Biomechanics of the squat
Introduction
Dunn et al. (1984) states the squat exercise has become one of the most important resistance-training exercises in sports training, general weight training, and physical rehabilitation. A study by Escamilla et al. (2001) states the squat measures lower body and trunk strength, the starting position for the squat is when the lifter is in the upright position with hips and knees near full extension. The lifter then descends until an imaginary line from the top of the knees to the hips moves in line or below the parallel position, and in a continuous motion the lifter ascends back to the upright position. The following report will look to analyse the different biomechanical factors which play a key role in the performing of the squat exercise.
Restricted vs unrestricted squat
Dunn et al. (1984) states incorrect technique is one of the most important factors contributing to injury when an athlete performs the squat exercise. Ariel (1974) suggests from a biomechanical viewpoint, it has been reported that the forward movement of the knees when doing the squat is linked with greater shearing forces on the knee. McLaughlin, Dillman, & Lardner (1977) carried out a study on national level power lifters and less skilled squatters, the study reported less killed squatters had the tendency to lean forwards, developing greater trunk torque. The more successful lifters moved their knees anteriorly to a lesser extent, generating lower knee extensor torque. Fry, Smith, & Schilling (2003) state it is clear that maximal torques for the knee during the exercise occurs in the bottom position (greatest knee flexion), while the maximal torque for the hips occurs during the second half of the concentric phase.
Chandler & Stone (1991) state common guidelines for correct technique when performing the squat include keeping the shins as vertical as possible in order to reduce shear stress on the knee, these guidelines suggest avoiding letting the knees travel past the toes. The squat can be performed in a restricted and unrestricted type; the restricted type only allows the knees to move until they reach the vertical line of the toes, and the unrestricted allows the knees to move as far past the toes as necessary. A study by Fry, Smith, & Schilling (2003) looked at the two technique variations, the participants were seven recreationally weight trained men, each participant did 1 set of 3 repetitions. The results from the study found significantly greater torque was produced at the hips and less torque was produced at the knees in the restricted squat when compared to the unrestricted squat. List, Gulay, & Lorenzetti (2010) state the range of motion during the pelvic and lumbar segment during squatting increases with a restriction in knee motion. So the stress on the lower back is lower during an unrestricted squat. For these reasons, the unrestricted squat may be the right choice for most athletes.
Stance width and foot rotation
Escamilla et al. (2001) states strength athletes often employ the barbell squat in their training or rehabilitation regimes. These athletes use the squat to improve hip, thigh, and back strength. However, varying squat stance widths and foot angles are employed in training depending on the athletes’ goals; the effectiveness of one stance over another is unclear. The study carried out by Escamilla et al. (2001) found trunk angle was not significantly different among the three stance groups (narrow stance, medium stance, & wide stance) at 45 degrees, 90 degrees, and maximum knee flexion. However, greater hip flexion, a more horizontal thigh position, and more vertical shank position were found in the medium stance and wide stance compared to the narrow stance. This happened because the narrow stance had around 4-6cm greater forward knee movement in the direction of the toes. Ariel (1974) states greater forward knee movements have been shown to increase knee shear forces. This suggests that using a medium or wide stance may be more effective than narrow stance to minimise knee shear forces.
Almosnino, Kingston, & Graham (2013) state trainees may adopt a stance width and foot rotation that they feel is most comfortable for them during performance. Out of the stance widths used in their study, the majority of participants preferred performing the squat with a stance width of shoulder width apart and feet rotated outwards 30 degrees.
Squat depth
Escamilla (2001) and Schoenfeld (2010) suggest that squatting depths below 90 degrees does not encourage greater neural stimuli of the quadriceps, because the activity signals remain constant. Abandonment of deep squats minimises the magnitude of tibio- and patellofemoral compressive stress as well. The quarter and half squat require higher weights to induce effective training stimuli to the leg and hip extensors due to the advantage of higher strength developing conditions at larger extension angles. Hartmann, Wirth, & Kluseman (2013) state it is unclear why higher risk of injury during deep squats is hypothesised, although lower weights are accomplished when performing deep squats, when deep squats are compared to half and quarter squats, lower knee joint and spinal stress can be expected. Providing the technique is performed accurately, with progressive training loads, the deep squat presents an effective training exercise for protection against injuries and strengthening of the lower extremities.
