Yes you read that right. In a recent study published in the Journal of the International Society of Sports Nutrition, researchers looked at the effect of peppermint oil on running performance. The researchers used .05ml of peppermint oil in a drink, consumed each day for 10 consecutive days.
The amount of total work performed by the test subjects was increased by a whopping 51%, including an increase in the time to exhaustion of about 25%.
While this study was done on endurance athletes, many gym rats have been using this technique for years on the week prior to maxing out.