It turns out, both those things can be true, but the differing advice has created some confusion.

Stretching can help make you more flexible, improve range of motion in your joints—and feel good. David Behm, who researches human kinetics at Memorial University of Newfoundland in St. John's, Canada, offers this advice on when to stretch and how to do it safely:

Warm up first

It's almost always good to stretch, but it's better if you warm up first, said Behm, author of "The Science and Physiology of Flexibility and Stretching." He recommends a light aerobic activity such as jogging, walking or cycling for five or 10 minutes.

Follow that with some static stretching, the traditional way of reaching and holding a position (think back to that gym class). You can then do activity-specific dynamic stretching, in which you warm up the muscles with repetitive movements like leg lifts.

Behm says one minute is "the magic number" for how long to do static stretching per muscle group without fatigue.

Expand your definition of 'stretching'