Strength training is often related to loads and repetitions as signs of progress. Fitness enthusiasts often make exaggerated claims of large loads, even maximum repetitions with a specific load. During a punishing workout, rest intervals play a major role in the training session’s ability to trigger anabolic hormone secretion, build endurance, encourage strength, as well as alter performance in succeeding sets.
In bodybuilding, a “rest interval” is the commonly applied term to the periods of rest in between sets of an exercise. During these intervals, the muscle is neither contracted nor extended – no resistance is applied. Proper rest interval length depends on training intensity, goals, fitness level and targeted energy systems.
The body can recruit three major energy systems during resistance training: adenosine triphosphate (ATP), supported by creatine phosphate (CP); glycolysis, chemical processes that breakdown glycogen for fuel; and aerobic metabolism, a system that uses oxygen to make energy from stored carbohydrate and fat. Rest intervals influence the relative involvement of all three energy systems. Heavy training loads, with long rest intervals (over three minutes), predominantly receive energy from ATP/CP. Moderate-heavy training, with moderate-to-short rest intervals (two to three minutes), is largely supported by ATP/CP and glycolysis with minor contributions from aerobic metabolism. Endurance training with light weights and high repetitions, using short rest intervals (less than two minutes), greatly involves aerobic metabolism.
It’s well understood that rest intervals significantly affect muscular strength, but less is known concerning muscular hypertrophy. Studies show that the majority of ATP/CP repletion occurs within three minutes after a working set is terminated. William Kraemer published a popular series of studies in the Journal of Strength and Conditioning Research in 1997. In his research, he clearly outlined the impact rest intervals have on performance. Kraemer reported differences in performance using three- and one-minute rest intervals. All participants were able to perform their 10-repetition maximum over three sets when three-minute rest intervals were used. When periods of rest were reduced to one minute, 10 repetitions could only be performed in the first set – eight and seven thereafter.
Accumulated increases in muscular strength, power and force are directly related to increases in muscular size in well-trained bodybuilders. Training heavy loads using long rest intervals better sustains strength, but the overall productivity of the program can decline with increased periods of rest. Despite being able to perform with heavier loads, the session’s total muscular power and force production can decline with excessively long rest intervals. Improving all of these functions will stimulate an increase in the cross-sectional area of muscle fibers. These are measures indicating a progressively more capable muscular system.
Muscular endurance is important in bodybuilding. Many strength coaches and advanced bodybuilders relate hypertrophic training to moderate-heavy loads with moderate-to-short rest intervals. Bodybuilders, who train to maximize muscular size, tend to stick to one- to two-minute rest intervals – many use super- and giant-sets with no rest. These restricted intervals often produce an increase in potent anabolic hormone secretion, important for hypertrophy. Metabolite production also increases, such as lactate, which can further stimulate growth-producing events. Short rest intervals stimulate local blood flow, important for increasing protein synthesis by accelerating amino acid and metabolite transport.
The rest intervals an athlete needs to sustain and develop strength and size will be – for the most part – an individual variable. Training experience helps build effective motor control and tolerance to the physical and mental discomforts associated with resistance training. Some people are innately able to recover and compensate from a set quicker, with a strong rebound. A number of athletes have great endurance capacities, either through genetic predisposition or from a history of aerobic training. Program design issues also affect the required rest interval for an athlete; such as exercise selection and order, repetition velocity and training volume.
Heavy resistance training with rest intervals over three minutes is an effective way to increase muscular strength and size. Even so, it appears through exercise science and the experiences of successful bodybuilders, maximal hypertophy is often the result of a variation in rest intervals – either through linear or nonlinear periodization programs applying a progressive overload.
Bottom line, using the same loads and sets does not mean muscular power is being preserved if total workout duration becomes significantly longer. In general, longer rest intervals should translate to heavier loads or more repetitions – to provide a progressive overload. It’s important to be actively aware of the time spent inactive between sets. No matter the length, keep rest intervals tight while training, to avoid drifting into thought or surrendering to exhaustion. Most commercial fitness facilities have clocks hanging on the walls – otherwise, a stop watch should be in the gym bag. A training log that documents rest intervals can help tailor the program for peak strength performance.
Progression and Resistance Training. President’s Council on Physical Fitness and Sports Research Digest. Series 6, No. 3, September 2005.
Kraemer WJ, Ratamess NA. Fundamentals of resistance training: progression and exercise prescription. Med Sci Sports Exerc 2004; 36: 674–688.
Position Stand. Progression Models in Resistance Training for Healthy Adults. Medicine & Science in Sports & Exercise. 34(2):364-380, February 2002.
- Intensity during resistance training
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