Article

Effect of Knee Position on Hip and Knee Torques During the Barbell Squat

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Abstract

Unlabelled: Some recommendations suggest keeping the shank as vertical as possible during the barbell squat, thus keeping the knees from moving past the toes. This study examined joint kinetics occurring when forward displacement of the knees is restricted vs. when such movement is not restricted. Seven weight-trained men (mean +/- SD; age = 27.9 +/- 5.2 years) were videotaped while performing 2 variations of parallel barbell squats (barbell load = body weight). Either the knees were permitted to move anteriorly past the toes (unrestricted) or a wooden barrier prevented the knees from moving anteriorly past the toes (restricted). Differences resulted between static knee and hip torques for both types of squat as well as when both squat variations were compared with each other (p < 0.05). For the unrestricted squat, knee torque (N.m; mean +/- SD) = 150.1 +/- 50.8 and hip torque = 28.2 +/- 65.0. For the restricted squat, knee torque = 117.3 +/- 34.2 and hip torque = 302.7 +/- 71.2. Restricted squats also produced more anterior lean of the trunk and shank and a greater internal angle at the knees and ankles. The squat technique used can affect the distribution of forces between the knees and hips and on the kinematic properties of the exercise. Practical applications: Although restricting forward movement of the knees may minimize stress on the knees, it is likely that forces are inappropriately transferred to the hips and low-back region. Thus, appropriate joint loading during this exercise may require the knees to move slightly past the toes.

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... The HBBS can further be defined with an upright torso and greater flexion at the knee throughout the movement, resulting in a "deep" squat where the crease of the hips is noticeably inferior to the top of the knee. It is believed that more weight can be lifted in the LBBS than the HBBS, possibly due to a suspected shorter moment arm, as well as increased forces in the lumbar muscles and ligaments (13,14,30). Of the 2 variations, the LBBS is mired in variations of bar placement, foot stance-width, and orientation, as well as overall technical cues for proper execution (14). ...
... In addition, the gluteus maximus, hip adductors, hip abductors, and erector spinae further assist in the movement (9,11,14,23). An athlete's specific goals, mobility impairments, and injury history should be assessed to choose the variation best suited for the athlete (13,28,36). For instance, squat variations (front and HBBS) used in weightlifting are heavily characterized by greater hip and knee flexion, as well as an upright torso, ultimately to facilitate the specific demands of the snatch and clean and jerk (14). ...
... For instance, squat variations (front and HBBS) used in weightlifting are heavily characterized by greater hip and knee flexion, as well as an upright torso, ultimately to facilitate the specific demands of the snatch and clean and jerk (14). Conversely, powerlifting uses the LBBS, distinguished by reduced anterior cruciate ligament strain and knee forces, commensurate with increased lumbar muscle forces to potentially lift a higher absolute load (13,14,30). The primary considerations for determining squat variation are preexisting mobility, muscular strength, and injury history (14,20,33). ...
Article
The low-bar back squat (LBBS) is a barbell squat variation that emphasizes hip musculature through use of forward lean. This characteristic, among others, allows greater loads to be lifted and can facilitate rehabilitation in a compromised knee joint. Correct technique should be instructed to promote proper execution. This article aims to discuss the anatomical and technical differences between the high-bar back squat and LBBS, define LBBS-specific technique, and provide practitioners strategies to select the best version for their lifters.
... A long-held theory within the clinical and strength and conditioning setting is that shank inclination during squatting should be minimized to reduce loading on the knee. 1 Although it is unknown what level of loading is injurious to the knee, previous studies have shown that squatting with the knees forward of the toes (ie, forward shank position) increases the knee-extensor moment (KEM). [1][2][3] Squatting in a way that results in higher KEMs can result in increased patellofemoral joint stress, 4,5 patellar tendon loading, 6,7 and strain on the anterior cruciate ligament (ACL). 8 In contrast to the known relationship between the forward shank position and the KEM, it also has been reported that a forward trunk lean can lessen the KEM during squatting. ...
... To participate, subjects had to confirm that they had participated in an exercise program during the past 5 years that included squatting exercises. Exclusion criteria included the following: (1) history of lower-extremity surgery or other major lower-extremity injury in the previous 12 months, (2) knee pain or knee pathology in the past 12 months, (3) any pain when squatting, (4) any previous injury that would prevent the ability to perform a barbell squat with 35% body weight, and (5) pregnancy. Prior to data collection, written informed consent was obtained from all individual subjects. ...
... It should be noted, however, that greater degrees of forward trunk lean would also increase the demand on the back extensors. 2,18,19 The results of our study need to be interpreted in light of several limitations. First, we collapsed data for all subjects across 8 separate conditions (aimed at producing diverse combinations of trunk and shank positions). ...
Article
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Context: A limitation of previous studies on squatting mechanics is that the influence of trunk and shank inclination on the knee-extensor moment (KEM) has been studied in isolation. Objective: The purpose of the current study was to determine the influence of segment orientation on the KEM during freestanding barbell squatting. Design: Repeated-measures cross sectional. Setting: University research laboratory. Participants: Sixteen healthy individuals (8 males and 8 females). Intervention: Each participant performed 8 squat conditions in which shank and trunk inclinations were manipulated. Main outcome measures: 3D kinematic and kinetic data were collected at 250 and 1500 Hz, respectively. Regression analysis was conducted to identify the individual relationships between the KEM and the trunk and shank inclination at 60° and 90° of knee flexion. To identify the best predictor(s) of the KEM, stepwise regression was implemented. Results: Increased shank inclination increased the KEM (P < .001, R2 = .21-.25). Conversely, increased trunk inclination decreased the KEM (P < .001, R2 = .49-.50). For the stepwise regression, trunk inclination entered first and explained the greatest variance in the KEM (all P < .001, R2 = .49-.50). Shank inclination entered second (all P < .010, R2 = .53-.54) and explained an additional 3% to 5% of the variance. Conclusions: Our results confirm that inclination of the trunk and shank have an opposing relationship with the KEM. Increased forward shank posture increases the KEM, while increased forward trunk posture decreases the KEM. However, when viewed in combination, the trunk was the superior predictor of the KEM, highlighting the fact that increased quadriceps demand created by a forward shank can be offset by trunk inclination.
... Specifically, manipulation of stance width, bar position, foot rotation, trunk position, knee position, and squat depth have been shown to influence demand of the hip and knee extensors during the barbell back squat. [1][2][3][4][5][6][7][8][9] Sagittal plane inclination of the trunk and tibia are of particular interest as both have been reported to independently influence the demand on the hip and knee extensors during squatting. Specifically, increasing forward trunk lean during squatting has been shown to increase the hip extensor moment, while simultaneously decreasing the knee extensor moment. ...
... Specifically, increasing forward trunk lean during squatting has been shown to increase the hip extensor moment, while simultaneously decreasing the knee extensor moment. [1][2][3]5 Conversely, forward inclination of the tibia has been reported to increase the knee extensor moment while simultaneously decreasing the hip extensor moment. [1][2][3]5,7 Previous investigations related to the biomechanical demands of squatting are limited for two primary reasons. ...
... [1][2][3]5 Conversely, forward inclination of the tibia has been reported to increase the knee extensor moment while simultaneously decreasing the hip extensor moment. [1][2][3]5,7 Previous investigations related to the biomechanical demands of squatting are limited for two primary reasons. First, many biomechanical studies do not control for confounding variables known to influence hip and knee extensor demand in the squat, such as stance width or foot rotation, 5,7,10,11 limiting interpretation and application of their results. ...
Article
Sagittal plane inclination of the trunk and tibia have been shown to independently modulate hip and knee extensor moments during squatting. The purpose of this study was to determine if the difference between sagittal plane trunk and tibia inclinations can be used to approximate the relative demand of the hip and knee extensors across a range of squatting conditions. Kinematic and kinetic data were obtained from 16 participants during 8 squat conditions in which trunk and tibia inclination were manipulated. The average hip/knee extensor moment ratio (HKR) was calculated during the lowering (eccentric) phase of each squat condition using inverse dynamics equations. Linear regression evaluated the association between the difference in trunk and tibia inclination at peak knee flexion and the average HKR. Across all squat conditions, the difference between trunk and tibia inclinations explained 70% of the variance in the average HKR (p < 0.001). The squat was knee extensor biased (HKR ≤ 1.0) when the tibia was at least 8 degrees more inclined than the trunk. The results of this study indicate that the relationship between sagittal plane trunk and tibia inclination can be used to estimate the relative demand of the hip and knee extensors.
... However, varying performance responses have been found following these activities (38,59,69). Differences in exercise range of motion have been shown to affect mechanical and physiological demands (52) and may also influence postpriming performance responses after squatting tasks. When intensity is equated, a deeper squat will result in greater mechanical work compared with more shallow variations (104). ...
... The authors suggested that the oxidative potential of MHC IIa muscle fibers may be important in restoring adenosine triphosphate (ATP) postexercise to elicit a same-day potentiation response that offsets fatigue (22,62). A higher percentage of these fibers strongly correlates with greater relative MHC IIa area, an indicator of the strength training history (51,52,54,142). As such, the magnitude of potentiation or fatigue following resistance priming exercise completed on the same day may be influenced by training status (21,22). Nevertheless, further research examining the relationship between these muscle adaptations and the postexercise response subsequent to resistance priming strategies with lower exercise volumes that may be effective to improve performance within this time frame is needed. ...
... For example, the hip joint extensors work maximally only when there is an opportunity to extend the trunk from a forward inclined position (Lees et al., 2004;Vanrenterghem et al., 2008). However, when an external load is positioned across the shoulders, trunk inclination is restricted to prevent the moment arm of the external resistance becoming too large, minimising resistive torque and shear forces experienced at the lumbar spine (Fry, Smith, & Schilling, 2003;Swinton et al., 2012). Conversely, when the position of the external load is changed the range of motion at the hip may not be limited to the same degree, if at all (Lees et al., 2004). ...
... However, when an external load is positioned across the shoulders, trunk inclination is restricted to prevent the moment arm of the external resistance becoming too large, minimising resistive torque and shear forces experienced at the lumbar spine (Fry et al., 2003;Swinton et al., 2012). Conversely, when the position of the external load is changed the range of motion at the hip may not be limited to the same degree, if at all (Lees et al., 2004). ...
