Muscular endurance is the ability of a muscle or muscle group to exert force against a resistance over a sustained period of time. It is typically assessed by measuring the length of time (duration) a muscle can exert force without fatigue, or by measuring the number of times (repetitions) that a given task can be performed without fatigue. Muscular strength, on the other hand, is a measure of the maximum force that can be produced by a muscle, and is typically assessed by the one-repetition maximum (1 RM) weightload in an exercise (e.g., leg press and bench press). An increase in muscular strength
is always accompanied by a certain level of increased muscular endurance, so it is impossible to strictly separate these two important components of muscular fitness.
Many everyday activities require a significant amount of muscular endurance (e.g., walking up stairs, yard work, and shoveling snow). The ability to carry out activities of daily living can increase self-esteem and foster a sense of independence, especially for older adults. Furthermore, a high level of muscular endurance of the torso muscles, more so than muscular strength or even range of motion of the spine, has been associated with improved back health.
Resistance training programs for new exercisers typically start with lifting loads and repetitions that emphasize developing muscular endurance (e.g., weight loads of 50% 1RM for 15 to 20 repetitions). This is the recommended approach because endurance-focused training is lower intensity than strength-focused programming, which could require the exerciser to lift loads of 80% 1RM for only 6 repetitions. Although heavy resistance training may not be indicated for all exercisers, it is often important for muscular health and proper function to include a progression toward increased strength in a resistance-training plan. Both muscular endurance and muscular strength are crucial elements of a well-rounded fitness program.