A new study by University of Michigan researchers confirms what many skiers have known for a while: There’s a greater chance of getting injured on your last run of the day. The U of M’s School of Kinesiology had subjects perform one-legged squats to the point of fatigue and then tested their reactions to various jumping and movement commands. Researchers found that both legs, not just the fatigued leg, showed potentially harmful changes in mechanics, which could result in ACL injuries. During testing, a flashing light cued the subjects to jump in a certain direction, and the more fatigued the subjects became, the less likely they were able to react quickly and safely to the unexpected command. The study suggest that training your mind to react to unexpected stimuli, like trees or moguls, can be just as important to injury prevention as hitting the gym. And for Pete’s sake, don’t boost off that wind lip when you’re heading back to the lodge at the end of the day.