After doing 8 weeks of intense interval exercise, young men can breathe in about 5% more oxygen per minute, but taking an ashwagandha supplement doesn't help any more than a fake pill, and because they might gain a little weight, their oxygen use relative to body weight doesn't really improve.

A study on young men doing intense exercise for 8 weeks found that those taking a dummy pill got better at using oxygen in their muscles, but those taking ashwagandha didn't improve at all - suggesting the herb might actually block the normal benefits exercise has on muscle oxygen use.

Taking ashwagandha root extract (300mg twice daily for 8 weeks) can help healthy athletes improve their VO2 max, which measures how well their body uses oxygen during exercise.

Taking ashwagandha supplements (600mg daily for 8 weeks) won't change your blood test results - at least not in a meaningful way - if you're a healthy young man doing HIIT workouts.

Doing short bursts of intense exercise for 12 weeks doesn't improve the maximum oxygen your body can use during exercise in people with excess body fat, even though they can exercise longer before getting tired.

Doing regular exercise for 12 weeks helped improve heart and lung fitness in obese black South African women, as measured by their ability to use oxygen during exercise. This finding is from the abstract summary - full study details were not available