Greater Fatigue During Repeated-Sprint Exercise with Shortened Recovery is not Associated with Changes in Systemic Acid-Base Balance

Abstract

Repeated-sprint activity leads to a decline in mechanical performance (power output), a phenomenon called muscle fatigue. Changes in acid-base status (i.e., metabolic acidosis) have previously been suggested to contribute to fatigue during repeated-sprint exercise. One way to test this hypothesis would be to determine if differences in fatigue, as a result of different repeated-sprint protocols, could be explained by differences in acid-base status. PURPOSE: The present study investigated the effects of varying the recovery time between consecutive sprints on repeated-sprint exercise performance and possible contributing mechanisms. METHODS: Eight young men completed two trials of 18, 4-s cycling sprints, in a random order, on two occasions. In one trial the exercise protocol consisted of 3 sets of 6 sprints separated by 20-s passive recovery intervals. Between each set of sprints subjects rested for 180 s (short recovery protocol; SRP). In the second trial, the exercise protocol consisted of 6 sets of 3 sprints, also separated by 20-s passive recovery intervals. Between each set of sprints subjects rested for 180 s (long recovery protocol; LRP). RESULTS: Relative to the first sprint, PPO decreased more during the SRP compared with LRP over the first 6 sprints (16.1% vs. 8.2%; P = 0.03), 12 sprints (19.4% vs. 11.8%; P = 0.05), and 18 sprints (23.3% vs. 11.7%; P = 0.004). Similarly, the decrease in TW was higher in SRP compared with LRP at any time point (10.1% – 12.6%; P = 0.01–0.003). Relative to the LRP, the SRP trial resulted in a substantial decrease in total work after sprint 6(−6.1%;P=0.002), sprint 12 (−6.2%; P=0.002) and sprint 18 (−7.4%; P=0.003). Despite these differences in repeated-sprint exercise performance, changes in blood acid-base status (pH, lactate, HCO3-), cardiovascular load (heart rate) and rating of perceived exertion (RPE) did not differ between the two conditions at any time point (i.e., rest, sprint 6, sprint 12 and sprint 18). CONCLUSION: Differences in repeated-sprint exercise performance, associated with the reduction of the available rest time between sprints, could not be explained by acute changes in systemic acid-base status.