthropometrical and physiological parameters included; body weight, cardiovascular endurance, muscular endurance, speed, agility, visual reaction time, anaerobic power and body composition. body composition analyzer (in body 220) was used to assess the body fat percentage, reaction time was measured with visual reaction time apparatus(Satrap company, Iran), Bruce protocol was used to estimate vo2 max, a 40-yard sprint test was used to assess the speed, 4×9 m shuttle run test was required to assess agility , 1-min bilateral jump was used for assess the lower extremities endurance and 15 second ergo- jump and Sargent test was required to assess the anaerobic power of the subjects. And inferential statistics Kolmogorov-Smirnov test was used to check the normality distribution, using a paired t- test tests to compare variables before and after training, with a significant level of (p≤0.05) Result The results of functional test are presented in table 1. The bf % of the subjects significantly decreased .The result of body weight, agility, visual reaction time and anaerobic power (ergo jump test) test were slightly lower in after training. The result of anaerobic power, aerobic test and muscle endurance significantly increased. Table 1. P-value t(8) post-test pre-test Variable 0.347 1 61.55±8.30 81.88±8.44 Weight (kg) *0.000 5.888 15.05±5.04 16.78±5.38 BF (%) 0.128 -1.7 6.29±0.255 6.19±0.288 Speed (m/s) *0.001 -5.406 146.44±8.38 141.55±9.51 Muscle endurance( rep∙min-1) 0.176 1.486 9.24±0.241 9.35±0.352 Agility (s) 0.127 1.705 0.416±0.048 0.438±0.352 Visual reaction time(ms) *0.01 -3.344 909.01±136.46 878.66±121.40 Aneorobic power sargent (w) 0.787 0.279 35.33±5.97 35.55±7.95 aneorobic power ergo-jump (w∙kg-1) *0.000 -8.083 55.55±5.57 48.55±5.12 VO2max (ml∙kg-1∙min-1) * Differences are significant at the 0.05 level. Discussion and Conclusion In previous studies cited that having good anaerobic and aerobic capacity, power, agility are most important factors needed to achieve good result in taekwondo(2, 3). In this regard, the main emphasize of general preparation phase is enhance the cardiovascular endurance and muscular strength, significant reduction in bf% and significant increase in aerobic and anaerobic factors following exercise was similar to the other investigation(4, 5). Finally, these results can be use as a feedback to the coaches to review the applied training protocols.
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Background: Squatting is a core exercise for many purposes. However, there is still controversy surrounding the practice of targeting specific muscle groups when performing the back squat with different stance widths or foot positions. Therefore, this study aimed to assess lower limb muscle activation during different form of back squat when adopting three different foot angles. Methods: Eight male active participants (age 24.0±0.8 years, height 1.80±0.63m and mass 85.8±8.7kg) performed maximal isometric squat, back squat with an overload of 80% of 1 repetition maximum, and countermovement jump (CMJ) when adopting three foot rotation angles: parallel (0°); +10° outward (external rotation); +20° outward (external rotation). We calculated the root mean square of the electromyographic signals recorded from eight participant's dominant leg muscles. Results: During the descending phase of the back squat, the 20° external foot rotation elicited greater activation of the biceps femoris (+35%; p = 0.027) and gastrocnemius medialis (+70%; p = 0.040) compared to parallel foot. There were no significant differences among the other muscles and exercise conditions. Conclusions: The +20° foot position increased BF and GasM muscle activity only during the downward phase of the back squat. Strength coaches should consider the present findings when selecting specific resistance exercises aiming to improve athletes' strength and physical fitness.
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The objective was to assess how patellofemoral loads (joint force and stress) change while lunging with step length and step height variations. Sixteen participants performed a forward lunge using short and long steps at ground level and up to a 10-cm platform. Electromyography, ground reaction force, and 3D motion were captured, and patellofemoral loads were calculated as a function of knee angle. Repeated-measures 2-way analysis of variance (P < .05) was employed. Patellofemoral loads in the lead knee were greater with long step at the beginning of landing (10°-30° knee angle) and the end of pushoff (10°-40°) and greater with short step during the deep knee flexion portion of the lunge (50°-100°). Patellofemoral loads were greater at ground level than 10-cm platform during lunge descent (50°-100°) and lunge ascent (40°-70°). Patellofemoral loads generally increased as knee flexion increased and decreased as knee flexion decreased. To gradually increase patellofemoral loads, perform forward lunge in the following sequence: (1) minimal knee flexion (0°-30°), (2) moderate knee flexion (0°-60°), (3) long step and deep knee flexion (0°-100°) up to a 10-cm platform, and (4) long step and deep knee flexion (0°-100°) at ground level.
