What is muscular endurance?

In one line

Muscular endurance is the ability of a muscle to keep producing the same force over and over, or to hold it, for a long time.

What is muscular endurance?
The 'how many can you do?' kind of fitness
When people talk about how many push-ups they can do without stopping, or how long they can hold a plank, the term 'muscular endurance' comes up. It is a different ability from being strong. This post explains what muscular endurance is, how it differs from strength, and how it is measured.
In short
A muscle repeating or holding the same force
Muscular endurance is the ability of a muscle to keep producing the same force over and over, or to hold it, for a long time. A Korean dictionary also defines it as the ability to keep exerting a steady muscle force over a long time. The Korean word joins 'muscle' and 'endurance' (the power to hold out for a long time).
First, strength vs endurance
'How hard' and 'how long'
Strength means the force of a muscle, especially the greatest force it can produce at once. Muscular endurance looks at how many times, or how long, you can lift a lighter weight than that. Even for the same muscle, 'how hard' and 'how long' are different abilities that are measured separately.
Where it is used
Anything that repeats the same movement
Muscular endurance is used in any task that repeats the same movement many times. Researchers see it as important not only for sports but also for daily life, which involves a lot of repeated work. U.S. health authorities also list it, along with strength and power, as a part of muscle fitness.
Two kinds of muscular endurance
Repeating force and holding force
The ability to repeat the same movement while the joints move is called 'dynamic muscular endurance', and it is measured by the number of reps. The ability to hold force in one position without moving the joints is called 'static muscular endurance', and it is measured by how long you hold. Push-up count is close to the first; plank time is close to the second.
How it is measured
Count reps with a set weight until you can't
Muscular endurance is often measured by counting how many reps you can do with a chosen weight until you cannot do another. There are two ways to choose that weight. One uses the same weight every time; the other uses a weight matched to your current maximum strength (for example, 60% of your max).
When you get stronger
More reps with the same weight
When strength training makes you stronger, the same weight becomes relatively lighter than before. So muscular endurance measured with the same weight rose well after strength training. Muscular endurance measured with a weight matched to your current max rose in far fewer cases.
How it is built
Many reps with a light weight
In one study of people new to training, the group that did more than 20 reps per set with a light weight improved muscular endurance the most. The group that lifted heavy for only a few reps improved maximum strength the most. Researchers see that how many reps you do per set changes which ability mainly grows.
Common myth
Is muscular endurance the same as the fitness for long runs?
No. The fitness for long runs or bike rides is 'cardiorespiratory fitness': the ability to keep up exercise that uses the large muscles of the whole body for a long time. Muscular endurance is the ability of the muscles in one area, like the arms or legs, to repeat or hold the same movement. U.S. health authorities also list the two as different parts of fitness.
Summary
A muscle repeating or holding the same force
Muscular endurance is the ability of a muscle to keep producing the same force over and over, or to hold it, for a long time. It is an ability of the muscles in one area, so it is a different part of fitness from cardiorespiratory fitness, which uses the whole body for a long time. Related terms: strength, cardiorespiratory fitness, rest time between sets.