Thesis
Full-text available
The effects of external loading on jumping mechanics have been extensively investigated; however, review of the body of knowledge revealed a number of methodological issues, as well as a common omission of key mechanical theory, with limited studies investigating the effects of changing the position of the external load. Therefore, the primary aim of this thesis was to investigate the effects of changing the position of the external load and training status on system centre of mass and lower limb joint mechanics during countermovement jumping, with a particular emphasis on power output. Section 3 (Mundy, Lake, Carden, Smith, & Lauder, 2016a) established that the force platform method and the combined method cannot be used interchangeably within practice for measuring power output, and argued that the force platform method should be adopted as the criterion method. Using the force platform method, section 4 (Mundy, Smith, Lauder, & Lake, 2016b) established that the effects of barbell loading on system centre of mass mechanics reported are often overemphasised, and it was argued that investigating the complex interaction between the underpinning force, temporal and spatial components is of interest to practitioners. Section 5 demonstrated that practitioners may overcome the constraints of barbell loading by changing the position of the external load to arms’ length using a hexagonal barbell, which facilitated greater system centre of mass and lower limb joint mechanics in strength-power trained athletes. However, as the effects of external load have been posited to be population specific, section 6 demonstrated that regardless of the magnitude of the external load, strength-power trained athletes produced significantly greater hip joint peak power outputs than their recreationally trained counterparts. As such, the findings of the thesis support the hypothesis that practitioners should prescribe the position of external loading that maximise hip joint peak power output. In conclusion, this thesis has not only made significant steps towards providing a standardised method of measuring power output, but it has also offered a revealing insight into the effects of training status, as well as the effects of changing the position and magnitude of the external load on system centre of mass and lower limb joint mechanics during countermovement jumping.
... To create and evaluate these guidelines, a number of studies have investigated the kinematics, muscle activity, and loading conditions that occur in the lower extremities during different execution forms of the squat exercise. A comparison between the restricted knee (where the knee should not pass anteriorly of the toe) and the unrestricted knee (where the knee is free to pass beyond the toe) techniques during squatting shows that the range of motion (RoM) of the knee [9,10] and of the lumbar and thoracic spine differs significantly and furthermore when adding a greater load [11]. With increasing load, the RoM of the lumbar curvature decreases significantly, and the thoracic curvature RoM decreases with increased additional load on the barbell from 25 to 50% of participant's body weight [11]. ...
... While anterior-posterior translation of the knee during squats or deep knee bends has been studied [9,10,26,27], the mediolateral displacement (leading to varus or valgus postures) has only been examined using cohorts with excessive medial knee displacement, showing that increasing knee valgus angles result in an increasing risk factor for injury. To lower mediolateral movements, changes in the squatting variations such as heel lifts or improving strength in the ankle is recommended [7,[22][23][24][25]. ...
Article
Full-text available
Following publication of the original article [1], the authors reported an error in the following sentence on page 8: “In general, knee varus (negative ΔD*) is a much more common deficit than valgus, and a more negative ΔD* value in the novice squatters compared to the experienced ones was therefore expected.”
... A projeção do tronco à frente (Figura 5) aumenta a sobrecarga na região lombar (20) , logo esse é um movimento que deve ser evitado. Alguns dos fatores que induzem a maior projeção do tronco à frente são: 1) falta de mobilidade nos tornozelos; 2) desproporção entre o comprimento do fêmur e do tronco, sendo maior comprimento relativo do fêmur e menor comprimento relativo do tronco; 3) menor distância entre os pés; 4) barra posicionada mais abaixo nas costas; 5) desequilíbrio entre a força do quadríceps e glúteo máximo, havendo uma maior força relativa dos glúteos; e 6) maior intenção de, desnecessariamente, ativar os extensores do quadril (glúteo máximo e isquiotibiais). ...
... Outro fator que contribui para a projeção excessiva do tronco à frente é a preocupação com a projeção do joelho à frente da linha da ponta dos pés. Fry et al. (20) observaram que, ao limitar os joelhos à linha da ponta dos pés, aumenta-se a força na porção inferior da coluna, comparativamente ao agachamento realizado naturalmente, ou seja, com uma projeção natural do joelho à frente da ponta dos pés. Dessa forma, para executar adequadamente o movimento, pode ser necessário que os joelhos se projetem de forma natural à frente da linha da ponta dos pés. ...
... Familiarization to the bar motion may limit the increases in trunk muscle activity as subjects become more accustomed to the motion of the FB. The calculated moments at the knee were similar to other studies in which subjects performed back squats to parallel (Fry et al., 2003;Wretenberg et al., 1996). They reported moments ranging from 150.1 to 191 Nm, which our results fall within that range. ...
... They reported moments ranging from 150.1 to 191 Nm, which our results fall within that range. Likewise, our SB data were a similar match for hip moments, but as indicated by our data, the FB was higher than the steel bar results in the studies mentioned (Fry et al., 2003;Wretenberg et al., 1996). ...
Article
Full-text available
The flexible barbell is purported to improve training gains compared with an Olympic steel barbell (SB) during the back squat exercise with Division I collegiate American football programs. The two bars loaded at 30% 1-repetition maximum were compared with ten trained Division I American football players (n = 10; age = 19.5 years; body mass = 89.4 kg; body height = 182.0 cm) completing 10 repetitions of the back squat exercise. Analysis included integrated-peak values of electromyography of the rectus femoris, biceps femoris, rectus abdominis, erector spinae, external oblique, vastus lateralis, ground reaction forces, and joint kinematics and kinetics of the hip, knee, and ankle. The flexible bar elicited significant increases in peak joint kinetics (Hip Moment: 229 ± 54 Nm vs. 209 ± 52 Nm; Hip Power: 494 ± 151 W vs. 382 ± 134 W; Knee Power: 305 ± 108 W vs. 241 ± 63 W), peak vertical ground reaction forces (1195 ± 209 N vs. 1120 ± 203 N), and muscle activity (Vastus Lateralis: 75.7 vs. 66.5%, Rectus Abdominis: 190 vs. 115%, Rectus Femoris: 69.8 vs. 59.9%, External Oblique: 115 vs. 69.0%). Greater vertical ground reaction forces, hip moment, hip power, knee power, and muscle activity of the vastus lateralis, rectus abdominis, rectus femoris, and external oblique suggest the FB provides biomechanical and physiological mechanisms for training gains over the SB for 30% of 1-repetition maximum loads.
... The squat is a commonly used exercise to improve lower extremity strength in rehabilitation and fitness (Anderson et al, 1998;Cheatham et al, 2017;Escamilla et al., 2001;Fry et al, 2003;Jung et al., 2017;McCurdy et al, 2005). Squat exercises lead to high activation in the knee extensor and hip extensor, and are used to improve squat ability such as maximal squat strength (Aspe and Swinton, 2014;Bazyler et al, 2014). ...
... Squat exercises lead to high activation in the knee extensor and hip extensor, and are used to improve squat ability such as maximal squat strength (Aspe and Swinton, 2014;Bazyler et al, 2014). Squat ability is required for weightlifters and basketball players, who must re-peatedly perform squatting actions, and short track runners, speed skaters, and wrestlers, among others, who need to hold a squat position (Fry et al, 2003). ...
... To create and evaluate these guidelines, a number of studies have investigated the kinematics, muscle activity, and loading conditions that occur in the lower extremities during different execution forms of the squat exercise. A comparison between the restricted knee (where the knee should not pass anteriorly of the toe) and the unrestricted knee (where the knee is free to pass beyond the toe) techniques during squatting shows that the range of motion (RoM) of the knee [9,10] and of the lumbar and thoracic spine differs significantly and furthermore when adding a greater load [11]. With increasing load, the RoM of the lumbar curvature decreases significantly, and the thoracic curvature RoM decreases with increased additional load on the barbell from 25 to 50% of participant's body weight [11]. ...
... While anterior-posterior translation of the knee during squats or deep knee bends has been studied [9,10,26,27], the mediolateral displacement (leading to varus or valgus postures) has only been examined using cohorts with excessive medial knee displacement, showing that increasing knee valgus angles result in an increasing risk factor for injury. To lower mediolateral movements, changes in the squatting variations such as heel lifts or improving strength in the ankle is recommended [7,[22][23][24][25]. ...
Article
Full-text available
Background Squatting is a core exercise for many purposes. The tissue loading during squatting is crucial for positive adaptation and to avoid injury. This study aimed to evaluate the effect of narrow, hip and wide stance widths, foot position angles (0°, 21°, and 42°), strength exercise experience, and barbell load (0 and 50% body weight, experts only) during squatting. Methods Novice (N = 21) and experienced (N = 21) squatters performed 9 different variations of squats (3 stance widths, 3 foot placement angles). A 3D motion capture system (100 Hz) and two force plates (2000 Hz) were used to record mediolateral knee displacement (ΔD*), range of motion (RoM) at the hip and knee joints, and joint moments at the hip, knee, and lower back. Results Both stance width and foot placement angles affected the moments at the hip and knee joints in the frontal and sagittal planes. ΔD* varied with stance width, foot placement angles and between the subjects’ level of experience with the squat exercise as follows: increasing foot angle led to an increased foot angle led to an increased ΔD*, while an increased stance width resulted in a decreased ΔD*; novice squatters showed a higher ΔD*, while additional weight triggered a decreased ΔD*. Conclusions Suitable stance width and foot placement angles should be chosen according to the targeted joint moments. In order to avoid injury, special care should be taken in extreme positions (narrow stand-42° and wide stance-0°) where large knee and hips joint moments were observed. Electronic supplementary material The online version of this article (10.1186/s13102-018-0103-7) contains supplementary material, which is available to authorized users.
... concentric action (Frost, Cronin, & Newton, 2010). Such change in momentum is directly proportional to the change in velocity and the mass of the load. ...
Article
The purpose of this study was to explore the level of inter- and intra-individual variability in the kinematic profiles of the back squat movement among skilled weightlifters. Ten competitive weightlifters volunteered for participation in this study. Barbell velocity (VBarbell) and angular velocity of the ankle (ωAnkle), knee (ωKnee) and hip joint (ωHip) were obtained by kinematic recording of six trials at 90% of 1RM in the back squat. Inter-individual variability was assessed by analysing inter-individual differences in the velocity curves through the statistical parametric mapping method. Intra-individual variability was assessed through a correlation analysis between the barbell velocity curves of each trial for each participant. Partial least squares regression analysis, was performed to relate changes in intra-individual variability to movement and anthropometric characteristics. Significant inter- and intra-individual differences were identified in VBarbell, ωAnkle, ωKnee, and ωHip (p ≤ 0.05). Having a short trunk and thigh, and a long shin in combination with greater anterior-posterior displacement of the barbell and slower velocities during the acceleration phase increased intra-individual movement consistency over movement variability. The results of the present study clearly demonstrate that skilled weightlifters display both significant inter- and intra-individual variability in the successful execution of the back squat.
