The effect of speed and influence of individual muscles on hamstring mechanics during the swing phase of sprinting
Introduction
Acute hamstring strain injuries are commonly linked with maximal speed running in a variety of sports such as track, football and soccer (Gabbe et al., 2005; Woods et al., 2004). While it is generally agreed that strain injuries are the result of exceeding the local mechanical limits of the muscle tissue, little is known on how running speed changes the mechanical demands of the hamstrings. Such information is relevant for establishing a scientific basis for injury prevention programs and rehabilitative approaches that can mitigate the high risk for re-injury (Orchard and Best, 2002). For example, a recent study found that the performance of rehabilitative exercises targeting neuromuscular control of muscles in the lumbo-pelvic region (e.g. abdominal obliques, erector spinae, illiopsoas) reduced hamstring re-injury rates compared to a stretching and strengthening approach (Sherry and Best, 2004). However, the complexities of multi-segmental dynamics (Zajac and Gordon, 1989) make it challenging to understand how lumbo-pelvic muscles may influence hamstring mechanics, and hence injury risk.
Prior studies have shown that the biarticular hamstrings are active (Jonhagen et al., 1996; Swanson and Caldwell, 2000; Wood, 1987) and undergo a stretch-shortening cycle (Thelen et al., 2005a) during the second half of the swing phase of sprinting. The hamstrings do a substantial amount of negative work over this period, with the peak stretch of the hamstring musculotendon unit occurring during late swing (Thelen et al., 2005b; van Don, 1998; Wood, 1987). Thus, the hamstrings are likely susceptible to a lengthening contraction injury during late swing. We have previously shown that peak musculotendon stretch is invariant as speed increases from submaximal to maximal speeds (Thelen et al., 2005b). The purpose of this study was to utilize simulations of subject-specific sprinting dynamics to test the hypothesis that sprinting speed increases the loading and negative work required of the hamstrings. We also evaluated the sensitivity of hamstring stretch to perturbations in individual muscle forces, to understand the potential influence that lumbo-pelvic muscles have on injury risk.
Section snippets
Subjects
19 athletes participated in this study (Table 1). All subjects had experience sprinting on a treadmill. Testing was conducted at two sites: the Orthopedic Specialty Hospital in Murray, UT and the University of Wisconsin-Madison in Madison, WI. The testing protocol was approved by the Institutional Review Boards at both institutions and all subjects provided informed consent in accordance with institutional policies.
Experimental protocol
Whole body kinematics were recorded using 40 reflective markers placed on each
Results
The CMC algorithm generated simulations that closely tracked the experimental kinematics (Fig. 3). For the swing phase simulations, RMS errors for the hip and knee angles were 1.0±0.7° for hip flexion–extension, 0.7±0.3° for hip abduction–adduction, and 2.2±1.2° for knee flexion–extension. For the double float simulations, the average RMS errors for the actuated 21 DOF were 3.3±4.3°. The simulated muscle excitation patterns of the lower limb muscles were similar to measured EMG signals (Fig. 4
Discussion
In this study, we used forward dynamic simulations of sprinting to investigate changes in hamstring mechanics with speed. The salient findings were that speed significantly increases the amount of negative work the hamstrings do, and magnifies the influence that individual muscles, particularly the muscles in the lumbo-pelvic region, have on hamstring stretch.
Previous studies investigating joint mechanics (Kuitunen et al., 2002; Mann, 1981; Swanson and Caldwell, 2000) and muscle activation
Conflict of interest
There is no conflict of interest.
Acknowledgments
We gratefully acknowledge the financial support provided by the Aircast Foundation, National Football League Charities and a NSF Graduate Fellowship to E. Chumanov. We thank Stephen Swanson, Li Li, Michael Young, Ron Kipp and Tiffany Heath who participated in the kinematics data collections and Marc Schmaltz who helped recruit subjects for the EMG analysis. We also thank Allison Arnold, Ph.D., for the hamstring musculoskeletal models that were adapted for this study.
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