One of the most common questions about weight training aka resistance training is how long should you rest between each exercise set. If you take a look at the relevant research concerning this topic there are some good answers.
For a long time, researchers believed that shorter rest periods were better for increasing muscle size which was thought to occur because of increased levels of metabolic stress by not allowing complete recovery. However, research done in 2015 shows that using longer rest periods actually results in better results for both increased muscle size and increased muscle strength. It is thought that this occurs because longer rest periods allow a higher training volume (more repetitions of each exercise).
Another study which looked at the effects of rest interval length on training volume discovered another important item: reduction in training volume occurs mainly between 1 and 2-minute rest periods. The percentage difference between 2 and 3-minute rest periods is much smaller, except when doing 5 or more sets of an exercise. So, for people doing 3 – 4 sets per exercise, 2 minutes is a good rest interval, but if doing 5 or more sets you should probably extend the rest interval to 3 minutes.
Another important piece of information is that recreational lifters who self-determine rest periods tend to rest just under 2 minutes between sets meaning that for most lifters doing 3 to 4 sets of several exercises whose goal is increased muscle size and strength you probably do not need to time your rest intervals and can go just go by feel.