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Effect of Knee Position on Hip and Knee Torques During the Barbell Squat
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.
... 1,36 The instructions to position the knee behind the toes are often used to reduce the PF joint reaction force and knee extension moment. 4,14,20,27,35 However, the strict restriction of forward knee movement simultaneously increases forward trunk inclination and lumbar lordosis, which is a concern because of the increased load on the lower back. 14,26 Real-time feedback regarding PF joint reaction force also reduces the PF joint reaction force for patients with PFP during bodyweight squatting, 21 whereas its clinical use is limited. ...
... 4,14,20,27,35 However, the strict restriction of forward knee movement simultaneously increases forward trunk inclination and lumbar lordosis, which is a concern because of the increased load on the lower back. 14,26 Real-time feedback regarding PF joint reaction force also reduces the PF joint reaction force for patients with PFP during bodyweight squatting, 21 whereas its clinical use is limited. Recent studies have reported that an anterior center-of-pressure (COP) position is associated with a smaller knee extension moment during double-leg squatting. ...
... Moreover, the ankle dorsiflexion angle and trunk forward inclination angle were also determined because these variables can affect the PF joint reaction force and/or knee extension moment during squatting. 14,17,20,27,35 For the AP-COP position, the mean positions were calculated 18 in the descent phases of knee flexion of .60°. 18 The PF joint reaction force was normalized to each participant's body weight (BW; product of body mass and gravity acceleration) and the knee extension moment was normalized to each participant's body mass. ...
Background
Exercise therapy is the cornerstone of patellofemoral (PF) pain management. However, whether squat exercises are therapeutic or detrimental depends on their technique and the resulting load on the PF joint.
Purpose/Hypothesis
The purpose of this study was to investigate whether real-time feedback to position the center-of-pressure (COP) anteriorly could reduce the PF joint reaction force and stress during bodyweight double-leg squatting. It was hypothesized that an anterior COP position would decrease the PF joint reaction force and stress without changing the trunk flexion angle, whereas a posterior COP position would increase the PF joint reaction force and stress.
Study Design
Controlled laboratory study.
Methods
Sixteen men (age, 22.9 ± 1.5 years; height, 173.6 ± 5.2 cm; and body mass, 63 ± 6.8 kg) performed double-leg squatting under 4 conditions—natural, anterior, middle, and posterior COP. Kinematic and kinetic data were obtained via standard 3-dimensional motion analysis and force plate data. The PF joint reaction force and stress were calculated via a musculoskeletal modeling approach.
Results
PF joint loading was significantly reduced in the anterior and middle COP conditions compared with the natural condition. At 90° of knee flexion, the PF joint reaction force decreased by 11% and 9% in the anterior and middle COP conditions, respectively, compared with that in the natural condition (anterior: P < .001, 95% CI −0.996 to −0.277 bodyweight; middle: P = .011, 95% CI −0.795 to −0.087 bodyweight). Moreover, the peak PF joint stress decreased by 9% and 7% in the anterior and middle COP conditions, respectively, compared with the natural condition (anterior: P = .001, 95% CI −0.659 to −0.146 MPa; middle: P = .023, 95% CI −0.600 to −0.036 MPa). Compared with those under the natural condition, the trunk forward inclination angles did not increase under anterior or middle COP conditions.
Conclusions
Real-time feedback for anterior COP positioning is an effective strategy for reducing the PF joint reaction force and stress during double-leg squatting without increasing trunk forward lean.
Clinical Relevance
The incorporation of real-time feedback regarding the anteroposterior COP position is useful for reducing PF joint loading during double-leg squatting, which may be helpful in the rehabilitation of PF pain patients. Instructions to position the COP anteriorly may also be useful in reducing PF joint loading during double-leg squatting.
... Abnormal COM displacement can cause joint instability, reduce training efficiency, and increase injury risk. This underscores the importance of optimizing COM control in squat training [14]. Dynamic changes in COM displacement are influenced by joint moments and trunk flexion angles, which vary across squat modes. ...
... While existing studies provide valuable insights, they often fail to establish a clear quantitative relationship between COM displacement and joint moments, particularly in the sagittal plane. Despite extensive research on squat biomechanics, systematic and quantitative analyses of how anterior-posterior COM displacement affects torque distribution and movement stability remain limited [14,[17][18][19][20][21][22]. To bridge this gap, this study employs factor regression analysis as a robust tool to explore the relationship between COM displacement and joint moments. ...
... Previous studies have extensively explored the modes of COM in the vertical and lateral directions [14]. However, the displacement of the COM in the anterior-posterior direction plays a crucial role in the balance and stability of the movement, and such modes may significantly affect training outcomes and athletic performance [12,19,30,31]. ...
Background: Barbell squats are commonly used in strength training, but the anterior–posterior displacement of the Center of Mass (COM) may impair joint stability and increase injury risk. This study investigates the key factors influencing COM displacement during different squat modes.; Methods: This study recruited 15 male strength training enthusiasts, who performed 60% of their one-repetition maximum (1RM) in the Front Barbell Squat (FBS), High Bar Back Squat (HBBS), and Low Bar Back Squat (LBBS). Joint moments at both the hip, knee, and ankle were collected using a motion capture system and force plates, and a factor regression analysis was conducted using SPSS.; Results: In the FBS, primary factors influencing COM displacement included right knee adduction–abduction (38.59%), knee flexion–extension (31.08%), and hip internal–external rotation (29.83%). In the HBBS, they were right ankle internal–external rotation (19.13%), hip flexion–extension (−19.07%), and left knee flexion–extension (19.05%). In the LBBS, the key factors were left knee adduction–abduction (27.82%), right ankle internal–external rotation (27.59%), and left ankle internal–external rotation (26.12%).; Conclusion: The study identifies key factors affecting COM displacement across squat modes, with knee flexion–extension being dominant in the FBS and hip moments more significant in the HBBS and LBBS. These findings have implications for optimizing squat training and injury prevention strategies.
... For example, doubling the load will double the extensor torques at the hip, knee, and ankle. (Further details concerning the static stick figure and its limitations are provided in Appendix A.) Despite its limitations, the static stick figure in Appendix A can explain the findings of studies that examined many variations of the squat exercise, such as comparing the high-bar with the lowbar back squat (20,21,36), the front squat with the back squat (11,23,37), restricted with unrestricted squats (18), and the back squat with the box squat (33). However, less is known about the squat using the safety-squat bar (SSB). ...
... Our findings also contribute to the larger body of literature concerning squatting mechanics. A more upright posture during squatting decreases the demand on the hip extensors for the same given load (18,29). Although some studies have found an increased demand on the knee extensors with a more upright posture for the same given load (18,36), others have not (28). ...
... A more upright posture during squatting decreases the demand on the hip extensors for the same given load (18,29). Although some studies have found an increased demand on the knee extensors with a more upright posture for the same given load (18,36), others have not (28). However, these relationships are confounded by the fact that more weight can be lifted with a more flexed hip, as demonstrated when comparing the front squat with the back squat (11,23,37) and, to a lesser extent, the high barbell with low barbell squat (20,36). ...
Johansson, DG, Marchetti, PH, Stecyk, SD, and Flanagan, SP. A biomechanical comparison between the safety-squat bar and traditional barbell back squat. J Strength Cond Res 38(5): 825-834, 2024-The primary objectives for this investigation were to compare the kinematic and kinetic differences between performing a parallel back squat using a traditional barbell (TB) or a safety-squat bar (SSB). Fifteen healthy, recreationally trained male subjects (23 + 4 years of age) performed the back squat with a TB and an SSB at 85% of their respective 1 repetition maximum with each barbell while instrumented for biomechanical analysis. Standard inverse dynamics techniques were used to determine joint kinematic and kinetic measures. A 2 3 3 (exercise 3 joint) factorial analysis of variance with repeated measures was used to determine the kinetic and kinematic differences between the squats while using the different barbells. Fisher's least significant difference post hoc comparisons showed that the TB resulted in significantly greater maximum hip flexion angle (129.33 6 11.8˚vs. 122.11 6 12.1˚; p , 0.001; d 5 1.80), peak hip net joint extensor torque (2.54 6 0.4 Nm·kg 21 vs. 2.40 6 0.4 Nm·kg 21 ; p 5 0.001; d 5 1.10), hip net extensor torque mechanical energy expenditure (MEE; 2.81 6 0.5 Nm·kg 21 vs. 2.58 6 0.6 Nm·kg 21 ; p 5 0.002; d 5 0.97), and ankle net joint plantar flexor torque MEE (0.32 6 0.09 J·kg 21 vs. 0.28 6 0.06 J·kg 21 ; p 5 0.029; d 5 0.63), while also lifting significantly (123.17 6 20.8 kg vs. 117.17 6 20.8 kg; p 5 0.005; d 5 0.858) more weight than the SSB. The SSB resulted in significantly higher maximum knee flexion angles (116.82 6 5.8˚vs. 115.65 6 5.6˚; p 5 0.011; d 5 0.75) than the TB, with no significant difference in kinetics at the knee. The TB may be preferred to the SSB for developing the hip extensors and lifting higher maximum loads. The SSB may be advantageous in situations where a more upright posture or a lower load is preferred while creating a similar demand for the knee joint.
... The low bar squat is most commonly associated with the sport of powerlifting, while the high bar squat is more typically associated with the sport of weightlifting [35,45]. Generally, the low bar squat is characterized by a larger degree of hip flexion and a hip movement that may be greater than the knee movement [44][45][46]. Conversely, the high bar squat is performed in a more upright position resulting in a more equal distribution of joint movement forces between the knee and the hip joints [44,45]. It should also be noted that squats, particularly high bar full and partial back squats, can be performed explosively, using plantar flexion, and rising on the balls of the feet [47]. ...
... Although motion capture technology has advanced well over the last forty years, squat mechanics are still being analyzed largely in the sagittal plane because of the anteriorposterior movement that primarily occurs at the trunk and the joints of the lower extremities [19,92,93]. In the back squat, a typical RoM for an experienced lifter would require ankle dorsiflexion of about 20 to 25 • , knee flexion to an internal angle of 95 • in a half squat and approximately 60 • in a parallel squat, and flexing the hip to a range of 85 to 110 • as a lifter reaches the peak descent position [34,43,46,66,68,88]. ...
... Of importance from both practical and analytical standpoints is squat symmetry. Observation suggests that both sides of the kinematic squat sequence are similar [34,46,88]. Salem et al. [94] examined the squat 30 ± 12 weeks after ACL reconstruction and indicated that during a high bar squat, lower extremity RoM on both legs was relatively similar with less than a 3 • difference between each side of the body for the three joints (ankle, knee, and hip) examined. ...
