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A closer look at how stretching may benefit the body

Below is the final installment of a two-part discussion on the merits of stretching with Michael Fredericson, MD, who has served as head team physician with the Stanford Sports Medicine Program since 1992. Here Fredericson talks about whether the conventional reach-and-hold approach to lengthening one's muscles is outdated, the effectiveness of stretching before a workout versus afterwards, and the role of genetics in flexibility.

A number of athletes have abandoned static stretching for dynamic stretching routines, which incorporates movements mimicking a specific sport in an exaggerated yet controlled manner. Is dynamic stretching more effective than the traditional reach-and-hold approach?

As mentioned in yesterday’s entry, the evidence suggests that increasing range of motion beyond function, as routinely done through prolonged static stretching, is not beneficial and can actually cause injury and decrease performance. The basic principle of dynamic stretching is to stretch those muscle-tendon units required for a specific motion.

One advantage of dynamic stretching is an increase in muscle and core temperatures. Since dynamic stretching often involves continuous movement it maintains warmth in the body core and muscles. This can be significant because athletes' core temperature can drop by two to three degrees while sitting and stretching for 10-15 minutes. Dynamic stretching also prepares the muscles and joints in a more sport specific manner than static stretching through coordination and motor ability, stimulates the nervous system and forces athletes' to mentally prepare for the task at hand.

Additionally, studies have found that athletes’ vertical jump is lower after a session of static stretching than without stretching. Moreover the measure of vertical jump was greater for dynamic stretching versus static stretching or no stretching. For these reasons we now recommend that athletes in sports requiring lower-extremity power use dynamic stretching techniques in warm-up to enhance functional flexibility while improving performance.

Some experts say stretching before exercising can make individuals slower, weaker and more prone to injury. When is the appropriate time to stretch?

The goal of stretching before exercise is to warm up the connective tissue in the muscles and tendons. Dynamic stretching may also activate the neural circuits required for simultaneous contraction and relaxation of muscle-tendon units with exercise. As discussed yesterday, prolonged static stretching prior to exercise may acutely impair muscle strength with a lesser effect on power. The extent to which these effects are apparent when stretching is combined with other aspects of a pre-participation warm-up, such as practice drills, is not known, although it is prudent to avoid static stretches or only do them for shorter bouts to warm-up the tissue.

A limited number of studies of varying quality have shown mixed results on the issue of the affects of pre-participation stretching on injury prevention and athletic performance. The general consensus is stretching, in addition to warm-up, does not affect the incidence of overuse injuries. There is evidence showing stretching prior to a workout reduces the incidence of muscle strains but further research is needed. In addition, light stretching after a workout has been shown to improve blood flow to working muscles and aid in systemic circulation.

But overall, the research concludes that the most significant risk factors for injury are a history of chronic injury or injury in the past four months, higher body mass index and switching pre-run stretching routines, which implies that an immediate shift in a workout routine may be more important than the regimen itself.

Past studies suggest that to a large degree flexibility is genetic and that while some small portion of an individual’s flexibility is adaptable, it takes a significant amount of work to increase a person’s flexibility even a small amount. Does this mean that stretching is pointless?

Stretching is definitely not pointless. Some people are more flexible genetically and we see this in those who excel in sports such as gymnastics. Others may not need as much flexibility.

However, personal experience suggests regular stretching can help offset muscle imbalances, maintain flexibility, which may otherwise decline with age or inactivity, and prevent common back and neck problems through improved flexibility.

The key is to know when and how to stretch for the purposes of warming up versus improving overall flexibility. The research is fairly compelling that prolonged static stretching does not offer many short-term benefits when performed before exercise. This why we now suggest a more dynamic warm-up routine. If a person is restricted in a certain muscle group, then prolonged static stretching is advised after their sport activity when muscles are sufficiently warmed up.

Salar Deldar, a third-year medical resident at Stanford, contributed information to this entry.

Previously: A conversation about the merits of stretchingIs barefoot running better for the body? and How physical activity influences health
Photo by julieverive

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