Variación diurna de la fuerza muscular en mujeres jóvenes entrenadas. Efecto de la cafeína para la mejora del rendimiento

Abstract

Background: There is previous scientific evidence that neuromuscular performance has a diurnal variation (with higher levels during the afternoon compared to the morning), and that this fact can be compensated by ergogenic aids (e.g., caffeine) in male athletes. However, it is still unknown whether these findings may be applied to female athletes. Given the increased interest in understanding women’ sport physiology and performance during the last decades and the scarce of well-designed studies addressing this research question, it is of scientific and practical interest to know whether the use of caffeine may reverse the hypothetical timeof- day variation in neuromuscular performance in female athletes. Objective and hypothesis: The main objective of the present Doctoral Thesis was to investigate the effect of an acute intake of caffeine on the diurnal variation of neuromuscular performance in resistance-trained women. We hypothesize that caffeine (i) increases neuromuscular performance independently of the time-of-day, and (ii) promotes similar neuromuscular performance in the morning when compared to the afternoon without the ingestion of caffeine. Material and methods: A total of 15 resistance-trained women participated in the current triple-blind, placebo-controlled, crossover experimental study. We assessed neuromuscular performance (i.e., ballistic (countermovement jump [CMJ] height and bench press throw [BPT] peak velocity), maximal strength (squat and bench press one-repetition maximum [1RM]], and strength-endurance [average velocity of the set during squat and number of repetitions-to-failure in bench press]) 4 times at within 7 days. The participants ingested an acute dose of caffeine (3 mg/kg) or a placebo at 9-11 am and/or 17-19 pm. Results: CMJ height (P=0.016) and BPT peak velocity (P=0.012) were higher in the afternoon than in the morning. Compared to placebo, caffeine intake increased CMJ height by 3.1% in the morning and 1.6% in the afternoon (P=0.035), but it had no effect on BPT peak velocity (P=0.381). Maximal strength and strength-endurance performances were not affected by the time-of-day or caffeine intake (all P>0.3). No significant interaction (time-of-day x substance) was observed in any of the above-mentioned outcomes (all P>0.1). Conclusion: In summary, the main findings of the Doctoral Thesis are that an acute dose of caffeine in the morning is effective to partially restore lower-body strength performance to levels found in the afternoon in resistance-trained women.