The effect of speed and influence of individual muscles on hamstring mechanics during the swing phase of sprinting

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Abstract

The purpose of this study was to characterize the effect of speed and influence of individual muscles on hamstring stretch, loading, and work during the swing phase of sprinting. We measured three-dimensional kinematics and electromyography (EMG) activities of 19 athletes sprinting on a treadmill at speeds ranging from 80% to 100% of maximum speed. We then generated muscle-actuated forward dynamic simulations of swing and double float phases of the sprinting gait cycle. Simulated lower extremity joint angles and model predicted excitations were similar to measured quantities. Swing phase simulations were used to characterize the effects of speed on the peak stretch, maximum force, and negative work of the biceps femoris long head (BF), the most often injured hamstring muscle. Perturbations of the double float simulations were used to assess the influence of individual muscles on BF stretch.

Peak hamstring musculotendon stretch occurred at ∼90% of the gait cycle (late swing) and was independent of speed. Peak hamstring force and negative musculotendon work increased significantly with speed (p<0.05). Muscles in the lumbo-pelvic region had greater influence on hamstring stretch than muscles acting about the knee and ankle. In particular, the hip flexors were found to induce substantial hamstring stretch in the opposite limb, with that influence increasing with running speed. We conclude that hamstring strain injury during sprinting may be related to the performance of large amounts of negative work over repeated strides and/or resulting from a perturbation in pelvic muscle coordination that induces excessive hamstring stretch in a single stride.

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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