The 5–15 minutes of light exercising or stretching after a workout is known as the
a. duration.
b. cool-down.
c. warm-up.
d. training intensity.

The 5–15 minutes of light exercising or stretching after a workout is known as the b. cool-down. A cool down is a necessary part of any workout routine. It has several benefits such as preventing injury, promoting relaxation, improving flexibility, and pacing your heart rate. Cooling down is just as important as the exercise itself, so don't forget to do this when you workout.

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That’s what i was going to say.