Abstract: There is substantial evidence indicating that increased maximum strength as a result of training with squats, particularly full and parallel squats, is associated with superior athletic capabilities, such as sprinting, jumping and agility. Although full and parallel squats have been strongly associated with sport performance, there is also some evidence that the use of partial squats may provide angle specific adaptations that are likely advantageous for specific sporting activities. Partial squats may be particularly advantageous when trained in conjunction with full or parallel squats, as this practice results in a greater training effect. There is a paucity of evidence that squatting is associated with excessive injuries to the knees, lower back, or other structures. Evidence does indicate that squatting, including full squats, can be undertaken safely, provided an appropriate training methodology is applied. Indeed, based on scientific data, the cost/benefit ratio indicates that squats should be recommended and should be a central strength training exercise for the preparation of athletes in most sports, particularly those requiring strong and powerful whole body and lower body movements.
... Since the 1980s, there has been a widespread perception that the barbell squat should be performed with an upright posture and that the knees should not be moved beyond the tips of the toes. According to this traditional dogma, anterior knee movement should be limited in the sagittal plane once a vertical line with the tips of the feet is achieved [1,2]. Widely accepted instructions for proper knee positioning during barbell squats [2,3] are based on previous studies [4][5][6] that showed that anterior knee displacement (AKD) past the toes is associated with greater shearing forces in the knees, specifically the tibiofemoral joints [4], and that moving the knees anteriorly to a lesser extent during squatting generates lower knee extensor torque [5]. ...
... According to this traditional dogma, anterior knee movement should be limited in the sagittal plane once a vertical line with the tips of the feet is achieved [1,2]. Widely accepted instructions for proper knee positioning during barbell squats [2,3] are based on previous studies [4][5][6] that showed that anterior knee displacement (AKD) past the toes is associated with greater shearing forces in the knees, specifically the tibiofemoral joints [4], and that moving the knees anteriorly to a lesser extent during squatting generates lower knee extensor torque [5]. Based on these findings, it has become standard practice to maintain the shin as vertical as possible and that "maximal forward movement of the knees should place them no more than slightly in front of the toes" when squatting in order to lessen the shear stress placed on the knee [3]. ...
... Based on these findings, it has become standard practice to maintain the shin as vertical as possible and that "maximal forward movement of the knees should place them no more than slightly in front of the toes" when squatting in order to lessen the shear stress placed on the knee [3]. From a practical standpoint, these guidelines advise against allowing the knees to displace anteriorly past the toes [1][2][3]. Although not reported in the literature, the recommendation to not or only slightly push the knees over the tips of the toes seems to be a very vague statement, as disproportionately large feet in relation to the lower extremities of an individual will likely not lead to reduced shearing forces. ...
Based on seminal research from the 1970s and 1980s, the myth that the knees should only move as far anterior during the barbell squat until they vertically align with the tips of the feet in the sagittal plane still exists today. However, the role of both the hip joint and the lumbar spine, which are exposed to high peak torques during this deliberate restriction in range of motion, has remained largely unnoticed in the traditional literature. More recent anthropometric and biomechanical studies have found disparate results regarding anterior knee displacement during barbell squatting. For a large number of athletes, it may be favorable or even necessary to allow a certain degree of anterior knee displacement in order to achieve optimal training outcomes and minimize the biomechanical stress imparted on the lumbar spine and hip. Overall, restricting this natural movement is likely not an effective strategy for healthy trained individuals. With the exception of knee rehabilitation patients, the contemporary literature suggests it should not be practiced on a general basis.
... It is believed that a training protocol with high loads and a low number of repetitions is effective for improving muscle strength and one with medium loads and a high number of repetitions is effective when the aim is muscle hypertrophy (Choi et al., 1998). For squats, in addition to the lifted load and the number of repetitions, stance width (Escamilla et al., 2001), squatting depth (Bryanton et al., 2012), and the knee position (Fry et al., 2003) are variables to be considered depending on the training objective (Rippetoe, 2011). The load characteristics of the body during squats vary depending on these variables; especially, the posture at the bottom position would be an important variable. ...
... The bottom position posture is defined not only by the squat depth, but also by the knee position. Fry et al. (2003) compared the lower limb joint kinetics during squats in different knee positions at the bottom position, and reported that greater knee joint torque and the lower hip joint torque were produced when in the knee dominant posture (i.e., the knee placed past the toe at the bottom position). Consequently, there is no doubt that the bottom position posture has a major effect on the load characteristics of the squat. ...
... In addition, the mechanical work of the knee joint was significantly greater in the knee posture than in the hip posture, but its value was not twice as high. Fry et al. (2003) reported the effect of the posture on barbell squats, with the knee extension torque being greater and the hip extension torque being less in the knee dominant posture than in the hip dominant posture. In the knee posture, the knee joint is located within 80% of the length of the foot anterior to the toe. ...
This study aimed to investigate squat jump and countermovement jump kinetics in the knee dominant and hip dominant postures. Participants included 12 male sports science students. They were instructed to perform a squat jump and a countermovement jump with two squat postures: knee-and hip-dominant postures. The jumping motion and ground reaction force were recorded using a motion capture system and a force plate, respectively. A p-value of 0.05 was considered statistically significant. There was a significant interaction for the maximal knee joint extension torque, with the knee-countermovement jump being more than twice higher than that of other conditions, but not for mechanical work of the knee joint, which was significantly greater in the knee posture than in the hip posture. No significant interactions were found in mechanical work and maximal extension torque of the hip joint, both of which were significantly greater in the hip posture than in the knee posture, and in the countermovement jump than in the squat jump. This study showed that the effects of countermovement and posture were different for joints and that these effects were independent in the hip joint, but interacted in the knee joint. In the knee joint, the posture increased the effect of countermovement on extension torque, but the effect on mechanical work was small. This suggests that countermovement in the knee posture has little effect on the lifting work, but results in a great load on the knee extensors.
... The main risk factor occurs during knee flexion, when the vertical line that passes through the anterior region of the tibia crosses the vertical line that passes through the toe's tips (of the same side) (Bolgla et al. 2018;Crossley et al. 2019;Fry et al. 2003;Pereira et al. 2020;2022b, c;Powers et al. 2017). Another risk factor that can be pointed out is the difference in strength between the thigh and hip muscles (of the same side), which makes the syndrome symptomatic (Narici et al. 2021;Pereira et al. 2020;Scott et al. 2020;Søgaard and Sjøgaard 2017). ...
... The risk assessed was that of the tibial translation movement in the anterior plane in front of the ipsilateral fingers, as reported in the literature as harmful (Brechter and Powers 2002;Collins et al. 2013;Crossley et al. 2004;Fry et al. 2003;Lorenzetti et al. 2018;Pereira et al. 2022b;Powers et al. 2017;Schütz et al. 2014). ...
... According to the literature, such a movement justifies the implementation of prevention measures (Brechter and Powers 2002;Collins et al. 2013;Crossley et al. 2004;Fry et al. 2003;Neal et al. 2019;Pereira et al. 2022b;Powers et al. 2017;Willy et al. 2019). ...
Patellofemoral pain syndrome (PFPS) is a musculoskeletal disorder in the anterior region of the knee, affecting people of different ages. When it is necessary to go up and down many stairs in a work context, there is a risk of increased wear on the knee joint and, consequently, PFPS. The main objective of this work was to identify the risk of contracting PFPS associated with the action of going up and down stairs in the workplace. An analysis of workers’ movement on an oil platform without lifts was carried out in the circulation by stairs between the different floors. It has been found that leg movements made when going up and down stairs can be harmful to the knee joints. A recommendation was made to change the way workers go up and down stairs to reduce the overload on the joint knee and the risk of contracting or worsening PFPS.
... The first one is based on the knowledge about the degrees of knee flexion, considering its anterior translational movement over the anterior tibial line as the main factor of PFPS worsening [22,40,45,49,53,54,65]. ...
... The anterior translation of the knee with the anterior tibial line in front of the ipsilateral toes line during any squat type [22,24,33,46,49,53,65]. Thus, a difference of strength on the patellar tendon of 18.8% compared to 11.5% was found during the forward lunge squat exercise when the anterior tibial line was translocated from the knee to the front tibial line anterior to the ipsilateral toes line [34]. ...
... This syndrome may or may not be symptomatic. It occurs mainly due to tension overload on the patellofemoral ligament in knee flexion between 60 • and 90 • , and when, during knee flexion, the vertical line passing through the anterior region of the tibia crosses the vertical line passing through the tips of the toes (on the same side) [22,40,45,49,53,54,65]. ...
Patellofemoral pain syndrome (PFPS) is highly prevalent; it can cause severe pain and evolve into progressive functional loss, leading to difficulties performing daily tasks such as climbing and descending stairs and squatting. This systematic review aimed to find evidence, in the literature, of squat movements that can cause or worsen PFPS. This work was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement, and its protocol was registered in PROSPERO (CRD42019128711). From the 6570 collected records, 37 were included. From these 37 articles, 27 present a causal relationship between knee flexion and PFPS, 8 describe a relationship, considering the greater existence of muscle contractions, and one article did not describe this relationship in its results. The main limitations stem from the fact that different studies used different evaluation parameters to compare the force exerted on the patellofemoral joint. Furthermore, most studies are focused on sports populations. After analysing the included works, it was concluded that all squat exercises can cause tension overload in the knee, especially with a knee flexion between 60° and 90° degrees. The main causal/worsening factors of PFPS symptoms are the knee translocation forward the toes (on the same body side) when flexing the knee, and the muscle imbalance between the thigh muscles.
... The effects of ankle dorsiflexion and the resulting anterior knee position on the knee extensor moment during double-leg squatting, as well as the effects of trunk flexion, have been well studied [7][8][9][10][11]. Reduced ankle dorsiflexion and increased trunk flexion decrease the knee extensor moment while increasing the hip extensor moment during double-leg squatting [7][8][9][10][11]. ...
... The effects of ankle dorsiflexion and the resulting anterior knee position on the knee extensor moment during double-leg squatting, as well as the effects of trunk flexion, have been well studied [7][8][9][10][11]. Reduced ankle dorsiflexion and increased trunk flexion decrease the knee extensor moment while increasing the hip extensor moment during double-leg squatting [7][8][9][10][11]. However, increased trunk flexion is concerned about the increase in the load on the low back [10,12]. ...