... The squat is a highly utilized, multi-joint resistance training exercise that requires coordinated efforts spanning the trunk, pelvis, and lower extremity musculature. 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 (concentric) portion of back squats (Escamilla, 2001;Flanagan et al., 2015;Flanagan and Salem, 2008;Fry et al., 2003;Hirata and Duarte, 2007;Lorenzetti et al., 2012). Previous research has delineated the concentric (upward) portion of the back squat into three distinct regions: Acceleration, when vertical bar velocity is increasing from zero to peak positive, Sticking/Failure Region, vertical velocity decreases to a local minima, and finally the Strength and Deceleration Region which ends when the person is fully standing erect (Escamilla et al., 2000). ...
Article
The back squat is a complex movement with significant demands on the lower extremities and trunk to raise an external load. The back squat is simultaneously an open and closed kinetic chain movement that requires coordination of the entire body for successful completion of the lift. Therefore, this study aimed to examine coordination of the thigh and shank, trunk and thigh, and the hip and knee during the concentric phase of maximum, supra-maximum (at 105% max), and sub-maximum (at 80% max) back squats. Fourteen resistance trained adults participated in this study. Maximum back squat loads were determined using a previously determined progressive load protocol. Motion capture of the trunk and lower extremities and ground reaction force data were recorded during all squats. Angle-angle plots and modified vector coding were performed to analyze segment and joint coupling angles and knee-hip moments. Overall, the concentric phase of back squats depict a transition from early knee dominance to hip dominance as the system ascends. Interestingly, all squats presented with coupling of thigh-rising and trunk-falling. Based on the angle-angle plots and the modified vector coding results, the prolonged coupling of trunk falling and thigh rising likely resulted in too large of a moment arm for the external load for the participants to overcome during Supramax conditions.
... 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. Furthermore, when HTs were assessed, Contreras et al. (2015) showed that HT produced substantial recruitment of the gluteal musculature. ...
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.
... Maddigan M, Button D, Behm D., 2014& Okkonen, O. & Häkkinen, K. 2013) similar activation of the Quads muscle pushing a sled compared to a squat manoeuvre and squat type exercises. In addition, it has been found in multiple studies(Okkonen, O. & Häkkinen, K., 2013& Fry, A.C., Smith, J.C., & Schilling, B.K., 2003 that performing a squat without proper form can increase stress at the knee joint. ...
Article
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Introduction: The XPO Trainer used in this research is a novel device which provides low rolling resistance at low speeds with an immediate and automatic proportional increase in resistance with increased speed. Purpose: To examine the impact of using the XPO Trainer on gait and neuromuscular activation at low and high speeds in young, seemingly healthy adults. Materials and Methods: This work consisted of 35 healthy adults (age: 24.9 ± 3.2 years, weight: 149.8 ± 8 lbs, height: 66.6 ± 4.4 inches). Each participant wore accelerometers/gyroscopes sensors around each wrist and ankle, chest, and low back and surface electromyography (EMG) electrodes on their dominant leg over the quadriceps (QUAD), hamstring (HAM), anterior tibialis (TA), and gastrocnemius (GA). To initiate the tasks, participants walked then ran 40 feet with and without the XPO Trainer sled. Subjects did a total of 3 trials per tasks (total of 12) with one minute of rest between tasks to reduce fatigue factor. The data from the EMG and Mobility Lab sensors were then processed and compared through the SPSS 24 system for a repeated-measures ANOVA. Results: EMG- The QUAD muscle exhibited a substantial higher muscle activation between walk (45.39 ± 24.43) and walk push (74.40 ± 56.73) tasks. Gait Parameters- There was a significant modification (p ≤ .05) between the different gait variables and tasks, including cadence, gait speed, stride length and trunk velocity while pushing the sled. Conclusion/Clinical Relevance: With the XPO Trainer being a novel device, it is important to understand how it affects the activation and response for muscles during different activities before using it as a training tool. Understanding the effect this particular sled can provide on the different components of the (temporospatial) gait parameters and muscle activation is valuable for a clinically appropriate application to specific populations.
... Exercise professionals must take into consideration how altering squat technique may influence the entire kinetic chain. 39,40 Also, we did not standardize squat rate during testing (eg, via metronome). We did consider incorporating this into our testing protocol; however, we were concerned that it may limit a participant's ability to attend to exercise instruction, which we believed was a more critical aspect of this study. ...
Article
CONTEXT: The bodyweight squat exercise is a common component of treatment and prevention for patellofemoral pain; however, it can also place a high load on the patellofemoral joint. Restricting anterior motion of the knees relative to the toes during squatting appears to reduce patellofemoral loading. However, exercise professionals typically rely on verbal instructions to alter squat technique. OBJECTIVE: The purpose of this study was to evaluate the influence of verbal instructions regarding squat technique on patellofemoral joint loading. DESIGN: Cross-sectional study. SETTING: Motion analysis laboratory. PARTICIPANTS: Eleven uninjured females. PROTOCOL: Participants performed bodyweight squats before (baseline) and after receiving verbal instructions to limit anterior knee motion. Two different types of verbal instruction were used; one intended to promote an internal focus of attention and the other intended to promote an external focus of attention. Three-dimensional kinematics and kinetics were recorded using a multi-camera system and force plate. MAIN OUTCOME MEASURES: Sagittal plane patellofemoral joint forces and stress were estimated using a musculoskeletal model. RESULTS: Participants demonstrated a reduction in patellofemoral joint forces (35.4 N/kg vs. 31.3 N/kg; p=.008) and stress (10.7 MPa vs. 9.2 MPa; p=.002) after receiving instructions promoting an internal focus of attention, compared to their baseline trials. Participants also demonstrated a reduction in patellofemoral joint forces (35.4 N/kg vs. 32.3 N/kg; p=.03) and stress (10.7 MPa vs. 9.6 MPa; p=.04) after receiving instructions promoting an external focus of attention (vs. baseline). However, there were not significant differences in patellofemoral forces (p=.84) or stress (p=.41) for trials performed with an internal vs. external attentional focus. CONCLUSION: It appears that verbal instruction regarding knee position influences patellofemoral joint loading during squatting.
... This scoring system was based on the relationships between joint position, loading, and the risk of injury. For example, correct knee alignment over the toes helps to reduce shearing forces at the knee joint during squatting (24). Increased knee valgus has been identified as a risk factor for knee injury (60), including noncontact anterior cruciate ligament tears (2) and patellofemoral pain syndrome (60). ...
Article
O'Connor, S, McCaffrey, N, Whyte, EF, and Moran, KA. Can a standardized visual assessment of squatting technique and core stability predict injury? J Strength Cond Res XX(X): 000-000, 2019-This study examined whether a standardized visual assessment of squatting technique and core stability can predict injury. Male adolescent and collegiate Gaelic players (n = 627) were assessed using the alternative core/trunk stability push-up test and a developed scoring system for the overhead squat and single-leg squat (SLS) that examined both overall impression and segmental criteria. A single summative score from the overall impression scores of all 3 tests was calculated. Sustained injuries were examined over a season. Results indicated that the single summative score did not predict those that sustained a lower-extremity injury, trunk injury, or whole-body injury, and receiver operating characteristic curves were also unable to generate an optimal cutoff point for prediction. When segmental criteria were included in multivariate analyses, the tests were able to predict whole-body injury (p < 0.0001) and lower-extremity injury (p < 0.0001). However, although specificity was high (80.6%, 76.5%), sensitivity of the models was low (40.2%, 44.2%). The most common score was "good" for the overhead squat (46.4%) and SLS (47.6%), and "good" and "excellent" for the alternative core stability push-up test (33.5%, 49.1%), with "poor" core stability increasing the odds of sustaining a lower-extremity injury (odds ratio = 1.52 [0.92-2.51]). The findings suggest that although segmental scoring could be incorporated by strength and conditioning coaches and clinicians, they should be used predominantly as a preliminary screening tool to highlight players requiring a more thorough assessment.
... Patellar tendon force is lower at lower knee flexion angles when performing a squat from a horizontal and decline surface [60]. Reduce anterior knee translation by preventing knees to pass anterior to the toes Knee torque is reduced by 20% when preventing anterior knee translation during a barbell squat, but also increases hip and trunk torque 10-fold [61]. Patellofemoral stress is reduced at 90°knee flexion during a wall squat when the feet are further versus closer to the wall [56], and there is less patellofemoral joint stress when taking a larger step versus a shorter step when performing a forward lunge [62]. ...
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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.
... Previous studies have extensively examined the effects of load magnitudes, squat depths, and squat techniques on low-back and lower extremity loading to identify optimal training strategies and minimise injury risk (Hartmann et al., 2013). While greater loads and depths generally increase lower extremity joint moments and muscle activities (Bryanton et al., 2012;Cotter et al., 2013), greater trunk flexion could decrease knee moments but increase low-back and hip moments in back squats (Fry et al., 2003). ...
Article
The purpose was to quantify trunk and lower extremity biomechanics among back and front squats with a straight bar and four squats with different anterior-posterior load placements imposed by a transformer bar. Ten males and eight females performed six squat conditions: back and front squats with a straight bar, back and front squats with a transformer bar, and squats with more posteriorly or anteriorly placed loads with a transformer bar. A constant load of 70% of the participant’s one-repetition maximum in the straight-bar front squat was used. Kinematic and kinetic data were collected to quantify joint biomechanics at an estimated parallel squat position in the descending and ascending phases. Squats with more anteriorly placed load significantly decreased trunk flexion and pelvis anterior tilt angles with large effect sizes but increased low-back extension moments with medium to large effect sizes. Hip, knee, and ankle extension moments were generally similar among most conditions. Participants adjusted their trunk and pelvis to mediate the effects of load placements on low-back and lower extremity moments. While lower extremity loading was similar among different squats, the different trunk and pelvis angles and low-back moments should be taken into consideration for people with low-back impairment. KEYWORDS: Low back, hip, knee, squatting, load placement
... The squat is an exercise that indirectly improves the quality of life of sports and non-sports people by increasing the hip and knee extensor strength [8]. 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]. ...
