Phys Ed: How Necessary Is Stretching?
By GRETCHEN REYNOLDS
Max Oppenheim/Getty Images
For research published earlier this year, physiologists at Nebraska Wesleyan University had distance-running members of the school’s track and field team sit on the ground, legs stretched before them, feet pressed firmly up against a box; then the runners, both men and women, bent forward, reaching as far as they could past their toes. This is the classic sit-and-reach test, a well-established measurement of hamstring flexibility. The runners, as a group, didn’t have exceptional elasticity, although this varied from person to person.
Overall, the women were more supple, as might have been expected. Far more telling was the correlation between the various runners’ tight or loose hamstring muscles and their running economy, a measure of how much oxygen they used while striding. Economy is often cited as one of the factors that divide great runners from merely fast ones. Kenyan distance runners, for instance, have been found to be significantly more economical in their running than comparable Western elites.
When the Nebraska Wesleyan researchers compared the runners’ sit-and-reach scores to the measurements of their economy, which had been garnered from a treadmill test, they found that, across the board, the tightest runners were the most economical. This was true throughout the groups and within the genders. The inflexible men were more economical than the women, and for both men and women, those with the tightest hamstrings had the best running economy. They also typically had the fastest 10-kilometer race times. Probably, the researchers concluded, tighter muscles allow “for greater elastic energy storage and use” during each stride. Inflexibility, in other words, seems to make running easier.
For years, flexibility has been widely considered a cornerstone of health and fitness. Many of us stretch before or after every workout and fret if we can’t lean over and touch our toes. We gape enviously at yogis wrapping their legs around their ears. “It’s been drummed into people that they should stretch, stretch, stretch — that they have to be flexible,” says Dr. Duane Knudson, professor of biomechanics at Texas State University in San Marcos, who has extensively studied flexibility and muscle response. “But there’s not much scientific support for that.”
In fact, the latest science suggests that extremely loose muscles and tendons are generally unnecessary (unless you aspire to join a gymnastics squad), may be undesirable and are, for the most part, unachievable, anyway. “To a large degree, flexibility is genetic,” says Dr. Malachy McHugh, the director of research for the Nicholas Institute of Sports Medicine and Athletic Trauma at Lenox Hill Hospital in New York and an expert on flexibility. You’re born stretchy or not. “Some small portion” of each person’s flexibility “is adaptable,” McHugh adds, “but it takes a long time and a lot of work to get even that small adaptation. It’s a bit depressing, really.”
What happens to our muscles and tendons, then, when we dutifully stretch before a run or other workout? Doesn’t this lengthen our muscles, increasing our flexibility and range of motion?
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According to the science, the answer appears to be no. “There are two elements” involved in stretching a muscle, Dr. McHugh says. One is the muscle itself. The other is the mind, which sends various messages to the muscles and tendons telling them how to respond to your stretching when the discomfort of the stretching becomes too much. What changes as you stretch a muscle is primarily the message, not the physical structure of the muscle. “You’ll start to develop a tolerance” for the discomfort of the stretch, Dr. McHugh says. Your brain will allow you to hold the stretch longer. But the muscles and tendons themselves will not have changed much. You will feel less tight. But even this sensation of elasticity is short-lived, Dr. McHugh says. In a new review article of the effects of stretching that he co-wrote and that will be published soon in The Scandinavian Journal of Medicine and Science in Sports, he looked at the measurable impacts of a number of different stretching regimens. What he found was that when people performed four 90-second stretches of their hamstrings, their “passive resistance” to the stretching decreased by about 18 percent — they felt much looser — but the effect had passed in less than an hour. To achieve a longer-lasting impact, and to stretch all of the muscles involved in running or other sports, he says, would probably require as much as an hour of concerted stretching. “And the effects still wouldn’t be permanent,” he says. “You only see changes” in the actual, physical structure of the muscles “after months of stretching, for hours at a time. Most people aren’t going to do that.”
And most of us don’t need to. “Flexibility is a functional thing,” Dr. Knudson says. “You only need enough range of motion in your joints to avoid injury. More is not necessarily better.” For runners, extremely tight hamstrings and joints have been found in some studies (but not all studies) to contribute to overuse injuries. But somewhat tight hamstrings, as the Nebraska Wesleyan study showed, can make you more economical. Some degree of inflexibility may make you a better runner.
How then to judge your own flexibility? “The sit-and-reach test is pretty good” for at-home evaluations, Dr. Knudson says, at least of your back and hamstring muscles. Using a staircase, sit and straighten your legs so that your feet push against the bottom step, toes upright. Stretch forward. “Try to lay your chest onto your thighs,” he says. If you can reach past your toes, you’re more than flexible enough. (No one yet has devised a way to reduce flexibility, by the way, although some Olympic-level coaches in other countries are rumored to be trying.)
If, on the other hand, “you can’t get anywhere near your toes, and the lower part of your back is practically pointing backward” as you reach, then you might need to try to increase your hamstring flexibility, Dr. Knudson says, to avoid injuring yourself while running, cycling or otherwise exercising. You can find multiple hamstring stretches on YouTube, although you should consult with a physical therapist before replicating them at home; proper technique is important to avoid injury. “You won’t get a lot of change,” Dr. Knudson says, ” but a little may be all you need.”
