CLANSEY, A. C., M. HANLON, E. S. WALLACE, and M. J. LAKE. Effects of Fatigue on Running Mechanics Associated with Tibial Stress Fracture Risk. Med. Sci. Sports Exerc., Vol. 44, No. 10, pp. 1917-1923, 2012. Purpose: The purpose of this study was to investigate the acute effects of progressive fatigue on the parameters of running mechanics previously associated with tibial stress fracture risk. Methods: Twenty-one trained male distance runners performed three sets (Pre, Mid, and Post) of six overground running trials at 4.5 m.s(-1) (+/- 5%). Kinematic and kinetic data were collected during each trial using a 12-camera motion capture system, force platform, and head and leg accelerometers. Between tests, each runner ran on a treadmill for 20 min at their corresponding lactate threshold (LT) speed. Perceived exertion levels (RPE) were recorded at the third and last minute of each treadmill run. Results: RPE scores increased from 11.8 +/- 1.3 to 14.4 +/- 1.5 at the end of the first LT run and then further to 17.4 +/- 1.6 by the end of the second LT run. Peak rearfoot eversion, peak axial head acceleration, peak free moment and vertical force loading rates were shown to increase (P < 0.05) with moderate-large effect sizes during the progression from Pre to Post tests, although vertical impact peak and peak axial tibial acceleration were not significantly affected by the high-intensity running bouts. Conclusion: Previously identified risk factors for impact-related injuries (such as tibial stress fracture) are modified with fatigue. Because fatigue is associated with a reduced tolerance for impact, these findings lend support to the importance of those measures to identify individuals at risk of injury from lower limb impact loading during running.
