Muscular endurance is the ability of a muscle or group of muscles to repeatedly exert force against resistance. Performing multiple repetitions of an exercise is a form of muscular endurance, as is running or swimming. If your muscles have to contract in a similar pattern more than one time you are using muscular endurance.
Many factors contribute to muscular endurance, including strength, fiber type, training and diet. A larger, stronger muscle can perform the same task under load more times than a weaker muscle. If you can bench press 300 pounds you will be able to perform more repetitions with 100 pounds than if you could only bench 200 pounds. A larger muscle also holds more glycogen, the sugar that you use for energy, so it will be able to sustain a series of contractions -- or perform work -- for a longer period.
Muscle Fiber Types
Several types of muscle fibers make up your muscles. Slow fibers do not generate as much force but are far more resistant to fatigue. Fast, fatigue-resistant fibers generate more force and can maintain this ability over time, but not as long as slow fibers. Fast fibers generate the most force but wear out the quickest. A muscle is composed of all types of fibers, but some muscles such as the soleus, one of the muscles in your calf, has a high percentage of slow fibers and is very resistant to fatigue. Some of the muscles responsible for focusing the eye have a very high percentage of fast fibers. Fortunately, it takes less than a second to focus the pupil.
The fibers in your muscles that fatigue can fail because of a lack of energy. Glycogen, or sugar, is required for both peak and sustained muscular effort. A diet low in carbohydrates can sometimes make it difficult to sustain muscular endurance. So, if you wish to have optimal muscular endurance, you need to eat plenty of fruits and vegetables. Additional carbohydrates following a workout can help you recover faster and promote muscular endurance as well. Creatine monohydrate, which your body produces naturally, can also help with short-term muscular endurance.
Training for Endurance
Training can promote muscular endurance, assuming you put in extra effort. Don't just lengthen existing training sessions; perform another workout on your next day off, but train with only 60 percent of the volume and 60 percent of the intensity. This will not only help you recover by increasing blood flow to your muscles, but will help promote endurance by increasing your tolerance for training volume. Combined with a proper diet, carefully calibrated training will help to increase your muscular endurance for competitive sports or recreational activities.