Strenuous physical activity lowers blood levels of coenzyme Q10 (CoQ10).1 However, the effects of CoQ10 on how the healthy body responds to exercise have been inconsistent, with several studies finding no improvement.2, 3, 4, 5 A few studies, using at least four weeks of CoQ10 supplementation at 60 to 100 mg per day, have reported improvements in measures of work capacity ranging from 3 to 29% in sedentary people and from 4 to 32% in trained athletes.6 However, recent double-blind and/or placebo-controlled trials in trained athletes, using performance measures such as time to exhaustion and total performance, have found either no significant improvement or significantly poorer results in those taking CoQ10.7, 8, 9