Muscle Oxygenation Patterns during a 20-km Time Trial with Intermediate Sprints and Recoveries.

Abstract

PURPOSE: Pacing strategies are necessary during endurance events in which the goal is to finish in as little time as possible. Both anaerobic and aerobic attributable sources of ATP are used during such efforts. Rating of Perceived Exertion (RPE) increases linearly as heart rate (HR) and power output (PO) increases, however these markers of intensity are not instantaneous. Near infrared spectroscopy (NIRS) allows for the measurement of local muscle oxygen saturation (SmO2) which may respond to short-term fluctuations in PO. Previously, SmO2 has shown a moderate correlation with oxygen consumption (VO2) and HR during an incremental exercise. The purpose of this study was to determine how SmO2 changes with increases in PO during a non-incremental cycling time trial (20-km) with various interspersed sprints and if decrements in PO due to shorter rest times were associated with lower SmO2. METHODS: Well-trained cyclists (n=9) (VO2max=55.4±10.4 ml∙kg-1∙min-1; POmax=305±45 W), habituated to 20-km trial, performed a self-paced 20-km time trial and two time trials with 1-km sprints imposed, separated by 2- or 4-km of self-paced cycling. SmO2 saturation, PO, and HR were measured. RPE was recorded each kilometer. Pearson’s partial correlations were used to analyze relationship between SmO2 and PO. A one-way analysis of variance was used to determine if there were differences in finishing times between trials. RESULTS: There was a significant inverse relationship between SmO2 and PO during all time trials (r = -0.263, P < 0.0001). There was no significant difference (p = .572) between the finishing times amongst 20-km protocols. CONCLUSIONS: This study revealed that the imposed sprints caused reciprocal changes in the extent of SmO2 and PO that are larger than the changes in a self-paced time trial. In other words, as the subjects were instructed to significantly increase their PO to simulate a break-away, the SmO2 decreased in a reciprocal manner.