Background: β-hydroxy β-methylbutryate (HMB) is a metabolite of leucine amino acid and it has several ergogenic benefits. Previous studies also showed that it may affect beneficially the testosterone and cortisol concentration in athletes. Due to the contradiction results between studies, we aimed to conduct this meta-analysis to assess the HMB supplementation effect on testosterone and cortisol in trained athletes. Methods: Scopus, Medline and Google scholar were systematically searched up to August 2020. The Cochrane Collaboration tool for evaluating the risk of bias was applied for assessing the studies quality. Random effects model, weighted mean difference (WMD), and 95% confidence interval (CI) were used for estimating the overall effect. Between-study heterogeneity was evaluated applying the chi-squared and I2 statistic. Results: Seven articles were included in the meta-analysis. Although, the meta-analysis generally showed that HMB consumption did not have any effect on the cortisol and testosterone concentration (P > 0.05), but subgroup analysis based on the exercise type, showed a significant decrease in the cortisol concentration in resistance training exercises (WMD= -3.30; 95% CI: -5.50, -1.10; P= 0.003) and a significant increase in the testosterone concentration in aerobic and anaerobic combined sports (WMD= 1.56; 95% CI: 0.07, 3.05; P= 0.040). Conclusion: The results indicate that HMB supplementation in athletes can reduce the concentration of cortisol in resistance exercises and increase the concentration of testosterone in aerobic and anaerobic combined exercises. Nevertheless, more studies are required to confirm these results.

Exercise-induced muscle damage (EIMD) causes to increased soreness, impaired function of muscles, and reductions in muscle force. Accumulating evidence suggests beneficial effects of creatine on EIMD. Nevertheless, outcomes differ substantially across various articles. The main aim of this meta analysis was to evaluate the effect of creatine on recovery following EIMD. Medline, Embase, Cochrane Library, Scopus and Google scholar were systematically searched up to July 2020. The Cochrane Collaboration tool for examining risk of bias was applied for assessing the quality of studies. Weighted mean difference (WMD), 95 percent confidence interval (CI) and random effects model, were applied for estimating the overall effect. Between studies heterogeneity was examined using the chi-squared and I2 statistic. Nine studies met the inclusion criteria. Pooled data showed that creatine significantly reduced CK concentration overall (WMD = -30.94; 95% CI: -53.19, -8.69; P = 0.006) and at three follow-up times 48, 72 and 96 hours) in comparison with placebo. In contrast, effects were not significant in LDH concentration overall (WMD = -5.99; 95% CI: -14.49, 2.50; P= 0.167), but creatine supplementation leaded to a significant reduction in LDH concentrations in trials with 48 hours measurement of LDH. The current data indicates that creatine consumption is better than rest after diverse forms of damaging and exhaustive exercise or passive recovery. The benefits relate to a decrease in muscle damage indices and Improved muscle function because of muscle power loss after exercise.