Back squat and Front squat
Two forms of squat are the back squat and the front squat, people concerned with fitness often perform the back squat, and the front squat isn’t used as often. Although both techniques both work the lower back, hip, and leg muscles, there are variations in the technique required to perform them and the muscular involvement. The amount of weight an individual can lift varies on the technique used, but greater weights are often performed using the back squat.
Gullet et al. (2009) states the back squat (Figure 1) involves positioning the barbell across the shoulders on the trapezius, and allowing the hips and knees to slowly flex until the thighs are parallel to the floor. The individual then extends the hips and knees until reaching the starting position, with emphasis on keeping the back flat, the heels on the floor, and the knees aligned over the feet.
Figure 1. Back squat
Dunn et al. (1984) states the squat exercise has become one of the most important resistance-training exercises in sports training, general weight training, and physical rehabilitation. A study by Escamilla et al. (2001) states the squat measures lower body and trunk strength, the starting position for the squat is when the lifter is in the upright position with hips and knees near full extension. The lifter then descends until an imaginary line from the top of the knees to the hips moves in line or below the parallel position, and in a continuous motion the lifter ascends back to the upright position. The following report will look to analyse the different biomechanical factors which play a key role in the performing of the squat exercise.
Restricted vs unrestricted squat
Dunn et al. (1984) states incorrect technique is one of the most important factors contributing to injury when an athlete performs the squat exercise. Ariel (1974) suggests from a biomechanical viewpoint, it has been reported that the forward movement of the knees when doing the squat is linked with greater shearing forces on the knee. McLaughlin, Dillman, & Lardner (1977) carried out a study on national level power lifters and less skilled squatters, the study reported less killed squatters had the tendency to lean forwards, developing greater trunk torque. The more successful lifters moved their knees anteriorly to a lesser extent, generating lower knee extensor torque. Fry, Smith, & Schilling (2003) state it is clear that maximal torques for the knee during the exercise occurs in the bottom position (greatest knee flexion), while the maximal torque for the hips occurs during the second half of the concentric phase.
Chandler & Stone (1991) state common guidelines for correct technique when performing the squat include keeping the shins as vertical as possible in order to reduce shear stress on the knee, these guidelines suggest avoiding letting the knees travel past the toes. The squat can be performed in a restricted and unrestricted type; the restricted type only allows the knees to move until they reach the vertical line of the toes, and the unrestricted allows the knees to move as far past the toes as necessary. A study by Fry, Smith, & Schilling (2003) looked at the two technique variations, the participants were seven recreationally weight trained men, each participant did 1 set of 3 repetitions. The results from the study found significantly greater torque was produced at the hips and less torque was produced at the knees in the restricted squat when compared to the unrestricted squat. List, Gulay, & Lorenzetti (2010) state the range of motion during the pelvic and lumbar segment during squatting increases with a restriction in knee motion. So the stress on the lower back is lower during an unrestricted squat. For these reasons, the unrestricted squat may be the right choice for most athletes.
Stance width and foot rotation
Escamilla et al. (2001) states strength athletes often employ the barbell squat in their training or rehabilitation regimes. These athletes use the squat to improve hip, thigh, and back strength. However, varying squat stance widths and foot angles are employed in training depending on the athletes’ goals; the effectiveness of one stance over another is unclear. The study carried out by Escamilla et al. (2001) found trunk angle was not significantly different among the three stance groups (narrow stance, medium stance, & wide stance) at 45 degrees, 90 degrees, and maximum knee flexion. However, greater hip flexion, a more horizontal thigh position, and more vertical shank position were found in the medium stance and wide stance compared to the narrow stance. This happened because the narrow stance had around 4-6cm greater forward knee movement in the direction of the toes. Ariel (1974) states greater forward knee movements have been shown to increase knee shear forces. This suggests that using a medium or wide stance may be more effective than narrow stance to minimise knee shear forces.
