Caffeine In Conjunction With Resistance Exercise On Vagal Modulation In Resistance-trained Women

Abstract

PURPOSE: To examine the effects of caffeine alone, or in conjunction, with acute resistance exercise, in resistance-trained women on performance and measures of vagal modulation. METHODS: Eleven resistance-trained women (Age Mean±SD: 24±4yrs) consumed either a placebo (PL) or caffeine (4mg/kg) 72 hours apart, in a double-blind, crossover fashion. Forty-five minutes following supplementation, participants performed two sets of 10 repetitions at 75% 1-repetition maximum (1RM), and one set with repetitions to failure at 70% 1RM on the squat and bench press. Log transformed root mean square of successive differences (lnRMSSD), and high frequency power (lnHF), as well as sample entropy (SampEn), and Lempel-Ziv entropy (LZEn) were assessed at rest (Rest1), 45 minutes post-consumption (Rest2), immediately post-exercise (Post1), and 10 minutes post-exercise (Post2). Two-way ANOVAs were used to analyze the effects of condition (PL, caffeine), across time (Rest1, Rest2, Rec1, Rec2). RESULTS: The repetitions on the fatiguing set were similar between conditions for the squat (p=1.0), and the bench press (p=0.7). There were no significant condition by time effects for vagal tone. There was a significant main effect of time (p=0.0001) for lnRMSSD (Rest1: 4.52±0.73ms; Rest2: 4.48±0.64ms; Rec1: 2.72±0.66ms; Rec2: 2.28±0.55ms) such that it significantly decreased during Rec1 and Rec2 compared to Rest1 and Rest2. There was a significant main effect of time (p=0.0001) for lnHF (Rest1: 8.12±1.23ms2; Rest2: 8.00±1.09ms2; Rec1: 4.79±2.50ms2; Rec2: 4.02±1.02 ms2) with it decreasing at Rec1, and Rec2, compared to Rest1 and Rest2. There was a significant main effect of time (p=0.0001) for SampEn (Rest: Rest1: 1.43±.19; Rest2: 1.40±0.19; Rec1: 1.09±0.32; Rec2: 1.09±0.31) such that SampEn was significantly decreased compared to Rest at Rest2, Rec1 and Rec2. Additionally, there was a significant main effect of time (p=0.004) for LZEn (Rest1: 0.73±.09; Rest2: 0.77±0.06; Rec1: 0.66±0.13; Rec2: 0.54±0.16) with Rec2 being significantly attenuated compared to Rest2. CONCLUSIONS: These data demonstrate that 4mg/kg of caffeine consumption does not have an ergogenic effect. In addition, when performed in conjunction with resistance exercise, it does not further decrease measures of vagal modulation in resistance-trained women.