Time of Exercise: Repetitions and Sets To improve Fitness
You must do enough repetitions of each exercise to fatigue your muscles. The number of repetitions needed to cause fatigue depends on the amount of resistance: The heavier the weight, the fewer repetitions to reach fatigue. In general, a heavy weight and a low number of repetitions (1-5) build strength and overload primarily fast-twitch fibers, whereas a light weight and a high number of repetitions (15-20) build endurance and overload primarily slow-twitch fibers.
For a general fitness program to build both strength and endurance, try to do about 8-12 repetitions of each exercise; a few exercises, such as abdominal crunches and calf raises, may require more. To avoid injury, older (approximately age 50-60 and above) and frailer people should perform more repetitions (10-15) using a lighter weight.
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In weight training, a set refers to a group of repetitions of an exercise followed by a rest period. To develop strength and endurance for general fitness, you can make gains doing a single set of each exercise, provided you use enough resistance to fatigue your muscles. (You should just barely be able to complete the 8-12 repetitions using good form for each exercise.) Doing more than one set of each exercise will increase strength development; most serious weight trainers do at least three sets of each exercise (see the section “More Advanced Strength Training Programs” [pp. 106-107] for guidelines on more advanced programs).
If you perform more than one set of an exercise, you need to rest long enough between sets to allow your muscles to work with enough intensity to increase fitness. The length of the rest interval depends on the amount of resistance. In a program to develop a combination of strength and endurance for wellness, a rest period of one-three minutes between sets is appropriate. If you are lifting heavier loads to build strength, rest three-five minutes between sets. You can save time in your workouts by alternating sets of different exercises. One muscle group can rest between sets while you work on another group.
Overtraining doing more exercise than your body can recover from can occur in response to heavy resistance training. Possible signs of overtraining include lack of progress or decreased performance, chronic fatigue, decreased coordination, and chronic muscle soreness. The best remedy