Hamstring Muscle Mechanics and Function During Sprinting
Darryl G. Thelen, PhD

Assistant Professor
University of Wisconsin-Madison

The hamstrings are the most commonly injured muscle group in sports that involve high speed sprinting. Effective treatment and rehabilitation of individuals with hamstring strain injuries remains a challenge, as demonstrated by an approximately one-third rate of recurrent injuries. Suggestions for preventing hamstring injuries are often generic and broad due, in part, to a limited scientific understanding of the mechanics and function of the hamstring muscles during sprinting. To fill this void, we are conducting a systematic analysis of hamstring muscle lengths, loads and energetic function during the gait cycle of sprinting humans. These data will enable us to describe how a high-speed, three-dimensional movement is produced at the individual muscle level where the injury is occurring.

Our first objective is to characterize hamstring muscle kinematics during treadmill and overground sprinting in healthy subjects. It is generally believed that acute hamstring muscle strain injuries occur as a result of a lengthening contraction during the sprinting gait cycle. However, it is not well understood where in the gait cycle such conditions occur, or how increasing to maximum running speed affects the mechanical state of the hamstring muscles. We will measure three-dimensional kinematics and lower extremity electromyographic (EMG) signals during treadmill sprint running at 60%, 80%, 90% and 100% of maximal running speed on a treadmill, and during overground sprint running at 100% of maximal overground speed. Experimental data will be used along with a scaled, three-dimensional musculoskeletal model to determine muscle-tendon lengths and velocities throughout the gait cycle. These data will lend new insights into the kinematic state of the hamstring muscles throughout the gait cycle, and an understanding of how hamstring muscle-tendon stretch varies between treadmill and overground sprinting.

Our second objective is to characterize hamstring muscle kinetics and mechanical function during sprinting. It has been suggested that the function of the hamstring muscles is critical to sprinting performance, with the muscle possibly acting eccentrically to decelerate the rapidly moving swing leg prior to foot contact. Biarticular muscles, such as the hamstring muscles, have unique energetic capabilities and could potentially accomplish this task by absorbing energy and/or transferring energy across multiple body segments. While electromyographic signals can be used to determine when hamstring muscles are active, they do not provide an indication of how the muscles control and generate sprinting movement. In this study, we will also use novel computational algorithms to estimate the muscle fiber lengths, forces and powers used to drive the movement. This will be followed by analytical techniques to compute the specific mechanical energy contributions of the hamstring muscles to leg and body motion during sprinting.

Collectively, successful completion of the two objectives will elucidate the basic mechanics and function of the hamstring muscles during sprinting. Such information will lend insights into the biomechanical mechanisms of hamstring injuries, and thus provide a scientific basis for evaluating treatment strategies and methods of injury prevention.