The rest portion of your workout is just as important as the types of exercises you do and the amount of weight you lift. Rest gives your body a chance to get rid of waste products, restore balance and energy, and prepare your muscles for the next round of exercise. How much rest you take between arm exercises depends upon how much weight you use and your training goals.
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Lifting for Strength
If your primary goal with dumbbell arm exercises is to improve strength, then that means you'll be working with some fairly heavy weights. Exercising with heavy weights will lead to muscle fatigue by the end of your set. In order to complete the next set with as much force and power as was used in the previous set, you'll have to give your arms a relatively long rest. The National Strength and Conditioning Association recommends a rest length of two to five minutes for maximum muscle recovery and optimal strength gains to occur.
Upping Your Power
Training for power with dumbbell arm exercises such as hang cleans, snatches and push jerks requires maximum rates of force. Once your muscles produce this force to complete one set of the exercise, they require ample rest to restore peak function and power for the next set. The NSCA again suggests a rest period of two to five minutes for such exercises. Due to the technical nature of power exercises, if you fail to allow full recovery, your form is likely to suffer.
Lifting to generate hypertrophy, or muscle growth, in your arms is a bit more conservative in terms of rest periods. When it comes to stimulating muscle growth, complete muscle recovery is not the goal. Instead, begin the next set before full recovery has been achieved. Forcing your muscles to work to and through fatigue helps create an optimal environment for muscle growth to occur, especially when using high volume with moderate weights. Follow the guidelines of the NSCA and aim for 30 to 90 seconds of rest.
Elevate Your Endurance
Muscular endurance is the ability of a muscle to maintain or repeat a submaximal contraction for an extended period of time. Using light dumbbells to perform arm exercises is an effective way to increase the endurance of your shoulders, biceps, triceps and forearms. Endurance training is generally carried out with high repetitions, low weights and short rest periods -- the NSCA recommends 30 seconds or less. It would be difficult to perform three sets of 15 biceps curls with only 30 seconds of rest. So instead, train for endurance in a circuit fashion. For example, complete 15 biceps curls, followed immediately by 15 triceps extensions, 15 wrist curls and 15 wrist extensions. Repeat two to three times.