Multiple randomized controlled trials have shown a statistically significant increase in strength and power output from ashwagandha extract supplementation. One of the studies showed more than a 40-pound increase and more than a 10-pound increase in the one-re-max (1RM) for bench press and leg extension, respectively. Muscle size, serum testosterone, and muscle recovery as measured by plasma creatine kinase were also improved versus placebo.
Numerous double-blind studies have shown a reliable and significant increase in power output, up to 8%, from caffeine supplementation.
In a double-blind study, leucine increased power output from 31.0% to 40.8%.