Characterization Of Fatigue In A Short Bout Of Running

Abstract

All runners experience physiological fatigue during a run. Research shows physiological stress induced by fatigue influences changes in running biomechanics. However, past studies have focused on a limited number of kinematic variables during fatigue. To understand the interrelationship between a plurality of kinematic variables, a study was conducted to observe changes in stride length (SL), ground contact time (GCT), foot strike angle (FSA), and cadence (CAD). It was hypothesized fatigue would yield a decreased CAD, increased GCT and SL, and shift subjects to a more rear-foot FSA. PURPOSE: To examine the influence of physiological fatigue on running biomechanics during a short bout of high-intensity running. METHODS: Male and female athletes of all levels (n=36; 15 female; 33 ± 9 years; 70.11 ± 13.66 kg; 171.37 ± 9.75 cm) participated in a 20-minute treadmill fatiguing protocol. Subjects first ran 5 minutes at their preferred pace (speed one), followed by ten minutes at a fatiguing pace (speed two), and ended with five minutes at speed one. Speed two was .67-.89 m/s faster than speed one, near estimated vVO2max. Kinematic time series data from a shoe embedded accelerometer was collected for the following metrics: CAD, SL, GCT, and FSA. The first 30 seconds of speed two (fatigue start) was analyzed and compared to the last 30 seconds of speed two (fatigue end). Subjects were considered fatigued when heart rate met or exceeded 90% age predicted max and RPE ≥ 17. Significant differences between fatigue start and fatigue end were tested with a varied samples t-test. RESULTS: Significant differences were identified between fatigue start and fatigue end for CAD (173.36+13.91 vs 169.92+11.99 steps/min, p<0.001), SL (2.45+0.34 vs 2.50+0.34 meters, p=0.003), and GCT (279.61+44.25 vs 285.25+44.44 ms, p=0.004). CAD decreased while SL and GCT increased. No significant difference was observed for FSA. CONCLUSION: This study demonstrated biomechanical changes in running form from the beginning to the end of a short, high-intensity fatiguing run. The direction of change for cadence, stride length, and ground contact time confirmed the hypothesis. Changes in foot strike angle were not confirmed.