All the rest

The answer is not simple. Rest time depends on a number of factors including your desired goal and how long you've been training for. While time is a common way to gauge rest between sets, there are other methods you may use as well.

To understand rest between sets, first you must understand what happens during a set. Initially your muscles use adenosine triphosphate (ATP) to power contractions. The levels of ATP available are limited. The cells have a very limited ability to replenish ATP during the activity before having to switch to other methods to fuel the activity.

Fortunately, your body can replenish ATP when you are resting. About 50% or half of the depleted ATP is replaced after one minute of total rest. Almost all of the ATP that the body can replenish (just over 95%) is restored after about three minutes of rest.

These are averages and may vary from individual to individual. ATP is also not the only factor to consider. Your neurological system is also stressed during the training, and this may take several times longer to recover. Have you ever found you suddenly just cannot move your arms, or find that your arms are shaking uncontrollably during an intense set? This is an example of the neurological fatigue taking place.

The amount of ATP present in the muscle when you perform another set can influence the effect of your training. Generally, shorter rest periods cater more to muscular endurance and stamina, as well as general strength and conditioning. If your goal is to increase the number of push-ups or pull-ups you can perform during one session or to improve your endurance during a competitive event that requires repeated bouts of all-out effort, a short rest period is the way to go. Keeping rest short also ensures heart rate is elevated and results in both higher calories burned during the workout and a greater Exercise Post Oxygen Consumption (EPOC) meaning elevated metabolism after the training is complete.

On the converse, if your goal is to gain strength, you require all of the ATP in your cell. Otherwise, you will not be able to perform maximal contractions necessary to produce the desired result of improving strength. For this reason, power-lifters might rest 5 to 10 minutes between sets to allow for full ATP and neurological recovery.

Shorter rest (2 - 3 minutes) is typically for a goal of hypertrophy or muscle growth. This allows enough rest to subsequently overload the muscle without allowing for complete recovery between sets. This increases the intensity of the overall workout and may help increase the amount of muscle growth that results.

You'll find many programs geared to fat loss suggest rest periods in the 45 second to 1 ½ minute range. This is because this compromise allows you to build muscle while keeping your heart rate elevated. It is believed that keeping the heart rate elevated will help burn more fat.

Heart rate is an important factor when considering rest. While a beginner may take several minutes for their heart rate to slow after an intense set, an experienced lifter will actually recover faster (this is one of the adaptations to training). For this reason, an experienced lifter may have to rest for a shorter duration in order to achieve the same results. An easy way to gauge this is to monitor your heart rate during training. Find out how many beats per minute it is at after the desired rest period, and then begin to target your training based on this. You'll find you have to rest longer between sets later in the workout, but over time your rest periods should reduce as your body begins to recover more quickly between sets.

Finally, a very easy way to gauge when you are ready to pick up the weights again is your breath. The condition of being out of breath typically indicates a very high heart rate. Your body is having trouble getting oxygen fast enough to meet demand. When you are able to carry on a comfortable conversation, your heart rate has slowed to the point where you are again utilizing oxygen efficiently (and burning a higher percentage of calories from fat). Therefore, waiting until you can speak freely before starting the next set is one way of computing your rest without a watch.

As you can see, rest is a very important parameter of overall training. Be conscious of your rest periods and use them as another way to modify your training over time - one way to increase the intensity of a workout, for example, is to keep the weights, sets, and reps the same but reduce the rest time. Whether you use a watch, your heart rate or ability to carry on a conversation, these techniques should help you achieve all the rest you need.