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.
... the squat has been the subject of many biomechanical evaluations in the areas of kinetics, kinematics, and muscle recruitment and in various stance and load conditions [4]. the primary muscles involved in squats surround the hip and knee joints (e.g. quadriceps, gluteal muscles), which generate 80-90% of the lower extremity moments [2,[6][7][8]. in addition to stance and load variations, many training accessories exist for the squat that athletes and recreational exercisers use for enhancing training or preventing injury. ...
... 36 Interactively, restricting forward movement of the knees may minimize stress on the knees, and it is likely that forces are inappropriately transferred to the hips and low-back region. 37 Therefore, it is also necessary to strengthen psoas and gluteal muscle exercise after UKA to ensure the stability of the knee. Last but not the least, we have some thoughts about the overall design of this study. ...
Article
Few studies have assessed knee range of motion (ROM) and moments of patients with mobile-bearing unicompartmental knee arthroplasty (MB UKA) during active deep flexion activities. We analyze knee kinematic and kinetic parameters during postoperative squatting-standing activity, aiming to evaluate the efficacy of MB UKA and postoperative rehabilitation progress. This was a clinical cohort study. We followed up with 37 patients diagnosed with medial knee osteoarthritis (OA) with primary UKA. After screening 31 patients were recruited to take gait tests. Squatting-standing activities were performed under the test of 10-camera motion analysis system and force plates preoperatively at different stages after UKA (12, 18, and 24 months). The average duration of follow-up was 24.4 months (from 22.8 to 26.7 months). Hip-knee-ankle angle improved significantly compared with pre-UKA as well as scores of American Knee Society Score, numeric rating scale, ORS, and Western Ontario and McMasters. University Osteoarthritis Index. About 83.6% (31/37) of follow-up patients completed squatting-standing activity independently. At 1-year follow-up, peak varus angle (20.6 ± 2.8 degrees), internal rotation angle (13.6 ± 1.8 degrees), extensor moment (1.44 ± 0.04N*m/kg), and internal rotator moment (0.02 ± 0.005N*m/kg) of UKA knees were inferior to contralateral knees. Peak adductor moment (0.76 ± 0.05N*m/kg) was superior to contralateral knees. At 2-year follow-up, peak flexion angle (125.0 ± 2.8 degrees) showed a growing trend meanwhile extensor (1.70 ± 0.03N*m/kg) and adductor (0.68 ± 0.06 N*m/kg) moment closely resembled those of the contralateral knee. MB UKA could alleviate the affected knee mainly in flexion-extension ROM and moment meanwhile did not affect the biomechanical indicators of healthy limbs. OA knees in the early postoperative period showed decreased extensor moment and increased adductor moment during active deep flexion activity. Better ROM and relatively more natural extensor and adductor moment of UKA knee with rehabilitation time increasing may predict ideal rehabilitation outcome in the medium or longer term.
... Combined with knee kinematics changes (time to maximal flexion), such results suggest that expectations regarding a weight to lift trigger similar adaptations in patients experiencing mild cLBP and healthy individuals. Although no difference was noted in joint angles, probably due to high heterogeneity and relatively low loads, the current observations seems congruent with the broadly accepted idea that deeper knee flexion during squatting technique contributes to the unloading of hip and the back articulations [41]. Interestingly, minor differences were found in a few kinematic variables indicating that participants with LBP respond similarly, but not exactly as healthy individuals to load expectations. ...
Article
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Objective This study aimed to investigate how load expectations modulate neuromuscular and postural strategies in the anticipation of a freestyle lifting task with varying expected loads in individuals with and without chronic low back pain (cLBP). Methods Forty-seven participants, 28 with cLBP pain and 19 without, were recruited and completed a series of freestyle lifting trials (3 sets of box lifted for a total of 36 lifts). Verbal cues were used to modulate their expectations about the boxes’ weight: no expectation, lighter or heavier load expectations. Following each set, participants rated their perceived exertion on a visual analog scale. During the lifting protocol, kinematics (time to maximal flexion, angular velocity and joint angles), electromyography muscle activity (erector spinae and quadriceps) and center of pressure displacement were simultaneously recorded. Results Results showed that time to maximal knee flexion was modulated by load expectations in both groups (mean lighter load expectations = 1.15 ± 0.32 sec.; mean heavier load expectations = 1.06 ± 0.31 sec.). Results also showed a load expectations X group interaction for that time to maximal hip and lumbar flexion. Time to maximal hip flexion decreased with heavier load expectations (mean lighter load expectations = 1.20 ± 0.36; mean heavier load expectations = 1.16 ± 0.33) for cLBP only. Time to maximal lumbar flexion increased with heavier load expectation (mean lighter load expectations = 1.41 ± 0.27 sec.; mean lighter load expectations = 1.46 ± 0.29 sec.) for participants without LBP. However, no difference in lumbar, hip nor knee angles were observed between groups or conditions. Results highlighted significant load expectation effects for erector spinae electromyography activity, as lower muscle activations was observed for both groups with heavier load expectations (mean = 0.32 ± 0.15), compared to lighter load expectations (mean = 0.52 ± 0.27). Force plates analyses did not reveal any significant load expectation effects. Conclusion Present findings showed that load expectations modulate movement strategies and muscle activation similarly but not identically in individuals with chronic low back pain and healthy adults during freestyle lifting. Results of the present study partially differ from previous studies and suggest only minor differences in lifting strategies between healthy individuals and individuals with cLBP experiencing low level of pain and disability. More studies are needed to investigate the potential role of load expectations in the development and persistence of chronic low back pain.
... 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]. Various repetition and set schemes for the back squat may be implemented depending on the training goal, including submaximal and supramaximal training [9,19,20]. ...
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.
... Furthermore, there are front (Aspe and Swinton 2014;Clark et al., 2012;Contreras et al., 2016), back (Aspe and Swinton 2014;Clark et al., 2012;Gullett et al., 2009) and overhead squats (Gullett et al., 2009) with various bar positioning, which have been previously analyzed. In the squat exercise, several factors or conditions can influence the muscle activity, including the knee angle (Gryzlo et al., 1994), foot width McCaw and Melrose, 1999), rotation of the lower limbs Ninos et al., 1997;Signorile et al., 1995), or whether the knees going over the toes or not (Fry et al., 2003;Isear et al., 1997). In addition, the position of the center of gravity (COG) has been reported as a critical factor for electromyographic activity of lower extremity muscles (Kvist and Gillquist, 2001;Nishiwaki et al., 2006), although active control of the posture was not examined in these reports. ...
Article
The squat exercise is a fundamental movement in athletic training and rehabilitation. In this study, we measured muscle activities in a normal squat posture (NSP) and a squat posture with the center of foot pressure (COP) intentionally shifted forward as far as possible (FSP). Ten healthy men performed double-limb squats, adopting the NSP and FSP, with three knee flexion angles (30, 60, and 90 degrees). The muscle activities of the vastus medialis (VM), semitendinosus (ST), tibialis anterior (TA), and gastrocnemius muscle lateral head (GL) were measured using surface electromyography, and activity patterns were analyzed. Compared to that for the NSP, the COP was significantly shifted forward in the FSP by at least 30% of the foot length for all knee flexion angles (p < 0.05). At all knee flexion angles, VM muscle activity significantly decreased, while GL muscle activity increased, in the FSP compared to that for the NSP (p < 0.05). In addition, ST muscle activity increased significantly in the FSP compared to that for the NSP at knee flexion angles of 30 and 60 degrees (p < 0.05). TA muscle activity significantly decreased in the FSP compared to that for the NSP at only 90 degrees of knee flexion (p < 0.05). These results demonstrate that muscle activity patterns vary significantly according to squat posture. Thus, the active control of the COP position during the squat can be a new training approach in targeting specific muscle groups.
... Trained individuals produce higher peak ground reaction force (GRF) during the back-squat compared with other lower extremity exercises including the deadlift, lunge, and step-up (13). Because the kinematics of the back-squat are similar to activities of daily living and athletic performance (e.g., lifting objects from the ground), improving squat strength can improve quality of life by increasing maximal strength, thus reducing the relative force production requirement to accomplish a task (16). ...
Article
Choe, KH, Coburn, JW, Costa, PB, and Pamukoff, DN. Hip and knee kinetics during a back-squat and deadlift. J Strength Cond Res XX(X): 000-000, 2018-The back-squat and deadlift are performed to improve hip and knee extensor function. The purpose of this study was to compare lower extremity joint kinetics (peak net joint moments [NJMs] and positive joint work [PJW]) between the back-squat and deadlift. Twenty-eight resistance-trained subjects (17 men: 23.7 ± 4.3 years, 1.76 ± 0.09 m, 78.11 ± 10.91 kg; 11 women: 23.0 ± 1.9 years, 1.66 ± 0.06 m, 65.36 ± 7.84 kg) were recruited. One repetition maximum (1RM) testing and biomechanical analyses occurred on separate days. Three-dimensional biomechanics of the back-squat and deadlift were recorded at 70 and 85% 1RM for each exercise. The deadlift demonstrated larger hip extensor NJM than the back-squat {3.59 (95% confidence interval [CI]: 3.30-3.88) vs. 2.98 (95% CI: 2.72-3.23) Nm·kg, d = 0.81, p < 0.001}. However, the back-squat had a larger knee extensor NJM compared with the deadlift (2.14 [95% CI: 1.88-2.40] vs. 1.18 [95% CI: 0.99-1.37] Nm·kg, d = 1.44 p < 0.001). More knee PJW was performed during the back-squat compared with the deadlift (1.85 [95% CI: 1.60-2.09] vs. 0.46 [95% CI: 0.35-0.58] J·kg, d = 2.10, p < 0.001). However, there was more hip PJW during the deadlift compared with the back-squat (3.22 [95% CI: 2.97-3.47] vs. 2.37 [95% CI: 2.21-2.54] J·kg, d = 1.30, p < 0.001). Larger hip extensor NJM and PJW during the deadlift suggest that individuals targeting their hip extensors may yield greater benefit from the deadlift compared with the back-squat. However, larger knee extensor NJM and PJW during the back-squat suggest that individuals targeting their knee extensor muscles may benefit from incorporating the back-squat compared with the deadlift.