With This Rinse, Performance Improves
By GINA KOLATA
Exercise scientists say they have stumbled on an amazing discovery. Athletes can improve their performance in intense bouts of exercise, lasting an hour or so, if they merely rinse their mouths with a carbohydrate solution. They don�t even have to swallow it.
It has to be real carbohydrates, though; the scientists used a solution of water and a flavorless starch derivative called maltodextrin. Artificial sweeteners have no effect.
And the scientists think they have figured out why it works. It appears that the brain can sense carbohydrates in the mouth, even tasteless ones. The sensors are different from the ones for sweetness, and they prompt the brain to respond, spurring on the athlete.
Many athletes depend on sugary beverages to keep them going. But often, when blood is diverted from the stomach to working muscles during intense exercise, drinks or foods cause stomach cramps. So a carbohydrate rinse can be a way to get the same effect.
�You can get an advantage from tricking your brain,� said a discoverer of the effect, Matt Bridge, a senior lecturer in coaching and sports science at the University of Birmingham in England. �Your brain tells your body, �Carbohydrates are on the way.� � And with that message, muscles and nerves are prompted to work harder and longer.�
It�s a relatively small effect, said George A. Brooks, an exercise researcher at the University of California, Berkeley, who was not involved with the research. But a small difference, he added, �can make a big difference in competition.�
The discovery began with some puzzling findings dating to the 1990s.
Until then, exercise scientists thought they knew why it could help to eat or drink carbohydrates during a long endurance event like a marathon. Muscles can use up their glycogen, the storage form of glucose, during long exercise sessions. But if athletes consume carbohydrates, they can provide a new source of fuel for their starving muscles.
That theory predicts that carbohydrates should have no effect on performance in shorter races, an hour or less. Muscles can�t use up their glycogen that fast, and by the time the body metabolizes the carbohydrates for fuel, the race is almost over.
Then came a handful of studies showing that carbohydrates did have an effect in short exercise sessions. Athletes, often trained cyclists, rode hard and fast for an hour or so after drinking either a beverage containing carbohydrates or one that tasted the same but contained an artificial sweetener.
In intense exercise sessions lasting more than half an hour, the athletes were able to go faster or keep going longer when they had the drink with carbohydrates. Their performance improved as much as 14 percent.
Some studies, though, did not find an effect. And the difference seemed to be that athletes who were hungry showed improved performance.
It made no sense. Could the body somehow have metabolized the carbohydrates in the drinks and put them to use in such a short time? Did the muscles even need carbohydrates in such short bouts of exercise?
Asker Jeukendrup, an exercise physiologist at the University of Birmingham, and his colleagues put that idea to the test. They were among the first researchers to discover a carbohydrate effect in cyclists riding hard for an hour, and they had been puzzling over what could account for it.
So they gave trained cyclists intravenous infusions of glucose or, as a control, intravenous salt water, before asking them to ride as fast as they could for about 24 miles, about an hour. The intravenous glucose meant the athletes had large amounts of sugar available right away � no digestion required. But it had no effect on their performance.
Next they tried what seemed like a crazy idea. They asked the cyclists to do the same ride, but first to rinse their mouths with the maltodextrin solution (or, as a control, with water).
�The results were remarkable,� the researchers wrote. Just rinsing with a carbohydrate had the same effect as drinking it.
Other scientists repeated the experiment. One group used runners, asking them to run for 30 minutes or, in another study, 60 minutes. Rinsing the mouth with carbohydrates consistently led them to run farther, as compared with rinsing with placebos.
Dr. Jeukendrup and his colleagues continued to tweak the study conditions. What happened, they asked, if athletes ate breakfast before rinsing with carbohydrates, or drinking a carbohydrate solution? Then, they found, carbohydrates had no effect.
Meanwhile, neuroscientists found that rodent brains, at least, responded to carbohydrates in the mouth independently of their response to sweetness. It is carbohydrates that matter, and so artificial sweeteners do not stimulate these pathways that go from the mouth to the brain.
Then Dr. Bridge and his colleagues in Birmingham used functional magnetic-resonance imaging to determine whether glucose, which tastes sweet, has the same effect on the brain as the tasteless carbohydrate maltodextrin. They also tested artificial sweeteners for comparison. The brain scan results confirmed the exercise study results: Carbohydrates activated brain areas involved with rewards and muscle activity. Artificial sweeteners did not.
Is rinsing worthwhile for most athletes? Scott J. Montain, an exercise researcher at the United States Army Research Institute of Environmental Medicine, thinks not. The effect is real, he said, but added, �Endurance competitors are better off just consuming the calories.� That way they get real fuel, instead of �sipping and then spitting out expensive, sticky spit.�
Dr. Jeukendrup and Dr. Bridge, though, say they use the mouth-rinsing trick themselves.
�You do notice a benefit,� Dr. Bridge said. But he noted that in a study, the athletes don�t know if they are getting carbohydrates or not. �If you know you are doing it,� he said, �then there�s a chance it�s a placebo effect.�
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