Background: This study assessed the impact of acute caffeine intake on muscular strength, power, and endurance performance between resistance-trained male and female individuals according to load in upper- and lower-body exercises. Methods: Here, 76 resistance-trained individuals (38 females, 38 males) participated in a study comparing caffeine and a placebo. Each received either 3 mg/kg of caffeine or a placebo 60 min before tests measuring muscular strength and power through bench press and back squat exercises at different intensities (25%, 50%, 75%, 90% 1RM). Muscular endurance at 65% 1RM was also assessed by performing reps until reaching task failure. Results: Compared to placebo, caffeine increased mean, peak and time to reach peak velocity and power output (p < 0.01, η_p² = 0.242–0.293) in the muscular strength/power test in males and females. This effect was particularly observed in the back squat exercise at 50%, 75% and 90% 1RM (2.5–8.5%, p < 0.05, g = 1.0–2.4). For muscular endurance, caffeine increased the number of repetitions, mean velocity and power output (p < 0.001, η_p² = 0.177–0.255) in both sexes and exercises (3.0–8.9%, p < 0.05, g = 0.15–0.33). Conclusions: Acute caffeine intake resulted in a similar ergogenic effect on muscular strength, power, and endurance performance in upper- and lower-body exercises for male and female resistance-trained participants.

Background: Caffeine and sodium bicarbonate individually enhance muscular endurance by delaying fatigue, but their combined effects have scarcely been studied. Objectives: This study aimed to evaluate the acute effects of co-ingesting caffeine and sodium bicarbonate on muscular endurance at different loads in bench press and back squat exercises. Methods: Twenty-seven recreationally trained participants (female/male: 14/14; age: 23 ± 3.6 years) were randomized to four conditions in a double-blind, crossover design: (a) sodium bicarbonate and caffeine (NaHCO₃ + CAF); (b) sodium bicarbonate (NaHCO₃); (c) caffeine (CAF); (d) placebo (PLA); ingesting 0.3 g/kg NaHCO₃, 3 mg/kg caffeine or placebo (maltodextrin). Participants performed two muscle endurance tests on bench press and back squat exercises at 65% and 85% 1RM, performing as many repetitions as possible in one set until task failure. Results: CAF increased the number of repetitions (p < 0.001; η_p² = 0.111), mean velocity (V_mean, p = 0.043, η_p² = 0.16), and mean power output (W_mean, p = 0.034, η_p² = 0.15) compared to placebo. These effects were observed in back squat exercise at 65%1RM in V_mean (3.7%, p = 0.050, g = 1.144) and W_mean (5.2%, p = 0.047, g = 0.986) and at 85%1RM in V_mean (5.4%, p = 0.043, g = 0.22) and W_mean (5.5%, p = 0.050, g = 0.25). No ergogenic effects were found in NaHCO₃ + CAF) or NaHCO₃ conditions. Conclusions: CAF increased muscular endurance performance in male and female participants by increasing the number of repetitions, mean velocity, and power output; however, when NaHCO₃ was ingested, these effects were not detected.

Background: Sleep is essential for athletic performance, yet the specific effects of sleep deprivation are not well defined. Evidence in resistance-trained populations is limited regarding sex-specific responses and velocity-based performance across different loads. Purpose: This study examined sex differences in the impact of total (0 h) and partial (4 h) sleep deprivation versus normal sleep (8 h) on strength, power, and endurance performance in resistance-trained individuals. Methods: Twenty-four resistance-trained participants (male/female, 12/12; age: 22 ± 3 years) completed a randomized, cross-over, counterbalanced trial including one baseline control night (8 h at home sleep) and three experimental conditions in the laboratory: (a) 8 h sleep (NS), (b) 4 h sleep (ESD), (c) 0 h sleep (SD). Strength was assessed at 25%, 50%, 75%, 90% and 100% 1RM for bench press and back squat (half-squat depth, ~90° knee flexion), in a Smith machine, followed by a muscular endurance test at 65% 1RM (set-to-failure). Isometric strength and vertical jump test were also performed. Results: At 50% 1RM, significant sleep and sleep-by-sex effects were observed for V_mean in both exercise (p < 0.05, η_p² > 0.09), an effect only noted in males, with reduced performance under ESD and SD compared to NS (7–13%, p < 0.05, g > 0.50). In the muscular endurance test, sleep and sleep-by-sex effects were found (p < 0.05, η_p² < 0.22), an effect only found in females during the back squat, showing performance declines in V_mean in ESD and SD compared to NS (7–12%, p < 0.05, g > 0.2). Conclusions: Total and partial sleep deprivation impairs muscular performance differently by sex. Males experienced reduced strength at moderate loads, while females showed declines in muscular endurance.

