It is important to avoid isostatic stretches because they can

 This type of stretching in younger people may disrupt muscle growth. Teenagers normally stop growing in height at the age of 16, but their muscle tissues continue to grow until the age of 18. If you are performing in an event, do not incorporate isostatic stretching as part of your warm-up routine. Isostatic contractions fatigue the muslce, which will prevent you from performing at your best during an event.

The answer is either 3 or 4