Dietary supplementation strategies for improving training adaptations, antioxidant status and performance of volleyball players: A systematic review

<p dir="ltr"><b>Purpose</b> Volleyball demands high physical performance including agility, speed, endurance and muscular strength. As volleyball players explore methods to achieve efficiency in these areas, nutritional supplementation has been considered a valuable adjunct to accomplish this goal. This systematic review aimed to comprehensively explore the effects of different dietary supplementation strategies on the training adaptations, antioxidant status and performance of volleyball players.</p><p dir="ltr"><b>Methods</b> A search was conducted in PubMed, Web of Science, Cochrane, Google Scholar, and EbscoHost on 28th July 2023 and updated on 12th May 2024. Studies were included if the participants were volleyball players, taking a dietary supplement and evaluated sports-related outcomes. The risk of bias was assessed using Cochrane's revised risk of bias tool, RoB2.</p><p dir="ltr"><b>Results</b> The review included 19 trials investigating supplements such as branched-chain amino acids (BCAA), creatine, N-acetylcysteine (NAC), hydroxy-methyl-butyrate (HMB), grape seed extract (GSE), nitrate, caffeine, iron and magnesium. Outcomes including vertical jump (VJ) height, endurance, oxidative stress, cell damage, muscle strength, and anaerobic and aerobic capacity were considered. Caffeine supplementation improved VJ height and agility while creatine, BCAA, HMB and mineral supplementation may improve anaerobic performance and muscle strength without a clear positive effect on VJ height, subject to a limited number of studies on each supplement. Creatine and BCAA effects were inconsistent concerning muscle damage.</p><p dir="ltr"><b>Conclusions</b> Among the investigated supplements, caffeine showed the most promising data to enhance physical performance and agility. NAC and GSE could improve antioxidant status. More research is needed to assess other supplements’ effectiveness in volleyball players.</p><p dir="ltr"><b>Protocol Registration</b> https://doi.org/10.17605/OSF.IO/8RD9V.</p>