... The premise of maintaining a vertical shank is to decrease knee flexion because increased knee flexion leads to increased compressive and shear forces at the knee (10) as well as increased patella femoral joint force (24). Actively restricting forward knee travel has been shown to increase hip torque and may increase forces at the spine (12). It is important, in terms of reducing injury risk, to determine if and how the SSB alters squat mechanics, specifically trunk forward flexion, knee flexion, and forward translation. ...
Article
Hecker, KA, Carlson, LA, and Lawrence, MA. Effects of the safety squat bar on trunk and lower-body mechanics during a back squat. J Strength Cond Res XX(X): 000-000, 2018-The purpose of this study was to determine whether the safety squat bar (SSB) alters the mechanics and muscle activity of a back squat compared with a standard barbell (ST). Motion and muscle activation of the trunk and lower extremity were measured while 12 competitive powerlifters (8 males, 4 females, age 31.5 ± 6.3 years, body mass 88.1 ± 20.7 kg, competitive lifting experience 3.3 ± 2.8 years) squatted 3 sets of 5 repetitions at 75% of their 3 repetition maximum (3RM). Mean muscle activity and peak joint flexion angles were measured for the trunk and one lower extremity. A repeated-measures analysis of variance (p = 0.05) revealed an 11.3% decrease in 3RM when using the SSB. When using the SSB, there was a decrease in trunk and hip flexion (7.3 and 5.7° respectively) and a 50.3% increase in lower trapezius activation. However, using the SSB decreased activation of the rectus abdominis (46.3%), medial hamstring (17.1%), lateral hamstring (15.1%), vastus lateralis (9.3%), and medial gastrocnemius (18.8%). Squatting with the SSB resulted in a more upright trunk angle, which places less stress on the lower back, a commonly injured area when squatting. Decreases in lower-extremity muscle activation are likely due to the decreased load used, suggesting that the SSB may not be as effective as a standard bar to increase lower-extremity strength. However, the increase in the lower trapezius with the lighter load suggests that midback musculature may be challenged more by the SSB than a standard barbell.
... Previous studies suggest that joint kinetics and kinematics vary at differing loads [10][11][12] and/or positioning 13,14 during the performance of the back squat, an important exercise for strengthpower athletes. 15 In experienced squatters, hip contributions predominate at heavier loads in which fatigue is more likely to be present. ...
Article
Purpose:: To provide a joint level analysis of traditional (TS) and cluster (CS) set structure during the back squat exercise. Methods:: Eight men (24±3 y; 177.3±7.9 cm; 82.7±11.0 kg; 11.9±3.5 %bodyfat; 150.3±23.0 kg one-repetition maximum [1RM]) performed the back squat exercise (80%1RM) using TS (4 x 6, 2 min inter-set rest) and CS (4 x [2 x 3], 30-sec intra-set rest, 90-sec inter-set rest), randomly. Lower limb kinematics were collected by motion capture as well as kinetic data via bilateral force platforms. Results:: CS attenuated the loss in mean power (TS, -21.6±3.9%; CS, -12.4±7.5%; p = 0.042), though no differences in gross movement pattern (sagittal plane joint angles) within and between conditions were observed (p≥0.05). However, joint power produced at the hip increased from REP 1 through REP 6 during TS, while a decrease was noted at the knee. A similar pattern was observed in the CS condition, but limited to the hip. Joint power produced at the hip increased from REP 1 through REP 3, but returned to REP 1 values before a similar increase through REP 6, resulting in differences between conditions (REP 4, p = 0.018; REP 5, p = 0.022). Conclusions:: Sagittal plane joint angles did not change in either condition, though CS elicited greater power. Differing joint power contributions (hip and knee) suggest potential central mechanism that may contribute to enhanced power output during CS and warrant further study. Practitioners should consider incorporating CS into training to promote greater power adaptations and mitigate fatigue.
... 25 NJT and flexions of the lower extremity joints were selected as the dependent variables because both have been key variables in previous squat studies. 1,7,15,16 The ASISs for dynamic trials were calculated using the rigid body method. 26 The hip joint center was located using the Tylkowski eAndriacchi hybrid method 27 and the joint between the fourth and fifth lumbar vertebrae (L4/5) was located using the MacKinnon method. ...
Article
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Background/objective There is a lack of information about relationship between physical characteristics and biomechanics of the lower extremity during the squat. Additionally, studies did not examine sex-related differences. The purpose of this study was to investigate relationships between physical characteristics and biomechanics of the lower extremity during the squat, and to determine if any sex differences are present. Methods Fifty three participants recruited (21.82 ± 2.3 years; 75.56 ± 14.98 kg; 171.57 ± 8.38 cm) performed three squats with 75% of one repetition maximum. Femur to tibia length ratio, hip and ankle joints’ flexibilities, and relative muscular strength were measured and used as physical characteristics. Net joint torques (NJT) and flexion angles of the lower extremity were extracted as dependent variables. Multiple regression (stepwise) analysis was conducted to examine the relationships with physical characteristics being factors. Pearson correlation coefficients were calculated to determine intercorrelations among the dependent variables. Results Relative muscular strength was related to hip NJT and knee flexion angle, and hip flexibility was related to ankle dorsiflexion. Hip and knee NJT showed moderate correlations with the corresponding flexion angles (r = .48-.53; p < .01). Ankle dorsiflexion angle showed weak to moderate correlations with hip NJT and hip flexion angle (r = -.36-.50; p <.01) and a moderate correlation with knee NJT. No significant sex difference was observed (r = .52; p < .05). Conclusion Biomechanics of the lower extremity has been shown to correlate more with relative muscular strength and joint flexibility than with leg length ratio.
... Characteristics of movement behavior associated with higher knee extensor moments (or quadriceps muscle activity) during athletic tasks include an upright trunk [21][22][23] and forward displacement of the tibia (knee pass the toe). [23][24][25][26] In a previous publication, our group reported that the relative orientation of the trunk and tibia in the sagittal plane could be used to estimate the average HKR during various squat conditions. 27 More specifically, the difference between the sagittal plane trunk and tibia inclination at peak knee flexion explained 70% of the variance in the average HKR during the lowering phase of the squat. ...
Article
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Given that increased use of the knee extensors relative to the hip extensors may contribute to various knee injuries, there is a need for a practical method to characterize movement behavior indicative of how individuals utilize the hip and knee extensors during dynamic tasks. The purpose of the current study was to determine whether the difference between sagittal plane trunk and tibia orientations obtained from 2D video (2D trunk–tibia) could be used to predict the average hip/knee extensor moment ratio during athletic movements. Thirty-nine healthy athletes (15 males and 24 females) performed 6 tasks (step down, drop jump, lateral shuffle, deceleration, triple hop, and side-step-cut). Lower-extremity kinetics (3D) and sagittal plane video (2D) were collected simultaneously. Linear regression analysis was performed to determine if the 2D trunk–tibia angle at peak knee flexion predicted the average hip/knee extensor moment ratio during the deceleration phase of each task. For each task, an increase in the 2D trunk–tibia angle predicted an increase in the average hip/knee extensor moment ratio when adjusted for body mass (all P < .013, R ² = .17–.77). The 2D trunk–tibia angle represents a practical method to characterize movement behavior that is indicative of how individuals utilize the hip and knee extensors during dynamic tasks.
... Correct technical performance is crucial to getting the benefits of squatting (Schoenfeld et al., 2010;Yavuz & Edgar, 2017). On the contrary, deviations are associated with the risk of overloading and accidents (Fry et al. 2003, Hartmann & Wirth, 2014. The entire movement must be controlled. ...
Article
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PURPOSE Squats are among the basic exercises that have become an integral part of exercise programs. It is commonly used by athletes in many sports. Its potential is shown in the development of strength, power, and overall sports performance. The aim of the study was to verify inconsistent views on deep squats, technical design, and related health risks. METHODS For the purposes of the review, the terms "squat, knee, biomechanics, deep, patellofemoral, back squat, performance, arthritis, health, injury, risk" were used. RESULTS It turns out that the technique of performing a deep squat has its strict principles, which must be respected and which have a significant impact on the benefits and risks. From loading, the lower position represents an increase in compressive and shear forces on the patellofemoral joint, however, this is a natural state that is not risky. Health hazards cannot be based on analytical-mathematical models, which are insufficient in this aspect. Extreme long-term exposure carries the risk of permanent consequences in the form of osteoarthritis. For prophylaxis or convalescence, it is possible to use effective aids like sleeves, kinesio taping, bandage or "knee savers". CONCLUSIONS With optimal technique and sensible exercise selection, there is no greater risk in healthy individuals without degenerative anatomical changes. In order to assess the effects of the squat forces on the ankle, knee, hip, spine, it is necessary to consider the technique and also individual anatomical differences.
... One of the more challenging tasks in interpreting the present results is deducing whether the observed decrease in KWI is enough of a decline to pose an increased risk of injury. It is well established in the literature that excessive medial knee collapse is associated with increased knee dysfunction and pain (Escamilla, 2001;Fry, Smith, & Schilling, 2003;Kritz et al., 2009). If left uncorrected, individuals are at a heightened risk of developing patellofemoral syndrome (Hollman et al., 2014;Kritz et al., 2009), ACL tears (Hewett et al., 2005) and degeneration of the meniscus . ...
Article
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This study examined the influence of the Theraband TM CLX gold band on lower-limb muscle activity and kinematics during an overhead barbell squat. Participants performed two sets (band and no-band) of 12 repetitions of overhead barbell squats at 25% bodyweight. Three-dimensional kinematics were measured using motion capture with rigid bodies placed bilaterally on the foot, shank, thigh and thorax. Electromyography was collected from seven, bilateral muscles of the lower-limb and was unchanged for all muscles between conditions. Medial knee collapse was calculated using a knee-width index (KWI) ratio of the distance between the lateral epicondyles of the femur and the lateral malleoli. Average KWI was smaller during the band condition for the concentric (No band: 0.99 ± 0.05, Band: 0.97 ± 0.06, p < 0.05) and eccentric phases (No band: 1.00 ± 0.06, Band: 0.97 ± 0.05, p < 0.05). KWI was significantly smaller with the use of the Theraband TM CLX. As the gold band is the strongest of the CLX offerings, any benefit of increased proprioception may have been lost due to the high resistance of the band. Further research examining the dose-response of elastic band resistance to knee alignment may be needed to inform proper exercise prescription.
... Therefore, incorrect head movements can cause incorrect body compensation, resulting in injury [2,7,8]. Changes in the gaze direction and head position can affect the spine kinematics [1]; there have been many discussions on the expected effect and safety of squat exercise. ...
