The effect of physiologically determined intensity on running variability in healthy men

Running patterns present non-random fluctuations in their temporal structure that represent a system's adaptability and result from the dynamic interaction between the central nervous system, body and environment. Changes in one would lead to readjustment of the others to preserve adaptability. Running speed was shown to affect these fluctuations when determined through self-selected speed. Because the locomotor system adapts to changing demands while preserving its functional organisation, we hypothesised that running at different physiologically defined intensities would not alter running variability. Thirteen males visited the laboratory twice. First, they completed an incremental test to determine the domains of physiological intensity. Then, participants ran two 8-min long trials on a treadmill at their moderate and heavy intensities. Stride time variability was determined through coefficient of variation (i.e. magnitude of variability) and detrended fluctuations analysis (i.e. temporal structure of variability). Paired samples t-tests were used to assess differences between intensity domains. We found no differences between intensities for the magnitude or temporal structure of variability. Differences were found in mean stride time, oxygen uptake and ventilation. This study showed the presence of complex, non-random fluctuations, regardless of running intensity. Moreover, it shows that running variability of healthy male runners remains unaltered at different running intensities.