Your muscles are capable of continuous, low-intensity work with low intensity for long periods of time without getting fatigued. A decrease in this capacity causes problems in the same activities as enumerated for cardiorespiratory endurance like running, jogging, climbing stairs etc.
Often, while climbing stairs or running you feel great discomfort or pain in your legs despite having good cardiorespiratory endurance. This is due to the lack of muscular endurance in your lower body muscles that impede you while climbing the stairs.
The term muscular endurance is highly misunderstood by some so called “fitness experts”. They believe that muscular endurance is achieved by doing resistance/strength training using lighter weights that allow for higher repetitions. Muscular endurance is only challenged in endurance type activities that are done for a minimum of 20 minutes at the very least and involve 100s to 1000s of repetitions of the muscles used in the activity. In resistance/strength training, even if we were to take an extremely high volume of repetitions, the intensity could never be low enough to allow more than approximately 50 to 70 repetitions. This would in no way equip the person with the muscular endurance needed in an endurance type event.
RELATION BETWEEN CARDIO RESPIRATORY ENDURANCE AND MUSCULAR ENDURANCE
Cardio respiratory endurance and muscular endurance are very closely related to each other. If you lack cardio respiratory endurance then it will surely affect your muscular endurance. If a person has great muscular endurance in his legs, he still won’t be able to run for a long period without cardiorespiratory endurance. Once cardiovascular fatigue sets in, it is impossible to use the body's full potential. For instance, no matter how muscularly strong and fast a boxer is, he cannot use his strength to punch hard once cardiovascular fatigue sets in.
For instance, if a person has great cardiorespiratory endurance but does not have good muscular endurance in his legs, he will not be able to run long distances. A tennis player with great cardiorespiratory endurance but lacking in muscular endurance is not going to be able to hit the ball hard consistently over the long duration of an entire match, even if his cardiorespiratory system is not tired.
HOW TO IMPROVE MUSCULAR ENDURANCE ?
Muscular endurance develops along with cardiorespiratory endurance by doing cardio/aerobic exercises. However, unlike cardiorespiratory endurance, muscular endurance is achieved locally in only those muscles that are used in that cardio/aerobic activity.
For instance, running will improve cardiorespiratory endurance and Muscular endurance only in the lower body. So, to achieve uniform muscular endurance all throughout the body, K11 recommends CROSS TRAINING.
This is where the modalities of doing cardio are constantly changed to include both the upper body and the lower body equally. An example would be to devote 3 days a week of cardio to different activities. That can be running on a treadmill on Monday, Swimming on Wednesday and elliptical trainer on Friday. This will ensure that all parts of the body get conditioned with muscular endurance. Boxers, Tennis players, Squash players all require both Muscular strength and Muscular endurance. They should not make the mistake of wasting time with High repetition resistance training as they will get neither muscular strength nor endurance. They should do low repetition high intensity resistance training for muscular strength. Their on court practice will build the muscular endurance that they need. A tennis player will develop good muscular endurance in his upper body by doing forehand and back hand shots against a ball throwing machine continuously for a long duration of time. A boxer will develop good muscular endurance by working the heavy bag for long continuous durations.