Article
Squats are frequently performed to strengthen the quadriceps (Quad) and gluteus maximus (GM) in sports and clinical fields. Since the squat itself produces a large knee contact force, clarifying the relationship between the squat techniques and the knee contact force is important. However, the influence of different squat techniques on the medial knee contact force (KCFmed), which would result in knee disease, remains unclear. This study aimed to investigate the influence of various squat techniques on KCFmed during bodyweight squats. Since muscle strengthening by the squat is inevitable, we additionally aimed to explore the effect of a different squat technique on the quadriceps (Quad) and gluteus maximus (GM) forces. Twelve healthy adults performed squats with different stance widths (narrow stance, NS; middle stance, MS; and wide stance, WS) and different toe directions (0° of forefoot abduction – NEUT and 30°forefoot abduction – OUT). The KCFmed, Quad force, and GM force were computed using a musculoskeletal model with marker trajectories and ground reaction forces. The KCFmed in NS was significantly larger than that in MS and WS, and KCFmed in OUT was significantly larger than that in NEUT. The Quad force in OUT was significantly larger than that in the NEUT, and the GM force significantly became larger as the stance width became narrower. These findings suggest that squats in MS and NEUT may be suitable for reducing KCFmed while maintaining the Quad and GM forces.
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Objective: Osteoarthritis is the most common type of knee arthritis that can be affected by excessive and compressive loads and can affect one or more compartments of the knee: medial, lateral, and patellofemoral. The medial compartment tends to be the most vulnerable to injuries and research suggests that a better understanding of the medial to lateral load distribution conditions could provide insights to the quantitative usage of knee compartments in activities of daily life. Methods: To that end, we present a novel method to quantify the directional bias of asymmetry between the medial and lateral compartment knee joint load by recording knee acoustical emissions and analyzing them using a deep neural network in a subject independent model. We placed four miniature contact microphones on the medial and lateral sides of the patella on both the left and right leg. We compared the handcrafted audio features with the automated features extracted from the convolutional autoencoder which is an unsupervised model that learns the comprehensive representation of the input to determine whether these automated features can better represent the signals characteristic in regard to the structural asymmetry of the knee joint. The input to the convolutional auto encoder (CAE) is a time-frequency representation and different types of these images such as spectrogram and scalogram are compared. We also compared the multi-sensor fusion approach with the performance of a single sensor to determine the robustness of using multiple sensors. Results: Using a representation learning based approach, we developed a subject independent classification model capable of classifying the asymmetry of the medial and lateral joint load across subjects (accuracy = 83%). Conclusion: The result indicates that wavelet coherence which is the time-frequency correlation of two signals using a wavelet transform yields the best accuracy. Significance: These findings suggest that acoustic signals could potentially quantify the direction of medial to lateral load distribution which would broaden the implications for wearable sensing technology for monitoring cartilage health and factors responsible for cartilage breakdown and assessing appropriate rehabilitation exercises without overloading on one side.
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Este estudo teve como objetivo comparar as respostas cardiovasculares e de óxido nítrico (NO) à contração isométrica voluntária máxima (CIVM) com diferentes grupos musculares (leg press [LEP] e preensão manual isométrica [IHG]) de adolescentes com e sem síndrome de Down (SD). Alem de comparar a força IHG absoluta e relativa entre os grupos. Onze adolescentes com SD (14,1 ± 1,0 anos) e dez sem SD (13,7 ± 1,25 anos) realizaram duas sessões experimentais de exercícios LEP e IHG: 1) sessão de familiarização e 2) 3 tentativas x 5 segundos de contração na CIVM com 3- intervalo mínimo de descanso. A pressão arterial (PA), a frequência cardíaca (FC) e o NO foram coletados em repouso, imediatamente após a sessão de exercício e 10 minutos após o exercício. A dosagem de NO na saliva foi realizada pelo método colorimétrico de Griess. Não houve diferenças para respostas cardiovasculares e NO entre os grupos para CIVM. No entanto, o SD teve uma resposta cardiovascular menor, mas não significativamente, em repouso e após os testes de CIVM do que aqueles sem SD. O grupo SD apresentou maior concentração de NO em repouso, recuperação e após IHG quando comparado ao grupo não SD (P <0,05). Além disso, adolescentes com SD apresentaram menor nível de força de IHG absoluta e relativa quando comparados àqueles sem SD (P = 0,001). Indivíduos com SD apresentam menor resposta cardiovascular em repouso e após testes de CIVM e maior resposta de NO após o exercício quando comparados ao grupo sem SD.
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Objective: To systematically review and synthesise patellofemoral joint reaction force (PFJRF) in healthy individuals and those with patellofemoral pain and osteoarthritis (OA), during everyday activities, therapeutic exercises and with physical interventions (eg, foot orthotics, footwear, taping, bracing). Design: A systematic review with meta-analysis. Data sources: Medline, Embase, Scopus, CINAHL, SportDiscus and Cochrane Library databases were searched. Eligibility criteria: Observational and interventional studies reporting PFJRF during everyday activities, therapeutic exercises, and physical interventions. Results: In healthy individuals, the weighted average of mean (±SD) peak PFJRF for everyday activities were: walking 0.9±0.4 body weight (BW), stair ascent 3.2±0.7 BW, stair descent 2.8±0.5 BW and running 5.2±1.2 BW. In those with patellofemoral pain, peak PFJRF were: walking 0.8±0.2 BW, stair ascent 2.5±0.5 BW, stair descent 2.6±0.5 BW, running 4.1±0.9 BW. Only single studies reported peak PFJRF during everyday activities in individuals with patellofemoral OA/articular cartilage defects (walking 1.3±0.5 BW, stair ascent 1.6±0.4 BW, stair descent 1.0±0.5 BW). The PFJRF was reported for many different exercises and physical interventions; however, considerable variability precluded any pooled estimates. Summary: Everyday activities and exercises involving larger knee flexion (eg, squatting) expose the patellofemoral joint to higher PFJRF than those involving smaller knee flexion (eg, walking). There were no discernable differences in peak PFJRF during everyday activities between healthy individuals and those with patellofemoral pain/OA. The information on PFJRF may be used to select appropriate variations of exercises and physical interventions.
