Hands off! Your hands should stay firmly at your sides when on the treadmill. Holding on makes it easier, which translates to fewer calories burned, says Irv Rubenstein, PhD, exercise physiologist and founder of S.T.E.P.S., a fitness facility in Nashville, TN. Rubenstein suggests that if you're supporting five percent of your body weight on the treadmill, you’re actually reducing your calorie burn by the same amount. If you're walking for 30 minutes at a brisk walk (4 mph) and would normally burn 300 calories, you'll burn 15 fewer calories each workout. Do that five days a week for a year and you'll burn nearly 4,000 fewer calories, which amounts to more than a pound of fat!