One the most common injuries in sports is a pulled hamstring. Various mechanismscan cause hamstring pulls, including strength imbalances between the quadriceps andhamstrings, weak hamstrings, tight hamstrings, and asynchronous firing by the nervesthat innervate the hamstrings. Out of all of these proposed mechanisms, weakness in thehamstrings gets the most attention.
Traditionally among coaches and sports medicine specialists, leg curls have beenthe exercise of choice for the hamstrings. This is probably due to the hamstrings’ well-described isolated function of knee flexion and hip extension. A better understanding ofhow the description of muscle function originated will enlighten us and show us how tobetter view muscle function for optimum training.
The isolated functions of muscles were first described in cadavers, who wereobviously in horizontal, nonstanding positions. In this position, the mainline of the bodycontacts the ground. Therefore, any muscle action must pull the extremity (e.g., the legand foot) toward the mainline of the body. The classification of origin and insertionis derived from this observation. Further, when studying the cadaver in the lab, theeccentric component of muscle action cannot really be appreciated, especially in thetransverse plane.
Therefore, traditional descriptions of muscle actions have only focusedon concentric muscle action. Rarely is the eccentric component or movement in thetransverse plane well documented or emphasized.There is a tremendous difference between a muscle’s isolated function and amuscle’s integrated function. In the case of the hamstrings, when the foot hits the groundduring running, the integrated function greatly expands beyond its traditional description.During running, the foot contacts the ground and the body’s center of mass moves overthe foot. Due to its ground contact, the foot, not the hip, acts as the origin of movement.Unlike in the cadaver lab, where the hips lie against the ground (or table), in running,the hips move over the foot (because it is stationary against the ground). If viewed fromthis perspective, hamstring function becomes easier to understand.
Additionally, takingthe eccentric and rotational role of the hamstrings into consideration can provide a betterunderstanding of their conditioning. This is especially relevant since most hamstring pullsoccur during the eccentric actions of the blocking and plant phases, with the majorityoccurring during the plant phase.Let’s get a more detailed view of the hamstrings’ major functions during running.
Figure 1, A-E
E
Let’s get a more detailed view of the hamstrings’ major functions during running.
Figure 1, A-E
femoris) after heel strike—1E
Like other muscles that cross two joints, the hamstrings sometimes performeconcentrically prior to foot strike. Econcentric is a term PT Gary Gray (2) coined todescribe situations where a single muscle is simultaneously working concentrically at one
joint (e.g., hip) and eccentrically at another joint (e.g., knee); this action is illustrated bythe right leg in figures 1C and 1D.
With this basic understanding of how the hamstrings work functionally duringrunning, using a leg curl to condition or rehabilitate them does not seem prudent. Theisolated and unnatural movement of the leg curl could make the hamstrings more prone to
injury. Most athletes perform leg curls, yet athletic training rooms across the country areplagued by hamstring pulls. Part II of this article will illustrate a protocol that can helpdevelop stronger and more functional hamstrings.
References
1) Clark, M. 1999. A scientific approach to lower extremity functional anatomy.
Scottsdale, AZ: The Athletic Institute.
2) Gray, G.W. 1996. Chain reaction festival (Course Manual). Adrian, MI:
Wynn Marketing.