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The standing lunge is an activity commonly used to quantify in-vivo knee kinematics with fluoroscopy. The ability to perform the standing lunge varies between subjects and can necessitate movement accommodations to successfully complete the desired range of motion. We proposed a supine leg press as an alternative to the standing lunge that aimed to provide a similar evaluation of knee motion while increasing the measured range of motion. Tibiofemoral kinematics of 53 non-symptomatic adults (27 men, 26 women, 50.8 ± 7.0 yrs.) were calculated from the tracked high speed-stereo radiography (HSSR) images for supine leg press and standing lunge using CT-segmented bony geometries of the right lower limb. The supine leg press proved to be a useful alternative to the standing lunge while providing 46.2° greater range of motion in knee flexion. The difference in angle-matched kinematics across a 100° flexion range between the leg press and lunge was 0.70° in varus-valgus rotation, 1.5° in internal-external rotation, 1.0 mm in medial-lateral translation, 2.3 mm in anterior-posterior translation, and 0.46 mm in superior-inferior translation for men. The angle-matched difference for women across 100° was 0.58° in varus-valgus rotation, 2.4° internal-external rotation, 0.70 mm medial-lateral translation, 2.1 mm anterior-posterior translation, and 0.78 mm superior-inferior translation. The similar kinematics, while having a greater range of motion, and control of the applied load makes the supine leg press an alternative for quantifying in-vivo knee kinematics.
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Introduction in wrestling the ankle is most frequent site for joint sprains. That involved approximately 38 percent of all wrestling injuries(1).during wrestling exercise or competition following the collision or performs various actions, uncontrolled pressure may be applied to the ankle of the wrestlers, which in some cases require medical treatment, in such situations, a common treatment technique is the use of cooling method. However, in most cases, the athlete should immediately return to practice or competition after applying the cold. Although cryotherapy is commonly used in the treatment of acute and chronic athletic injuries, the deleterious effects of limb cooling, such as decreased nerve and muscle function, slowed sensation and inhibition of normal relaxes, may put an athlete at increased risk of additional injury(2). Reduction of proprioception receptors pulses and postural reflex responses may lead to cause abnormal situation of body and finally, increase the risk of ankle joint injury, especially during athletic activities(3). The purpose of this study is the effect of a short period of Cryotherapy on ankle position sense in professional wrestlers. Methodology 14 Professional wrestler (age 24+3 years old, and weight 74.1+19.2 kg) participated in this study. They all had at least 5 years training experience with provincial and national championships. All participants read and signed an approved informed consent form. Electrogoniometer (J-TECH Made in America) was used To measure the accuracy of the reproduce of the ankle joint angle and dominant limb was used for the same conditions of participant. In present study aims reproduce the angle of ankle joint, movement and angles plntar and dorsi flexion, respectively, 20 and 10 ° were considered. Initially, each subject was asked to move his ankle to the target angle with open eyes three times and remain for three seconds in that situation and maintaining this position in his short-term memory. Then, to eliminate visual interference during measurement of the test the eyes of participant was closed by blindfold and he was asked to move his ankle in two condition first in active and then with the move of examiner to the target angle in passive form. Error angel defines as the difference between the target angle and the angle created by the participants reproduced, regardless of whether the error was a positive or negative. Each movement was repeated three times and then average of error angles for each movement was taken as the main record. After that, the subjects medal-lateral of ankle, with distance 30 cm for 5 seconds under cold applied by using spray cooling (COLD SPRAY product of manufacturing HAGER company, made in Germany) And the test was repeated again. Inferential statistics Kolmogorov-Smirnov test was used to check the normality distribution, using a paired t- test tests to compare variables before and after cooling, with a significant level of (p≤0.05) Results Test results are presented In Table 1. Results show that the Regeneration error after using the spray increased 0.23 and 0.29 degree respectively In active and passive dorsiflexion and it was 0.8 and 0.1 degree respectively In active and passive plantar flexion, but this increases was not statistically significant. P-value t(13) post-test pre-test variable name 0.599 -0.538 2.59+1.45 2.36+1.29 Regeneration error of active dorsi Flexion 0.863 -0.176 3.85+1.14 3.77+1.11 Regeneration error of active plantar Flexion 0.492 -0.707 2.66+1.05 2.37+0.95 Regeneration error of passive dorsi Flexion 0.863 -0.176 3.03+1.032 2.93+0.954 Regeneration error of active plantar Flexion Conclusions: The results showed that short-term local cooling by using cold spray on ankle joint position sense of professional wrestlers is not significantly change It appears that the use of cold spray for a short time only has an immediate effect on the skin receptors. But the muscle spindles and joint receptors as deeper receptors, which have a key role in joint position sense, are not affected that this results are corresponded with Beyranvand et al research(4).
