A. There is no real textbook answer for that question. I've been in gyms for over 25 years and have seen some crazy things. One thing that frustrates me is when I see someone resting between sets reading a newspaper or magazine. True story... I literally saw someone fall asleep while resting on Nautilus equipment this year at Healthtrax! Obviously you're taking too long of a break if you have time to read an article or god forbid, fall asleep!!!!
There are two types of rest between sets during strength training. There is Passive Rest and Active Rest. The amount of rest and type of rest will depend largely on your fitness goals.
PASSIVE REST
During PASSIVE REST, you sit between sets with no activity. This is usually used when trying to build muscle and strength such as powerlifting, body building and body sculpting. When lifting weights for instance, a typical set will last approximately 30-60 seconds depending on how many repetitions and how much weight is being lifted. You will require more time between exercise sets to recuperate when lifting heavier weight. You may require a little more passive rest time when performing certain exercises which require larger muscles such as squats and leg press. This is because during the previous mentioned exercises, the larger muscles and load on the muscles will require more oxygen for fuel. This will create a cardiovascular demand which will leave you breathing heavy and lactic acid build up. You will want to take a longer break to allow the muscular and cardiovascular systems time to recuperate.
Generally a rest period will last anywhere from 15-60 seconds or longer. I tell clients to listen to their body. If they are watching a clock to pace out their rest period and are giving 1 minute breaks but feel they are ready to go on to the next set after 30 seconds, they are not optimizing their workout potential. However, if they set a rest period of 30 seconds and are still breathing heavy at the beginning of the next heavy set of exercise, they will not achieve maximum muscle efficiency.
ACTIVE REST
I have written a blog about active rest in the past. This form of rest is excellent for people who are trying to improve muscular and cardiovascular endurance or trying to burn more calories in a shorter period of time. With active rest, upon completion of an exercise, you immediately either perform another exercise for a different muscle group as in a "super set" or do form of cardio exercise such as jump rope, jumping jacks etc. Stretching the muscles worked during the exercise completed is also a form of active rest. There is really no right or wrong way to active rest. Just as there are literally dozens of ways to exercise our bodies, there are many variations to active rest.
BOTTOM LINE
How long you will rest between sets will depend on your goals and current fitness level. If you are just beginning to workout, you may require a little more time to recuperate between exercises. As you progress and your body adapts to the stimulus of strength training, you will be able to move on to the next set with less rest. If your goal is to increase strength or build muscle, you will want to lift heavier weight. This will create more demand on the muscular and cardiovascular systems. You will want to rest until you're heart rate drops a bit and the lactic acid disperses from the worked muscles. This way you will be able to attempt the next set more effectively. If you want to increase your cardiovascular and muscular endurance while burning more calories, decrease your rest time between sets. You will not want to attempt maximum strength lifts during active rest but focus more shaping rather than building up your body.
*Always consult your physician and a Certified Personal Trainer before attempting an exercise program to ensure safety and proper technique.