William M. Miller, Matthew A. Chatlaong, Daphney M. Stanford, Matthew B. Jessee. University of Mississippi, University, MS.

BACKGROUND: Caffeine (CAFF) ingestion is known to enhance muscular responses to exercise. Blood flow restriction (BFR) studies typically require CAFF abstinence (ABS) prior to BFR exercise (BFR-ex). Yet, this hasn’t been tested in habituated CAFF users. The aim of this study was to compare the acute muscular responses to BFR-ex following habitual CAFF intake and acute ABS. METHODS: 10 participants completed a 3 visit within-subjects (2-14d apart) study. Visit 1 involved familiarization, CAFF intake form, and one-repetition maximum (1RM). Visits 2-3 consisted of dominant arm BFR-ex (3 sets of biceps curls to failure at 30% 1RM, 40% AOP, 30s inter-set rest). In a counterbalanced order, one visit was with CAFF and the other ABS (both 1hr after typical intake). Maximal voluntary contractions (MVC, N) were taken pre- and post-BFR-ex. Electromyography amplitude (EMGa) of the biceps brachii was measured during MVCs and BFR-ex and normalized as a percentage of peak activation during pre-MVC (%Pre). Normalized EMGa during BFR-ex was averaged over the first 3 and last 3 repetitions for each set. Repetitions (REP) completed were recorded for each set. Bayesian RMANOVAs were conducted for all variables to find the most probable alternative model vs. the null (BF10). EMGa for MVC was compared with a Bayes paired t-test. Data are mean±SD. RESULTS: A main effect of time (BF10=6.740e+6) suggests MVC decreased from pre- (234.8±56.0) to post (143.8±54.2). Anecdotal evidence suggests there may be no difference (BF10=.374) in MVC EMGa between CAFF (93.1±54.3%) and ABS (82.1±40.2%). A main effect of time (BF10=1.923e+22) for REPs indicated higher REPs completed in set 1 (33.7±9.7) vs. 2 (11.2±3.2, BF10=1.143e+8) and 3 (8.9±3.0, BF10=1.159e+9); and set 2 vs. 3 (BF10=217.4). A main effect of time (BF10=38.213) indicated that exercise EMGa increased from the beginning (112.7±45.4) to the end of set 1 (209.1±114.9, BF10=486.856), and from the beginning (168.1±73.2) to the end of set 2 (198.2±103.5, BF10=3.221). However, weak evidence suggests no difference from the beginning (175.4±79.6) to end of set 3 (186.2±99.1, BF10=0.576). CONCLUSION: Muscular responses to BFR-ex appear to not differ between ABS vs. CAFF. Future studies may not require participants to ABS from CAFF prior to BFR-ex.

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