... It was found that the total squat score for the younger group was significantly higher than the middle and the older groups, but we surprisingly found that there was no difference between the middle and older aged participants. Squat performance has been studied between the younger and the older population, and squat is known as an appropriate rehabilitation exercise for post-ligament reconstruction surgery (44,45). To the best of our knowledge, this is the first time that squat exercise has been studied among younger, middle-aged, and older populations in Japan. ...
Article
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COVID-19 has changed our lives and limited our ability to have adequate physical activity (PA). It is necessary to replace outdoor PA with home-based fitness. However, people lack access, skills, and even motivation for home-based fitness. To address these issues, we designed a free access self-monitoring and coaching and music-based interactive online squat fitness system. Body weight squat was utilized for fitness exercise and evaluated based on three indices: knee width, hip depth, and rhythm. An online survey on changes in exercise due to the COVID-19 pandemic and exercise habits was conducted to investigate the effect of the COVID-19 pandemic on PA. We collected data from 557 respondents 5 months after the system first released and analyzed 200 visitors' performance on squat exercise and the other relevant parameters. Visitors were divided into three groups according to their age: younger, middle, and older groups. Results showed that the younger group had better squat performance than the middle and older groups in terms of hip depth and rhythm. We highlighted the lessons learned about the system design, fitness performance evaluation, and social aspects, for future study of the design and development of similar home-based fitness systems. We provided first-hand results on the relation between the COVID-19 pandemic and physical exercise among different age groups in Japan, which was valuable for policy making in the post-COVID-19 era.
... The average hip extension in the second section remained the same as in the first section, while the flexion value increased. It may be concluded that only the hip may not be held responsible for the shifting of the weight distribution, which is contrary to some studies [27,31,32]. The ROM of the ankle significantly increased by 10% compared to the first section. ...
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Citation: Erman, B.; Ozkol, M.Z.; Ivanović, J.; Arslan, H.;Ćosić, M.; Yuzbasioglu, Y.; Dopsaj, M.; Aksit, T. The purpose of this study was to analyse in detail body weight squat (BWS)’ fatigue effect on the range of motions (ROM) of the hip, knee, ankle and ground reaction forces (GRF). Twenty male recreational athletes (24.0 ± 3.1 years, 178.85 ± 7.12 cm and 78.7 ± 11.45 kg) participated in this study. BWS were performed on four load cell platforms until the participants failed to continue. Participants performed 73 ± 27 repetitions and the duration to complete of the repetitions was 140.72 ± 62.28 s during the BWS exercise. The forefoot and hindfoot of the feet were on two load cells, thus, there were two under each foot. All of the data collected was divided into three sections for analysis (24 ± 9 repetitions for each). In terms of GRF of the fore feet and hind feet, significant differences and medium to large effect size were found between each section (p = 0.006~0.040, ES = 0.693~0.492). No significant differences were found between right and left leg in all sections. Significant differences were found in the ROM of the hip between the sections of first-third (p = 0.044, ES = 0.482) and second-third (p = 0.034, ES = 0.510), the ROM of the knee first-third (p = 0.014, ES = 0.602) and second-third (p = 0.005, ES = 0.701) and for the ROM of the ankle first-second (p = 0.045, ES = 0.479). As a result, end-of-exercise fatigue caused an increase in the ROM of the hip, knee and ankle. Thus, it is observed that fatigue induced increased ROM, also increases the GRF towards the forefeet.
... Sitting, lifting, and other movements and postures similar to the squat are often used in daily life, and as such, the squat is often used as an exercise to improve activities of daily living. It has been reported that the squatting strategy differs between the lower back pain group and the non-lower back pain group 10) , and it is known that the load on the lumbar region varies with the squatting strategy 11,12) . During the downward phase of the squat, the extensors of the lower extremities perform eccentric contractions, and during the upward phase, the extensors of the lower extremities perform concentric contractions to control the vertical movement of the center of gravity. ...
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[Purpose] This study aimed to investigate the relationships among the changes in iliopsoas muscle thickness, hip angle, and lower limb joint moment during squatting in different pelvic positions to help in performing hip-dominant squatting exercises. [Participants and Methods] The participants were seven healthy adult males. The measurement task consisted of squatting with 60 degrees of knee flexion in three positions: the anterior, neutral, and posterior pelvic tilt positions. The iliopsoas muscle thickness was measured in the center of the inguinal region using ultrasonography. A three-dimensional motion analysis system was used to measure the joint angles and joint moments. [Results] There were no significant differences in pelvic angles between the pelvic positions. The hip angle differences were significantly higher in the anterior and neutral pelvic tilt positions compared to those in the posterior tilt position. Only the anterior pelvic tilt position had a significantly positive correlation with iliopsoas muscle thickness and hip angle differences. [Conclusion] Squatting in the neutral or posterior pelvic tilt position was not associated with hip angle and iliopsoas muscle thickness changes, whereas squatting in an anterior pelvic tilt position was associated with changes in the iliopsoas muscle thickness and hip flexion angle. Our findings suggest that activation of the iliopsoas muscle might be necessary to promote hip-dominant squatting.
... Biomechanical analysis offers insight to the underlying kinematics and kinetics of a training exercise, providing coaches and athletes conceptual understanding to bring objectivity to sport-specific exercise selection [16]. Investigating the musculoskeletal demand placed on the lower limb and pelvic-trunk joints is fundamental to biomechanical analyses of strength training exercises [17][18][19][20][21][22], although has yet to be undertaken for the hip thrust. Specifically, for the hip joint, whilst authors have proposed that the hip thrust requires a consistent hip extension moment and greater muscular "tension" when hip joint is close to full extension [4,5,7,8], there is currently no joint kinetic evidence to support these ideas. ...
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Barbell hip thrust exercises have risen in popularity within the biomechanics and strength and conditioning literature over recent years, as a method of developing the hip extensor musculature. Biomechanical analysis of the hip thrust beyond electromyography is yet to be conducted. The aim of this study was therefore to perform the first comprehensive biomechanical analysis the barbell hip thrust. Nineteen resistance trained males performed three repetitions of the barbell hip thrust at 70% one-repetition maximum. Kinematic (250 Hz) and kinetic (1000 Hz) data were used to calculate angle, angular velocity, moment and power data at the ankle, knee, hip and pelvic-trunk joint during the lifting phase. Results highlighted that the hip thrust elicits significantly ( p < 0.05) greater bilateral extensor demand at the hip joint in comparison with the knee and pelvic-trunk joints, whilst ankle joint kinetics were found to be negligible. Against contemporary belief, hip extensor moments were not found to be consistent throughout the repetition and instead diminished throughout the lifting phase. The current study provides unique insight to joint kinematics and kinetics of the barbell hip thrust, based on a novel approach, that offers a robust evidence base for practitioners to guide exercise selection.
... These strategies are associated with changes in joint moments between the knee and the hip joint. For example, during the barbell back squat and landing tasks, a smaller trunk flexion will lead to an increase in the internal knee extension moment [32] which will likely be accompanied by an increase in quadriceps activation [33]. Future studies should investigate the effect of these different sagittal plane strategies during the single-leg squat on hip and knee loads in the frontal and transverse planes. ...
Article
Background Limited passive ankle dorsiflexion range has been associated with increased knee valgus during functional tasks. Increased knee valgus is considered a contributing factor for musculoskeletal disorders in the lower limb. There is conflicting evidence supporting this association. The extent of passive ankle dorsiflexion range is associated with dynamic ankle dorsiflexion range and the way how these variables are related to lower limb or trunk kinematics is unclear. Research question What is the association between passive ankle dorsiflexion range or dynamic ankle dorsiflexion range with shank, thigh, pelvis or trunk movements during the single-leg squat? Methods This is a cross-sectional study with a convenience sample. Thirty uninjured participants performed the single-leg squat with their dominant limb. Ankle, shank, thigh, pelvis and trunk 3D kinematics were recorded. Passive ankle dorsiflexion range was assessed through the weight-bearing lunge test and the dynamic ankle dorsiflexion range was defined as the ankle dorsiflexion range of motion in the sagittal plane during the single-leg squat. Results Greater passive ankle dorsiflexion range was associated with smaller thigh internal rotation (r= -.38). Greater dynamic ankle dorsiflexion range was associated with smaller trunk flexion (r = .59) and pelvis anteversion (r= -.47). Passive ankle dorsiflexion range and dynamic ankle dorsiflexion range were not associated. Significance Greater passive ankle dorsiflexion range seems to be associated with a better lower limb alignment during the single-leg squat, while dynamic ankle dorsiflexion range seems to reflect different lower limb and trunk kinematic strategies.
... This is congruent with the nature of the movement and the imposed tempo. Compared to the low-bar squat, the back squat places a greater demand on quadriceps muscles due to a more upright trunk position [81][82][83]. The tempo required participants to control the eccentric phase and pause in a deep squat position. ...
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Background: Self-administered massage interventions with a roller massager are commonly used as part of warm-ups and post-workout recovery routines. There is yet no clear consensus regarding the practical guidelines for efficient embedded interventions. Objectives: The present randomized crossover pilot trial aimed at examining the effects of a rolling intervention with a roller massager embedded within the rests periods of a resistance training protocol. The rolling intervention targeted quadriceps muscles. Setting: Participants (n = 14) performed two resistance training protocols expected to elicit momentary muscle failure. The protocol consisted in 10 sets of 10 rest-pause repetitions of back squats, with a poundage set up at 50% of the maximal one-repetition. Two min were allocated to recovery between sets. During the recovery periods, participants completed a rolling routine with a roller massager for 60 s (Roller-massager), or underwent passive recovery (Control). The total workload, concentric power, thigh circumference rate of perceived exertion (RPE) and delayed onset of muscle soreness (DOMS) from 24 h to 120 h after completion of the protocol were the dependent variables. Results: Roller-massager was associated with a reduction in total workload (-11.6%), concentric power (-5.1%) and an increase in perceived exertion compared to Control (p < 0.05). Roller-massager was also associated with reduced thigh circumference after the resistance training protocol, indicating reduced muscle swelling, and reduced DOMS 24 h to 120 h post-workout (p < 0.001). Conclusion: These findings support that embedded rolling with a roller massager hinders performance and increases effort perception. Embedded interventions may not be suitable during conditioning periods designed to maximize training intensity.