López-Samanes, Á, Pérez-López, A, Martín-López, J, Montalvo-Alonso, JJ, Muñoz, A, Conejero, M, Sánchez-Jorge, S, -Moreno-Pérez, D, Quintana-Milla, I, and Scanlan, A. Neuromuscular characteristics differ between elite, subelite, and amateur female volleyball players. J Strength Cond Res 40(11): e1228–e1235, 2026—Adequate neuromuscular development is crucial for female volleyball players to optimally execute game-related tasks; however, neuromuscular differences between playing levels remain underexplored within this population. Thus, the aim of this study was to compare neuromuscular characteristics between elite, subelite, and amateur female volleyball players. Sixty-one female players (22.9 ± 5.4 years) participating in the first-national (elite), second (subelite), and third and fourth (amateur) Spanish Volleyball Divisions took part in this study. Subjects underwent a neuromuscular testing battery consisting of standing spike, jumping spike, countermovement jump, squat jump, maximal spike jump, isometric handgrip, modified agility t test, and star excursion balance assessments. Regarding neuromuscular performance, elite, female volleyball players had faster standing and jumping spike velocities than subelite and amateur players ( p < 0.001; η _p ² = 0.31–0.36), higher maximal spike jump height than amateur players ( p < 0.001; η _p ² = 0.31), and a stronger isometric handgrip than subelite (both sides) and amateur (only nondominant side) players ( p < 0.01, η _p ² = 0.17–0.23). Moreover, subelite players had quicker modified agility t test performance than amateur players ( p < 0.001, η _p ² = 0.21). For dynamic balance, elite players exhibited superior posteromedial and posterolateral performance (both sides) than amateur players ( p < 0.001, η _p ² = 0.26–0.31), whereas subelite players had better anterior performance (both sides) than amateur players ( p = 0.002–0.04; η _p ² = 0.17–0.20). Elite female volleyball players were characterized as possessing superior hitting velocities, lower-body strength/power, isometric strength, and dynamic balance than lower-level players. In contrast, subelite players differentiated from amateur players with faster change-of-direction speed, greater strength, and better dynamic balance. These novel data may help inform the development of targeted training, assessment, and player identification strategies according to playing level in practice among female volleyball teams.

Background/Objectives: Caffeine is a well-established ergogenic aid in many strength- and endurance-based sports, but its efficacy in sport climbing remains underexplored despite the sport’s unique physical demands on grip strength, power, and muscular endurance. Therefore, this study examined the acute impact of a low caffeine dose (3 mg/kg) on climbing-specific performance, including pull-up and grip tests, in intermediate-advanced climbers. Methods: In a triple-blind, randomized, crossover design, thirteen male climbers (age: 28.2 ± 8.6 years) completed two experimental trials (caffeine vs. placebo). Performance was assessed via a pull-up one-repetition maximum (1RM) and power test at various loads, a pull-up muscular endurance test, and grip tests including maximum dead-hang time, maximum dead-hang strength, and rate of force development (RFD). Results: Caffeine did not significantly enhance performance in any measured variable. While a non-significant increase in peak power was observed at 80% 1RM (+8.0%, 95% CI: −0.232 to 0.304, p > 0.05, g = 0.348), effects at other loads and on pull-up endurance were trivial based on effect size (e.g., repetitions: +3.3%, 95% CI: −3.30 to 4.37, p = 0.292, g = 0.061). For grip metrics, caffeine was associated with a modest reduction in endurance time (+7.4%, p = 0.162, g = 0.171) and a slight increase in maximum strength (+2.4%, p = 0.060, g = 0.120). RFD was unaffected (p > 0.169, g < 0.13). Despite the lack of objective improvement, participants reported significantly greater subjective feelings of strength, energy, and alertness with caffeine (p < 0.05). Conclusions: A 3 mg/kg dose of caffeine, while altering psycho-physiological state, did not elicit statistically or practically meaningful ergogenic effects on pull-up or grip performance in climbers. Higher doses or sport-specific performance tests should be investigated in future research.

Purpose : Neuromuscular performance is influenced by diurnal variation, but it remains unclear whether sex moderates these patterns in team sport athletes. This study examined whether sex moderates the effect of time of day on neuromuscular performance in volleyball players. Methods : One hundred and two volleyball players (46 males and 56 females) completed a randomized battery of tests in the morning (08:00–10:00) and evening (18:00–20:00) on separate days. The battery included vertical jumps (squat, countermovement, and spike jumps), spike performance (standing and jumping spike), agility (modified T test), isometric handgrip strength, and dynamic balance (modified star excursion balance test). Results : A significant sex-by-time interaction was observed in squat jump ( P = .002, ), with males showing higher evening values, whereas females showed no significant change. A sex-by-time interaction was also found in jumping spike ( P = .045, ), agility ( P = .027, ), and dynamic balance (ie, posterolateral) on the dominant leg ( P = .005, d = 0.26), reflecting different response patterns between sexes. No significant changes were observed in other dynamic balance directions ( P > .05). A significant time-of-day effect was observed, indicating higher evening performance in all jump tests ( P = .005, ), ball velocity in spike velocity ( P = .002, ), and isometric handgrip strength ( P = .001, ). Conclusion : Sex-specific differences were limited to a few tasks and were generally small in magnitude, whereas a consistent enhancement in neuromuscular performance in the evening compared with the morning emerged as the primary finding, regardless of sex.