Betaine as an Ergogenic Aid to Improve Muscle Fatigue in Physical Exercise: A Systematic Review of Randomized Clinical Trials

Objectives:This systematic review aims to investigate the influence of betaine supplementation on muscle fatigue during exercise.Methodology: To this end, the PRISMA guidelines were adopted and the study was registered with PROSPERO (CRD42023469111).Searches were conducted using specific keywords according to the PICOS strategy on March 12, 2024, in the PubMed, Cochrane Library, Web of Science, Embase and SCOPUS databases. Randomized clinical trials(RCTs)in adults of both sexes that used betaine as a supplement, compared to placebo, to improve muscle fatigue during physical exercise were included. Animal studies and studies with concomitant use of betaine and other supplements were excluded. Muscle fatigue was assessed using the one-repetition maximum test and blood lactate during leg press or squat and bench press exercises. The risk of bias of the included studies was assessed using the Cochrane RoB2 tool and the certainty of the evidence using GRADE. Results: Five RCTs were included, inwhich a total of 93 participants were evaluated; all were male, with 57 individuals allocated to the intervention group with a mean age of 19.18±2.67 years, and 58 individuals in the control group with a mean age of 19.66±2.44 years. Betaine promoted more repetitions until muscle fatigue in the leg press or squat (n = 3) and bench press (n = 2), with reductions in serum lactate in two of these studies. Conclusion: Betaine can be considered as a potential ergogenic resource for improving muscle fatigue, providing a greater number of repetitions in exercises and eliminating lactate in the blood.