For years I have been instructing how difficult/impossible it is for hamstrings to be involved during the back squat movement bio-mechanically and supporting with research.
Well, add this to the collection of excellent coverage: LINK
Literature does not support the view of hamstrings involvement during the back squat and here are a few other great articles:
- Isear Jr, J. A., Erickson, J. C., & Worrell, T. W. (1997). EMG analysis of lower extremity muscle recruitment patterns during an unloaded squat. Medicine & Science in Sports & Exercise, 29(4), 532.
- McCaw, S. T., & Melrose, D. R. (1999). Stance width and bar load effects on leg muscle activity during the parallel squat. Medicine & Science in Sports & Exercise, 31(3), 428.
- Escamilla, R. F., Fleisig, G. S., Zheng, N., Lander, J. E., Barrentine, S. W., Andrews, J. R., & Moorman, C. T. (2001). Effects of technique variations on knee biomechanics during the squat and leg press. Medicine & Science in Sports & Exercise, 33(9), 1552-1566.
- Manabe, Y., Shimada, K., & Ogata, M. (2007). Effect of slow movement and stretch-shortening cycle on lower extremity muscle activity and joint moments during squat. Journal of Sports Medicine and Physical Fitness, 47(1), 1-12.
- Paoli, A., Marcolin, G., & Petrone, N. (2009). The effect of stance width on the electromyographical activity of eight superficial thigh muscles during back squat with different bar loads. The Journal of Strength & Conditioning Research, 23(1), 246-250.
- Li, Y., Cao, C., & Chen, X. (2013). Similar Electromyographic Activities of Lower Limbs Between Squatting on a Reebok Core Board and Ground. The Journal of Strength & Conditioning Research, 27(5), 1349-1353.
- Aspe, R. R., & Swinton, P. A. (2014). Electromyographic and kinetic comparison of the back squat and overhead squat. The Journal of Strength & Conditioning Research, 28(10), 2827-2836.
- Yavuz, H. U., Erdağ, D., Amca, A. M., & Aritan, S. (2015). Kinematic and EMG activities during front and back squat variations in maximum loads. Journal of sports sciences, (ahead-of-print), 1-9.
- Contreras, B., Vigotsky, A. D., Schoenfeld, B. J., Beardsley, C., & Cronin, J. (2015). A Comparison of Gluteus Maximus, Biceps Femoris, and Vastus Lateralis EMG Amplitude in the Parallel, Full, and Front Squat Variations in Resistance Trained Females. Journal of applied biomechanics.
One of the best was the MRI research on German bodybuilders and muscle recruitment in a book called “Muscle Meets Magnet – a revolutionary MRI analysis of muscle use during lifting” by Per A Tesch, PhD (1993).