Forgive us for sounding like a broken record, but one more time: You won’t bulk up by lifting hefty dumbbells. And if you keep doing lots of repetitions with light weights, all you’ll get is an aerobic workout. To sculpt your body, muscle fatigue is key. Choose a load that only allows you to complete six to eight quality reps, with the last one being the hardest. Source: Pete McCall, exercise physiologist with the American Council on Exercise
