Muscular fitness has two components: muscular strength and muscular endurance.
Muscular strength is the greatest amount of force a muscle
or muscle group can exert in a single effort.
Muscular endurance is the ability of a muscle or muscle group
to do repeated contractions against a less-than-maximum resistance
for a given time.
Although muscular endurance and strength are separate fitness
components, they are closely related. Progressively working against
resistance will produce gains in both of these components.