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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.
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Altering foot stance is often prescribed as a method of isolating muscles during the parallel squat. The purpose of this study was to compare activity in six muscles crossing the hip and/or knee joints when the parallel squat is performed with different stances and bar loads. Nine male lifters served as subjects. Within 7 d of determining IRM on the squat with shoulder width stance, surface EMG data were collected (800 Hz) from the rectus femoris, vastus medialis, vastus lateralis, adductor longus, gluteus maximus, and biceps femoris while subjects completed five nonconsecutive reps of the squat using shoulder width, narrow (75% shoulder width), and wide (140% shoulder width) stances with low and high loads (60% and 75% 1RM, respectively). Rep time was controlled. A goniometer on the right knee was used to identify descent and ascent phases. Integrated EMG values were calculated for each muscle during phases of each rep, and the 5-rep means for each subject were used in a repeated measures ANOVA (phase x load x stance, alpha = 0.05). For rectus femoris, vastus medialis, and vastus lateralis, only the load effect was significant. Adductor longus exhibited a stance by phase interaction and a load effect. Gluteus maximus exhibited a load by stance interaction and a phase effect. Biceps femoris activity was highest during the ascent phase. The results suggest that stance width does not cause isolation within the quadriceps but does influence muscle activity on the medial thigh and buttocks.
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This study compared the relationship between surface electromyographic (EMG) activity and isometric force of m. quadriceps femoris (QF) in the single-joint knee extension (KE) and the multi-joint leg press (LP) exercises. Nine healthy men performed unilateral actions at a knee angle of 90 degrees at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC). EMG was measured from m. vastus lateralis (VL), m. vastus medialis (VM), m. rectus femoris (RF), and m. biceps femoris (BF). There were no differences in maximum EMG activity of individual muscles between KE and LP. The QF EMG/force relationship was nonlinear in each exercise modality. VL showed no deviation from linearity in neither exercise, whereas VM and RF did. BF activity increased linearly with increased loads. The EMG/force relationship of all quadricep muscles studied appears to be similar in isometric multi-joint LP and single-joint KE actions at a knee angle of 90 degrees. This would indicate the strategy of reciprocal force increment among muscles involved is comparable in the two models. Furthermore, these data suggest a nonuniform recruitment pattern among the three superficial QF muscles and surface EMG recordings from VL to be most reliable in predicting force output.
Chapter
The knee joint, the largest and most complex synovial joint in the human body, is an anatomical region subject to injuries from activities in various fields including athletics, industry, and recreation. Because this joint is between the longest bones in the body, the femur and the tibia, the forces and moments of force around this joint produce torques of such magnitude that injuries ensue. In athletics, various injuries may occur by overloading the knee joint (Nicholas, 1970; Peterson, 1970). In several studies (Kennedy and Fowler, 1971; Marshall and Olsson, 1971; Newman, 1969; Slocum and Larson, 1968), it was found that the instability of the knee joint was the result of the application of excessive external rotation and abduction forces to a flexed, weight-bearing knee.
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Three high-skilled powerlifters performed parallel squats with different burden weights. Using a sagittal plane biomechanical model, the moments of force about the bilateral axes of the lumbo-sacral, hip, knee, and ankle joints were determined. A local biomechanical model of the knee was used in order to calculate the knee joint forces induced. The greatest moments were found in the lumbo-sacral joint. The maximum hip moment was greater than that of the knee moment which was greater than the ankle moment. The knee moment had a flexing direction and reached its maximum at the deepest position of the squat, while the lumbo-sacral and hip moments were found to reach their maxima during the first half second of the ascent. One lift that caused a bilateral quadriceps tendon rupture was stimulated and was found to give a maximum knee flexing moment ranging between 335 Nm and 550 Nm. This moment induced a force in each quadriceps tendon of between 10.9 kN and 18.3 kN at the occasion of rupture.
Article
The purpose of this study was to see if vastus medialis oblique/vastus lateralis (VMO:VL) ratios could be increased by widening the squat stance and if the VMO activity increases with deeper ranges of knee flexion. Fifteen healthy subjects performed unloaded narrow and wide stance squats through three ranges of knee flexion: 30 degrees, 60 degrees, and 90 degrees. The two squat stances were compared using a 2 x 3 ANOVA to see if the wide-stance squat had any significant difference in EMG activity for VMO:VL ratios compared to the narrow-stance squat. The difference in EMG activity of the VMO between the various angles for both squat stances was also compared. The ANOVA revealed no significant differences between the squat stances for VMO:VL ratios but did show the VMO:VL ratios to be significantly higher with increasing knee flexion angles. These findings suggest that the VMO is active throughout the 90 degrees range and that increasing knee flexion angles can elicit greater activity of the VMO relative to the VL.