... Previously, limitations in ankle DF-ROM of approximately 12° have been shown to inhibit full knee flexion from being accessed during squatting (7,25). As knee flexion is a primary contributor to lowering the athlete's center of mass (38), other joints must compensate within the kinetic chain to allow for the task to be successfully completed (1,15). Consequently, increased peak knee valgus angle (2,27) and altered spinal alignment (23) have been identified during squatting where diminished ankle DF-ROM was present. ...
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The purpose of this study was to investigate the effect of unilateral restrictions in ankle dorsiflexion range of motion (DF-ROM) on inter-limb vertical ground reaction forces (vGRF) asymmetries. Twenty healthy and physically active volunteers (age 23 ± 3 years; height 1.72 ± 0.1m; mass 74.9 ± 20.3 kg) performed three barefoot bodyweight squats (control condition) and with a 10º custom built forefoot wedge under the right foot to artificially imitate ankle DF-ROM restriction (wedge condition). Force data was used to calculate the mean asymmetry index score for the upper descent phase (UDP), lower descent phase (LDP), lower ascent phase (LAP) and upper ascent phase (UAP) during the bilateral squat. Significant differences were found for comparisons for each phase between conditions, with effect sizes ranging between 0.7–1.1. Asymmetry index scores indicated that for all phases, the unrestricted limb in the wedge condition produced greater vGRF. Therefore, inter-limb differences in ankle DF-ROM can cause inter-limb asymmetries in vGRF during bilateral squatting. As such, athletes with asymmetrical squat mechanics should be screened for inter-limb differences in ankle DF-ROM to ascertain whether it is a contributing factor.
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The purpose of this study was to investigate the consciousness among young people (n = 1016) on training body part(s), using a questionnaire-based survey showing participants a picture of a single-joint exercise. The participants were shown a picture of knee-extension exercise (KNEE-EXT), and were asked to identify the body part(s) they felt were being trained. On seeing the picture, more than 90% of the participants felt that KNEE-EXT can train the anterior thigh part. However, more than 90% of the participants who had no experience doing KNEE-EXT felt that the exercise trained not only the anterior thigh part but also other parts, including the trunk, the posterior thigh, and the upper limb. Among those participants who had performed KNEE-EXT without the experience of strength-training under professional supervision, approximately 80% felt that the exercise was appropriate to train not only the anterior thigh but also other parts. These results suggest that performing exercises by referring to only a picture may result in the individuals not properly understanding how the body part(s) should be trained during exercise, even in single-joint exercises. Appropriate supervision is of even greater importance especially for strength-training beginners. Furthermore, even among participants who had an experience of exercise under professional supervision, approximately 60% had a similar response. Therefore, to enhance the benefits of exercises, individuals (even those who have had experience in training under professional supervision) should always be instructed under appropriate supervision on the correct technique and knowledge about the exercises.
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Current literature supports the benefits of nonoperative conservative treatment with physical therapy along with activity modification for femoroacetabular impingement. Despite this fact, there is a gap in the literature detailing appropriate physical therapy management of this injury. The goal of this article is to present conservative physical therapy treatment options for femoroacetabular impingement. Improving joint mobility through posterior and lateral joint glide of the femur, strengthening the surrounding hip musculature, and re-educating functional movement to limit excessive adduction/internal rotation during hip flexion can be helpful for decreasing symptoms and allowing patients to return to their prior level of function.
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Background: Joint replacement surgery is procedure that has increasingly been performed intending to improve quality of life for the population living with orthopedic condition. In the joints of the lower limb, the knee joint is mostly replaced and next is the hip joint. Recently the hip joint replacement is commonly replacing with internal prosthesis in elderly individuals, to prevent the complications. Now a day’s THR Is the most common surgery in the general population. According to previous rehabilitation program of THR, ambulation starts 6 th or 7 th day of surgery, which could not able to prevent the post- operative complications such as pulmonary embolism, urinary retention, blood clotting, DVT after THR. For reducing the post-operative complications and to improve the functional activity and QOL, we will ambulate the patients on 3 rd post-operative day. Methodology: 32 subjects with the unilateral THR were taking for the study and divided into two groups. Group 1 were ambulating within the 3rd day of the surgery and Group 2 was ambulating on 7th day of surgery. Pain was measured with VAS, ROM is measured from goniometer and QOL is measured with the WOMAC score. Results: Results of the early ambulation on 3rd day is showing the significant improvement (p< 0.05) of postoperative pain and QOL of the unilateral THR subjects. Conclusion: On the basis of above study we concluded that early ambulation within 3rd day of surgery will make difference in QOL and functional stability following unilateral THR subjects.
Article
BACKGROUND: Comparison of knee loads on a Smith machine, which utilised in for maintenance of health and rehabilitation, has not been attempted. OBJECTIVE: This study compared lower limb muscle and knee joint forces during front and back squats performed on a Smith Machine. METHODS: Eleven participants performed front and back squats with loads at 40%, 60% and 80% of their back squat 1-RMs. Ground reaction forces and three-dimensional full body motion were collected and used for modelling lower limb muscle and knee joint forces. RESULTS: Larger loads increased tibiofemoral compressive force during back squat at 80% compared to 40% (p< 0.01; d= 1.58) and to 60% (p< 0.01; d= 1.37). Patellofemoral compressive (p= 0.96) and tibiofemoral shear forces (p= 0.55) were not influenced by external load or type of squat. Gluteus medius and minimus produced more force at 80% compared to 60% (p= 0.01; d= 1.10) and to 40% (p< 0.01; d= 1.87) without differences for other muscles (p= 0.09–0.91). CONCLUSIONS: Greater external load was associated with increase in gluteus medius and minimus force and with increased tibiofemoral compressive force without effects on tibiofemoral shear force, patellofemoral compressive force or other lower limb muscle forces.
Chapter
In this paper, we explore the use of numerical optimization techniques to synthesize realistic human-like squat motions. For this purpose, a two-step optimization-based synthesis scheme, inspired by whole-body controllers from robotics, is proposed. In step I, a reduced set of physically-relevant criteria is optimized to produce the state and torque patterns with a joint-actuated model. Afterwards, muscle activities are computed in step II with a muscle-actuated model. To validate the approach, the synthesized kinetic and muscle activities of two squat strategies obtained through the scheme are analyzed and compared to captured movement and electromyographic data. The outcome shows that it is feasible to synthesize human-like squats without motion capture data while exhibiting several main features of the motor function strategies. However, disparities related to the simple modeling of the actuators are observed.
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The squat is considered the most popular exercise for strengthening the lower limbs as well as being widely used for muscle sport training and competition. An individual’s development of a squat supports key aspects of daily activity as well as being a fundamental exercise used in strength and conditioning to improve both strength and power. Muscle sports such as powerlifting and weightlifting are heavily dependent on both strength and force – their assessment can be used for training interventions, talent identification and competition. The aim of this study is to compare maximal strength (1RM) and peak force at maximal lift variables at different declining squat angle protocols in resistance trained individuals. It is hypothesised that maximal strength and peak force at maximal lift will increase when squats are performed at a declining angle. Seven participants (age 30.4 ± 8.9 years, height 1.8 ± 0.1 m, weight 85.3 ± 6.8 kg) performed 1RM testing at each declining surface variable (0°, 5°, 10° and 15°) – data was collected for both maximal strength (kg) and peak force at maximal lift (N). There was no significance in data for both maximal strength (F(3) = 1.167, p = 0.35, h2 = 0.163) and peak force at maximal lift (F(1.705) = 0.0179, p = 0.806, h2 = 0.029) between conditions. Although no main effect was observed, post hoc calculations for the comparative analysis of effect size (Cohen’s d) was made. A moderate effect size was observed when comparing maximal strength data at 0° (flat) vs. 5° (0.69) and 5° vs. 10° (0.48). Despite this study suffering from being underpowered (35% of the suggested sample size), contemporary studies have suggested that whilst data may not be statistically significant (p-value), moderate-to-large effect size (Cohen’s d) calculations provide an alternative representation for the magnitude of data. This study serves as one of the first comprehensive explorations into the effects of declining squat protocols on athletic performance. Future research should focus on improving statistical significance of the data through meeting estimated sample size calculations (20 participants). Keywords: squat • maximal strength • peak force • decline • performance
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Pain and injuries are considered a common problem among elite athletes and recreational lifters performing the squat, bench press and deadlift. Since all three lifts engage multiple joints and expose the lifters’ bodies to high physical demands often several times a week, it has been suggested that their injuries might be related to the excessively heavy loads, the large range of motion during the exercises, insufficient resting times between training sessions and/or faulty lifting technique. However, no previous article has summarised what is known about specific injuries and the injury aetiology associated with the three lifts. Thus, the aim of this narrative review was to summarise what is known about the relationships between the powerlifting exercises and the specific injuries or movement impairments that are common among lifters and recreationally active individuals.
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Evaluation of the compressive load acting on the lumbar spine (L3-L4) during half-squat exercises executed with a barbell resting on the subject's shoulders was undertaken. The kinematics of the upper body segments of two male and two female subjects as well as the barbell were described using data obtained by means of an optoelectronic system (CoSTEL). L3-L4 compressive load was calculated using a model of the anatomy of the trunk musculoskeletal system. Filtered surface electromyographic trunk flexor recordings from the obliquus externus and rectus abdominis and trunk extensor erectores spinae muscles as well as measurement of the ground reaction forces were also carried out for predicted result validation. During half-squat exercises with barbell loads in the range 0.8 to 1.6 times body weight the compressive loads on the L3-L4 segment vary between 6 and 10 times body weight. Erectores spinae contraction force was predicted to be between 30 and 50% of the relevant maximal isometric force. The magnitude of trunk flexion was found to be the variable which influenced most spinal compression load.
Article
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 determine whether regression equations could be developed, as an alternative to biochemical models, to predict the peak L4(L5 disc compression force during dynamic, sagittal plane lifting. Eighteen male subjects performed a squat and a stoop lift with loads of 6, 14, 22, 29, and 32 kg. Each lift was analysed with a linked segment biomechanical model that output the compression force time history during the lift. The peak compression served as the dependent variable for two regression models. The independent variables in each model were measures which described the subject's body dimensions, body posture, internal lifting mechanics, load location and load effects. A ‘lab’ model was developed (R=0·93) which required only four inputs and had an RMS error of only 8·3% between the biomechanical model estimate of the peak L4/L5 disc compression force and that predicted from the regression equation. A seven variable ‘field’ model was developed with an R of 0·90 and an RMS error of 9·7%. It was concluded that both of the proposed models were potentially useful to the practising ergonomist interested in easily and quickly estimating lumbar compression forces during dynamic sagittal plane lifting.
