Training in your rep range ensures progress.
Working out with the correct amount of weight will help you reach your goals and keep you from wasting time at the gym. Instead of guessing how much your dumbbells should weigh, use the repetition range based on your fitness goal to guide you. Exercising within your repetition range ensures that every workout is designed to give you the body -- or conditioning -- you want.
Wow, That's Heavy!
When you consider whether a dumbbell is heavy or light, you will have a different perception than the person on the bench beside you. While you struggle to curl a 20-pound set of dumbbells five times, he can curl it 30 times with ease. Since heavy or light in regard to dumbbells is subjective, a better way to look at the dumbbell weight is in terms of repetition range.
Don't Go Through the Motions
Your current workout probably consists of three sets of eight to 12 repetitions -- or something similar. If you simply go through the motions of doing those 12 reps then going to the next set, you are not weight training properly. A rep range of eight to 12 repetitions means that you can complete between eight and 12 repetitions while number 13 would be physically impossible. As you gain strength and progress past 12 reps, increase the weight to stay within this range. If you are unable to do eight repetitions, decrease the weight to achieve the rep range.
Dumbbells for Tight Body
If your goal is putting on muscle mass, your dumbbells are going to be moderately heavy. According to the National Strength and Conditioning Association and the American College of Sports Medicine, training with a rep range of six to 12 repetitions is the most effective for hypertrophy, the increase in muscle volume. For maximizing hypertrophy, gradually change this range over time to a rep range of six to eight repetitions. Exercise choices for hypertrophy vary between multi-joint exercises such as the dumbbell chest press and single-joint exercises such as biceps concentration curl. Muscular toning is best done with the same principles but with a rep range of eight to 12.
Dumbbells for Strength or Endurance, Not Both
For strength and power, your dumbbell weight goes up and you'll consider it very heavy. A repetition range of two to five reps is recommended with a focus on multi-joint exercises such as the dumbbell row or dumbbell lunges.
Endurance training focuses on a lighter weight and a higher rep range of 13 to 20 reps. It is recommended for increasing aerobic power and to prevent muscles from exhausting during prolonged aerobic exercise.