During my fitness professional career, one of the many questions I’m asked is how much time is necessary to rest between weight-lifting sets. Every fitness participant has a unique set of circumstances and goals. Some simply want the benefits of a lean muscular or toned body, while others may train for specific sports or activities. The magic number for rest period length is not available at this time. However, a significant amount of research has helped provide a guide to help us reach our goals.

If you have been blessed by having parents with great athletic physiques or use anabolic enhancement drugs, then you can train with whatever rest periods you wish and obtain substantial results. However, most of us have to take a different approach when striving for muscle growth. Primarily, clinically researched training techniques.

Muscle growth is caused by stress placed on the muscle during exercise and is common in weight-lifting athletes. The stimulus for increasing muscle mass can come from weight training or any other physical activity. An increase in the size of a muscle is primarily a reflection of an enlargement of the diameter of existing muscle fibers through the addition of new myofibrilar and sarcoplasmic protein. Myofibrils are cable-like structures found in muscle cells responsible for force generation and active shortening (flexing). Myofibrilar proteins are the different proteins that make up myofibrils. Sarcoplasmic proteins are those proteins found in other muscular structures that aid in the facilitation of muscle contraction.

Muscle growth is also associated with fast twitch (Type II) muscle fibers. Type II muscle are used during short duration, high-force/power producing activities such as weight-lifting, jumping, sprinting, etc. Some studies have shown that weight-lifters and power-lifters possess Type II fibers, which are two times larger than the slow-twitch (Type I) fibers of the same muscle. Type I fibers are used during long duration, low force production activities such as distance running, etc.

So how much rest does one need between sets to enhance muscle growth? One of the most extreme degrees of muscle growth can be seen in bodybuilders. They usually advise rest as minimal as possible (< 60 seconds). However, it isn’t quite that easy to answer. Olympic weight-lifters and power-lifters are big & muscular too. But these athletes use rest method periods of up to three minutes or longer. It has been shown that the cross-sectional area of a bodybuilder’s muscles is not significantly different when compared to a weight-lifter’s. It was found in these studies that although bodybuilders had the same size muscles as a whole, the size of the individual Type I and Type II fibers was different. The bodybuilders had large Type II fibers and large Type I fibers; while the weightlifters had very large Type II fibers and smaller Type I fibers. These taken together equaled the same size muscle in both athletes. No one knows exactly why there is a difference between the athletes, but it may be due to the fact that bodybuilders perform large amounts of aerobic exercise in their routines. Remember, Type I fibers are more suited for and receptive to aerobic exercise. More research is needed, but I would recommend trying both shorter (< 60 seconds) and longer (> 3 minutes) rest periods, and use the one that achieves the results you want.

If you prefer strength and are not concerned about large muscles, you should be prepared to gain some degree of muscle growth. Getting strong and growing muscle go hand-in-hand. Bigger muscles usually mean stronger muscles. When participants wish to increase their strength, they usually mean their one-repetition maximum (1 RM), or the heaviest weight they can lift one time with proper form and no assistance. For increasing 1 RM most effectively, a near-maximal or maximal load for the given number of repetitions is used. This usually requires longer rest periods (three to five minutes) between sets.

This is due to the fact that the replenishment of the proper anaerobic energy sources takes approximately that amount of time. Those sources include adenosine-triphosphate (ATP) and creatine phosphate (CP), which are needed for anaerobic activity. Therefore, if you want strength, increase your rest periods for the best results.

The ability to repeat or maintain high intensity activity (sprint running, sprint cycling, football plays, weight-lifting, etc.) is known as High-Intensity Exercise Endurance (HIEE) in the world of exercise and sports science. The optimum rest period length for increasing HIEE has not been determined through academic research. However, it has been generally accepted that shorter rest periods are more beneficial. High lactate levels (lactic acid) accumulate in the muscles during activities that demand high bursts of activity for one to three minutes, such as wrestling, long-sprint running (400-1,000 meters) and swimming (100 – 200 meters). These athletes must endure this accumulation of lactic acid during training to increase performance, or just to complete their event during competition. If you have ever trained hard you know how painful this can be. Therefore, it is thought that if you train with shorter rest periods it may be more beneficial because you adapt to the greater levels of lactate in the muscle while exercising.

However, two studies have shown that there is either no difference between shorter or longer rest periods, or that longer rest periods were more beneficial for increasing HIEE. Think about the activity you are performing and how long it takes you to perform it. If it is an activity of low-force production and long duration (running, biking, etc.), you will most likely require less time for that energy system to recover before the next bout. The opposite is true for high-force producing, short-duration activities (weightlifting, sprinting, etc.) that can take from three to eight minutes for energy source replenishment.

It’s obvious that there is no exact figure on how long one’s rest period between sets should be. If maximizing all three variables (muscle growth, strength, and HIEE) in combination is your goal, then there is good evidence that longer rest periods (3 – 5 minutes) could provide optimal benefits. Until there is more conclusive evidence, athletes and other trainees should use the rest period length experience and use the method that works best for achieving their goals.