Knee Valgus Collapse from Dave Parise CPT FPTA MES on Vimeo.
Many beginners cave inward at the knees during a squat on account of insufficient ankle dorsiflexion range of motion or very poor gluteal strength. I surmise that the lateral hamstrings (biceps femoris long head) would be stretched to a greater degree in knee valgus, whereas the adductors and possibly the medial hamstrings (semitendinosus and semimembranosus) but not the gluteus maximus or lateral hamstrings (biceps femoris long head) might have greater hip extension moment arms in knee valgus, but this would require research for verificaiton. A recent article published in Clinical Biomechanics with the title, indicates that the hip external rotators (namely the piriformis and obturator internus) are in fact strong extensors of the hip, and their length is increased in hip flexion and adduction (meaning that they produce greater passive elastic force at the bottom of a squat, and this is enhanced when the knees are caved inward). Considering that the hips are heavily reliaed opon as load increase in the squat, it makes sense that lifters would resort to mechanical strategies that would enhance the strength of the hips with maximal squat loads.
My current position on the knees out debate is that:
- Beginners must learn the rules before they can break the rules and master the knees out technique when squatting
- A “valgus twitch” is acceptable for powerlifters and Olympic weightlifters as long as it’s not associated with knee pain
- Since many individuals appear to be stronger in slight knee valgus, this indicates that their hip extension torque production is stronger in slight hip adduction and internal rotation
- Future research should investigate the hip extension torque capabilities and partition the individual contributors to hip extension torque in deep hip flexion with varying levels of knee varus/valgus