... Reduced ankle dorsiflexion and increased trunk flexion decrease the knee extensor moment while increasing the hip extensor moment during double-leg squatting [7][8][9][10][11]. However, increased trunk flexion is concerned about the increase in the load on the low back [10,12]. Reduced ankle dorsiflexion is also associated with an increase in hip flexion angle, hip extensor moment and lumbar lordosis [7,10,12], which is related to the increase in the load on the hip joint and low back [10,12]. ...
Abstract Background Squatting exercises are commonly used in rehabilitation for knee joint disorders; in these exercises, control of knee extensor moment is important to enhance training effects and to avoid adverse effects. Ankle dorsiflexion and trunk flexion are widely used to reduce knee extensor moments during squatting, but the increased load on the low back is a concern. The purpose of this study was to determine whether the anterior–posterior (AP) center-of-pressure (COP) position and the AP-COP position in combination with ankle dorsiflexion and trunk flexion angles can predict the contribution of the knee extensor moment during double-leg squatting. Methods Twenty-eight healthy individuals (14 female and 14 male participants, age 22.8 ± 1.3 years) performed three sets of five consecutive double-leg squats. Kinematics and kinetics were analyzed using a three-dimensional motion analysis system with force plates. Univariate and multivariate regression analyses were performed to predict the contribution of the knee extensor moment (% total support moment) from AP-COP position, ankle dorsiflexion, and trunk flexion. Results The AP-COP position was a significant predictor of the knee extensor moment contribution (R 2 = 0.168, P = 0.030). Multivariate analysis showed that the ankle dorsiflexion angle (ΔR 2 = 0.561, β = 0.842) and AP-COP position (ΔR 2 = 0.296, β = − 0.499) predicted the knee extensor moment contribution (model R 2 = 0.857, P
... Trunk flexion, anterior-posterior knee positioning, shank inclination and the ankle dorsiflexion angle have been widely studied for their effects on the knee extensor moment, patellofemoral joint stress and anterior tibial force during double-leg squatting (Biscarini et al., 2011;Fry et al., 2003;Kernozek et al., 2018;Lorenzetti et al., 2012;Straub et al., 2021). Greater trunk flexion decreases the knee extensor moment (Biscarini et al., 2011;Straub et al., 2021), and restriction of anterior knee shifting decreases the knee extensor moment and increases the hip extensor moment (Fry et al., 2003;Lorenzetti et al., 2012;Straub et al., 2021). ...
... Trunk flexion, anterior-posterior knee positioning, shank inclination and the ankle dorsiflexion angle have been widely studied for their effects on the knee extensor moment, patellofemoral joint stress and anterior tibial force during double-leg squatting (Biscarini et al., 2011;Fry et al., 2003;Kernozek et al., 2018;Lorenzetti et al., 2012;Straub et al., 2021). Greater trunk flexion decreases the knee extensor moment (Biscarini et al., 2011;Straub et al., 2021), and restriction of anterior knee shifting decreases the knee extensor moment and increases the hip extensor moment (Fry et al., 2003;Lorenzetti et al., 2012;Straub et al., 2021). On the other hand, a few studies reported that the anterior-posterior center of pressure (AP-COP) is also associated with lower limb joint moment coordination during squatting, showing that side-to-side differences in the AP-COP position were associated with those in the ankle extensor moment during double-leg squatting (Flanagan and Salem, 2007) and that the AP-COP position predicted hip-to-knee and ankle-to-knee extensor moment ratios for patients after anterior cruciate ligament reconstruction (Chan and Sigward, 2020). ...
... The knee extensor moment was significantly smaller under the anterior COP condition than under the posterior COP condition. Trunk flexion and anteriorposterior knee position (or shank inclination) are well studied as indicators of the knee extensor moment (Biscarini et al., 2011;Fry et al., 2003;Kernozek et al., 2018;Lorenzetti et al., 2012;Straub et al., 2021). The present finding adds the AP-COP position as a new indicator of the knee extensor moment. ...
The effects of changes in the anterior-posterior center of pressure (AP-COP) position on the lower limb joint moments during double-leg squatting remain unclear. The purpose of this study was to determine the effects of AP-COP positional changes on the hip, knee, and ankle extensor moments during double-leg squatting. Sixteen male participants (22.1 ± 1.5 years) performed double-leg squatting under two conditions (anterior and posterior COP conditions) with visual feedback on their COP positions. Kinematics and kinetics were analyzed using a three-dimensional motion analysis system and force plates. The hip, knee and ankle flexion angles and extensor moments at peak vertical ground reaction force were compared between the two conditions using paired t tests. The COP position was 53.5 ± 2.4% of the foot length, starting from the heel, under the anterior condition and 44.4 ± 2.1% under the posterior condition (P < 0.001). The knee extensor moment was significantly smaller under the anterior than the posterior COP condition (P = 0.003, 95% confidence interval (CI) -0.087 to -0.021 Nm/kg/m), while the ankle extensor moment significantly larger under the anterior COP condition than under the posterior COP condition (P < 0.001, 95% CI 0.113 to 0.147 Nm/kg/m). There was no significant difference in hip extensor moment (P = 0.431). The ankle dorsiflexion angle was significantly larger under the anterior than the posterior COP condition (P = 0.003, 95% CI 0.6 to 2.6°), while there was no difference in trunk, hip, or knee flexion angle. The present results indicate that changes in the AP-COP position mainly affect the ankle and knee extensor moments during double-leg squatting, while the effect on the lower limb joint and trunk flexion angles was limited. Visual feedback on the AP-COP position could be useful for modifying the ankle and knee extensor moments during double-leg squatting.
... Squats are fundamental weight-training exercises widely popular among athletes and the general population, serving to enhance muscular strength, function, athletic performance, and injury prevention [1][2][3][4]. As a multi-joint exercise, proper kinematic patterns are essential for injury prevention and achieving the intended training objectives [5]. ...
... Specifically, as participants achieved improved trunk stability and reduced forward lean, a compensatory increase in knee anterior displacement occurred to maintain balance during the squat. This mechanical relationship between trunk position and knee moment aligns with previous research [3]. While the training programs effectively enhanced trunk stability, they may not have directly influenced knee joint mechanics, as knee moment is also affected by individual factors such as squat technique and lower limb mobility. ...
This study analyzed the effects of an 8-week diaphragmatic core training program on postural stability during high-intensity squats and examined its efficacy in injury prevention and performance enhancement. Thirty-seven male participants were randomly assigned to three groups: diaphragmatic core training group (DCTG, n = 12), core training group (CTG, n = 13), and control group (CG, n = 12). Outcome measurements included diaphragm thickness, respiratory function (mean and maximal respiratory pressures), and squat postural stability (distance between the sacral and upper body center points, peak trunk extension moment, peak knee flexion moment, and dynamic postural stability index). Compared to both CTG and CG, DCTG demonstrated significantly greater improvements in diaphragm thickness (DCTG: 34.62% increase vs. CTG: 1.36% and CG: 3.62%, p < 0.001), mean respiratory pressure (DCTG: 18.88% vs. CTG: 1.31% and CG: 0.02%, p < 0.001), and maximal respiratory pressure (DCTG: 18.62% vs. CTG: 0.72% and CG: 1.90%, p < 0.001). DCTG also showed superior improvements in postural stability measures, including reductions in the distance between sacral and upper body center points (DCTG: −6.19% vs. CTG: −3.26% and CG: +4.55%, p < 0.05), peak trunk extension moment (DCTG: −15.22% vs. CTG: −5.29% and CG: +19.31%, p < 0.001), and dynamic postural stability index (DCTG: −28.13% vs. CTG: −21.43% and CG: no change, p < 0.001). No significant between-group differences were observed in peak knee flexion moment. Core training incorporating diaphragmatic strengthening was more effective than conventional training in improving postural stability during high-intensity squats. Core training programs, including diaphragmatic strengthening exercises, may contribute to injury prevention and performance enhancement in exercises requiring lumbar stability, such as squats.
... The squat is considered one of the best exercises to improve physical fitness as its execution requires the simultaneous recruitment and coordination of multiple muscle groups of the trunk and lower limbs (1). In fact, it is a multijoint exercise that mainly involves the hips, knees, and ankles, and which athletes of different sports perform to train the strength of lower limbs and back muscles (2)(3)(4). ...
... Given the widespread use of the squat among athletes, there are several studies that have analyzed the biomechanics of the gesture with the aim of improving performance and preventing injuries (1,3,(12)(13)(14)(15)(16)(17)(18). In fact, it is recommended to perform the squat, which is a closed kinetic chain exercise, with minimal anterior knee displacement in order to optimize performance and reduce the risk of injury (19)(20)(21)(22). ...
Introduction
This study aimed to evaluate the angular kinematics of the hip, knee, ankle, and the linear kinematics of the barbell during the back squat (BS) at different load intensities in powerlifters and weightlifters.
Methods
Seventeen athletes were recruited (n = 14 powerlifters; n = 3 weightlifters). The 1-RM of the BS of each participant was calculated and, 1-week after, each participant was asked to perform 5 trials of the BS at different load intensities (i.e., 60%, 70%, 80%, 90%, 100%) of the 1-RM. An action camera recorded the execution of each BS trial in the sagittal plane and, afterward, the videos were analyzed by measuring the range of motion (ROM) of hip, knee, and ankle for the angular kinematics, and the timing, distances, speeds, and accelerations of the barbell for the linear kinematics.
Results
Regarding the angular kinematics, no significant differences were found in the parameters in the starting and ending positions among the 5 trials, while a significant decrease was found in the hip relative angle (p = 0.026) in the maximum flexion position as load intensity increased. Regarding the linear kinematics, a significant difference was found in the descent acceleration (p = 0.049) in the descent phase, while a significant difference was found in the ascent speed (p < .001) and vertical speed of ascent (p < .001) in the ascent phase, which decreased as load intensity increased.
Discussion
Our findings show that the angular and linear kinematics of BS change as load intensity increases.
... During squatting, the lower back muscles play an important role while stabilizing the upper body, and, consequently, the whole movement 4 . The squat exercise uses mono and biarticular Systematic Review and Meta-Analysis muscles, with a force variation that depends on joint position (due to changes in the moment arm and to the length-tension relationship) 5,6 . In addition, squatting also represents a safe exercise for the knee joint, in view of the co-contraction of knee extensors and flexors that dynamically stabilize this joint 7 . ...
... Studies evaluating acute effects with the same target population showed no differences in the knee extensors' activation between partial and deep squats 5,15 . However, these studies were excluded from the current review for not meeting the eligibility criteria (studies of intervention), or because they had incomplete data (another population, such as sedentary and bodybuilders), thus preventing their qualitative analysis. ...
