In my recent blog post titled How Many Reps Should I Do?, I discussed the relationship between training goals and repetition count. Of equal significance to improvements in performance is the the relationship between training goals and rest periods between sets and exercises. Like repetition count, the former will determine what the latter should be. For example, if your primary training goal is to increase strength, your rest periods will be different than if your primary training goal is to increase muscular endurance.
As I discussed previously, the load and rep count is determined based on training goal, whether that’s power, strength, hypertrophy, or endurance. Heavier loads call for fewer reps, and as a result, longer rest periods. Thus, there is a correlative relationship between load, number of reps, and rest period.
Optimal results are seen when rest periods as follows:
POWER and STRENGTH
The optimal rest period guidelines for power and strength are equal. Because the loads lifted are near-maximal, and the reps are low (1-6 reps), greater rest periods between sets are than those for or hypertrophy and muscular endurance training. At least 2 minutes, or between 2-5, or 3-5 minutes is recommended for optimal strength and power improvements. The lower body structural exercises (e.g. back squat) generally require a little more rest than upper body structural exercises (e.g. bench press)
The optimal rest period guidelines for hypertrophy are between 30 and 90 seconds between each set/exercise. Some research suggests that the athlete begin the next set before completely recovery has occurred. Keep in mind, however, that the high metabolic demand of certain exercises must be considered when determining rest periods. For example, completing 3 sets of bench press at 10RM will likely require the full 90 seconds or rest in between each set, whereas 3 sets of dumbbell bicep curls at 10RM may only require 30-60 seconds of rest.
The optimal rest period guidelines for muscular endurance is the shortest of all training goals. It Loads are lighter, reps are higher, and rest periods are intentionally kept short - 30 seconds or less. By keeping the rest to a minimum, the specificity of the training goal can be obtained.
Note: Similar to the repetition maximum standards, the rest periods shown above should primarily apply to the “core” total body structural exercises - those that require large muscle groups and muscle mass to perform. The major core exercises are: squat, deadlift, bench press, overhead press, snatch, power clean, clean and jerk, etc. The same rest periods shouldn’t necessarily apply to “assistance” exercises such as bicep curls, tricep extensions, lateral raises, and crunches. The reason being is that the amount of muscle mass that a bicep curl, for example, requires, is far less than that for a power clean. So for practical application of the guidelines discussed above, only follow this protocol for the core exercises. Also, keep in mind that rest periods may need to be extended for those with little training experience.
All of the above information is taken from the National Strength And Conditioning Association's Essentials of Strength Training and Conditioning 4th Edition.