3.1. Search outcomes and overview of included studies
Our initial search led to 184 relevant studies. After removing
duplications, a wide range of screening of the titles and abstracts, the
careful assessment was performed on 142 related articles. Of these, 11
articles remained after considering the inclusion and exclusion criteria
for the eligibility. Eventually, 7 articles, including, 8 effect sizes,
which studied a total of 235 participants aged 16.1 –24.9 years, were
identified in the current systematic review and meta-analysis.Figure 1 represents the selection process and reasons for
excluding the studies. The data in Table 1 illustrates the main
characteristics of the articles in our systematic review and
meta-analysis.
In brief, the studies (by 235 participants) were published between 2001
and 2017. The duration of these RCTs ranged between 1.5 to 12 weeks. 2
studies used a randomized crossover design (19, 29), one of them was
also single blind (30) and the other studies had the design of
double-blind. Two studies were conducted in Poland (19, 29), 1 in the
United States (30), 1 in Iran (31), 2 in Australia (20, 32) and 1 in
Israel (7). The effect of exercise on testosterone and cortisol
concentration was examined in 7 studies (7, 19, 20, 29-32); and 8 effect
sizes were extracted from these studies for testosterone and cortisol
concentration. The total number of subjects who completed the studies in
inclusion criteria was 121 subjects in the intervention and 107 in the
placebo groups. The dose of HMB supplementation was 3 g/day in all
studies.