Author(s): SMITH, E., KUIKMAN, M., WEAKLEY, J., TEE, N., MCCORMICK, R., ACKERMAN, K., ELLIOTT-SALE, K., STELLINGWERFF, T., HARRIS, R., MCKAY, A., BURKE, L., Institution: AUSTRALIAN CATHOLIC UNIVERSITY, Country: AUSTRALIA, Abstract-ID: 915

INTRODUCTION:
Athletes often implement acute, adaptable, periods of low energy availability (EA) to facilitate performance goals, such as reducing body mass to meet weigh-in targets, altering body composition for competition, or intensified training blocks with increased exercise energy expenditure (EEE). Prolonged low EA is problematic, as it is associated with negative health and performance outcomes. Yet the time course for maladaptations to occur once adequate EA “thresholds” are consistently unmet remains unclear. The method of reducing EA (i.e., dietary restriction or increased EEE) may also influence physiological outcomes. This is relevant in tailoring athlete training/nutritional protocols to alter body composition whilst minimising negative consequences. Additionally, there is some evidence that women may be more sensitive to the physiological effects of acute low EA than men. However, studies examining sex differences are scarce, particularly among trained athletes. We therefore examined how 24 h EA manipulations, induced by diet or exercise, influenced next day substrate oxidation, postprandial metabolism, and performance among trained women and men.
METHODS:
In a Latin Square design, 20 endurance athletes (10 females using monophasic oral contraceptives and 10 males) undertook five trials, each comprising three consecutive days. Day one was a standardised period of high EA; EA was manipulated on day two; and post-intervention testing occurred on day three. EA on day two was low/high/higher EA (LEA/HEA/GEA) at 15/45/75 kcal·kg·FFM·day-1, respectively. Participants received prescribed food and drink pre-packaged and weighed before each trial. Conditions of LEA/HEA were separately achieved by manipulations of EEE/energy intake (LEA/HEA[REST/EX]). On day three, fasted peak fat oxidation during cycling and two-hour postprandial metabolism (high carbohydrate/energy meal) were assessed, alongside performance tests: Wingate, countermovement jump (CMJ), squat jump (SJ), isometric mid-thigh pull (IMTP), and the Stroop Colour and Word Test.
RESULTS:
Highest peak fat oxidation occurred under LEA induced by exercise (p<0.01), with no difference between sexes. Postprandial glucose (p<0.01) and insulin (p<0.05) responses were highest across both sexes when LEA was induced by diet. Relative peak/mean power throughout the Wingate and CMJ/SJ jump height was greater in males than females (p<0.01), but there was no difference between EA conditions for the Wingate/CMJ (p>0.05). During the SJ, jump height was lower under GEA than LEAREST (p=0.045) and HEAEX (p=0.023) across both sexes. IMTP peak force and the Stroop effect did not change with altered EA.
CONCLUSION:
Acute (24 h) exercise-induced manipulations in EA influence fasted substrate oxidation more than LEA induced by diet alone, while 24 hours of LEA appeared not to impair strength/power, sprint capacity, or cognitive performance, at least when measured post-prandially. Finally, the responses to EA manipulations did not differ between sexes.