Low Energy Availability Impairs Anaerobic Exercise Performance but Not Muscle Strength in Trained Females

BACKGROUND: Low energy availability (LEA) is a well-known problem in sports and has - in addition to menstrual dysfunction - shown to negatively impact bone health, endocrine function, and mental health in the long term. Yet, how LEA influences physical performance and physiological parameters related to performance is still uncertain. PURPOSE: To investigate the impact of 10 days of LEA on physical performance, muscle glycogen content, and sarcoplasmic reticulum (SR) function in young trained females. METHODS: Thirty young trained eumenorrheic females were matched in pairs based on training history and randomized into two groups; 10 days of LEA (25 kcal/kg lean mass (LM)/day) + supervised training (n = 15, LM; 45.9 ± 5.5 kg, VO2max; 45.5 ± 3.3 ml/kg/min, 12 repetitions max leg press (RM); 78.6 ± 14.8 kg) or 10 days of energy balance (50 kcal/kg LM/day) + supervised training (n = 15, LM; 44.7 ± 5.8, VO2max; 44.7 ± 2.5 ml/kg/min, 12 RM; 78.2 ± 30.1 kg). Before the intervention, both groups underwent a five-day energy-balanced control period with supervised training. Next, the 10-day intervention followed with either an energy-restricted diet or an energy-balanced diet matched for protein content (2.2 g/kg LM/day). Before and after the intervention period, a muscle biopsy and a series of physical performance tests were performed. RESULTS: LEA resulted in a significant reduction in 4-minute time trial performance (p = 0.002, mean Δpower output: LEA; -5.4 W 95%CI (-0.4 ; -10.4), EB; 4.9 W 95%CI (0.15 ; 9.9), repeated sprint ability (p = 0.02, mean Δpower output: LEA; -28.7 W 95%CI (-7.7 ; 50.0), EB; 2.5 W 95%CI (-19.2 ; 24.2), and muscle glycogen content (p = 0.0001, mean Δmmol/kg/dry: LEA; -81.9 95%CI (-123.5 ; -40.2), EB; 64.2 95%CI (23.5 ; 104.9) in comparison to control. Furthermore, SR Ca2+ release rate was significantly increased after the intervention in control in comparison to LEA (p = 0.048, Δ μmol Ca2+/g protein/s: EB; 0.54 95%CI (0.04 ; 1.05), LEA; -0.21 95%CI (-0.71 ; 0.30). No between-group differences were observed in SR Ca2+ uptake or measures of maximal dynamic and isometric muscle strength. CONCLUSION: Ten days of LEA results in reduced muscle glycogen content and impaired anaerobic exercise performance but no effect on muscle strength or SR Ca2+ uptake. This study was funded by Team Danmark