Author(s): ZUKERMAN RICHMAN, G., KODESH, E., IBRAHIM, R., JONES, A.M., WILKERSON, D.P., REUVENY, R., SEGEL, M.J., Institution: TEL AVIV UNIVERSITY, Country: ISRAEL, Abstract-ID: 1655

INTRODUCTION:
Exercise-induced fatigue (EIF), a reduction in muscle force or power output following prolonged or high-intensity exercise, is a key factor in endurance sports. Oxygen uptake (VO2) kinetics reflect the metabolic response of working muscles, and are related to EIF, exercise tolerance and performance. To date, these relationships have been studied only regarding what the exercise bout itself provoked; the effect of different fatiguing efforts on VO2 kinetics, EIF and performance in a consecutive effort, mimicking conditions in training and racing, has not been studied. We studied the effect of two fatiguing protocols on VO2 kinetics and EIF during a subsequent severe-intensity effort.
METHODS:
Twelve male endurance athletes participated in a random-order cross-over study, involving five visits (V1-V5). At V1, participants performed a graded cardiopulmonary exercise test to exhaustion, to assess the gas exchange threshold (GET), the respiratory compensation point (RCP) and VO2max, so as to individualize workloads in subsequent tests; and familiarization with time to exhaustion (TTE) and sprint performance (ST) tests. During each of visits V2-V5, participants completed one of two equal work fatiguing protocols (FPs): heavy constant exercise (CONT) at an intensity corresponding to 90% of RCP; or severe intermittent exercise (INT) at 120% of RCP with recovery periods at 50% of RCP. Each FP was performed on two different consecutive visits, in random order. VO2 kinetics were assessed pre- and post- FPs (i.e. fresh and fatigued, respectively).
RESULTS:
No significant differences were found in VO2 kinetics measured in a subsequent effort after CONT and INT (tau=35.3+/-8 vs. 33.5+/-5 sec, amplitude=2471+/-697 vs. 2590+/-546 mL/min). Additionally, TTE duration (413+/-153 vs. 359+/-124 sec) and ST peak power output (1106+/-230 vs. 1091+/-229 W) did not differ significantly. However, when comparing pre- to post- FP values, a significant increase in VO2 amplitude was observed only post-INT (2404+/-639 vs. 2590+/-546 mL/min, p=0.012). During FPs - cumulative O2 uptake was greater in CONT than INT (40.8+/-7.7 vs. 39.2+/-8.8 L, p=0.04), and excess post-exercise O2 consumption was significantly greater after INT compared to CONT (2.39+/-0.48 vs. 2.06+/-0.27 L, p=0.04).
CONCLUSION:
When total work is equal, different high-intensity aerobic fatiguing efforts (continuous vs. intermittent) have a similar effect on VO2 kinetics, EIF, and performance during a subsequent effort.