Article
The seated knee extension is commonly used with the parallel squat to promote balance between the vastus medialis (VM) and vastus lateralis (VL). No controlled studies have examined the relative contributions of each muscle during these exercises, so this study employed EMG analysis to determine their contributions. Ten experienced lifters performed squats and knee extensions at their 10-RM. Sets were separated by 15 min rest and the order of performance was reversed between sessions, which were 1 week apart. EMG was collected on the VL and VM of the dominant leg during the first and last repetition of each exercise. Since EMG activity differed significantly between the two testing days, each was analyzed separately. No significant differences were found between the root mean square of the amplitude of the EMG for the VL and VM during either exercise. The parallel squat elicited more electrical activity than the knee extension in both muscles, and the downward shift in frequency of the EMG signal was greater for both the VM and VL during the parallel squat. The results question the value of the knee extension as a supplemental exercise in this case. (C) 1994 National Strength and Conditioning Association
Article
To compare the effectiveness of 3 weight-training movements for the hamstrings, 11 weight-trained men performed 3 repetitions at 75% of 1 repetition maximum of the leg curl (LC), stiff-leg deadlift (SLDL), and back squat. Integrated electromyography (EMG) and peak EMG were analyzed in the biceps femoris and semitendinosus independantly during the concentric (CON) and eccentric (ECC) phase of each exercise. Results were as follows: CON-LC and CON-SLDL elicited the greatest integrated EMG activity, with no significant difference between exercises. The CON-squat showed approximately half as much integrated EMG activity as CON-LC and CON-SLDL. Highest peak EMG was found in the CON-LC and CON-SLDL, with no significant difference in these exercises. The CON-squat produced a peak EMG that was approximately 70% of LC and SLDL. We conclude that LC and SLDL involve the hamstrings to a similar degree; however, the back squat involves only about half as much hamstring integrated EMG activity as LC and SLDL. (C) 1999 National Strength and Conditioning Association
Article
Six experienced lifters performed 3 squats in each of 4 foot positions: -10[degrees] inward, 0[degrees], 10[degrees] outward, and 20[degrees] outward. These were performed at 2 weight conditions: 65 and 75% of 1 repetition maximum. Surface electromyographic activity of the vastus medialis, vastus lateralis, and rectus femoris on the right leg was analyzed in terms of the activity duration and peak levels of activity. Results and analysis of variance indicated that the foot rotation position did not influence the mean peak activity or mean duration of activity of vastus medialis, vastus lateralis, or rectus femoris. The practice of adopting foot rotation to selectively strengthen individual muscles of the quadriceps group was not supported by this study, which involved smaller, more readily adopted, and comfortable levels of foot rotation than did those previously investigated. (C) 2000 National Strength and Conditioning Association
Article
Many strength trainers believe that varying the foot position during the parallel squat or knee extension can target specific muscles of the quadriceps group. To test this theory, 10 men performed 3 parallel squats at added resistance equal to their body weight and 3 knee extensions at 8- to 10-RM resistance under 3 treatment conditions: toes pointed out, lateral rotation of the tibia (LR); toes straight forward, no rotation of the tibia (N); and inward, medial rotation of the tibia (MR). Lifts were separated by a 5-min rest. Bipolar surface electrodes placed on the bellies of the v. lateralis and v. medialis and on the lateral and medial portions of the rectus femoris revealed no significant differences in electrical activity for any muscle due to changes in foot position during the squat. During the knee extension, however, LR produced a significantly greater mean rmsEMG than the other foot positions across all muscles. Thus for the squat a lifter should choose the most stable and comfortable position. For the knee extension, however, maintaining a laterally rotated position is best. (C) 1995 National Strength and Conditioning Association
Article
The relationship between hip and knee joint load and quadriceps muscle activity during squatting exercise to different depths was studied. Eight young national class Olympic weightlifters performed squatting exercise to 4 different knee flexion angles; 45°, 90°, parallel and deep squats. They held a barbell across their shoulders with a weight of 65% of their one-repetition maximum. The loading moments of force about the hip and knee joints were calculated using a semidynamic method. Video was used for motion recording and electromyograhy for recording activity from die vastus lateralis, rectus femoris and biceps femoris muscles. The loading moment on the hip joint increased significantly from the 90° squat to the parallel, but there was no difference between the parallel and the deep. For the knee joint, there was no difference between the 45°, 90° and parallel, but for the deep squat the loading moment increased significantly. The muscular activity generally increased with increasing squatting depth, but mere were only minor insignificant differences between the parallel and the deep squats. We conclude that knee joint load can be limited by doing parallel instead of deep squats and that this will not decrease quadriceps muscle activity. To limit hip moment, the squat should not be deeper than 90°.
Article
Biomechanical analysis of the two-dimensional models composed from roentgenographic pictures and electromyographic analysis of the shear force exerted on the tibia during standing on both legs were conducted in 21 young adult males. The simultaneous contraction of the quadriceps and hamstrings was observed in all electromyograms. Amplitude observed on electromyograms of the hamstrings increased as the trunk flexion angle increased. The calculated average values of shear force were negative at every knee flexion angle (negative value means posteriorly directed force). As the trunk flexion angle increased, posterior drawer force increased at knee flexion angles of 30 degrees and 60 degrees. The simultaneous contraction of the quadriceps and the hamstrings was considered to be the main factor that influenced these results. Standing on both legs with knee and trunk flexion was considered to be applicable in the early stages after anterior cruciate ligament reconstruction.
