The First-Night Effect and Sex Differences in Strength and Muscular Endurance Performance

Introduction: The first-night effect, characterized by disturbed sleep in an unfamiliar environment, may impair next-day physical performance. However, whether this response differs between men and women remains unclear. This study investigated sex differences in the effects of sleeping in an unfamiliar environment on strength and muscular endurance in resistance-trained individuals. Methods: Thirty-two resistance-trained participants (16 women, 16 men; 23 ± 4 years) completed a randomized, counterbalanced crossover study involving two conditions: sleeping for 8 h at home or in the laboratory. The following morning, participants performed bench press and back squat strength tests across 25-90%1RM, followed by muscular endurance tests to failure at 65%1RM.

Inclusion Criteria: * Age between 18 and 35 years.• Body Mass Index (BMI) \< 25 kg/m². * Resistance-trained individuals (more than 2 years of structured training). * Healthy men and women without neurological, cardiometabolic, immunological, or physical conditions that prevent them from exercising. * Participants must be able to perform the tests described in the following section. Exclusion Criteria: * History of neuromuscular diseases, heart disease, or conditions that may affect liver or muscle metabolism. * Use of drugs, stimulants, or sports supplements that could interfere with the dietary supplement used in the study. * Sedentary habits (less than 150 minutes/week of moderate exercise).• Having undergone prolonged periods of physical inactivity in the 6 months prior to the study. * Engaging in strenuous exercise within 48 hours prior to the tests.• Failure to replicate the same food intake on both experimental days. * Consumption of caffeine or any other stimulant the day before the tests.