You’re likely to experience gains in muscle strength and power regardless of the weights you choose to lift during strength training, but it is true that heavier weights can help you increase the overall percentage of lean muscle mass in your body. If you can handle 20-pounders, then go for it, but make sure to always place your safety as a top priority.
Lifting 20-lb. weights, or "20s," may help you make more rapid progress in a strength training program than using resistance bands, body weight exercises or weight machines. According to the American Council on Exercise, free weights closely match real-life movements and “may be more effective in producing overall muscular strength and power gains.” Training with dumbbells can also increase stamina, improve bone health, enhance focus and help you stay at a healthy weight.
It’s not always possible to complete every exercise with the same amount of weight. Your abilities will vary depending on how strong each of your muscle groups is and whether you’re contending with injuries. For example, you may be able to do 12 reps of a hammer curl using 20-lb. dumbbells with your right arm but not your left, or you may be able to do chest presses with the weights but not lateral shoulder raises. You may also want to try squats with presses, lunges with curls, triceps kickbacks and deadlifts with your weights to evaluate your ability to complete each move with 20s.
If you want to gain muscle strength, American Council on Exercise scientist Jessica Matthews recommends using heavier weights to complete two to six total sets of four to eight repetitions of each exercise, with breaks of several minutes between each set. You’ll have less rest time if you want bigger muscles; Matthews suggests three to six sets of six to 12 reps of each exercise with heavy weights and resting for just 30 to 90 seconds between sets. For muscular endurance, use lighter weights, such as 5- to 10-lb. dumbbells, and complete more reps.
Form is critical when you perform weightlifting moves, as it allows you to get maximum muscle gains while minimizing your risk of injury. If you can’t keep proper form on an exercise because the weights you’re using are too heavy, use lighter dumbbells. Conversely, if you can easily complete a set or two with 20s, you may need to use heavier weights to build more muscle. Always clear a strength training program with your physician before beginning, and check your lifting technique against that of a fitness professional if possible.