Article
Ten male university student volunteers were selected to investigate the 3D articular force at the tibio-femoral joint during a half squat exercise, as affected by cadence, different barbell loads, and fatigue. Each subject was required to perform a half squat exercise with a barbell weight centered across the shoulders at two different cadences (1 and 2 s intervals) and three different loads (15, 22 and 30% of the one repetition maximum). Fifty repetitions at each experimental condition were recorded with an active optoelectronic kinematic data capture system (WATSMART) and a force plate (Kistler). Processing the data involved a photogrammetric technique to obtain subject tailored anthropometric data. The findings of this study were: 1) the maximal antero-posterior shear and compressive force consistently occurred at the lowest position of the weight, and the forces were very symmetrically disposed on either side of this halfway point; 2) the medio-lateral shear forces were small over the squat cycle with few peaks and troughs; 3) cadence increased the antero-posterior shear (50%) and the compressive forces (28%); 4) as a subject fatigues, load had a significant effect on the antero-posterior shear force; 5) fatigue increased all articular force components but it did not manifest itself until about halfway through the 50 repetitions of the exercise; 6) the antero-posterior shear force was most affected by fatigue; 7) cadence had a significant effect on fatigue for the medio-lateral shear and compressive forces.
Article
Integrated electromyographic (IEMG) activity of the vastus lateralis and vastus medialis muscles were recorded when normal male subjects performed isolated concentric and eccentric exercises on a special "sledge" apparatus, which was connected to a force plate. Four different submaximal energy levels were investigated in both exercise types. A single set of exercise included 80 contractions. The net mechanical efficiency was computed from the force plate record (mechanical work) and from the analysis of expired air (energy expenditure). The results indicated that IEMG activity increased with increasing knee angular velocity or mechanical work in concentric exercise, but in eccentric exercise IEMG stayed at very low levels at all energy levels. The net mechanical efficiency of concentric exercise was on the average 19.4% +/- 2.8%, and it did not change much with change in the narrow range of peak angular velocities. In eccentric exercise, however, mechanical efficiency increased in all subjects with increasing mechanical work or stretch velocity reaching in many instances values over 100%. This increase in mechanical efficiency was characterized by very low IEMG activity, which stayed approximately the same at all efficiency levels. In concentric exercise IEMG, energy expenditure and mechanical work changed in parallel when exercise intensity was increased.
Article
From knee extension moments measured with a dynamometer, the quadriceps muscle force, the patellar ligament force and the reaction force in the patellofemoral joint at various knee angles (0-90 degrees) were estimated. The information needed to calculate the combined effect of both patellofemoral and tibiofemoral joint on the mechanical advantage of the muscle was obtained from lateral-view radiographs of autopsy knees. The results show that the smallest quadriceps force (2,000 N) is exerted at maximal extension, and the largest force (8,000 N) at about 75 degrees of flexion. The patellar ligament force reaches a maximum (5,000 N) at 60 degrees. The reaction force in the patellofemoral joint is the smallest (1,000 N) at extension and is of the same values as the muscle force in a range from 75 to 90 degrees. Especially at large flexion angles, the value of the estimated forces is considerably larger (by 100%) than reported in the literature. This difference is attributed to the influence of the patellofemoral joint on the mechanical advantage of the muscle, which has not been taken into account in other studies.
Article
Controlled bending moments were applied to twelve human cadaver knee joints using a special loading fixture that allowed variation of both the Q-angle and the flexion angle. The joints were tested at three different Q-angles (physiological, increased 10 degrees, and decreased 10 degrees) and five different angles of flexion (ranging from 20 to 120 degrees). Based on one-third of values in the literature for maximum voluntary isometric quadriceps moments, we applied resultant knee moments of 23.6, 30.7, 47.2, and 35.0 newton-meters at 20, 30, 60, and 90 degrees of flexion, respectively. Based on two-thirds of reported maximum moments, we applied 47.2 newton-meters at 120 degrees of flexion. Normal patellofemoral-contact pressures, measured with a pressure-sensitive film, were remarkably uniformly distributed (+/- 0.25 megapascal ), with approximately the same pressure on the lateral and medial patellar facets. The maximum contact force occurred at 90 degrees of flexion. Extrapolating our measurements to full in vivo moments, we estimated maximum contact forces of 4600 newtons , or approximately 6.5 times body weight. Tendofemoral contact at 120 degrees of knee flexion supported one-third of the total contact force on the patella. A 10-degree increase in the Q-angle resulted in increased peak pressures (an increase of 45 per cent at 20 degrees of flexion). A decrease in the Q-angle resulted in unloading of the vertical crest and, in some knees, of parts of the lateral facet. However, these decreases were always associated with increased peak pressures (50 per cent more at 20 degrees of flexion) at other locations.
