Resumen de Changes in the Energy Cost of Running during a 24-h Treadmill Exercise.
Philippe Giménez, Guillaume Y. Millet, Hugo Kerherve, Laurent Olivier Messonnier, Léonard Feasson
AB Purpose: Although fatigue generally increases the energy cost of running (Cr), the changes of Cr and associated variables during an ultramarathon are not known. This study aimed to determine the changes of metabolic and cardiovascular adjustments during an ultraendurance exercise. Methods: Twelve healthy males ran 24 h on a motorized treadmill (24TR). Overall oxygen consumption (V[spacing dot above]O2 mL[middle dot]min-1[middle dot]kg-1), net energy cost (Cr J[middle dot]kg-1[middle dot]m-1), and respiratory exchange ratio (RER) were determined before, every 2 h, and after the 24TR at 8 km[middle dot]h-1. Running speed and heart rate (HR) were continuously measured during the 24TR. Results: V[spacing dot above]O2 increased (+7.6%, P < 0.001) during the 24TR, principally in the first 8 h of exercise. The RER mirrored changes in V[spacing dot above]O2, that is, decreased significantly until the eighth hour and remained constant thereafter. As a consequence of RER decrease, the increased Cr was markedly attenuated but was still significantly higher at the 8th and 12th hour compared with pre-24TR. Speed was constant over the first 6 h then significantly decreased during the 24TR. HR increased until the sixth hour (i.e., HR drift), then decreased until post-24TR. Furthermore, a significant positive correlation (R = 0.75, P < 0.01) was observed between the velocity sustained during the 24TR (expressed in percentage of the velocity attained at V[spacing dot above]O2max: %VV[spacing dot above]O2max) and the pre- to postchanges in Cr. Conclusions: The present study characterized accurately the changes of energy cost and substrate use during an extreme run, showing a plateau after 8 h of exercise. It is also concluded that the participants who maintained the highest %VV[spacing dot above]O2max were also those having most deteriorated their Cr over the 24TR, supporting the notion of a trade-off between running speed (relative to VV[spacing dot above]O2max) and Cr.
