The concurrent effects of strike pattern and ground-contact time on running economy

OBJECTIVES: Running economy is a key determinant of endurance performance, and understanding the biomechanical factors that affect it is of great theoretical and applied interest. This study aimed to analyse how the ground-contact time and strike pattern used by competitive runners concurrently affect running economy. DESIGN: Cross-sectional. METHODS: Fourteen sub-elite male competitive distance runners completed a 6-min submaximal running trial at 14kmh-1 on an outdoor track using their habitual strike pattern (n=7 rearfoot strikers: average age, 25.3 years old (SD=2.4); average weight, 64.7kg (SD=5.6); average height, 175.3cm (SD=5.2); n=7 midfoot strikers: average age, 25.0 years old (SD=2.8); average weight, 69.6kg (SD=4.0); average height, 180.1cm (SD=5.1). During the run, the oxygen uptake and ground-contact time were measured. RESULTS: Midfoot strikers showed a significantly shorter (p=0.015) mean contact time (0.228s (SD=0.009)) compared with rearfoot strikers (0.242s (SD=0.010)). Conversely, there was no significant difference (p>0.05) between the groups with respect to mean oxygen uptake (midfoot strikers: 48.4mlmin-1kg-1 (SD=5.3); rearfoot strikers: 49.8mlmin-1kg-1 (SD=6.4)). Linear modelling analysis showed that the effect of contact time on running economy was very similar in the two groups, with a 1ms longer contact time involving an approximately 0.51mlmin-1kg-1 lower oxygen uptake. In contrast, when controlling for contact time, midfoot striking involved an approximately 8.7mlmin-1kg-1 lower oxygen uptake compared with rearfoot striking. CONCLUSIONS: When adjusting the foot-ground contact biomechanics of a runner with the aim of maximising running economy, a trade-off between a midfoot strike and a long contact time must be pursued.