B ACKGROUND: Changes in range of motion during partial and deep squats can affect the electrical activity of the knee extensor muscles. There are results’ divergences between studies that evaluated the effects of deep and partial squats on the electrical activity of the knee extensor muscles. AIM: To systematically review the literature on the electromyographic activity of the knee extensor muscles during partial and deep squat exercises in subjects with strength training experience. METHOD: The search included MEDLINE (via Pubmed), Scielo, EMBASE, in addition to a manual search, until June 2023. Cross-sectional observational studies comparing partial squats (up to 90º of knee flexion) and deep squats (maximum knee flexion) that evaluated the electrical activation through surface electromyography in men and women with strength training experience were included. Methodological quality assessment was performed using the adapted Downs and Black tool, as suggested by the Cochrane Collaboration. RESULTS: Of the 636 articles identified, four studies were included. The included studies presented electromyographic values of the two squat variations. No difference was found in the activation of the rectus femoris, vastus medialis and vastus lateralis muscles between partial and deep squats. Regarding methodological quality, one study was classified as having moderate and the other three studies showing high methodological quality. CONCLUSION: The similarity in the knee extensors’ electromyographic activation between partial and deep squat exercises in men and women with strength training experience suggests that both exercises can be used for recruiting these muscles during physical fitness activities.
... [19]. It has been suggested that this compensation occurs due to decreased hip mobility or limited dorsiflexion angle [52,53]. More horizontal posture was adopted to compensate for changes in positioning of the lower leg and maintain the system center of mass over the base of support [53]. ...
... It has been suggested that this compensation occurs due to decreased hip mobility or limited dorsiflexion angle [52,53]. More horizontal posture was adopted to compensate for changes in positioning of the lower leg and maintain the system center of mass over the base of support [53]. In our study, tibia-torso angle variable was not found to be in correlation with running torso sagittal plane movements. ...
Purpose
Overhead squat assessment (OHSA) is a pre-activity dynamic movement analysis tool used to define deviations from an ideal motion pattern which known as compensation. Compensatory movements may result from abnormality in myofascial activity, length-tension relationships, neuro-motor control strategies, osteokinematics and arthrokinematics. The aim of this study is to identify the association between selected biomechanical variables of the ankle, knee, hip, pelvis, torso during OHSA and 16 km/h treadmill running tasks.
Methods
Thirteen national long distance male runners (17.3 ± 0.5 age (years); 5.89 ± 1.95 experience (years), 57.9 ± 3.7 body mass (kg); 175.4 ± 5.7 height (cm)) participated in this 2controlled laboratory study. Three-dimensional kinematics were collected at 250 Hz using a 9-camera Qualisys motion analysis system (Qualisys AB, Goteborg, Sweden) while participants performed 16 km/h treadmill running and OHSA tasks.
Results
Correlation coefficients demonstrated that OHSA pelvic anterior tilt angle was in a positive association with foot strike (FS), mid-stance (MS), and toe-off (TO) pelvic anterior tilt angles and MS tibial internal rotation on talus, MS ankle pronation, MS hip internal rotation. OHSA pelvic anterior tilt angle was in a negative association with TO hip extension. OHSA maximal hip adduction was positively correlated with MS and stance maximal knee adduction. FS, MS, stance maximal angular dorsiflexion values were positively correlated with OHSA dorsiflexion. Increased OHSA dorsiflexion angle was negatively associated with TO plantar flexion. OHSA pronation was positively associated with MS and stance pronation. MS hip internal rotation, MS hip adduction angles were increased, and MS ankle dorsiflexion was significantly decreased with the increase of trunk forward lean relative to tibia during OHSA.
Conclusions
OHSA was associated with some important and dysfunction-related hip, knee and ankle kinematics. Running coaches, may use OHSA as an assessment tool before the corrective training plan to detect injury-related compensation patterns to reduce the risk of injury and improve running technique.
... Limited ankle dorsiflexion has been found to negatively alter squat mechanics and is associated with increased knee valgus while squatting and aberrant flexion of the hips and lumbar spine, which may result in excessive compressive force on the lumbar discs (12,23,65,79,91). Furthermore, decreased hip ROM may also lead to compensatory movement patterns, which increase the risk of low back injury (50). In a deep squat, the hip crease is required to travel below the knee, with similar requirements relating to a successful catch position during a snatch (17,50,65). ...
... Furthermore, decreased hip ROM may also lead to compensatory movement patterns, which increase the risk of low back injury (50). In a deep squat, the hip crease is required to travel below the knee, with similar requirements relating to a successful catch position during a snatch (17,50,65). Improving ankle dorsiflexion may reduce lower limb injury rates with improved joint mobility shown to be beneficial in reducing the risk of sustaining musculoskeletal injury (64,76). ...
Fascial restrictions that occur in response to myofascial trigger points (MTrP), exercise-induced muscle damage (EIMD) and delayed onset of muscle soreness (DOMS) cause soft tissue to lose extensibility which contributes to abnormal muscle mechanics, reduced muscle length and decrements in joint range of motion (ROM) and actively contributes to musculoskeletal pain. Resistance training and in particular, weightlifting movements have unique mobility requirements imperative for movement efficacy and safety with ROM restrictions resulting in ineffective volume and intensity tolerance and dampened force output and power which may lead
to a failed lift or injury. Self-massage (SM) provides an expedient method to promote movement efficiency and reduce injury risk by improving ROM, muscular function and reducing pain and allows athletes to continue to train at their desired frequency with minimal disruption from MTrPs associated adverse effects. Thus, the aim of this review was to determine the efficacy of various self-massage tools in managing pain and mobility and to explore the potential benefits of SM on resistance training performance. Many SM devices are available for athletes to manage ROM restrictions and pain including differing densities of foam rollers, roller massagers, tennis balls and vibrating devices. To attenuate adverse training effects, a 10-to-20-minute bout consisting of 2-minute bouts of SM on the affected area may be beneficial. When selecting a SM device, athletes should note that foam rollers appear to be more effective than roller massagers, with vibrating
foam rollers eliciting an increased reduction to pain perception and tennis balls and soft massage balls shown to be efficacious in targeting smaller affected areas.
... The third type of squat is the front squat with the barbell held on the chest. The front squat is considered a safe exercise often used in rehabilitation or by beginners [16,18]. Studies of both types of squats indicate greater trunk verticalisation in the front squat, which translates into lower shear forces in the lumbar spine [16,18]. ...
... The front squat is considered a safe exercise often used in rehabilitation or by beginners [16,18]. Studies of both types of squats indicate greater trunk verticalisation in the front squat, which translates into lower shear forces in the lumbar spine [16,18]. On the other hand, Spitz [19] did not confirm a significant difference in barbell velocities, nor Davis [20] a significant difference in energy expenditure of the body during front and back squat performance. ...
Introduction. Front and back squats are multi-joint exercises used in sports to develop strength, power and muscle mass. Due to their movement structure and involvement of the main muscle groups, they are training measures that are used in strength training in various sports. A long-term training process leading to sports mastery requires the correct selection of loads as well as objective control of the training effects to date, both short-term and long-term. The aim of this study was to create a statistical model and to determine with it the character of the changes in the record scores in the front and back squat of young weight-lifters over a two-year training cycle.
Material and Methods. The study included 17 young athletes training in competitive weightlifting. Recorded scores in the front squat and back squat were measured seven times (every three months over a two-year training cycle). The progression method was used to determine the maximum load, and the repetition with the highest load (1RM) was used in the calculations.
Results. The subjects performed better in the back squat, but the difference between the results for both squats was approximately constant over the two-year training cycle. The time courses of both squats were similar over the analysed period. Systematic increases in maximum results were observed. The first statistically non-significant differences between the mean record values in successive measurements were found between the sixth and seventh measurements for both squats.
Conclusions. Determining the relationship between front and back squat record scores can contribute to the optimisation of training loads in sports using strength training. Obtaining an analytical form of the course of record scores over time for both squats helps to assess the skill level of athletes and predict their performance in the next training macro-cycle.
... This study has limitations. First, the knee and hip joint moments in squats depend on the patterns of lifting movement (4,7,10,11,19,21,33). In particular, the degrees of shank and trunk inclination could affect the distribution of joint extension moments between knee and hip (11,33). ...
... First, the knee and hip joint moments in squats depend on the patterns of lifting movement (4,7,10,11,19,21,33). In particular, the degrees of shank and trunk inclination could affect the distribution of joint extension moments between knee and hip (11,33). For this reason, the 4-month familiarization period was provided to attain potential maximum external loads and joint moments at 10RM. ...
Arakawa, H, Mori, M, and Tanimoto, M. Greater hip moments in rear-foot-elevated split squats than in conventional back squats with the same relative intensity of loads. J Strength Cond Res XX(X): 000-000, 2022-Rear-foot-elevated split squat (RFESS) is often performed as an alternative to conventional double-leg back squat (DLBS). This study aimed to compare 3-dimensional joint kinetics of DLBS and RFESS using the same relative intensity of loads. Eight male college rugby players performed 3 repetitions of DLBS and RFESS at 10-repetition-maximum (RM) loading. Before testing, both exercises were incorporated into the subjects' training program with a progressive increase in loads for 4 months. A 3-dimensional optical motion capture system and force platform were used for data collection. The 3-dimensional moments at the knee and hip joints in each of the 3 axes were calculated based on the inverse dynamic procedure. p values < 0.05 were considered statistically significant. The hip extension moment was 44% greater in the RFESS than in the DLBS at the bottom position (p < 0.01) and 47% greater for the peak value (p < 0.01) on harmonic averages. The hip abduction and external rotation moments at the bottom position were also greater in the RFESS than in the DLBS. The findings suggest that the magnitude of hip extension moment per leg in DLBS tends to be restricted to less than that expected from the given strength level. In conclusion, the mechanical contribution of hip extensors per leg can be greater in RFESS than in DLBS when using respective 10RM loads, even if the absolute load is smaller and the trunk is more upright in RFESS.
... It is the ability to perform and maintain efficient and accurate movement patterns that are fundamental to daily life [22]. The ability to perform functional movements is indispensable because it can prevent injuries [23] and pain [24]. To achieve functional movement, muscle strength, endurance, coordination, flexibility, balance, and movement efficiency are imperative [18]. ...
