Author(s): TORRES-SANTIAGO, M., GUISADO-CUADRADO, I., BENÍTEZ-MUÑOZ, J.A., RECACHA-PONCE, P., RODRÍGUEZ-REDONDO, B., ROMERO-PARRA, N., PEINADO, A.B., Institution: UNIVERSIDAD POLITÉCNICA DE MADRID, Country: SPAIN, Abstract-ID: 1061

INTRODUCTION:
Energy availability is a key determinant of physiological function and athletic performance (1). Despite the established evidence linking long-term low energy availability to compromised health (2), short-term low term energy intake (LEI) effects on cardiorespiratory and metabolic responses in female remain unclear. Therefore, this study aimed to investigate the effects of LEI on cardiorespiratory variables in exercising females under controlled nutritional interventions.
METHODS:
Nine naturally menstruating females with confirmed luteinizing hormone peak completed a treadmill interval protocol consisting of 8x3-min at 95% of the ventilatory threshold (VT2) with 90 s of active rest on two occasions. One occasion after six days of LEI [35 kcal·kg· fat-free mass (FFM)-1] and the other one under control conditions (60 kcal·kg· FFM-1). Oxygen consumption (VO₂) and relative to body weight (VO₂/kg), carbon dioxide production (VCO₂), ventilation (VE) and respiratory exchange ratio (RER) were continuously measured (JAEGER® Vyntus CPX) along heart rate (HR, Polar H10 device).
RESULTS:
A significant main effect of condition was observed for VO2/kg (p<0.001; LEI: 32.5±12.2 vs control: 30.9±12.2 ml/kg/min), RER (p<0.001; LEI: 0.9±0.08 vs control: 0.95±0.07), V̇E (p=0.013; LEI: 56.3±20.6 vs control: 54.5±20.3 l/min), and HR (p=0.004; LEI: 154±31 vs control: 151±30 bpm), with higher VO2/kg and HR values, alongside lower RER and V̇E values, following the LEI compared with the control condition. No significant differences were observed for VO2 or V̇CO2 (p > 0.05) nor weight (p=0.058).
CONCLUSION:
Short-term LEI may alter cardiorespiratory and metabolic responses to exercise in exercising females. The increase in VO2/kg with no increase in absolute VO2, may reflect the statistical trend to a reduction in body mass associated with LEI (3) rather than a real enhancement in aerobic capacity. In addition, higher HR values may reflect changes in autonomic control that can impact HR responses during exercise stress associated with energy availability (4). Lower RER values during LEI suggest a shift toward greater reliance on fat oxidation due to the reduced carbohydrate intake, which may reinforce the effects of short-term. Furthermore, lower VE values may indicate an alteration in ventilatory function despite cardiovascular strain as a compensatory response to maintain exercise response under LEI conditions (5).

References
1.Thomas, D.T. et al. (2016). J Acad Nutr Diet. doi:10.1016/j.jand.2015.12.006
2.Mountjoy, M. et al (2023). Br J Sports Med. doi:10.1136/bjsports-2023-106994
3.Burke, L.M. et al. (2023). Med Sci Sports Exerc. doi:10.1249/MSS.0000000000003074
4.Gallant, T.L. et al. (2024). Sports Med. doi:10.1007/s40279-024-02036-6
5.Oxfeldt, M. et al. (2023). Med Sci Sports Exerc. doi:10.1249/01.mss.0000987148.52126.c2