Experts bust common sports medicine myths

Several decades ago, investigators subscribed to muscle spasm theory, which held that unaccustomed exercise caused muscle spasms.

“The thought was that muscle spasms impeded blood flow to the muscle, causing ischemic pain and further spasm,” Valerie E. Cothran, MD, said during a presentation at the meeting. “Stretching the muscle was thought to restore blood flow to the muscle and interrupt the pain-spasm-pain cycle. This theory has been discredited for 40 years, but the practice of stretching before exercise persists.”

According to Dr. Cothran, of the department of family and community medicine at the University of Maryland, Baltimore, a limited number of randomized, controlled trials exist on the topic – and many are fraught with limitations, such as the evaluation of multiple stretching methods and variable types of sports activities and the inclusion of multiple cointerventions.

One systematic review evaluated 361 randomized, controlled trials and cohort studies of interventions that included stretching and that appeared in the medical literature from 1966 to 2002 (Med Sci Sports Exerc. 2004 Mar;36[3]:371-8). Studies with no controls were excluded from the analysis, as were those in which stretching could not be assessed independently or those that did not include people engaged in sports or fitness activities.

The researchers determined that stretching was not significantly associated with a reduction in total injuries (OR, 0.93). “There is not sufficient evidence to endorse or discontinue routine stretching before or after exercise to prevent injury among competitive or recreational athletes,” they concluded.

The following year, Lawrence Hart, MBBch, of McMaster University, Hamilton, Ont., assessed the same set of data but eliminated some of the confounding factors of the previous analysis, including studies that had limited statistical power (Clin J Sport Med. 2005 Mar;15[2]:113). The final meta-analysis included six studies.

Dr. Hart found that neither stretching of specific leg-muscle groups or multiple muscle groups led to a reduction in total injuries, such as shin splints, tibial stress reaction, or sprains/strains (OR, 0.93). In addition, reduction in injuries was not significantly greater for stretching of specific muscles or multiple muscle groups (OR, 0.80, and OR, 0.96, respectively). “Limited evidence showed stretching had no effects on injuries,” he concluded.

A more recent systematic review analyzed the efficacy of static stretching as part of a warm-up for the prevention of exercise-related injury (Res Sports Med. 2008;16[3]:213-31). The researchers reviewed 364 studies published after 1990 but before 2008, and they included seven in the final analysis: four randomized, controlled trials and three controlled trials.

All four randomized, controlled trials concluded that static stretching was ineffective in reducing the incidence of exercise-related injury, and only one of the three controlled trials concluded that static stretching reduced the incidence of exercise-related injury. In addition, three of the seven studies reported significant reductions in musculotendinous and ligament injuries following a static stretching protocol.

“There is moderate to strong evidence that routine application of static stretching does not reduce overall injury rates,” the researchers concluded. “There is preliminary evidence, however, that static stretching may reduce musculotendinous injuries.”

The final study Dr. Cothran discussed was a systematic review of two randomized, controlled trials and two prospective cohort studies on the effect of stretching in sports injury prevention that appeared in the literature between 1998 and 2008 (J Comm Health Sci. 2008;3[1]:51-8).

One cohort study found that stretching reduced the incidence of exercise-related injuries, while two randomized, controlled trials and one cohort study found that stretching did not produce a practical reduction on the occurrence of injuries. The researchers concluded that stretching exercises “do not give a practical, useful reduction in the risk of injuries.”

Some studies have demonstrated that explosive athletic performance such as sprinting may be compromised by acute stretching, noted Dr. Cothran, who is also program director of the primary care sports medicine fellowship at the University of Maryland, Baltimore. Current practice and research gaps include few recent randomized, controlled trials; few studies isolating stretching alone; and few that compare the different forms of stretching, such as dynamic and static stretching, she added.

“There is moderate to strong evidence that routine stretching before exercise will not reduce injury rates,” she concluded. “There is evidence that stretching before exercise may negatively affect performance. Flexibility training can be beneficial but should take place at alternative times and not before exercise.”

Dr. Joy disclosed that she receives funding from Savvysherpa and Dexcom for a project on the prevention of gestational diabetes. Dr. Roberts and Dr. Cothran reported having no financial disclosures.