People who are new to weight training tend to use dumbbells that are too light to gain strength or sculpt muscles, according to a study at Grand Valley State University in Allendale, MI. Choose a weight that feels heavy for 8 to 12 reps so that “you are barely able to complete the last rep of each set,” says lead author Stephen Glass, Ph.D. “It’s best to lift to fatigue.”

Make sure you bump up the weight as you get stronger!