... Squats are an example of a functional movement in which humans adapt variations to accomplish tasks of activities of daily living [25]. Squats can also be used as an essential functional training because they recruit multiple muscle groups during a single movement [23,24]. Lunge is also regarded as a functional activity and is used to assess hip muscle and knee performances [26][27][28]. ...
(1) Background: The present study investigated the agreement between the Azure Kinect and marker-based motion analysis during functional movements. (2) Methods: Twelve healthy adults participated in this study and performed a total of six different tasks including front view squat, side view squat, forward reach, lateral reach, front view lunge, and side view lunge. Movement data were collected using an Azure Kinect and 12 infrared cameras while the participants performed the movements. The comparability between marker-based motion analysis and Azure Kinect was visualized using Bland–Altman plots and scatter plots. (3) Results: During the front view of squat motions, hip and knee joint angles showed moderate and high level of concurrent validity, respectively. The side view of squat motions showed moderate to good in the visible hip joint angles, whereas hidden hip joint angle showed poor concurrent validity. The knee joint angles showed variation between excellent and moderate concurrent validity depending on the visibility. The forward reach motions showed moderate concurrent validity for both shoulder angles, whereas the lateral reach motions showed excellent concurrent validity. During the front view of lunge motions, both the hip and knee joint angles showed moderate concurrent validity. The side view of lunge motions showed variations in concurrent validity, while the right hip joint angle showed good concurrent validity; the left hip joint showed poor concurrent validity. (4) Conclusions: The overall agreement between the Azure Kinect and marker-based motion analysis system was moderate to good when the body segments were visible to the Azure Kinect, yet the accuracy of tracking hidden body parts is still a concern.
... The barbell squat is one of the most effective exercises for building lower extremity strength [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and is widely used for strength training and rehabilitation. During barbell squat training or competition, athletes often wear a type of heel lift shoe or use other means to elevate the heel, which is thought to improve the range of motion (ROM) of the lower extremity joints and improve stability of movement during the deep squat [16][17][18][19][20][21]. ...
... Barbell squats are commonly used for strength training and rehabilitation [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Heel elevation during a barbell squat is thought to improve deep squat movement patterns. ...
The effect of heel elevation on the barbell squat remains controversial, and further exploration of muscle activity might help find additional evidence. Therefore, 20 healthy adult participants (10 males and 10 females) were recruited for this study to analyze the effects of heel height on lower extremity kinematics, kinetics, and muscle activity using the OpenSim individualized musculoskeletal model. One-way repeated measures ANOVA was used for statistical analysis. The results showed that when the heel was raised, the participant’s ankle dorsiflexion angle significantly decreased, and the percentage of ankle work was increased (p < 0.05). In addition, there was a significant increase in activation of the vastus lateralis, biceps femoris, and gastrocnemius muscles and a decrease in muscle activation of the anterior tibialis muscle (p < 0.05). An increase in knee moments and work done and a reduction in hip work were observed in male subjects (p < 0.05). In conclusion, heel raises affect lower extremity kinematics and kinetics during the barbell squat and alter the distribution of muscle activation and biomechanical loading of the joints in the lower extremity of participants to some extent, and there were gender differences in the results.
... 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. ...
“Priming exercises” are gaining popularity as a precompetition strategy to improve subsequent performance. Although priming exercise has been shown to improve various neuromuscular performance measures within 48 hours, a number of studies have also found no change or significant decreases in performance following priming interventions. Inconsistencies in findings are likely due to the many different variables used in the research. In addition, evidence suggests that the potential performance response following a priming stimulus is likely to be influenced by individual characteristics. Therefore, the purpose of this review is to examine the available evidence and identify those variables that most strongly determine whether priming stimuli involving resistance and stretch-shortening cycle exercise tasks are likely to improve performance within 48 hours of that stimulus. In addition to making recommendations based on the evidence to date, directions for future research are also identified.
... Barbell squatting guidelines published by the National Strength and Conditioning Association have cited the importance in optimising force production and loading at each joint -notably the knees and hip(Sands, Wurth and Hewit, 2012). As a result, coaches should aim to develop correct lifting technique, optimising the kinetic environment for each joint to optimise performance(Fry, Smith and Schilling, 2003). Optimising the kinematics of a squat through the implementation of declining squat protocols has yet to explore the effects of these alterations on athletic (strength) performance. ...
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 absolute and relative strength. Muscle sports such as powerlifting and weightlifting are heavily dependent on the aspects of maximal strength and its’ assessment can be used for talent identification, training interventions and competition performance indicators. The aim of this study is to compare maximal strength (1RM) at different declining squat angle protocols in resistance trained individuals. It is hypothesised that maximal strength will increase when squats are performed at an increasing angle of decline. Twelve participants (age 29.3 ± 6.5 years, height 1.8 ± 0.1 m, weight 85.3 ± 11.5 kg) performed 1RM testing at each declining surface variable (0°, 5°, 10° and 15°) – data was collected for maximal strength as the maximum weight (kg) recorded on a single successful squat (1RM). There was a significant maximal strength difference (F(3.0) = 5.953, p = 0.002) between angled conditions. Post hoc calculations comparing maximal strength data highlighted a significant difference between specific conditions 0(flat)vs5 (p=0.019) and 0(flat)vs10 (p=0.004). All other comparisons were considered not significant (p<0.05). This study provides one of the first comprehensive explorations into the effects of declining squat protocols on maximal athletic performance. The findings from this study suggest that the potential benefits of using decline-angled surfaces can be used to induce significant increases in maximal strength for trained individuals when back squatting.
... Under conditions resulting in greater forward trunk flexion, moment forces increase about the hip. These reduced joint moments would be beneficial as they would require less internal moments being generated, which would reduce joint reaction forces [13,14,[31][32][33]. For novice athletes, modifications to the squat mechanism, such as EHs or squat widths, may be beneficial [17,[34][35][36][37]. Collectively, these findings indicate that EHs can improve squat stability by reducing the trunk lean and COP excursion. ...
The back squat (BS) is one of the most effective exercises for enhancing lower limb strength, but an unstable squat can increase shear forces in the lower back. Understanding how to assess the squat stability is useful for avoiding potential sports injury. During the BS, the trunk lean and center of pressure (COP) are relevant to squat safety, and these kinematics can be altered by elevating the heel. However, there is no relevant meta-analysis on the impact of different heel heights on squat stability. This study aims to bridge the gap in the literature by conducting a systematic review and network meta-analysis on how heel elevation affects squat stability. By quantifying the influence of different heel heights on key biomechanical parameters, such as the center of pressure deviation and ankle dorsiflexion, the study provides actionable insights for athletes, trainers, and clinicians. Fourteen articles were included, and the majority of these studies demonstrated that elevated heels (EHs) can reduce COP deviation and trunk lean. In addition, 25 mm heels may be the preferred option for squat stability in the AP direction when COP data and network meta-analysis are combined. However, in the ML direction, the capacity to maintain balance is rather questionable; when ankle peak dorsiflexion is combined, 8 mm heels have higher COP deviation values and 5 mm heels have lower COP deviation values. Regarding limitations, reliance on a single bias assessment tool (Cochrane Risk of Bias Tool) might not fully capture methodological variability across non-RCT studies. Future systematic reviews could consider using multiple bias assessment tools for robust assessmen
... These demanding exercises challenge the musculature of the trunk and posterior chain including the glutes, hamstrings, and erector spinae [1] as well as the knee extensors and flexors [2]. However, squat-related movements are often accepted as symmetrical between the left and right sides of the body [3,4]. Still, up to 31% of sub-elite to elite powerlifters reported injuries during the deadlift exercise [5]. ...
Background/Objectives: Asymmetries in force production, characterized by vertical ground reaction forces (VGRFs), during lower-limb bilateral movements such as deadlifting and squatting, are considered biomechanical risk factors for injury. Real-time biofeedback has been used to modify lower limb force production but typically implements monitors. The purpose of this study was to determine the effect of wearable visual biofeedback (WVBF) on asymmetries in VGRFs and knee joint angles and the rate of perceived exertion (RPE) during deadlift and body-weight squatting (BWS) exercises in recreational powerlifters. Methods: Thirteen healthy young adults between 18–35 years of age performed three tasks: deadlifting for mixed-grip style (MIX), double-overhand style (DO), and BWS. Each task included two conditions: with and without WVBF. A two-way (Condition X Task) mixed model analysis of variance was performed to compare the bilateral asymmetry index of VGRFs, knee angle, and RPE scores. Results: A main effect of the condition (with versus without WVBF) was detected for VGRF symmetry (F (1,12) = 62.785, p < 0.001). WVBF showed decreased VGRF asymmetry compared to no biofeedback. For knee angle, a significant condition X task interaction (F (2,24) = 3.505, p < 0.05) was observed. For RPE, a main effect of the condition was observed (F (1,12) = 8.995, p < 0.05). WVBF showed greater RPE compared to no biofeedback. Conclusions: These results indicated that WVBF could reduce VGRF asymmetry during deadlifting and squatting. In addition, targeting force production symmetry may not directly yield joint angle symmetry and may increase perceived exertion. These results could provide valuable insight into VGRF modulation during deadlifting and squatting exercises in athletic and potentially clinical settings when targeting VGRF symmetry.
... One method of strengthening the quadriceps muscles, which are significantly affected by sarcopenia, is squatting exercises. Numerous studies have examined the relationship between lower-limb muscle activity and the knee joint angle, knee joint position (i.e., whether the knee joint is placed in front of the toes), trunk tilt angle, and centre of gravity (COG) during squatting exercises (Nakamura & Ogata, 2016;Fry et al., 2003;Gullett et al., 2009). However, the characteristics of quadriceps activity at different trunk tilt angles during squatting have not been fully investigated. ...
This study aimed to clarify the relationship between different trunk inclination angles and knee joint positions while squatting and the activity of the vastus medialis obliquus (VMO). The participants were 24 healthy young males and females. The task was performed in the squatting position with the knee joint in 60° flexion. Group F (knee forward group) allowed the apex of the knee to move over the toes in the forward direction, and group B (knee backward group) allowed it to be aligned. Furthermore, group F was set to 0° forward tilt (F0), 20° forward tilt (F20), and 40° forward tilt (F40) of the trunk, whereas group B was set to 20° forward tilt (B20) and 40° forward tilt (B40). Surface electromyography (sEMG) was used to detect action potentials from the VMO, vastus medialis longus (VML), and rectus femoris (RF). sEMG analysis showed that the vertical trunk position was significantly higher than the anterior trunk position in all muscles (p < .05). F0 had the smallest displacement of the anterior-posterior centre of pressure. F0 with knee flexion of around 60° and body supported by both upper limbs is a suitable squatting limb for quadriceps training, particularly in the VMO.
