There is no evidence in the scientific literature that stretching prevents injuries, but it can help you to be stronger and faster. Longer muscles can exert a greater torque on joints to help you cycle and run faster, jump higher, throw further and lift heavier. Muscles and tendons tear when the force on them is greater than their inherent strength. Strength training, but not stretching, strengthens muscles. When you exercise against resistance, your muscles become larger and stronger and are less likely to tear.
There are two ways to stretch. You can stretch only as far as you can hold for several seconds or you can bounce as hard and as fast as you can. Research shows that bouncing gives you the maximum stretch, but it also increases your chance of injuring yourself. Icing or heating the muscles prior to stretching does not increase their ability to stretch, although warming up a muscle by exercising prior to stretching helps to prevent injuries. Always warm up your muscles before you stretch. Resting muscle temperature is around 97 degrees. Cycling slowly for several minutes will raise muscle temperature to more than 99 degrees and help to make it more pliable and resistant to injury. You can stretch after warming up or after you finish your workout. Fast, forceful stretching will give you greater flexibility than slow deliberate stretching, but it also will increase your chances of injuring yourself. Athletes can do bouncing short stretches and hope that it doesn't injure them. However, fitness exercisers probably should do slow deliberate stretches no further than they can hold for five seconds. If you compete in sports, try to stretch every day and do bouncing stretching no more than two or three times week.