Bouncing while stretching was a common practice in years past. This ballistic style of stretching has fallen out of favor. In fact the first research to show the dangers of this method of stretching was published in 1961.

The concern about trauma to the connective tissue from this practice was shown in other studies. Over time the word got out and most coaches and athletic trainers know better now.

It's not clear yet what (if any) method of stretching is best. We know warm-ups are important before stretching. It's also been reported that a 15- or 30-second stretch works better than shorter stretches. The effects of stretching on flexibility seem to last up to 90 minutes. A daily routine of stretching can increase flexibility that lasts several weeks.