... 4 For instance, Kristiansen et al. 4 explored the squat of skilled weightlifting athletes and their inter-and intra-individual variability while performing this exercise, and Fry et. al. 5 examined the effect of knee position on hip and knee torques during the back squat, while Escamilla et al. 6 explored biomechanical parameters while performing the back squat with varying stance widths, and Swinton et. al. 7 compared the biomechanics of the box squat, traditional squat, and powerlifting squat. ...
Background
It is important to assess the quality of fundamental movements, to discover deficits, evaluate mobility, balance, and stability, and identify movement dysfunction and asymmetries. However, little research has been performed on the assessment of fundamental movements with bodybuilders.
Purpose
The purpose of this research was to examine the quality of professional and amateur bodybuilders’ functional movements and the quality of the back squat performance. A secondary purpose was to discern whether greater experience in bodybuilding was associated with better scores on the back squat assessement (BSA).
Study design
Cross-Sectional Cohort
Methods
Twenty-six athletes were recruited to participate. The group of professional bodybuilders consisted of five men and six women, a total of 11 athletes. The group of amateur bodybuilders consisted of seven men and eight women, a total of 15 athletes. The Functional Movement Screen™ (FMS™) was used to assess the seven included fundamental patterns that evaluate an individual’s neuromuscular control, mobility, balance, and stability. The BSA was used to assess the quality of movement, dysfunction, deficit, or compensation during the squat exercise. Statistical analyses applied non-parametric tests (Wilcoxon, Mann-Whitney U, and Friedman’s) for dependent and independent samples, with significance set at p<0.05, and the Spearman correlation coefficient and Chi-square test were used to assess relationships between quantitative and qualitative variables.
Results
Overall, athletes with a higher total FMS™ score performed better on the BSA as well. The professional athletes scored 2.58 points higher than the amateurs on total FMS™ scores (p<0.001).
Professional athletes scored better on the BSA than amateurs (p<0.001). A statistically significant, positive moderate correlation was revealed between the FMS™ total score and the squat total score (r=0.68; p=0.005).
Conclusions
A higher FMS™ score in bodybuilders is associated with a higher BSA score. Professional bodybuilders have higher FMS™ scores and higher BSA scores than amateurs. Greater experience in bodybuilding is associated with the compliance with several BSA criteria: trunk position, frontal knee alignment, tibial translation angle, foot position in all three back squat variations with different external loads, and descent with the training weight.
Level of Evidence
3b
... One biomechanical aspect is an athlete's lifting technique resulting from individual anthropometry and mobility. The individual lifting technique, referring to joint ranges of motion and trajectories, results in the relative contribution of the involved muscles and, therefore, the stimulus to which they are exposed (16,53). Another important factor is muscle protein synthesis and therefore nutritional intake of protein and the absorption of amino acids (12). ...
The interchangeable use of terms such as muscle mass, volume, cross-sectional area, and thickness in discussions on the physiology of muscle hypertrophy has led to misconceptions in research and practice. This review aims to highlight the improperness of this approach and highlights the overlooked parameter of muscular density (MD). The hypothesis is that muscle density acts as a mediator, leading to inevitable muscle enlargement in long-term strength training. It is proposed that research in muscular adaptations to training should implement measures of MD to complement measurements of muscle size. This article aims to refine the understanding of muscular adaptations and optimize training strategies for athletes and fitness enthusiasts.
... It is used in a wide range of situations as a form of training to increase muscle strength and functional ability [1]. Squatting involves the contraction of the hip extensors, abductors, adductors, quadriceps, and triceps surae muscles [2], making it effective for training in clinical settings because most ADLs require lower-limb muscle coordination [3,4]. ...
Background
Squatting is commonly used in various settings to enhance muscle strength and performance. Both fast and slow squats have advantages as training to improve muscle function in the lower extremity muscles. Movement speed affects the variability of interjoint coordination and decreased variability can lead to overuse injuries owing to repetitive mechanical loading on the lower extremity joints. However, only a few studies have focused on interjoint coordination during squatting. This study aimed to clarify the kinematic and kinetic differences, as well as the interjoint coordination, during squatting at different speeds.
Methodology
Healthy young participants with no locomotor disease were recruited to perform descending parallel squats at different speeds (one, three, and five seconds) using a 3D motion analysis system and force plates. Joint moments and continuous relative phases were calculated and compared between the conditions.
Results
There were no significant differences in the mean values of lower limb joint moments among the three speed conditions. However, the mean absolute values of the continuous relative phase between the ankle and hip joints and the mean standard deviation of the continuous relative phase between each lower limb joint were significantly lower in the high-speed condition than in the medium- and low-speed conditions. Additionally, in the high-speed condition, the knee joint moved ahead of the hip joint in the knee-hip joint phase coordination pattern.
Conclusions
The joint load per unit time remained constant across all speed conditions. High-speed squatting may adapt to mechanical loading on the joints, although the knee joint moves ahead of the hip joint, exhibiting a highly coordinated movement. Conversely, low-speed squatting may reduce the risk of disability owing to the high variability of interjoint coordination. Therefore, squatting training should be based on individual characteristics and objectives.
... The squat may also be a beneficial resistance exercise for the nonathletic population because of the coordinated interactions in daily living. Thus, strengthening and increasing the ability to recruit several muscles, such as the gluteus maximus, hamstrings, and quadriceps femoris during everyday tasks (9). Given that the squat involves coordinated actions of the musculoskeletal system, a mechanical understanding of the imposed demands on the individual muscles for the optimal implementation of different squat techniques is required. ...
Larsen, S, de Zee, M, Kristiansen, EL, and van den Tillaar, R. A biomechanical comparison between a high and low barbell placement on net joint moments, kinematics, muscle forces, and muscle-specific moments in 3 repetition maximum back squats. J Strength Cond Res 38(7): 1221–1230, 2024—This study aimed to investigate the impact of a high barbell vs. low barbell placement on net joint moments, muscle forces, and muscle-specific moments in the lower extremity joints and muscles during maximum back squats. Twelve recreationally trained men (age = 25.3 ± 2.9 years, height = 179 ± 7.7 cm, and body mass = 82.8 ± 6.9 kg) volunteered for the study. A marker-based motion capture system and force plate data were used to calculate the net joint moments, and individual muscle forces were estimated using static optimization. Muscle forces were multiplied by their corresponding internal moment arms to determine muscle-specific moments. Statistical parametric mapping was used to analyze the effect of barbell placement as time-series data during the concentric phase. The 3 repetition maximum barbell load lifted by the subjects was 129.1 ± 13.4 kg and 130.2 ± 12.7 kg in the high bar and low bar, which were not significantly different from each other. Moreover, no significant differences were observed in net joint moments, muscle forces, or muscle-specific moments for the hip, knee, or ankle joint between the low- and high bar placements. The findings of this study suggest that barbell placement plays a minor role in lower extremity muscle forces and moment-specific moments when stance width is standardized, and barbell load lifted does not differ between barbell placements among recreationally resistance-trained men during maximal back squats. Therefore, the choice of barbell placement should be based on individual preference and comfort.
... 14,15 TIBIA INCLINATION Compared to trunk inclination, inclination of the tibia during squatting has an opposite influence on the knee flexion moment. 9,10,[16][17][18] Moving the tibia from a more upright position ( Figure 3A) to more forward position ( Figure 3B) shifts the knee joint center further away from the resultant ground reaction force vector, thereby increasing the knee flexion moment. Conversely, moving the tibia from a forward position ( Figure 3B) to more upright position ( Figure 3A) shifts the knee joint center closer to the resultant ground reaction force vector, thereby decreasing the knee flexion moment. ...
The squat is one of the most frequently prescribed exercises in the rehabilitative setting. Performance of the squat can be modified by changing parameters such as stance width, foot rotation, trunk position, tibia position, and depth. An understanding of how the various squatting techniques can influence joint loading and muscular demands is important for the proper prescription of this exercise for various clinical conditions. The purpose of this clinical commentary is to discuss how the biomechanical demands of the squat can be influenced by various modifiable parameters. General recommendations for specific clinical conditions are presented.
Level of Evidence
5
... 6 If the knee exceeds the toe, the compression load and shear force applied to the knee will increase, increasing the possibility of knee injuries. 7 Also, as the trunk leans in the forward direction, the shear force on the knee increases. 2 To prevent knee injury due to this, motor learning by training with a physical therapist and personal trainer or athletic trainer is necessary, and repetitive practice and provision of sensory feedback are essential for efficient motor learning. ...
Various sensory feedback methods are considered important for motor learning, but the effect of each sensory feedback method on effective squat learning still needs to be clarified. This study aimed to investigate the effect of sensory feedback types on the acquisition and retention of a squat. A double‐blinded, randomized controlled trial was carried out. Thirty‐healthy people were recruited and randomly assigned to the visual feedback group (VFG = 10), tactile feedback group (TFG = 10), and control group (CG = 10). VFG received visual feedback through video data of the participant performing squats, and TFG received tactile feedback through manual contact with a physical therapist. Both groups received feedback on the movements that needed correction after each set was completed. CG maintained rest without receiving any feedback. The retro‐reflexive marker, force plate, and electromyography were used to measure body angle, foot center of pressure (COP), and muscle activity. All assessments were measured to confirm a squat acquisition. VFG and TFG showed significant differences in neutral knee position (NKP), trunk forward lean (TFL), anterior knee displacement (AKD), and anteroposterior (AP) foot COP (p < 0.050). In addition, the acquisition was retained until 3 days later for NKP and a week later for TFL, AKD, and AP foot COP in VFG (p < 0.050), while the acquisition was not retained in TFG (p > 0.050). There was no statistically significant change in CG (p > 0.050). This study demonstrated that visual feedback positively affects the acquisition and retention of squats. Therefore, we recommend the use of visual feedback for squat acquisition and retention in exercise novices.
... This exercise demands high levels of body balance control and explosive joint torque. To improve the forces distribution on all involved joints and lift heavier loads, it is commonly recommended to avoid moving the knees forward past the toes too much or to maintain a near-vertical position of the shank [15], [16]. Restricting the shank-gravity angle within a certain range ensures that the majority of the weight is primarily supported by the shinbone, as the orange bar shown in Fig. 3(b), enhancing overall body stability and minimizing strain on the knees [17]. ...
