Changes in internal mechanical cost during over-ground running to exhaustion

Overview & Synopsis

Purpose: The purpose of this study was to determine, during an overground supra-threshold run, whether a change in the internal mechanical cost could occur during an exhaustive run and whether this change was related to the increase in the energy cost of running (Cr). Methods: The Cr of 14 endurance runners was measured from pulmonary gas exchange using a breath-by-breath portable gas analyzer (Cosmed K4b2, Rome, Italy), at the third and the last minute of an exhaustive exercise performed at their velocity corresponding to 95% of the maximal oxygen uptake (4.88 ± 0.38 m·s−1). At the same time, potential, kinetic, and internal mechanical costs (Cpe, Cke, and Cint) were measured with a 3D motion analysis system (ANIMAN3D). Results: Cint and Cr increased significantly within the third minute and the end of the supra-threshold exercise (respectively, 0.55 ± 0.07 vs 0.60 ± 0.07 J·kg−1·m−1 and 4.10 ± 0.39 vs 4.32 ± 0.42 J·kg−1·m−1; P ≤ 0.03). However, the percentage of variation of Cint and Cr were not correlated (r = 0.06; P = 0.84). Contrary to Cint, Cke and Cpe remained constant during the exercise (respectively, 1.33 ± 0.33 vs 1.38 ± 0.29 J·kg−1·m−1 P = 0.79 and 0.47 ± 0.11 vs 0.48 ± 0.10 J·kg−1·m−1; P = 0.67), but both parameters were significantly correlated with Cr (r = 0.43; P = 0.03 and r = 0.40; P = 0.03). Conclusion: During overground running to exhaustion, a significant increase in Cint occurred, but this did not account for the increase in Cr. Moreover, the increase in Cint has yet to be explained.