Article
The joint and muscle forces arising from and generated in the knee during the activity of squatting, and rising from a deep squat have been calculated. The analysis involved the consideration of a two-dimensional model. Data was then collected from each of the subjects performing the activity using: a force platform; a ciné film used in conjunction with the X-rays to describe accurately the configuration of the lower limb; EMG data; anthropometric data. A computer program was developed to analyse the data and compute the forces in the leg. Six subjects were tested and graphs of joint and muscle forces versus knee angle were obtained for each of them. A discussion follows. The results for ascent and descent, and slow and fast activities are compared.
Article
Fresh cadaver knees were tested at full extension and at 20 degrees of flexion in specially designed fixtures that allowed tibiofemoral contact forces of as much as 925 newtons (207 pounds) to be applied to the knee while movement of the joint was not restricted. Force versus displacement responses for anterior-posterior and medial-lateral movement of the tibia as well as moment versus rotation responses for varus-valgus angulation and tibial torsion were recorded with and without load both before and after medial and lateral meniscectomy. When joint contact force was applied, the loading apparatus could be adjusted so that the knee was in equilibrium and there was no tendency for the tibia to flex, extend, or subluxate anteriorly or posteriorly with respect to the femur. This position of static equilibrium (which we have called the neutral position) was represented graphically as the origin of the response curves. The slope of the response curve as it passed through the neutral position (neutral stiffness) is an important descriptive parameter for small movements about this equilibrium position. Laxity, the displacement (or rotation) of the tibia with respect to the femur at specified force (or moment) levels, also is a quantity of clinical interest. While a tibiofemoral contact force was applied, the anterior-posterior, medial-lateral, varus-valgus, and torsional stiffness at the neutral position always increased, while the corresponding laxities always decreased. Similar increases in joint stability associated with increased joint load were observed after medial and lateral meniscectomy. While a tibiofemoral contact force was applied to the knee, the joint was protected against varus-valgus angulation. In this situation, varus-valgus angulation of the tibia could not occur until the condylar lift-off moment (the force applied to the tibia multiplied by its distance from the condylar pivot point) had overcome the protective joint-load moment (the resultant joint force multiplied by its distance to the condylar pivot). Once this protective joint-load moment was exceeded, condylar lift-off and ligament stretch occurred. Joint load, whether generated by gravitational, dynamic, or muscular forces, is an important protective mechanism that avoids ligament strain. After medial and lateral meniscectomy in the fully extended, unloaded knee, anterior-posterior neutral stiffness and varus-valgus neutral stiffness were reduced significantly and varus-valgus laxity was increased significantly. When the knee was in 20 degrees of flexion, internal and external rotation of the tibia decreased anterior-posterior laxity and increased anterior-posterior neutral stiffness. Hyperextension of the knee increased neutral stiffness and decreased laxity during the varus-valgus test. Clinical relevance: Load on the knee has an important stabilizing effect on tibiofemoral motions because it limits displacements and rotations and thereby protects the ligaments from excessive strains produced by external forces and moments. Removal of the menisci often makes a knee looser in the unloaded condition, but does not affect the stability of the loaded knee.
Article
Successful reconstruction of ligaments requires knowledge of the properties of the intact ligament. This study examined the strength of the human posterior cruciate ligament (PCL), treating it as two separate fibre bundles. It was hypothesized (i) that the mechanical and material properties of the anterolateral (aPC) and the posteromedial (pPC) bundles of the PCL were significantly different and (ii) that previous studies have underestimated the strength of the whole PCL. The properties of the two bundles were measured in 10 donors (53-98 yr). The mechanical and material properties of the two bundles were found to be significantly different, the aPC was six times as strong as the pPC. The aPC had a mean strength of 1.6 kN. Allowing for age effects this study suggests that the strength of the PCL in young active people is 4 kN, which is higher than that suggested by previous studies. Because of the difference in the strengths of the two bundles, we conclude that the aPC is primarily responsible for the stabilising effect of the PCL. We therefore recommend that PCL reconstructions should be centered on the middle of the aPC bundle.
Article
Patellofemoral joint biomechanics during leg press and leg extension exercises were compared in 20 normal subjects (10 men, 10 women) aged 18 to 45 years. Knee moment, patellofemoral joint reaction force, and patellofemoral joint stress were calculated for each subject at four knee flexion angles (0°, 30°, 60°, and 90°) during leg press and leg extension exercises. All three parameters (knee moment, patellofemoral joint reaction force, and patellofemoral joint stress) were significantly greater in leg extension exercise than leg press exercise at 0° and 30° of knee flexion (P < 0.001). At 60° and 90° of knee flexion, all three param eters were significantly greater in leg press exercise than leg extension exercise (P < 0.001). Patellofemoral joint stresses for leg press and leg extension exercises intersected at 48° of knee flexion. This study demonstrates that patients with patello femoral joint arthritis may tolerate rehabilitation with leg press exercise better than with leg extension exercise in functional ranges of motion because of lower patel lofemoral joint stresses.
Article
The purpose of this study was to obtain lines of action and moment arms in the sagittal plane of the major force-carrying structures crossing the knee joint. The muscles and ligaments studied were the quadriceps, biceps femoris, semimembranosus, and semitendinosus muscles and the anterior and posterior cruciate and medial and lateral collateral ligaments. All lines of action and moment arms of the structures of interest were determined as a function of knee joint angles and were expressed using polynomial regression equations. This representation of the results allows for easy application of the findings to musculoskeletal models of the human knee joint.
