Decreased Energy Availability during Intensified Training Increases Fatigue and Reduces Performance in Competitive Female Runners

Abstract

PURPOSE: Functional overreaching (F-OR) is a state of high perceived fatigue and decreased performance, resulting from high training loads combined with inadequate recovery. While F-OR athletes show some performance gains after a taper period, the magnitude of these gains may be reduced compared to athletes who avoid F-OR during intensified training. As no studies have quantified the influence of changes in energy availability (EA) during intense training on F-OR and performance adaptations, we tested the hypothesis that athletes’ ability to maintain EA during high training loads would influence the occurrence of F-OR and subsequent training adaptations. METHODS: 12 eumenorrheic female distance runners followed a 10-week protocol with 3 phases: P1; 4 weeks of normal training volume, P2; 4 weeks at 130% of P1 volume, and P3; 2 weeks of taper at 50% of P1 volume. Over the last 7 days of each phase, runners wore a validated activity monitor 24hrs/day to assess active energy expenditure (AEE), comprised of training-specific exercise (ExEE) and habitual activity (HaEE) and logged all energy intake (EI). At the end of each phase, runners completed the REST-Q and a hunger questionnaire, and body composition was measured by DEXA. After 36 hours of rest, they performed a graded running test to volitional exhaustion. RESULTS: ExEE increased by 36% from P1 to P2 (450 to 550 kcal/d), and perceived fatigue increased significantly (+55±17%). While hunger ratings increased significantly (63 ± 15%), mean EI only increased by 86 ± 70 kcal/d (4%, NS); only 6 of the 12 runners increased EI. Mean EA did not decrease significantly (-1.3± 3.8%), however Δ EA was correlated to Δ EI but not to Δ ExEE or Δ HaEE. Importantly, [INCREMENT]EA from P1 to P2 was also directly correlated to Δ running performance, ΔVO2peak, Δ lean body mass (R= 0.80, 0.70 and 0.92), and inversely correlated to Δlack of energy from the REST-Q and Δ perceived exertion during submaximal exercise (R= -0.85,-0.72). Furthermore, the 6 runners displaying F-OR and decreased EA at P2 showed reduced performance gains at P3 (p=0.05) compared to the runners who did not develop F-OR. CONCLUSIONS: Our results emphasize the importance of maintaining EA during critical periods of intensified training, in order to avoid F-OR and to optimize the magnitude of performance gains after a taper period.