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The purpose of this study was to formulate a kinematic model of performance in the parallel squat, based on the movement characteristics of world class powerlifters, and to determine if the model could be utilized to assess technique differences between high and less-skilled subjects. Two trials were recorded via high-speed cinematography from a side view of twenty-four Ss during the 1974 U.S. Senior National A.A.U. Powerlifting Championships. Vertical and horizontal displacement patterns of three joint centers and the center of the bar were determined for the best trial of each S. These data were subsequently used to calculate desired linear and angular coordinates, velocities and accelerations for body segments and bar. Results indicated that although there was some variability in most kinematic parameters, vertical bar velocity was found to be very similar among competitors, even for Ss of different bodyweight. Consequently, the vertical velocity of the bar was selected as the parameter around which performance could be modeled in the parallel squat. A model was formulated by plotting the mean values in vertical bar velocity for all Ss scaled to a common time base. The resultant model was contrasted with vertical bar velocity data for less-skilled Ss to assess typical performance errors. (C)1977The American College of Sports Medicine
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This study investigated the muscular torques and joint forces during the parallel squat as performed by weightlifters. (JD)
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The purpose of this study was to formulate a kinematic model of performance in the parallel squat, based on the movement characteristics of world class powerlifters, and to determine if the model could be utilized to assess technique differences between high and less-skilled subjects. Two trials were recorded via high-speed cinematography from a side view of twenty-four Ss during the 1974 U.S. Senior National A.A.U. Powerlifting Championships. Vertical and horizontal displacement patterns of three joint centers and the center of the bar were determined for the best trial of each S. These data were subsequently used to calculate desired linear and angular coordinates, velocities and accelerations for body segments and bar. Results indicated that although there was some variability in most kinematic parameters, vertical bar velocity was found to be very similar among competitors, even for Ss of different bodyweight. Consequently, the vertical velocity of the bar was selected as the parameter around which performance could be modeled in the parallel squat. A model was formulated by plotting the mean values in vertical bar velocity for all Ss scaled to a common time base. The resultant model was contrasted with vertical bar velocity data for less-skilled Ss to assess typical performance errors.
Article
The structural properties of 27 pairs of human cadaver knees were evaluated. Specimens were equally divided into three groups of nine pairs each based on age: younger (22 to 35 years), middle (40 to 50 years), and older (60 to 97 years). Anterior-posterior displacement tests with the intact knee at 30 degrees and 90 degrees of flexion revealed a significant effect of knee flexion angle, but not of specimen age. Tensile tests of the femur-ACL-tibia complex were performed at 30 degrees of knee flexion with the ACL aligned vertically along the direction of applied tensile load. One knee from each pair was oriented anatomically (anatomical orientation), and the contralateral knee was oriented with the tibia aligned vertically (tibial orientation). Structural properties of the femur-ACL-tibia complex, as represented by the linear stiffness, ultimate load, and energy absorbed, were found to decrease significantly with specimen age and were also found to have higher values in specimens tested in the anatomical orientation. In the younger specimens, linear stiffness (242 +/- 28 N/mm) and ultimate load (2160 +/- 157 N) values found when the femur-ACL-tibia complex was tested in the anatomical orientation were higher than those reported previously in the literature. These values provide new baseline data for the design and selection of grafts for ACL replacement in an attempt to reproduce normal knee kinematics.
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The purpose of this study was to compare the knee extensor demands and low back injury risks of the front and back squat exercises. Highly strength-trained college-aged males (n = 8), who performed each type of squat (Load = 75% of front squat one repetition maximum), were filmed (50 fps) from the sagittal view. The body was modeled as a five link system. Film data were digitized and reduced through Newtonian mechanics to obtain joint forces and muscle moments. Mean and individual subject data results were examined. The maximum knee extensor moment comparison indicated similar knee extensor demands, so either squat exercise could be used to develop knee extensor strength. Both exercises had similar low back injury risks for four subjects, but sizable maximum trunk extensor moment and maximum lumbar compressive and shear force differences existed between the squat types for the other subjects. The latter data revealed that with the influence of trunk inclination either exercise had the greatest low back injury risk (i.e., with greater trunk inclination: greater trunk extensor demands and lumbar shear forces, but smaller lumbar compressive forces). For these four subjects low back injury risk was influenced more by trunk inclination than squat exercise type.
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Past studies have produced conflicting results as to the effect of squat exercises on knee stability. One hundred male and female college students were measured using a knee ligament arthrometer on nine tests of knee stability. Over an 8-wk training program, full or half squats did not consistently affect knee stability compared to non-squatting controls. To measure the effect of long-term squat training 27 male powerlifters (14 Elite or Master Class) and 28 male weightlifters (8 Elite or Master Class) were measured on the same tests. Powerlifters were significantly tighter than controls on the anterior drawer at 90 degrees of knee flexion. Both powerlifters and weightlifters were significantly tighter than controls on the quadriceps active drawer at 90 degrees of knee flexion. Data on powerlifters and weightlifters were also analyzed by years of experience and skill level. No effect of squat training on knee stability was demonstrated in any of the groups tested.
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Virtually all types of collagenous tissues have been transferred in and around the knee joint for intra-articular and extra-articular ligament reconstructions. However, the mechanical properties (in particular, strength) of such grafts have not been determined in tissues from young adult donors, where age and disuse-related effects have been excluded. To provide this information, we subjected ligament graft tissues to high-strain-rate failure tests to determine their strength and elongation properties. The results were compared with the mechanical properties of anterior cruciate ligaments from a similar young-adult donor population. The study indicated that some graft tissues used in ligament reconstructions are markedly weak and therefore are at risk for elongation and failure at low forces. Grafts utilizing prepatellar retinacular tissues (as in certain anterior-cruciate reconstructions) and others in which a somewhat narrow width of fascia lata or distal iliotibial tract is utilized are included in this at-risk group. Wider grafts from the iliotibial tract or fascia lata would of course proportionally increase ultimate strength. The semitendinosus and gracilis tendons are stronger, having 70 and 49 per cent, respectively, of the initial strength of anterior cruciate ligaments. The bone-patellar tendon-bone graft (fourteen to fifteen millimeters wide, medial or central portion) was the strongest, with a mean strength of 159 to 168 per cent of that of anterior cruciate ligaments. Patellar tendon-bone units, based on grip-to-grip motions, were found to be three to four times stiffer than similarly gripped anterior cruciate ligaments, while gracilis and semitendinosus tendon preparations had values that were nearly identical to those of anterior cruciate ligaments.(ABSTRACT TRUNCATED AT 250 WORDS)
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
The purpose of this study was to quantify the amount of anterior tibial displacement occurring in anterior cruciate ligament-deficient knees during two types of rehabilitation exercises: 1) resisted knee extension, an open kinetic chain exercise; and 2) the parallel squat, a closed kinetic chain exercise. An electrogoniometer system was applied to the anterior cruciate ligament-deficient knee of 11 volunteers and to the uninvolved normal knee in 9 of these volunteers. Anterior tibial displacement and the knee flexion angle were measured during each exercise using matched quadriceps loads and during the Lachman test. The anterior cruciate ligament-deficient knee had significantly greater anterior tibial displacement during extension from 64 degrees to 10 degrees in the knee extension exercise as compared to the parallel squat exercise. In addition, the amount of displacement during the Lachman test was significantly less than in the knee extension exercise, but significantly more than in the parallel squat exercise. No significant differences were found between measurements in the normal knee. We concluded that the stress to the anterior cruciate ligament, as indicated by anterior tibial displacement, is minimized by using the parallel squat, a closed kinetic chain exercise, when compared to the relative anterior tibial displacement during knee extension exercise.
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
Although closed (CKCE) and open (OKCE) kinetic chain exercises are used in athletic training and clinical environments, few studies have compared knee joint biomechanics while these exercises are performed dynamically. The purpose of this study was to quantify knee forces and muscle activity in CKCE (squat and leg press) and OKCE (knee extension). Ten male subjects performed three repetitions of each exercise at their 12-repetition maximum. Kinematic, kinetic, and electromyographic data were calculated using video cameras (60 Hz), force transducers (960 Hz), and EMG (960 Hz). Mathematical muscle modeling and optimization techniques were employed to estimate internal muscle forces. Overall, the squat generated approximately twice as much hamstring activity as the leg press and knee extensions. Quadriceps muscle activity was greatest in CKCE when the knee was near full flexion and in OKCE when the knee was near full extension. OKCE produced more rectus femoris activity while CKCE produced more vasti muscle activity. Tibiofemoral compressive force was greatest in CKCE near full flexion and in OKCE near full extension. Peak tension in the posterior cruciate ligament was approximately twice as great in CKCE, and increased with knee flexion. Tension in the anterior cruciate ligament was present only in OKCE, and occurred near full extension. Patellofemoral compressive force was greatest in CKCE near full flexion and in the mid-range of the knee extending phase in OKCE. An understanding of these results can help in choosing appropriate exercises for rehabilitation and training.
Coaches round table: The squat and its application to athletic performance
  • K Klein
  • B Kroll
  • T Mclaughun
  • P O Shea
  • And D Wathen
DUNN, B., K. KLEIN, B. KROLL, T. MCLAUGHUN, P. O'SHEA, AND D. WATHEN. Coaches round table: The squat and its application to athletic performance. Strength Cond. J. 6:10-22, 68. 1984.
A comparison of methods for determining kinematic properties of three barbell squat exercises
  • A C Fry
  • T A Aro
  • J A Bauer
  • And W J Kraemer
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Comparison of closed and open chain kinetic exercise in the anterior cruciate ligament-deficient knee Acknowledgments The authors would like to thank L Scruggs for their assistance with the data collection and their contributions to the preparation of this manuscript. Address correspondence to Dr
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YACK, H.J., C.E. COLLINS, AND T.J. WHIELDON. Comparison of closed and open chain kinetic exercise in the anterior cruciate ligament-deficient knee. Am. J. Sports Med. 21:49–54. 1993. Acknowledgments The authors would like to thank L.T. Ramsey, G. Calhoon, M. Matuszak, T. Ireland, D. Bullen, L.E. Wood, P. Grindstaff, and M. Scruggs for their assistance with the data collection and their contributions to the preparation of this manuscript. Address correspondence to Dr. Andrew C. Fry, afry@memphis.edu.