Article
A computer-based model of the knee was used to study forces in the cruciate ligaments induced by co-contraction of the extensor and flexor muscles, in the absence of external loads. Ligament forces are required whenever the components of the muscle forces parallel to the tibial plateau do not balance. When the extending effect of quadriceps exactly balances the flexing effect of hamstrings, the horizontal components of the two muscle forces also balance only at the critical flexion angle of 22 degrees. The calculations show that co-contraction of the quadriceps and hamstring muscles loads the anterior cruciate ligament from full extension to 22 degrees of flexion and loads the posterior cruciate at higher flexion angles. In these two regions of flexion, the forward pull of the patellar tendon on the tibia is, respectively, greater than or less than the backward pull of hamstrings. Simultaneous quadriceps and gastrocnemius contraction loads the anterior cruciate over the entire flexion range. Simultaneous contraction of all three muscle groups can unload the cruciate ligaments entirely at flexion angles above 22 degrees. These results may help the design of rational regimes of rehabilitation after ligament injury or repair.
Article
The purpose of this study was to analyze forces at the tibiofemoral joint during open and closed-kinetic-chain exercises. Five healthy subjects performed maximum isometric contractions at 30, 60, and 90 degrees of knee flexion during open-kinetic-chain extension, open-kinetic-chain flexion, and closed-kinetic-chain exercises. Electromyographic activity of the quadriceps and hamstrings, as well as load and torque-cell data, were recorded. Tibiofemoral shear and compression forces were calculated with use of a two-dimensional biomechanical model. The results showed that, during the open-kinetic-chain extension exercise, maximum posterior shear forces (the resisting forces to anterior drawer) of 285 +/- 120 newtons (mean and standard deviation) occurred at 30 degrees of knee flexion and maximum anterior shear forces (the resisting forces to posterior drawer) of 1780 +/- 699 newtons occurred at 90 degrees of knee flexion. The closed-kinetic-chain exercise produced significantly less posterior shear force at all angles when compared with the open-kinetic-chain extension exercise. In addition, the closed-kinetic-chain exercise produced significantly less anterior shear force at all angles except 30 degrees when compared with the open-kinetic-chain flexion exercise (p < 0.05). Analysis of tibiofemoral compression forces and electromyographic recruitment patterns revealed that the closed-kinetic-chain exercise produced significantly greater compression forces and increased muscular co-contraction at the same angles at which the open-kinetic-chain exercises produced maximum shear forces and minimum muscular co-contraction.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Eight Swedish national class weightlifters performed "high-bar" squats and six national class powerlifters performed "low-bar" squats, with a barbell weight of 65% of their 1 RM, and to parallel- and a deep-squatting depth. Ground reaction forces were measured with a Kistler piezo-electric force platform and motion was analyzed from a video record of the squats. A computer program based on free-body mechanics was designed to calculate moments of force about the hip and knee joints. EMG from vastus lateralis, rectus femoris, and biceps femoris was recorded and normalized. The peak moments of force were flexing both for the hip and the knee. The mean peak moments of force at the hip were for the weightlifters 230 Nm (deep) and 216 Nm (parallel), and for the powerlifters 324 Nm (deep), and 309 Nm (parallel). At the knee the mean peak moments for the weightlifters were 191 Nm (deep) and 131 Nm (parallel), and for the powerlifters 139 Nm (deep) and 92 Nm (parallel). The weightlifters had the load more equally distributed between hip and knee, whereas the powerlifters put relatively more load on the hip joint. The thigh muscular activity was slightly higher for the powerlifters.
Article
We chose to investigate tibiofemoral joint kinetics (compressive force, anteroposterior shear force, and extension torque) and electromyographic activity of the quadriceps, hamstring, and gastrocnemius muscles during open kinetic chain knee extension and closed kinetic chain leg press and squat. Ten uninjured male subjects performed 4 isotonic repetitions with a 12 repetition maximal weight for each exercise. Tibiofemoral forces were calculated using electromyographic, kinematic, and kinetic data. During the squat, the maximal compressive force was 6139 +/- 1708 N, occurring at 91 degrees of knee flexion; whereas the maximal compressive force for the knee extension exercise was 4598 +/- 2546 N (at 90 degrees knee flexion). During the closed kinetic chain exercises, a posterior shear force (posterior cruciate ligament stress) occurred throughout the range of motion, with the peak occurring from 85 degrees to 105 degrees of knee flexion. An anterior shear force (anterior cruciate ligament stress) was noted during open kinetic chain knee extension from 40 degrees to full extension; a peak force of 248 +/- 259 N was noted at 14 degrees of knee flexion. Electromyographic data indicated greater hamstring and quadriceps muscle co-contraction during the squat compared with the other two exercises. During the leg press, the quadriceps muscle electromyographic activity was approximately 39% to 52% of maximal velocity isometric contraction; whereas hamstring muscle activity was minimal (12% maximal velocity isometric contraction). This study demonstrated significant differences in tibiofemoral forces and muscle activity between the two closed kinetic chain exercises, and between the open and closed kinetic chain exercises.