Identifying the time of occurrence of a hamstring strain injury during treadmill running: A case study
Introduction
Muscle strain injuries are common, yet the mechanisms of injury remain vaguely defined (Croisier, 2004, Garrett, 1996). For example, despite the near 25% incidence rate of hamstring strains among sprinting athletes (Seward et al., 1993, Yamamoto, 1993), it remains debated whether the hamstrings are injured during the swing or stance phase of a sprinting gait cycle (Orchard et al., 2002). Current understanding of hamstring injury mechanisms is largely based on biomechanical analyses of injury-free running trials (Mann and Sprague, 1980, Thelen et al., 2005, van Don, 1998, Wood, 1987) and anecdotal evidence (Askling et al., 2000, Garrett et al., 1989) from injury cases. However, both sources of information carry inherent uncertainties when used to interpret injury mechanisms. The biomechanical conditions during the gait cycle in which injury occurs could differ from the conditions seen in uninjured gait cycles. Anecdotal information, e.g. the athlete’s perception of the time of injury, is based upon suspect temporal resolution given the neural delays between injury and perception. A prior case study was able to discern the moment of a gastrocnemius strain injury from a muscle response visible on video footage (Orchard et al., 2002). However, the video information could provide only a qualitative sense of the biomechanical conditions associated with injury. As rehabilitation programs are often based on assumed injury mechanisms, knowledge of such information could provide a scientific foundation for evaluating alternative strategies for preventing and treating hamstring strain injuries.
In this study, we report the analysis of three-dimensional kinematics of a running athlete that were obtained at the time of an acute hamstring strain injury. The objective of the study was to identify the period of the gait cycle during which the hamstring was likely injured. We used statistical analysis of marker kinematics to identify the earliest indications of a mechanical response to the injury. In addition, biomechanical modeling was used to estimate the lengths of the hamstrings throughout the running trial. By combining this information and considering neuromuscular latencies and electromechanical delays, this study provides novel quantitative insights into the timing and mechanisms of an in vivo hamstring strain injury.
Section snippets
Case history
A 31-year-old male professional skier (170 cm height; 70.5 kg mass) was participating in a pilot investigation in which he was asked to run on a treadmill at various speeds and inclinations. Subject consent was obtained in accordance with the institutional review board of The Orthopaedic Specialty Hospital (Murray, UT, USA). While not having a history of hamstring injury, the subject had previously sustained a left transfemoral fracture (10 years prior) and left hip dislocation (2 years prior).
Results
The stride period, τ, was 0.54 s during the trial in which the subject was injured. Based on the linear periodic prediction model, the earliest indication of injury occurred in the right greater trochanter marker at 1.62 s (Fig. 1). During the 80 ms following this initial indication, deviations were identified in the trajectories of markers on the knee, shank and foot (Table 1). The initial response corresponded to the mid-support phase of the running cycle when the hip (16°) and knee (50°) joints
Discussion
Using a unique kinematic data set, we have identified the likely time period of hamstring strain injury during a treadmill running trial. Based on responses evident in the lower and upper extremity markers and the length of the hamstring muscles, we conclude that the BF was likely injured during the late swing phase of the running gait cycle. This same phase of the running cycle has been identified as having the greatest potential for injury to the hamstring muscles based on the biomechanics of
Conclusion
The use of a linear periodic prediction model applied to marker kinematic trajectories provided a quantitative indication of the most likely time period of BF muscle strain injury during treadmill running. When considered in conjunction with estimates of musculotendon length, we conclude that the BF muscle likely underwent a lengthening contraction injury during the terminal swing phase of the running gait cycle.
Acknowledgements
We gratefully acknowledge the financial support provided by The Aircast Foundation and National Football League Charities, as well as a NSF Graduate Fellowship to E. Chumanov. We thank Allison Arnold, Ph.D., for the hamstring musculoskeletal models that were adapted for this study.
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