In brief: The effects of squatting exercise on heart rate and blood lactate levels were studied in five trained and five untrained men between the ages of 22 and 37. The subjects performed squats (sets of ten repetitions until exhaustion), resting for 2 1/2 minutes between sets. Total positive work was estimated with the following formula: (bar mass + body mass) X vertical displacement X repetitions. Heart rate, lactate, and rating of perceived exertion were measured immediately before exercise, after each set, and five minutes after reaching exhaustion. The trained subjects performed more total work and had higher heart rates and lactate levels at exhaustion than the untrained subjects, though heart rates and lactate levels were lower for trained subjects at a given bar mass or submaximal work load. The findings suggest that weight training may cause adaptations that result in reduced fatigue and/or enhanced recovery.