Warming up: the latest research into stretching

There’s increasing evidence that stretching before exercise doesn’t improve performance or reduce injury risk. And the most comprehensive review of its kind concluded that flexibility training has no known health benefits(1). Gary O’Donovan presents the evidence to help you decide if stretching is a waste of time.

I recently searched an electronic database for studies about static stretching, ballistic stretching and dynamic stretching (www.pubmed.com). In these studies, torque, 1-repetition maximum (using free weights), maximal voluntary contraction (on a machine), jump height and sprint time were the most common measures of strength and power. Unfortunately, many of the studies included a small number of participants (and had little chance of detecting differences in performance) and some used dodgy statistics(2).

 

 

Static stretching

Static stretching involves passive elongation of a muscle or group of muscles(3). I found 61 studies investigating the acute effects of static stretching on strength and power and the conclusions on performance were as follows:

• One study found an improvement in performance(4);
• Thirty-eight studies found reductions in performance(5-42);
• Twenty-two studies found no statistically significant differences in performance between stretching and non-stretching groups(43-64).

Two 15-second stretches or three 30-second stretches were sufficient to reduce performance and more demanding protocols reduced performance for 60-120 minutes following stretching(22,31). Several studies also found that static stretching reduced the elasticity and electrical activity of muscles.

It’s unclear if a second warm up can reduce the detrimental effects of static stretching on strength and power(13,65) but what’s undeniable is that the available evidence suggests that static stretching is a waste of time or, worse, is detrimental to performance!

 

 

Ballistic stretching

Ballistic stretching involves swinging, bouncing or bobbing movements and the final position is not held (3). I found six studies about the acute effects of ballistic stretching on strength and power: there were no reports of improved performance, one report of decreased performance (62) and five inconclusive reports (10, 38, 40, 56, 63). There were only 14 to 24 participants in each study and elasticity and electrical activity were not assessed. Thus, there is insufficient evidence to recommend ballistic stretching before exercise.

 

 

Dynamic stretching

Ballistic stretching and dynamic stretching are given the same definition in the latest American College of Sports Medicine manual(3); however, the prevailing definition of dynamic stretching in the UK is ‘flexibility in action’ and dynamic stretches include ankle flicks, buttock flicks, knee lifts, the ‘Russian walk’, the ‘walking lunge’ and the ‘walking hamstring’(66).

I found 10 studies about the acute effects of dynamic stretching on strength and power: six of these studies found improvements in performance(7,17,54,55,63,64), no studies found decrements in performance and three studies found no statistically significant differences in performance between stretching and non-stretching groups(45,47,49).

One study concluded that dynamic stretching was beneficial, but the authors compared changes in performance in the dynamic stretching and static stretching groups instead of the dynamic stretching and non-stretching groups(25). The available evidence suggests that dynamic stretching is beneficial; however, warming up probably improves performance and it is impossible to distinguish the effects of warming up and stretching in many dynamic stretches.

 

 

Stretching and endurance performance

The effects of stretching before exercise and flexibility training on endurance performance are not well documented. Static stretching did not significantly reduce endurance performance in a study of 11 physically active students(67), but it did reduce running economy and endurance performance in a study of 10 trained distance runners(68). US scientists found that a stretching programme did not reduce running economy, but the intervention only lasted 10 weeks(69). Cross-sectional studies can reflect years of exposure to stretching and a study of 34 international-standard distance runners found that the least flexible runners were also the most economical(70).

 

 

Stretching after exercise

Although no longer recommended before exercise, static stretching is still recommended during the cool-down(3). The advantages of stretching after exercise might include an increase in range of movement and a decrease in the risk of lower limb injury in those with tight muscles(78,84). The disadvantages of stretching after exercise might include a decrease in running economy(70) and an increase in the risk of lower limb injury in those with loose muscles(78).

Some people say that stretching increases their sense of wellbeing and some also stretch to reduce muscle soreness(82), but there is little evidence that stretching reduces soreness in the days after novel or unusually demanding exercise(85,86). Given limited and conflicting evidence, athletes and coaches should consider if any advantages are likely to be greater than any disadvantages before stretching after exercise.

 

 

Summary and conclusions

Large, robust RCTs help ensure that the healthcare budget is spent on interventions that actually work. Anecdotal evidence and testimonials are worthless. The existing evidence suggests that flexibility training has no known health benefits(1); however, ongoing trials may improve our understanding of the effects of stretching and yoga on back pain(87,88). In the meantime, the practical implications box, right, provides some recommendations on stretching for athletes seeking maximum performance.

Dr Gary O’Donovan is a lecturer in sport and exercise medicine at University of Exeter

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