Abstract
BACKGROUND: Rapid restoration of muscle glycogen stores is imperative for athletes undertaking consecutive strenuous exercise sessions with limited recovery time (e.g. ≤ 8 h). Strategies to optimise muscle glycogen re-synthesis in this situation are essential. This two-part systematic review and meta-analysis investigated the effect of consuming carbohydrate (CHO) with and without protein (PRO) on the rate of muscle glycogen re-synthesis during short-term post-exercise recovery (≤ 8 h). METHODS: Studies were identified via the online databases Web of Science and Scopus. Investigations that measured muscle glycogen via needle biopsy during recovery (with the first measurement taken ≤ 30 min post-exercise and at least one additional measure taken ≤ 8 h post-exercise) following a standardised exercise bout (any type) under the following control vs. intervention conditions were included in the meta-analysis: part 1, water (or non-nutrient beverage) vs. CHO, and part 2, CHO vs. CHO+PRO. Publications were examined for methodological quality using the Rosendal scale. Random-effects meta-analyses and meta-regression analyses were conducted to evaluate intervention efficacy. RESULTS: Overall, 29 trials (n = 246 participants) derived from 21 publications were included in this review. The quality assessment yielded a Rosendal score of 61 ± 8% (mean ± standard deviation). Part 1: 10 trials (n = 86) were reviewed. Ingesting CHO during recovery (1.02 ± 0.4 g·kg body mass (BM)(-1) h(-1)) improved the rate of muscle glycogen re-synthesis compared with water; change in muscle glycogen (MG(Δ)) re-synthesis rate = 23.5 mmol·kg dm(-1) h(-1), 95% CI 19.0-27.9, p < 0.001; I(2) = 66.8%. A significant positive correlation (R(2) = 0.44, p = 0.027) was observed between interval of CHO administration (≤ hourly vs. > hourly) and the mean difference in rate of re-synthesis between treatments. Part 2: 19 trials (n = 160) were reviewed. Ingesting CHO+PRO (CHO: 0.86 ± 0.2 g·kg BM(-1) h(-1); PRO: 0.27 ± 0.1 g·kg BM(-1) h(-1)) did not improve the rate of muscle glycogen re-synthesis compared to CHO alone (0.95 ± 0.3 g·kg BM(-1) h(-1)); MG(Δ) re-synthesis rate = 0.4 mmol·kg dm(-1) h(-1), 95% CI -2.7 to 3.4, p = 0.805; I(2) = 56.4%. CONCLUSIONS: Athletes with limited time for recovery between consecutive exercise sessions should prioritise regular intake of CHO, while co-ingesting PRO with CHO appears unlikely to enhance (or impede) the rate of muscle glycogen re-synthesis. TRIAL REGISTRATION: Registered at the International Prospective Register of Systematic Reviews (PROSPERO) (identification code CRD42020156841 ).