There is a lot of conflicting information regarding the efficacy of stretching. When you should, if you should, what type is best. To be clear, stretching is beneficial. The tricky part is the type and time.
Pre workout/warm up
Before a workout, used as a warm up, dynamic stretching is most effective. Dynamic stretching is when the stretches are short and ballistic. Another great way of stretching pre-workout is PNF, or proprioceptive neuromuscular facilitation. With PNF you would statically stretch the target muscle, then contract it isometrically, then stretch it statically again. This method is very effective for stretching through a greater range of motion and it helps to prepare the nervous system for training. Utilizing the wrong method of stretching is the reason for criticism of pre-workout stretching.
Post workout/cool down
After working out, stretching is still beneficial. Again, the key is the type used. Following a workout, static stretching seems to be the most useful for helping recovery, boosting strength gains, and enhancing flexibility. Static stretching is pretty straightforward, the target muscle is held in a stretch for a given time, then released. Static stretching post workout has been shown to lead to strength increases for most muscle groups.
Get your stretching in. Just be sure to use the right type depending on when you’re stretching.
Bonus: The stretching done in most yoga helps to decrease stress and improve immune function. Following yoga sessions, participants in a study had higher levels of testosterone and immunoglobulin and lower levels of cortisol, the stress hormone.