Emily E. Rouse, Sean P. Langan, Wayne M. Johnson, George J. Davies, Bryan L. Riemann. Georgia Southern University - Armstrong Campus, Savannah, GA.

BACKGROUND: Previous hamstring injury (HSI) remains a predictor for future HSI. With many HSI occurring with eccentric loading during late swing phase of sprinting, safe and controlled eccentric training prior to initiating a return to submaximal running may play a critical role in HSI rehabilitation. PURPOSE: To examine the relationship between isotonic knee flexion (KF) eccentric work and peak torque and generalized eccentric knee muscle torque and work during the swing phase of submaximal running. METHODS: Recreationally (n=17, 7 men) active and healthy participants (23.1±1.6yrs, 75.7±13.8kg, 1.71±.80m) completed base line testing for maximal 30° isometric hamstring strength (MVIC) and spring velocity (40m). At least 48hrs later, in a prone position, participants completed a fixed dynamometer isotonic (25% MVIC) eccentric (180°/s) to concentric KF assessment and 45s treadmill running at 80% maximal running velocity while kinematics of the dominant limb foot, shank, thigh, and pelvis were collected. During the KF isotonic trials, the torque applied by the participants was computed by taking into the account mass moments of inertia of the foot-shank and dynamometer attachment, along with gravity and the isotonic load to identify the peak torque and eccentric work (30° flexion to extension). KF muscle torque was computed during the swing phase of running by subtracting the gravitational and motion-dependent torques from the net joint torque. Following a review of scatterplots, separate simple linear regression models between the isotonic and running KF peak torques and work were conducted, followed by paired t-tests. RESULTS: The regression diagnostics supported the validity of both models. Isotonic KF peak torque (-124.8±27.7 Nm) was significantly associated (R2=.499, P=.002) with running KF muscle peak torque (-97.3±39.9 Nm). Isotonic work (-29.6±5.5 J) was significantly associated (R2=.286, P=.027) with running KF muscle work (-21.9±18.9 J). While KF peak torque (P<.001, d=.74) ) was significantly higher for the running compared to the isotonic assessment, there was no significant difference for work (P=.073, d=.45). CONCLUSIONS: These results quantify the relationship between eccentric isotonic KF muscle testing and submaximal KF running mechanics, which may be relevant for possible prevention and rehabilitation interventions. Future research should consider associations during higher velocity running.

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