They are the bookends of any workout, the fitness components that promise to reduce injuries and fight fatigue. But are warm-ups and cool-downs as essential as every personal trainer and piece of gym equipment would have us believe? Sports scientists are questioning some of the more entrenched elements of the pre and post-workout regime, claiming that many warm-up practices are ineffective or even bad for you, and that evidence for the benefits of cooling down is non-existent.

John Brewer, Professor of Sport at the University of Bedfordshire, says that a warm-up should achieve two things. “It should literally warm up the body to increase blood flow, and loosen the muscles to prepare them for activity,” he says. “Warm muscles pull oxygen from the bloodstream more easily and trigger the chemical reactions needed to produce energy more efficiently.” Most experts agree that 5-10 minutes of jogging or brisk walking is the best way to prepare the body. “You need nothing more vigorous than that to get going,” Brewer says. “In fact, studies have shown that too much of an aerobic warm-up will simply make you tired.”

Beyond that, though, what should you do? Surprisingly, it is the presumption that static stretching — the kind that involves holding a movement — primes muscles for activity that has been proved wrong. “The kind of stretches most people do before exercise, touching the toes or extending the hamstrings, have no advantage and could actually be detrimental, according to recent studies,” says Dr Karianne Backx, an exercise physiologist at the University of Wales Institute, Cardiff. “They do nothing to improve the body’s readiness for exercise and may leave muscles weaker.”

When Dr Ian Shrier, of the Centre for Epidemiology at the Jewish General Hospital in Montreal, reviewed the evidence on pre-workout stretching for The Physician and Sportsmedicine journal a few years ago, he found that stretching immediately before a gym session led to a reduction in muscle power. The effects were small and temporary, but significant enough for Shrier, a past president of the Canadian Academy of Sport Medicine, to recommend dropping stretches from warm-ups. “If one stretches, one should stretch after exercise or at a time not related to exercise,” he concluded. Other researchers have since confirmed his findings, some saying that stretching cuts muscle strength by up to 30 per cent.

Last year Bill Holcomb, a professor of athletic training at the University of Nevada, showed that using stretches to limit injury may have the opposite effect. Whereas previous studies had looked at stretching for 8-10 minutes as part of a serious athletic warm-up, Professor Holcomb looked at the effects of the average 90 seconds of stretching on the quadriceps and hamstring muscles performed by gym-goers. His results, published in the Journal of Strength and Conditioning Research, showed that even this small amount of stretching placed exercisers at a disadvantage. “Doing static stretches as a warm-up can reduce power, strength and performance,” he says.

Not that all kinds of stretching should be avoided. Experts think that dynamic stretching movements such as arm circling and side-stepping — the type we used to be told to avoid — can boost power, flexibility and range of motion. Instead of producing the kind of inhibitory response from the muscles that static stretching triggers, dynamic movements send a message from the brain to the muscles indicating that they are ready to work out.

“Ideally, they should be specific to the type of activity you are about to do,” Brewer says. “Your aims should be to activate all the joints, muscles and tendons that you are going to use when the workout proper begins.” A study published last year by the Centres for Disease Control in the US showed that the number of knee injuries among female footballers was cut by half when they followed a football-specific warm-up that included dynamic stretches.

While the warm-up has drawn interest from sports science researchers in recent years, the same is not true of the cool-down. In fact, a dearth of evidence about its usefulness has led some experts to suggest that it is a waste of time. One accepted fact is that intense exercise should never be stopped abruptly — when you work out hard, the heart pumps faster and blood vessels expand to promote blood flow to the legs and feet. If you stop too suddenly blood can start to pool in the lower limbs, causing dizziness.

“You should spend the last five minutes of a workout doing the same activity at a slower pace,” Dr Backx says. “But if you haven’t been exercising at a high intensity, then just walking around is fine.”

A popular misconception is that cool-down stretches will stop muscles from becoming sore by flushing out lactic acid, the waste product of exercise. “Soreness isn’t caused by lactic acid, but by minor damage to muscle fibres, and stretching will have no effect,” Professor Brewer says.

Indeed, a South African study of adults who had been asked to walk backwards on a treadmill for half an hour to cause calf-muscle stiffness found that those who did a ten-minute cool-down had no less soreness afterwards than those who did not.

“Ironically, the cool-down is the ideal time to perform static stretches if you want to boost overall flexibility because your muscles will be nice and warm,” Dr Backx says. “Just don’t expect a cool-down routine to perform miracles.”

HOW TO EXERCISE SAFELY

Raise your body temperature by walking briskly or jogging for 5-10 minutes before a workout.

Add five to ten dynamic movements to your warm-up — marching, crawling and kicking your buttocks with your heels are ideal. Leave static stretching — in which you hold a movement — until the cool-down.

Never stop intense exercise suddenly. For a cool-down, spend 5-10 minutes doing the same activity more slowly.

Never perform stretches on cold muscles, and never stretch to the point of pain.

Stretching after a workout will not prevent muscle soreness but it will improve overall flexibility.

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