Foot strike pattern and gait changes during a 161-km ultramarathon.

Foot strike pattern has not been examined during ultramarathons where fatigue or avoidance of impact might have greater effect on foot strike and other gait parameters than in shorter events. In this study, video analysis from 3 level sites at a 161-km ultramarathon was used to: (a) examine changes in foot strike pattern, stride rate, and stride length; (b) determine if foot strike pattern is related to performance; and (c) ascertain if post-race blood creatine phosphokinase (CK) concentrations differ by foot strike pattern. Rear-foot strike (RFS) prevalence was 79.9, 89.0, and 83.9% at 16.5, 90.3, and 161.1 km, respectively. There was a significant distance effect observed between the 90.3 and 161.1-km site for stride rate (p < 0.05) and across all distances for stride length (p < 0.0001), but stride rate and length were stable among the top 20 finishers. There was no effect (p = 0.3) of foot strike pattern on performance. However, top 20 finishers had greater use (p = 0.02) of a non-RFS pattern at 161.1 km than the remaining finishers. There was a trend toward greater post-race blood CK values among non-RFS runners compared with RFS runners, reaching significance at the 90.3 km site (p < 0.05). Thus, the increased RFS prevalence by race midpoint was likely because of greater muscular demands of non-RFS patterns as supported by the higher post-race blood CK concentrations among non-RFS runners. Faster runners maintained higher stride rates and lengths throughout the race and made greater use of a non-RFS pattern at the end of the race compared with the slower finishers.