In the last decades, gait variability (GV) has provided new insight into motor control. No study, though, quantified the GV together with bilateral symmetry at different running intensities in runners. For this aim, 16 male runners (35±6 y), after a simulated 10-km time trial (average speed, TT), performed randomly three 15-minute running bouts at TT running speed, 10% slower, and 10% faster than TT. Metabolic, perceptive, and spatiotemporal parameters with phase coordination index (PCI) were collected across all trials. The TT was 14.16±1.65 km·h-1, rating of perceived exertion of 8.94±0.36 a.u. and 95.25±5.83% of the maximum heart rate. The PCI was lower at TT speed than at other speeds (p=0.002). The energy cost of running was higher at slower speeds in comparison to TT speed and higher speed conditions (p=0.029 and p=0.017, respectively). The ratings of perceived exertion, heart rate, oxygen consumption, flight time, and stride length increased according to the speed (p<0.05). The finding that the PCI is better at 10-km race speed suggests that improved ability to modulate the right-left stepping control is related to an energetic optimization process impacting positively the talent development and performance in trained runners. Although the metabolic cost estimates are grounded in a robust theoretical framework, these findings necessitate further empirical verification.
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