Afterwards, but not as often as I should.
Currently I have such a busy schedule with 19hours of school that I get caught up with that and dont stretch enough.
Stretching before exercises is a ritual which athletes have been following for many years now. Surprisingly enough, it turns out that stretching is not as beneficial as we think. Several recent studies showed that pre-exercise stretching takes away 15-30 minutes of muscle strength and explosive muscle activity in such exercises as jumps.
Half-amplitude exercises which work on large muscle groups make a better warm-up, since the movements in those exercises are similar to those of your sport type. For example, bodybuilders should do complex exercises with light weights for warm-up, such as squats and bench-press. Tennis players can do low-intensity exercises with the tennis racquet before hitting the court. Runners, swimmers, cyclists, and skiers should start moving at low intensity before working at full power.
Stretching is important for building strength, increasing amplitude of movements, and improving athletic performance; but make sure to do stretching after the muscles have been warmed-up- after the workout! Many experts argue that stretching prevents injuries and speeds up recovery, yet there is no evidence to support those arguments.
One of the studies on this topic was published in the Journal of Strength & Conditioning Research
As others have said dynamic mobility/stretching is best in regards to pre-training. Never do static stretches before training...
Static stretches should be done at night after a warm shower. The CNS still causes muscular tension after training and won't lead to the full benefit of stretching. But, when taking a shower at night the CNS is relaxed and you will have the same warming affect from the shower as you would training. As always, stretches should never be painful and you should hold each stretch for one or two sets of 30 seconds.