3.3.2. Effects of HMB supplementation on testosterone
concentration
As outlined in Table 4 , our preliminary analysis indicated that
HMB consumption did not significantly improve serum testosterone
concentration (WMD= 0.75 nmol/L; 95% CI: -0.09, 1.58; P= 0.079). Also,
no significant heterogeneity was observed among studies (Cochran’s Q test
= 3.33, P= 0.853, I2 = 0.00%). Subgroup analysis was
conducted to check as to how the effect of HMB supplementation on serum
testosterone is different according to type of exercise activities
(Figure 3 ) or duration of the interventions (Figure
4 ). This analysis revealed that the pooled effect of HMB
supplementation on testosterone concentration was influenced by the
duration of the supplementation (<6 weeks versus ≥6 weeks), in
which a significant increase in testosterone concentration was found in
studies that lasted longer than 6 weeks (WMD= 1.60 nmol/L; 95% CI:
0.08, 3.12; P= 0.039). Also, subgroup analysis based on the type of
exercise training indicated that the increasing effect of HMB
supplementation on serum testosterone is significant in aerobic and
anaerobic combined activities (WMD= 1.60 nmol/L; 95% CI: 0.08, 3.12; P=
0.039). Subgroup analysis didn’t show any significant effect of HMB
supplementation on testosterone concentration in studies lasting lower
than six weeks (WMD= 0.38; 95% CI: -0.62, 1.38; P= 0.455) or on
resistance training exercise (WMD= 0.38 nmol/L; 95% CI: -0.63, 1.38; P=
0.464).