Effects Of Caffeine Abstinence On The Acute Response To Low-load Blood Flow Restriction Exercise

Abstract

Caffeine (CAFF) enhances muscular responses to exercise. Blood flow restriction (BFR) studies typically require CAFF abstinence (ABS) prior to BFR exercise (BFR-ex). The effect of ABS has not been tested in habituated CAFF users. PURPOSE: Compare acute muscular response to BFR-ex after habitual CAFF intake and acute ABS. METHODS: 15 participants completed a 3 visit (2-14d apart) within-subject study. Visit 1 involved familiarization, CAFF intake form, and maximum strength test (1RM). Visits 2-3 consisted of dominant arm BFR-ex (3 sets of armcurls to failure, 30% 1RM, 40% arterial occlusion pressure, 30s inter-set rest). One visit was with CAFF and the other ABS (counterbalanced, 1 hr after typical intake). Maximal voluntary contractions (MVC, N) were taken pre- and post-BFR-ex. Biceps electromyography amplitude (EMGa) was measured during MVC and BFR-ex, and normalized to preMVC (%Pre). EMGa during BFR-ex was averaged over the first and last 3 repetitions for each set. Bayesian RMANOVA were conducted to find the most probable model vs. the null (BF10) for all variables except EMGa and force during MVC (Bayes paired t-test). Data are mean ± SD. RESULTS: A time main effect (BF10 = 6.5e+7) suggestsforce decreased from pre (237.7 ± 61.5) to post (154.9 ± 47.2). Weak evidence suggests no difference in EMGa (BF10 = .39) between CAFF (130.3 ± 74.7) and ABS (160.7 ± 99.9) during MVC. A time main effect (BF10 = 1.7e+37) indicates more completed repetitions in set 1 (33.0 ± 8.5) vs. 2 (10.8 ± 3.3, BF10 = 1.3e+14) and 3 (9.0 ± 2.8, BF10 = 2.2e+15); and set 2 vs. 3 (BF10 = 240.1). A time main effect (BF10 = 128.5) indicates EMGa increased from beginning (133.5 ± 97.7) to end of set 1 (227.3 ± 123.1), BF10 = 972.1), and from beginning (176.4 ± 73.0) to end of set 2 (219.2 ± 116.3, BF10 = 58.4) during BFR-ex. Moderate evidence suggests a difference from beginning (186.5 ± 81.9) to end of set 3 (212.3 ± 122.4, BF10 = 3.5). Moderate to strong evidence suggests a difference in EMGa (all BF10 ≥ 4.9) at the beginning of each set during BFR-ex. A condition main effect (BF10 = 74.3) indicates strong evidence for higher EMGa in CAFF (216.0 ± 125.6) vs. ABS (169.1 ± 80.2, BF10 = 15.2) during BFR-ex. CONCLUSION: Muscular responses to BFR-ex appear to not differ between conditions, except EMGa during BFR-ex. ABS from CAFF may not be required prior to BFR-ex in future studies.