Almosnino, Kingston, & Graham (2013) state trainees may adopt a stance width and foot rotation that they feel is most comfortable for them during performance. Out of the stance widths used in their study, the majority of participants preferred performing the squat with a stance width of shoulder width apart and feet rotated outwards 30 degrees.
Squat depth
Escamilla (2001) and Schoenfeld (2010) suggest that squatting depths below 90 degrees does not encourage greater neural stimuli of the quadriceps, because the activity signals remain constant. Abandonment of deep squats minimises the magnitude of tibio- and patellofemoral compressive stress as well. The quarter and half squat require higher weights to induce effective training stimuli to the leg and hip extensors due to the advantage of higher strength developing conditions at larger extension angles. Hartmann, Wirth, & Kluseman (2013) state it is unclear why higher risk of injury during deep squats is hypothesised, although lower weights are accomplished when performing deep squats, when deep squats are compared to half and quarter squats, lower knee joint and spinal stress can be expected. Providing the technique is performed accurately, with progressive training loads, the deep squat presents an effective training exercise for protection against injuries and strengthening of the lower extremities.
Back squat and Front squat
Two forms of squat are the back squat and the front squat, people concerned with fitness often perform the back squat, and the front squat isn’t used as often. Although both techniques both work the lower back, hip, and leg muscles, there are variations in the technique required to perform them and the muscular involvement. The amount of weight an individual can lift varies on the technique used, but greater weights are often performed using the back squat.
Gullet et al. (2009) states the back squat (Figure 1) involves positioning the barbell across the shoulders on the trapezius, and allowing the hips and knees to slowly flex until the thighs are parallel to the floor. The individual then extends the hips and knees until reaching the starting position, with emphasis on keeping the back flat, the heels on the floor, and the knees aligned over the feet.
Figure 1. Back squat
The front squat (figure 2) involves the lifter positioning the barbell across the anterior deltoids and clavicles and fully flexing the elbows to position the upper arms parallel to the floor. The descending and ascending motions are much the same as in the back squat.
Figure 2. Front squat
Figure 2. Front squat
A study by Gullet et al. (2009) found bar position did not influence muscle activation, muscle activity was different between the ascending and descending phases, the front squat shown to be just as effective as the back squat for muscle recruitment.
Conclusion
This article has looked at the range of aspects that can be taken into consideration when performing squats; the key findings from the articles suggest the unrestricted squat may be better for athletes as there is less stress put on the lower back. Athletes should adopt a stance width and foot rotation they feel is comfortable for performance. In regards to squat depth, deep squats are effective for injury prevention and strengthening of the lower extremities. Finally minimal differences were found between back & front squats, therefore, the technique adopted should be favourable to the athlete.
References
Almosnino, S., Kingston, D. and Graham, R. (2013) Three-Dimensional knee joint movements during performance of the body weight squat: Effects of stance width and foot rotation. Journal of Applied Biomechanics. Vol. 29: 33-43.
Ariel, B.G. (1974) Biomechanical analysis of the knee joint during deep knee bends with heavy load. In: Biomechanics. (1st ed.) Baltimore: University Park Press: Nelson and C. Morehouse.
Chandler, T.J. and Stone, M.H. (1991) the squat exercise in athletic conditioning: A position statement and review of the literature. Strength & Conditioning Journal. Vol. 13: 51-60.
Dunn, B., Klein, K., Kroll, B., McLaughlin, T., O'Shea, P. and Wathen, D. (1984) Coaches round table: The squat and its application to athletic performance. Strength & Conditioning Journal. Vol. 6: 10-22.
Escamilla, R.F. (2001) Knee biomechanics of the dynamic squat exercise. Medicine and science in sports and exercise. Vol. 33: 127-141.
Escamilla, R.F., Fleisig, G.S., Lowry, T.M., Barrentine, S.W. and Andrews, J.R. (2001) A three-dimensional biomechanical analysis of the squat during varying stance widths. Medicine & Science in Sports & Exercise. Vol. 33, No. 6: 984-998.
Fry, A., Smith, C. and Schilling, B. (2003) Effect of Knee Position on Hip and Knee Torques During the Barbell Squat. Journal of Strength and Conditioning Research. Vol. 17, No. 4: 629-633.
