Ashwagandha increases muscle gain by regulating the ratio between testosterone and cortisol. Since testosterone levels decrease when cortisol levels increase, lowering cortisol directly improves testosterone levels and stimulates muscle gain and other benefits of testosterone.
Ashwagandha is also an efficient supplement to increase VO2 max. Obviously, the first prerequisite to increase VO2 max is a dedicated and structured training routine, but ashwagandha improves oxygen flow, which makes these training sessions easier and naturally further increases VO2 max.