Stretching and Muscle SorenessSome research suggests that stretching doesn't prevent muscle soreness after exercise. Researchers Robert Herbert, Ph.D., and Marcos de Noronha, Ph.D. of the University of Sydney conducted a systematic review and meta-analysis of 10 previously published studies of stretching either before or after athletic activity. They concluded that stretching before exercise doesn't prevent post-exercise muscle soreness. They also found little support for the theory that stretching immediately before exercise can prevent either overuse or acute sports injuries.
Stretching and PerformanceResearch physiologists at Nebraska Wesleyan University made the headlines in 2009 when they published study results indicating that more flexible runners had lower running economy (how efficiently they use oxygen) than runners with tight hamstrings. Consequently, those less flexible runners were faster than the 'flexible' runners. Yes, it was a very small study, and yes, they only measured sit and reach scores, but the results were still a bit surprising and brought more attention to the questions regarding the benefits of stretching.
Warm up vs. StretchingMuch of this confusion comes from a misinterpretation of research on warm up. These studies found that warming up by itself has no effect on range of motion, but that when the warm up is followed by stretching there is an increase in range of motion. Many people misinterpreted this finding to mean that stretching before exercise prevents injuries, even though the clinical research suggests otherwise. A better interpretation is that warming up prevents injury, whereas stretching has no effect on injury. If injury prevention is the primary objective, the evidence suggests that athletes should limit the stretching before exercise, and increase the warm up time. Studies do support that range of motion can be increased by a single fifteen to thirty second stretch for each muscle group per day. However, some people require a longer duration or more repetitions. Research also supports the idea that the optimal duration and frequency for stretching may vary by muscle group. The long-term effects of stretching on range of motion show that after six weeks, those who stretch for 30 seconds per muscle each day increased their range of motion much more than those who stretched 15 seconds per muscle each day. No additional increase was seen in the group that stretched for 60 seconds. Another 6 week study conducted found that one hamstring stretch of 30 seconds each day produced the same results as three stretches of 30 seconds. These studies support the use of thirty second stretches as part of general conditioning to improve range of motion.
I'm sure we'll continue to see headlines for and against stretching, but if you choose to stretch, it may be best to customize your routine to fit your needs. Assess your body and your sport and make sure you stretch (and strengthen) in order to reduce muscle imbalances.
In general, Proprioceptive Neuromuscular Facilitation (PNF) stretching has resulted in greater increases in range of motion compared with static or ballistic stretching, though some results have not been statistically significant. Static stretches are a bit easier to do and appear to have good results. Studies indicate that continuous stretching without rest may be better than cyclic stretching (applying a stretch, relaxing, and reapplying the stretch), however some research shows no difference. Most experts believe ballistic, or bouncing during a stretch, is dangerous because the muscle may reflexively contract if restretched quickly following a short relaxation period. Such eccentric contractions are believed to increase the risk of injury. In addition to improving range of motion, stretching is extremely relaxing and most athletes use stretching exercises to maintain a balance in body mechanics. But one of the biggest benefits of stretching may be something the research can't quantify: it just feels good.
Herbert RD, de Noronha M. Stretching to prevent or reduce muscle soreness after exercise. Cochrane Database of Systematic Reviews 2007, Issue 4.
Andersen, J. C. Stretching Before and After Exercise: Effect on Muscle Soreness and Injury Risk. Journal of Athletic Training 40(2005): 218-220
Witvrouw, Erik, Nele Mahieu, Lieven Danneels, and Peter McNair. Stretching and Injury Prevention An Obscure Relationship. Sports Medicine 34.7(2004): 443-449
Ian Shrier MD, PhD and Kav Gossal MD. The Myths and Truths of Stretching: Individualized Recommendations for Healthy Muscles, The Physician and Sportsmedicine, VOL 28, #8, August 2000.
Trehearn TL, Buresh RJ.. Sit-and-reach flexibility and running economy of men and women collegiate distance runners. J Strength Cond Res. 2009 Jan;23(1):158-62.