The answer to this changes depending on whether your goal is to increase your strength, power, muscle size or muscle endurance. While the typical gym goer will choose a rest period that is usually based more on their level of motivation, this topic has been studied extensively so we can rely on the science.
Strength and Power: When training with loads between 50% and 90% of your one-rep maximum, 3-5 minutes rest periods between sets provides enough recover time to do more repetitions over multiple sets. In studies, rest periods of 3-5 minutes between sets produced greater increases in absolute strength over time due to higher intensities and volumes while training. The findings were similar when the intended goal was increased Power.
Muscle Size: When training with moderate intensity sets, shorter rest periods of 30-60 seconds between sets have been proven to provide enough muscle recovery to provide maximum training intensity while doing repeated subsequent sets with the highest level of muscle contractibility. It was also suggested that this amount of rest between sets may be more effective due to greater levels of growth hormone released during these kind of workouts.
Endurance: If you are training for greater muscular endurance, intervals of 20 seconds to 60 seconds were found to be optimal for producing consistent repeated high velocity repetitions. The relatively shorter rest periods and high intensity sets were deemed to be most effective when an increase in muscular endurance was the goal.
The rest interval you choose between sets has a significant impact on how productive your workouts will be, and should be a part of our training we all pay more attention to. Another key issue is cardio vascular conditioning because if you are not in good enough cardio vascular condition, your heart may need more time to recover than your muscles do. That will slow your progress.
It’s important to train at an intensity level and pace that is safe and comfortable for you. Including cardio vascular conditioning in your training, regardless of your goal, will have a positive impact on your training, and therefore, your progress.
Sports Med. 2009;39(9):765-77. doi: 10.2165/11315230-000000000-00000.