Breaking the Fast: Examining sex differences in resistance training performance following semi-solid breakfast meals consisting of carbohydrate, fat and a viscous placebo: A counterbalanced crossover trial

Abstract

Purpose: The study aimed to compare sex differences in resistance training performance following semi-solid breakfast meals with different compositions while controlling for placebo effects from meal consumption. Methods: Seventeen resistance-trained participants, 7 females (22.0±2.8 years) and 10 males (23.6±1.1 years) consumed four breakfast meals in a single-blinded counterbalanced crossover design. Three of the meals were semi-solid and consisted of carbohydrate, fat, or viscous placebo, while one condition was water-only. Two hours after the meals, participants performed four sets of squats and knee-extension till repetition failure at 90% of 10RM, which was the primary outcome. Secondary outcomes were isometric exercise-induced force loss, subjective ratings of appetite before and 10-min and 2-hours after meals, pre-exercise perceived recovery, and post- exercise perceived exhaustion. The water-only condition was used to adjust for potential underlying sex differences in repetition fatigue resistance. Results were analyzed using repeated measures ANOVA and t-tests. Results: Overall, energy-containing breakfasts did not enhance performance. No significant sex differences (interactions) were observed for total repetitions when combining squat and knee-extension (repetitions compared to water-only, mean±SD; females; carbohydrate:5.6±12.3, fat:-2.0±25.1 placebo:-4.9±17.7 males; carbohydrate:0.5±9.3, fat:1.8±9.0, placebo:4.6±6.4, p=0.15), squat separately (interaction p=0.12), or knee-extension separately (interaction p=0.56). There were no sex differences in exercise-induced force loss (all conditions females: 20.2-22.4%, males: 20.9- 23.6%, p=0.78) or any of the subjective measures (p=0.35-0.78). Conclusion: The results indicate no sex differences in repetition performance following energy-containing breakfasts (carbohydrates or fat) nor meal-placebo effect. Interestingly, there was no beneficial effect of energy-containing breakfasts in females or males.