We investigated the effect of a one-time application of elastic constraints on movement-inherent variability during treadmill running. Eleven males ran two 35-min intervals while surface EMG was measured. In one of two 35-min intervals, after 10 min of running without tubes, elastic tubes (between hip and heels) were attached, followed by another 5 min of running without tubes. To assess variability, stride-to-stride iEMG variability was calculated. Significant increases in variability (36 % to 74 %) were observed during tube running, whereas running without tubes after the tube running block showed no significant differences. Results show that elastic tubes affect variability on a muscular level despite the constant environmental conditions and underline the nervous system's adaptability to cope with somehow unpredictable constraints since stride duration was unaltered.

• The elastic constraints led to an increase in iEMG variability but left stride duration variability unaltered.

• Runners adapted to the elastic cords, evident in an iEMG variability decrease over time towards normal running.

• Hardly any aftermaths were observed in the iEMG analyses when comparing normal running after the constrained running block to normal running.