The use of appropriate periods of rest is one of the most overlooked aspects of health and fitness today. In fact, many of the recently published weight training programs that promise to deliver results in just a few short weeks do not even bother to define rest even though the time between each set and session is absolutely critical. Too much rest will compromise the benefits of the session, and too little could actually reduce strength or lead to injury.
Sebastian Hirsch has pointed out that while undefined rest is a common problem among many lifters, the same is not often true of runners. This is because a serious running program is designed with the goal of improving both the aerobic and anaerobic capacity of the runner, and the amount of rest allowed during a training session will be based on the system that is targeted for improvement. Furthermore, runners become more acutely aware of how their performance is affected by even the slightest alteration in rest, with 30 seconds of rest between sets yielding far different results than several minutes.
Rest can also refer to the amount of sleep an individual gets, though sleep is not the only part of recovery that can make a difference. Since most jobs today are sedentary in nature, active recovery is an important part of training that can also result in reducing the chance of injury. This may be something as simple as a long walk or a brisk bike ride — anything that gets blood circulating through the body to aid in the recovery process.
To illustrate the importance of rest, take, for example, two men of similar strength and size who are following the same training program. The first, Hugo, sleeps five hours per night and does no form of active recovery in between training sessions. The other, Marcus, sleeps eight hours per night and takes a 45-minute walk with his dog every evening. It should be clear that Marcus is going to get more out of the program while Hugo is going to be left wondering why he is not improving at the rate he should.