The hamstrings are an essential component of the posterior chain of muscles stabilizing our back and legs.  Despite the hamstring’s importance, length, and strength production they remain a commonly injured muscle seen in our Boulder Physical Therapy practice.  Our previous post described the importance of using different exercises to target the top and bottom portions of the muscle but additional research shows the impact of machine vs. free weight exercises. 

Zebis and colleagues studied healthy volunteers to determine the relative contribution of the 3 hamstring muscles during commonly utilized strengthening exercises (Br J Sp Med. 2012).  Many exercises recruited the inside and outside hamstring muscles evenly including nordic hamstring curls, hamstring curls on a ball, and seated machine leg curls.  Two exercises targeted the 2 inside hamstring muscles more than the outside including a kettlebell swing and the romanian deadlift.  Conversely, horizontal back extensions against gravity and horizontal machine leg curls recruited the outside more than the inside hamstrings.