Wheeled bipedal robots (WBRs) have the capability to execute agile and versatile locomotion tasks. This paper focuses on improving the dynamic performance of WBRs through innovations in both hardware and software development. Inspired by the human barbell squat, a bionic mechanical design is proposed and implemented as shown in Fig. 1. It distributes the weight onto its hip and knee joints to improve the effectiveness of joint motors while maintaining a relatively large workspace of the base link. Meanwhile, a novel model-based controller is devised, synthesizing height-variable wheeled linear inverted pendulum (HV-wLIP) model, Control Lyapunov Function (CLF) and whole-body dynamics for theoretically guaranteed stability and efficient computation. Compared with other alternatives, as a more accurate approximation of the WBR dynamics, the HV-wLIP can enable more agile response and provide theory basis for WBR controller design. Experimental results demonstrate that the robot could perform human-like deep squat, and is capable of maintaining tracking CoM velocity while manipulating base states. Furthermore, it exhibited robustness against external disturbances and unknown terrains even in the wild.
... The risk of injury in the knee areas is particularly high when performing barbell squats [9], making strengthening and conditioning essential [10]. Squat motions must be performed correctly to reduce the risk of knee and back injuries [11]. The biomechanical elements of barbell squats are associated with high levels of knee flexion, which increases the likelihood of injury to the knee joint itself [3]. ...
Background:
Squats are one of the most widely used weight training methods worldwide, and the single most ubiquitous with regard to multi-joint resistance training.
Objective:
The objective of the present study was to investigate kinematic and kinetic changes in the lower extremities as a result of load increases during a back squat exercise, and to propose an association between back squats and lower extremity injuries.
Methods:
Eight individuals with experience of back squat training were recruited. The subjects performed back squats with loads of 25%, 50%, 100%, and 125% of their body weight. During the performance, the center of pressure (COP) sway; vertical center of mass (COM) velocity; joint moment; joint range of motion (ROM) of flexion/extension and adduction/abduction; and rotation of the ankle, knee, and hip joints were measured.
Results:
The participants' lower extremity joint ROM, vertical COM velocity, and COP variability did not change significantly with changes in weight loading. However, the moments applied to the lower extremity joints differed according to changes in barbell weight. The moments of plantar flexion (f= 54.362, p< 0.001), dorsiflexion (f= 8.475, p< 0.001), knee flexion (f= 12.013, p< 0.001), knee extension (f= 8.581, p< 0.001), hip flexion (f= 5.111, p< 0.001), and hip extension (f= 11.053, p< 0.001) increased in the sagittal plane (flexion/extension). There was also a significant increase in ankle eversion (f= 5.612, p= 0.004), hip abduction (f= 3.242, p= 0.037), and adduction (f= 5.846, p= 0.003) in the frontal plane (adduction/abduction). Among the moment variables in the transverse plane (rotation), there were significant differences in ankle internal rotation (f= 7.043, p= 0.001) and hip external rotation (f= 11.070, p< 0.001).
Conclusion:
As the barbell load increased, posture and performance were maintained, but rotational moments of the joints differed. It is expected that the joint directions that showed significant differences in this study are likely to be vulnerable to the risk of injury when an excessive load is applied to the body. Examples include the hip adduction moment, hip external rotation moment, and ankle internal rotation moment, and apply regardless of the increase in the rotational moments of joints from load increases.
... The squat is a widely performed exercise which builds lower body strength and induces muscle hypertrophy for athletes [1,2] as well as non-athlete individuals and is commonly prescribed for rehabilitation [3,4]. However, squats may cause pain in individuals with back and knee problems [5,6]. In addition, there are concerns over the effectiveness of the squat, a bilateral exercise, in sports that require brief temporary weight support with only a unilateral lower extremity. ...
... Hence, when fatigue of the elbow flexors accumulates, trainees are restricted in their ability to involve other muscle groups to assist in completing further repetitions. Conversely, when squatting, trainees are less restricted in their movements and can thus alter exercise execution and increase the involvement of different muscle groups [16,17], for example, to compensate for quadriceps fatigue, trainees may implement greater hip flexion, which leads to increased involvement of the hamstring and gluteal muscles [18,19]. We therefore speculate that exercises that offer fewer opportunities for exercise modifications lead to better RIR predictions. ...
Background
A key role of resistance training (RT) coaches is to personalize programs based on their trainees’ abilities and goals. Specifically, coaches often assess how many repetitions in reserve (RIR) their trainees have until task-failure. Coaches can then modify the number of repetitions assigned per set accordingly. However, coaches’ ability to predict the number of RIR is unknown.
Methods
Certified RT coaches ( n = 259) were randomly assigned to watch a video of one of eight trainees. The trainees performed two sets of barbell squats and preacher biceps-curls, using 70% or 80% of their 1RM, to task-failure. The coaches predicted trainees’ RIR at 33%, 66%, and 90% of the total number of repetitions the trainees completed in each set. We fitted a linear mixed model with various predictors to the prediction errors as the outcomes (i.e., signed and unsigned values of the predicted minus actual repetitions to task-failure).
Results
The overall average number of repetitions completed by the trainees was 13.9. The average absolute errors were 4.8, 2.0, and 1.2 repetitions for the 33%, 66%, and 90% time-points, respectively. The absolute prediction error increased for the biceps-curl compared to the squat (1.43, 95% CI [1.13, 1.74]), but decreased for heavier loads (− 1.17, 95% CI [− 2.16, − 0.19]), and in the second set of each exercise (− 1.20, 95% CI [− 1.38, − 1.02]). Surprisingly, coaches’ years of experience had a negligible effect on the absolute error (− 0.020, 95% CI [− 0.039, − 0.0007]). Finally, coaches underpredicted the RIR at early time-points but reverted to slight overprediction at later time-points.
Conclusions
Prior coaching experience seems to play a minor role in RIR predictions. However, even short-term exposures to new trainees performing different exercises can substantially improve coaches’ RIR predictions.
... On the other hand, in LBBS, the trunk is inclined more forward than in HBBS, and the moment arm of the hip joint is larger [17]. This indicates that the degree of trunk bending and the change in the moment arm of the lower extremity joints are related to the muscle activity of the trunk [18]. ...
This study aimed to investigate the effect of the load and bar position on trunk and lower extremity muscle activity during squat exercise. High bar back squats (HBBS) and low bar back squats (LBBS) were performed in random order at 50%, 60%, and 70% loads of one repetition maximum by 28 experienced healthy adult men who had been performing squats for at least one year. Before the experiment, the maximal voluntary contraction of the vastus medialis, vastus lateralis, rectus femoris, biceps femoris, rectus abdominis, transverse abdominis, external oblique, and erector spinae muscles was measured by means of surface electromyography. In addition, eccentric and concentric exercises were performed for 3 s each to measure the muscle activity. There was a significant difference in muscle activity according to the load for all muscles in the eccentric and concentric phases (p < 0.05), indicating that muscle activity increased as the load increased. In addition, in the comparison between HBBS and LBBS, significant differences were shown in all lower extremity muscles and all trunk muscles except for the external oblique in the concentric phase according to the bar position (p < 0.05). HBBS showed a higher muscle activity of the lower extremity in the eccentric and concentric phases than in LBBS, while LBBS showed a higher muscle activity of the trunk muscle in the eccentric and concentric phases than in HBBS (p < 0.05). HBBS requires more force in the lower extremity than LBBS and is particularly advantageous in strengthening the muscular strength of the quadriceps. In contrast, LBBS requires more muscle activity in the trunk than HBBS and is more effective in carrying heavier loads because of the advantage of body stability. This study suggests that rehabilitation experts apply the bar position and load as important variables affecting the intensity and method of training for target muscle strengthening of the lower extremities and trunk.
... Squatting is a commonly performed exercise for the athletes. [3,4] Another squat variation which is commonly used in athlete population is the overhead http://annalsofrscb.ro squat. [5] Wrong movement patterns such as medio lateral rotation of the hip, the knee alignment inside or outside the hip during the movement provokes the amount of compressive and shear forces at the ankle, knee and hip joints [6,7] and this likely increases the chances of injuries. ...
Background: Altered or poor mechanics of movement creates tissue damage and stress leading to overuse injuries. It was observed that athletes with muscle imbalance had decreased playing performance and were at risk for injuries. Tight post chain structures could probably lead to altered mechanics of the overhead squat. Aim: To know whether giving a wedge beneath the heels partly nullifies the tightness in the posterior chain and improves the mechanics of the overhead squat. Methods: 30 collegiate male athletes from cricket, football and basketball were taken with a mean age of (21.37 + 2.34) years. All of them performed five overhead squats with and without a two inch wooden wedge kept beneath the heels. Results: We found shoulder flexion to improve by 3.27⁰ (+ 7. 79⁰) with the presence of a two inch wedge. Statistically significant (p = 0.024) difference was noted in shoulder flexion (46.32+ 9.58), Hip flexion (98.88+ 17.43) and (p= 0.0002), Knee flexion (114.27+ 21.79) and (p= 0.006), Ankle dorsiflexion (46.32+ 9.58) and (p= <0.0001) and the results were statistically significant. Conclusion: Based on our results, there was an increase in the range available for dorsiflexion at the ankle with the use of two inch wedge resulted in following kinematic changes: decreased shoulder flexion, increased knee flexion and increased hip flexion. The significant change in hip flexion after the use of wedge can be attributed to the shift in the center of gravity entirely.
Dive into the fascinating world of medical exercise therapy, where science and movement intersect to reveal the secrets of our muscular system. Starting with a gripping introduction to evidence-based exercise therapy, this chapter navigates through the complex anatomy and vital functions of the skeletal muscle. Learn how muscle and fat mass influence body weight and discover the diversity and uniqueness of muscle types. With a deep dive into muscle physiology, a window opens to the world of the sensorimotor system, the processes of muscle contraction, and the vital energy provision processes that drive our movements. Be fascinated by the workings of muscle spindles, Golgi tendon organs, and other key receptors that make our myofascial system a marvel of nature. Explore the differences between muscle fiber types and their specific roles in our body. Deepen your understanding of the various forms of muscle work and how they shape our physical performance. Immerse yourself in the world of training-related biomechanics, explore the essence of torque in strength training, and learn how biomechanical principles can help you avoid injuries and achieve your training goals more efficiently. In conclusion, the difference between the open and closed system in training is discussed, an essential aspect for optimizing your training routine. This chapter promises not only a profound understanding of the basics of medical exercise therapy but also exciting insights that will revolutionize your perspective on movement and health. Get ready to expand your knowledge and elevate your training practice to the next level.