Gullett, J.C., Tillman, M.D., Gutierrez, G.M. and Chow, J.W. (2009) A Biomechanical Comparison of Back and Front Squats in Healthy Trained Individuals. Journal of Strength and Conditioning Research. Vol. 23, No. 1: 284-292.
Hartmann, H., Wirth, K. and Kluseman, M. (2013) Analysis of the load on the knee joint and vertebral column with changes in squatting depth and weight load. Sports Medicine. Vol. 43: 993-1008.
List, R., Gulay, T. and Lorenzetti, S. (2010) Kinematics of the trunk and the spine during unrestricted and restricted squats - a preliminary analysis. International Symposium on Biomechanics in Sports: Conference. Vol. 28
McLaughlin, T.M., Dillman, C.J. and Lardner, T.J. (1977) A kinematic model of performance in the parallel squat by champion powerlifters. Medicine and Science in Sports. Vol. 9: 128-133.
Schoenfeld, B.J. (2010) Squatting kinematics and kinetics and their application to exercise performance. Journal of Strength and Conditioning research. Vol. 24: 3497-3506.
Conclusion
This article has looked at the range of aspects that can be taken into consideration when performing squats; the key findings from the articles suggest the unrestricted squat may be better for athletes as there is less stress put on the lower back. Athletes should adopt a stance width and foot rotation they feel is comfortable for performance. In regards to squat depth, deep squats are effective for injury prevention and strengthening of the lower extremities. Finally minimal differences were found between back & front squats, therefore, the technique adopted should be favourable to the athlete.
References
Almosnino, S., Kingston, D. and Graham, R. (2013) Three-Dimensional knee joint movements during performance of the body weight squat: Effects of stance width and foot rotation. Journal of Applied Biomechanics. Vol. 29: 33-43.
Ariel, B.G. (1974) Biomechanical analysis of the knee joint during deep knee bends with heavy load. In: Biomechanics. (1st ed.) Baltimore: University Park Press: Nelson and C. Morehouse.
Chandler, T.J. and Stone, M.H. (1991) the squat exercise in athletic conditioning: A position statement and review of the literature. Strength & Conditioning Journal. Vol. 13: 51-60.
Dunn, B., Klein, K., Kroll, B., McLaughlin, T., O'Shea, P. and Wathen, D. (1984) Coaches round table: The squat and its application to athletic performance. Strength & Conditioning Journal. Vol. 6: 10-22.
Escamilla, R.F. (2001) Knee biomechanics of the dynamic squat exercise. Medicine and science in sports and exercise. Vol. 33: 127-141.
Escamilla, R.F., Fleisig, G.S., Lowry, T.M., Barrentine, S.W. and Andrews, J.R. (2001) A three-dimensional biomechanical analysis of the squat during varying stance widths. Medicine & Science in Sports & Exercise. Vol. 33, No. 6: 984-998.
Fry, A., Smith, C. and Schilling, B. (2003) Effect of Knee Position on Hip and Knee Torques During the Barbell Squat. Journal of Strength and Conditioning Research. Vol. 17, No. 4: 629-633.
Gullett, J.C., Tillman, M.D., Gutierrez, G.M. and Chow, J.W. (2009) A Biomechanical Comparison of Back and Front Squats in Healthy Trained Individuals. Journal of Strength and Conditioning Research. Vol. 23, No. 1: 284-292.
Hartmann, H., Wirth, K. and Kluseman, M. (2013) Analysis of the load on the knee joint and vertebral column with changes in squatting depth and weight load. Sports Medicine. Vol. 43: 993-1008.
List, R., Gulay, T. and Lorenzetti, S. (2010) Kinematics of the trunk and the spine during unrestricted and restricted squats - a preliminary analysis. International Symposium on Biomechanics in Sports: Conference. Vol. 28
McLaughlin, T.M., Dillman, C.J. and Lardner, T.J. (1977) A kinematic model of performance in the parallel squat by champion powerlifters. Medicine and Science in Sports. Vol. 9: 128-133.
Schoenfeld, B.J. (2010) Squatting kinematics and kinetics and their application to exercise performance. Journal of Strength and Conditioning research. Vol. 24: 3497-3506.