Based on your fitness goals, you should stay in a range of time to get different results. If your looking to build strength, you want to stay in the range of 2-5 minutes. This is because pure strength is all done in very short but high energy bursts. If your looking to build muscle size, stay in the range of 1-2 minutes. Optimal size growth is shown to be the best in this mid tier rest range. If your looking to train endurance, only rest for about 30-60 seconds. ~ Berceste