Kinematic and kinetic considerations in the back squat among recreationally resistance-trained men PhD no. 70-2025
Background
Resistance training with the barbell back squat (BBS) exercise is practiced in sports, recreation, and rehabilitation. Although extensively debated, it is commonly believed and recommended that maintaining a neutral lumbopelvic alignment during BBS is an important technical aspect that might reduce the risk of injury. There is limited knowledge of how objectively measurable factors affect the extent to which the lumbopelvic region moves into flexion during a BBS.
Purpose
The aim of the study was to investigate the association among anthropometric measurements, range of motion in the hips and ankle joints, lumbopelvic movement control tests, and flexion of the lumbopelvic region during execution of the BBS.
Study design
Observational, cross sectional.
Methods
Eighteen experienced powerlifters and Olympic weightlifters were included and measurements of lumbopelvic movements were collected with inertial measurement units during BBS performed at 70 % of 1RM. Examination of anthropometric properties, range of motion in the hip and ankle joints, and lumbopelvic movement control tests were collected as independent variables. Linear regression analysis was used to investigate which independent variables were associated with lumbopelvic flexion during a BBS.
Results
The linear regression showed that a higher range of motion in ankle dorsiflexion could statistically significantly explain an increased amplitude of lumbopelvic flexion during the BBS. Anthropometrics, range of motion of the hips, and performance in lumbopelvic movement control tests did not show any statistically significant associations.
Conclusions
The results suggest that strength and conditioning professionals and clinicians who instruct and assess lifting technique in the BBS and/or use the BBS to assess performance or as an intervention should recognize that a higher range of motion in the ankle joints might affect lumbopelvic flexion during the BBS. In practice, the value of an individual assessment of lifting technique focusing on the goal of the movement should be emphasized.
PurposeTo compare the spine hinge evaluated by sacral inertial measurement unit (IMU) versus both lumbar and sacral IMUs and to assess the influence of clinical variables on the spine hinge.Methods
The study included 20 healthy participants (10 men and 10 women) and 18 participants (6 men and 12 women) with low back pain. Participants performed a bodyweight squat with IMU sensors attached to the lumbar spine, sacrum, and lateral thigh. The spine hinge was evaluated by two methods: lumbosacral hinge (LS hinge), defined as an abrupt increase in LS flexion, and sacral hinge, defined as a change in sacral direction from forward to backward. The amount of and ratio (LS ratio) between sacral and lumbar rotations were evaluated.ResultsThe spine hinge detected only from the sacral IMU showed a high degree of agreement with that detected from both IMUs. The LS hinge occurred at a lower depth in females than in males (p = 0.001). Females had greater sacral rotation (p = 0.012) and a higher LS ratio (p < 0.001) than males. A larger passive hip flexion range was associated with later LS hinge occurrence in females (p = 0.041) but not in males (p = 0.965). Trunk muscle strength and presence of low back pain were not significant in either sex.ConclusionIMUs can detect the squat depth when the spine hinge occurs. A single sacral IMU is sufficient to detect the spine hinge. The movement patterns differ between sexes during squats, which should be considered to achieve the optimal squat depth.
The three most fundamental variations of the barbell squat with the bar placed on the shoulders are the high-bar back squat (HBBS), the low-bar back squat (LBBS), and the front squat (FS). There are significant kinematic, kinetic, and biomechanical distinctions between these variations that should be considered in the exercise selection. In comparison to the high-bar variations, the LBBS results in a greater hip joint torque and greater activation of the hip extensor muscles. In contrast, during the FS, the m. quadriceps is utilized more compared to the other two variations due to an increased torque in the knee joint. Regarding the relation between hip and knee joint torques, the HBBS is an intermediate and more balanced exercise variation than the LBBS and the FS. The HBBS is a fundamental exercise in athletic conditioning and a suitable starting point for novices, whereas the LBBS is preferred when the primary objective is to maximize weightlifting performance. The FS is crucial for athletes performing the clean and its derivates since it trains the required body position for a successful catch and might be the biomechanically advantageous variation if the goal is to target the knee extensor muscles. However, the differences in terms of knee extensor demands, muscle activation and kinematics between the HBBS and FS seem to be minimal, as the literature indicates similar results when comparing the FS to the HBBS. As far as analysis methods are concerned, even though 3D movement analysis is regarded as the gold standard for motion capture and analyzing kinematics, 2D models seem to serve as a valid initial guide in order to understand the kinematics and biomechanics of different squat variations.
Squatting is a common daily activity and fundamental exercise in resistance training and closed kinetic chain programs. The aim of the present study was to investigate the effects of an experimentally induced weakness of the gluteal muscles on joint kinematics, reactions forces (JRFs), and dynamic balance performance during deep bilateral squats in healthy young adults. Ten healthy adults received sequential blocks of 1) branch of the superior gluteal nerve to the tensor fasciae latae (SGNtfl) muscle, 2) superior gluteal nerve (SGN), and 3) inferior gluteal nerve (IGN) on the dominant right leg. At the control condition and following each block, the participants were instructed to perform deep bilateral squats standing on two force plates. Hip, knee, ankle, and pelvis kinematics did not differ significantly following iatrogenic weakness of gluteal muscles. The most important finding was the significant differences in JRFs following SGN and IGN block, with the affected hip, patellofemoral, and ankle joint demonstrating lower JRFs, whereas the contralateral joints demonstrated significantly higher JRFs, especially the patellofemoral joint which demonstrated an average maximum difference of 1.43 x body weight compared to the control condition. When performing a deep bilateral leg squat under SGN and IGN block, the subjects demonstrated an increased center of pressure (CoP) range and standard deviation (SD) in mediolateral compared to the control condition. These results imply that squat performance changes significantly following weakness of gluteal muscles and should be considered when assessing and training athletes or patients with these injuries. This article is protected by copyright. All rights reserved.
Objectives:
The effect of knee position on joint moments during squats has been studied; however, the effect of trunk angle has been less well investigated. This study evaluated the effect of both trunk and knee sagittal plane position on the distribution of moments between the hip and knee extensors during the bilateral squat.
Design:
Observational study.
Setting:
Biomechanics laboratory.
Participants:
One hundred individuals performed bilateral squats.
Main outcome measures:
Motion and force data were collected using motion capture and force plates. Trunk and shank angles and hip and knee moments were calculated. A linear regression was used to associate the ratio between the hip and knee moments (hip-to-knee moment ratio) with the sagittal plane trunk and shank angles, while accounting for six squat depths (between 60° and 110° of knee flexion) and side.
Results:
Trunk angle and shank angle each contributed to the hip-to-knee moment ratio (P < .001) with trunk accounting for a higher proportion of variance than the other variables. The hip-to-knee moment ratio increased with increasing trunk angle and with decreasing shank angle.
Conclusions:
This large cohort study supports the use of trunk position to instruct squat technique with the goal of modifying hip and knee moments.
The purpose was to specify lower extremity joint angles in different squats for the future development of adequate computational models of the joints.
Methods: We investigated joint angles in the lower extremity joints in 103 athletes in different types of squats with and withoutadded weight (barbell) 75% of 1 repetition maximum.results. the mean knee and hip flexion and ankle dorsiflexion angles in horizontal squats are respectively 113.42°, 128.21°, and 23.27°; in half-squats 70.60°, 87.94°, and 15.60°; in lunges 98.04°, 96.36°, and 8.02°; in Smith machine squats 94.42°, 106.28° and 4.46°. in a horizontal squat with a barbell, the knee joint flexion and the ankle joint dorsiflexion angles are significantly larger(by 4.56° and 3.11°, respectively) than in squats without added weight. the knee joint flexion and ankle dorsiflexion angles inlunges are significantly less in barbell squats (by 4.15° and 4.37°, respectively). the knee flexion angle in horizontal barbellsquats in male athletes is significantly larger than in female athletes (by 4.71°).
Conclusions: The mean knee and hip flexion and ankle dorsiflexion angles in different types of squats are established and maybe used for further research. Horizontal squats produce greater lower extremity joint angles.
Background
Performance asymmetries between the lower limbs have been reported across a variety of variables and for numerous motor tasks including double leg squats. Additionally, the degree of symmetry is often used as a recovery metric during rehabilitation programs.
Hypothesis/Purpose
The purpose of this investigation was to examine leg asymmetry during a bodyweight double leg squat task and assess the effects of squat speed in a physically active population.
Study Design
Cross-over Study Design.
Methods
Eighteen healthy individuals completed two sets of 20 squats at two tempos (preferred tempo and 60 bpm) while ground reaction force and center of pressure data were recorded using dual force plates. Peak vertical ground reaction force, force impulse, and center of pressure (COP) standard deviation in the anterior-posterior (AP) and mediolateral (ML) direction were calculated and analyzed to identify any differences between legs, tempo, and as a function of repetitions. Significance was set at ρ ≤ .05.
Results
The subjects exhibited greater ground reaction forces during the self-paced tempo compared to the metronome-paced tempo ( F 1,79 = 14.48, p < .001) with the preferred leg generating larger values than the non-preferred leg during the self-paced condition. There was also a significant tempo x leg interaction for force impulse ( F 1,79 = 5.927, p = 0.015). A greater amount of COP variability was found in the preferred leg compared to the non-preferred leg in both the AP ( F 1,79 = 30.147, p < 0.001) and ML ( F 1,79 = 41.204, p < 0.001) directions.
Conclusions
These findings highlight the importance of considering multiple levels of analysis when assessing lower limb symmetry as separate variables may provide differential evidence for asymmetry. Practically, these results emphasize the need for coaches and practitioners to consider different degrees of lower limb asymmetries that may impact the development and design of strength and rehabilitation programs.
Level of Evidence
3
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.
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.
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.
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
This study investigated the muscular torques and joint forces during the parallel squat as performed by weightlifters. (JD)
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.
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.
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.
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.
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)
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.
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.
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.
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
FRY, A.C., T.A. ARO, J.A. BAUER, AND W.J. KRAEMER. A comparison of methods for determining kinematic properties of
three barbell squat exercises. J. Hum. Move. Stud. 24:83-95. 1993.
The deep squat exercise as utilized in weight training for athletes and its effect on the ligaments of the knee
KLEIN, K.K. The deep squat exercise as utilized in weight training for athletes and its effect on the ligaments of the knee. J.
Assoc. Phys. Mental Rehab. 15:6-11. 1961.
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
- H J Yack
- C E Collins
- T J Whieldon T Ramsey
- G Calhoon
- M Matuszak
- T Ireland
- D Bullen
- L E Wood
- P Grindstaff
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.