Decreased Energy Availability During Intensified Training is Associated with Non-Functional Overreaching in Female Runners

Abstract

PURPOSE: We examined the hypothesis that failing to maintain energy availability (EA, calculated as energy intake (EI) - exercise energy expenditure (ExEE)) during intensified training (IT) would predispose athletes to a state of overreaching (OR; high perceived fatigue and prolonged performance impairment). METHODS: After 4 weeks of baseline training, 16 female runners (28 ± 5 yrs) performed 4 weeks of IT (130% of baseline volume), followed by a 2 week recovery, (REC, 50% of baseline). Over the last 7 days of each phase, ExEE was measured with chest-worn activity monitors (Actiheart) and EI was recorded using my Fitness Pal phone application. Running performance (distance covered during a graded treadmill test) and perceived fatigue (REST-Q) were assessed at the end of each phase to classify athletes as OR or acutely fatigued (AF, increased fatigue but no decrease in performance). VO2max, heart rate (HR), systolic blood pressure (SBP), plasma epinephrine and norepinephrine and blood lactate concentrations were measured at 65, 75 and 85% of VO2max and immediately after maximal exercise. RESULTS: 7 runners became OR and 9 were AF (Δperformance:-9±2% vs +4±2 %). Performance was still suppressed in OR after REC (-6 ± 5%). A significant decrease in EA was found in OR (-178±104 kcal/d), who failed to increase EI with IT. By contrast, AF increased EI (184±48 kcal/d) and maintained EA. ΔEA correlated with Δperformance and ΔVO2max (R = 0.61 and 0.66, p < 0.05). VO2max and peak lactate, epinephrine and norepinephrine, HR and SBP were suppressed in OR, but were maintained in AF after IT. At submaximal intensities at the same speed after IT, AF showed reduced HR, and lactate and norepinephrine responses, while OR showed no change in these variables but did have increased ratings of perceived exertion. CONCLUSIONS: Failure to maintain EA during IT was associated with a state of non-functional OR in female runners. High perceived fatigue and impaired performance in OR was accompanied by blunted physiological responses at maximal exercise and a lack of any desirable cardiovascular or endocrine-metabolic adaptation to submaximal intensities. In contrast, AF runners that increased EI to match ExEE with IT showed improved performance and lower HR, blood lactate and plasma norepinephrine at the same submaximal speeds after IT.