Brad Schoenfeld answers this question in his latest post over at Look Great Naked. Hamstrings are one of my weak areas so knowing if its possible to target different aspects of the muscle will help me maximize my efforts this offseason.
In this post I want to delve into the specifics of a study I recently published in the Journal of Strength and Conditioning Research that investigated muscle activation in two popular hamstrings exercises: the stiff leg deadlift and the lying leg curl. While other studies have evaluated differences between these exercises in activation of the medial hamstrings (semitendinosus and semimembranosus) versus the lateral hamstrings (biceps femoris), our study is unique in that we also looked at activity in the upper and lower aspects of the individual muscles.
My interest in undertaking this work revolves around an emerging body of research showing that, contrary to popular belief, muscle fibers do not necessarily span from origin to insertion. Rather, many muscles are compartmentalized so that fibers terminate intrafascicularly (within the fascicle) with each subdivision innervated by its own nerve branch. This structure provides a mechanism by which different exercises can conceivably target portions of a given muscle. It just so happens that several studies have shown that the hamstrings muscles are in fact partitioned in a manner that would potentially allow for such regional-specific activation. I thus decided to test this hyptothesis in the lab under controlled conditions.