Temporal Changes in Female Lower Body Running Mechanics during a Simulated 10 km Race

Abstract

During a 10 km run at race pace, lower extremity mechanics have been observed to change in male runners. Whether similar changes in mechanics occur in female runners is unknown. PURPOSE: The purpose of this study was to examine lower extremity running mechanics in female distance runners during a simulated 10 km race on a treadmill. METHODS: Five female distance runners (age: 30.6 ± 3.5yrs; ht: 169.4 ± 8.9 cm; wt: 59.1 ± 73 kg; VO2max = 3.45 ± 0.33 L/min) completed a pre-screening and graded exercise test (Day 1); 10 km time trial on a 400 m track (Day 2); and simulated 10 km run at race pace on a treadmill. Treadmill speed was 95 % of average running velocity of the Day 2 time trial. Reflective markers were placed on both the right and left lower extremities and kinematic data were sampled at 120Hz at 50 m (BASE), 4450 m (MID) and 9950 m (END) using a 6-camera optoelectronic motion capture system. Mechanical measures calculated: right and left step length and frequency, right and left maximum knee flexion (swing phase) and extension (stance phase). RESULTS: A time by side interaction for step length was found (BASE left: 1.27±0.05 meters; END left: 1.28±0.05 meters; BASE right: 1.27±0.05 meters; END right: 1.32±0.05 meters P>0.05) indicating differential changes in mechanics on the left and right extremities. Overall maximum knee flexion increased (BASE: 96.9±2.3°; MID: 99.6±3.1°; END: 102.4±4.5°; P<0.05) with no other significant changes found. Although not significant, effect sizes indicated trends for step frequency to decrease (BASE: 93.1±2.9 steps/min; END: 90.7±2.2 steps/min; P>0.05; ES=0.94) and maximum knee extension to increase (BASE: 2.0±3.6°; END: 5.8±5.3°; P>0.05; ES=0.85). CONCLUSION: These results indicate that knee flexion had the greatest change over a simulated 10 km race, however a trend for increased max knee extension and decreased step frequency were observed. The most noticeable effect was the maintenance of step length on the left lower extremity and increase in step length on the right lower extremity. The mechanism for this bilateral deviation is under investigation. These results confirm changes in lower body running mechanics occur in trained female runners and these changes are magnified over the duration of a race.