Thus, changes in the internal moment arm lengths of the gluteus maximus and hamstrings do not appear to explain the greater hip extension moment in greater degrees of hip flexion angle. (strengthandconditioningresearch.com)
Although many different biomechanical factors increased with jump training, it was the increase in hip flexion angle (which leads to a longer countermovement phase, a longer duration concentric phase, and more concentric work done) and an increase in hip joint work done that were most important for driving the gains in jump height, at least on a joint level. (strengthandconditioningresearch.com)
They report no gains in hip flexion range of motion from foam rolling the hamstrings for 8 weeks (9), indicating that effects of foam rolling are neither cumulative nor last over longer periods of time. (journals.lww.com)