Dietary Carbohydrate Intake and Skeletal Muscle Glycogen: A Systematic Review and Meta-Analysis to Determine Optimal Carbohydrate Loading Strategies

A high dietary carbohydrate intake in the days pre-competition is recommended to optimize glycogen stores for endurance exercise performance. However, previous reports show high variability in muscle glycogen concentrations between individuals following similar CHO intakes. Therefore, the amount of CHO, duration, and amount of exercise required to maximize glycogen stores pre-competition remains unclear. The aim of this systematic review and meta-analysis was to determine the relationship between dietary CHO availability and skeletal muscle glycogen, whilst identifying the effect of other covariates on muscle glycogen concentration. The analysis included trials (randomized or non-randomized from five online databases) published until June 2026, that reported CHO intake and exercise for ≥ 24 h prior to collection of muscle samples using biopsies to measure skeletal muscle glycogen. Included studies were assessed descriptively and quantitatively using linear and non-linear regression, and generic inverse-variance random-effects meta-analyses, including subgroups to investigate heterogeneity. Descriptive synthesis included 63 trials (n = 641 participants), 18 were included within the meta-analysis. Exploratory linear regression indicated a significant relationship between relative CHO intake and whole muscle glycogen for recreationally active (r² = 0.332, p < 0.001) and endurance trained individuals (r² = 0.490, p < 0.001). Meta-analyses revealed increased dietary CHO intake from a low-moderate (< 6.5 g·kg^-1·day^-1) to a high-very high intake (> 6.5 g·kg^-1·day^-1) significantly increased muscle glycogen concentrations (+191.9 mmol·kg^-1 DM, 95% CI from 142.8 to 241.1 mmol·kg^-1 DM, p < 0.0001) but displayed significant heterogeneity (p < 0.0001, I² = 94%). The delta CHO intake between study conditions (expressed as relative g·kg^-1·day^-1 and absolute g·day^-1) and duration of CHO loading interventions suggested a significant subgroup effect (p < 0.05) but failed to explain the heterogeneity in muscle glycogen concentration. Glycogen concentration primarily depends on quantity of CHO intake, with period of increased CHO intake, participant training status, and exercise all being key effectors. Based on current findings, to significantly increase pre-competition muscle glycogen stores athletes should consume > 8 g·kg^-1·day^-1 for 36-48 h pre-competition, with prior glycogen depleting exercise combined with consumption of high glycaemic index CHO allowing more rapid enhancement of stores (24-36 h). However, significant heterogeneity and confounding variables in previous research introduce uncertainty in these recommendations, and further well-controlled studies are required to determine the true optimal pre-exercise CHO intake to maximize glycogen concentrations.