Active people know the feeling all too well: a stiff and achy sensation in the muscles that sneaks up on the body 24 hours or more after, say, a hard run, a challenging weight lifting session or the first day back on the ski slopes. Sports scientists call it delayed onset of muscle soreness. Athletes call it a nuisance because even simple movements like walking down stairs can be an ordeal. If the soreness is severe enough, it can hamper the next workout or even ruin a ski vacation.
Because of the delay, some people may not even realize that the aches and pains were caused by an activity -- gardening, for example, or hammering nails -- engaged in days before."I've had patients call me up who think they have a virus," said Dr. Gary Wadler, a professor at the New York University School of Medicine and a specialist in sports medicine. The culprit for delayed muscle soreness is not, as some people used to think, the buildup of lactic acid, a byproduct of exercise that dissipates from the muscle tissues within an hour. That kind of soreness is considered acute. As soon as someone stops exercising, or shortly afterward, the burn goes away.
"It's not the key bad guy," said Dr. Michael Saunders, director of the Human Performance Laboratory at James Madison University in Harrisonburg, Va. No one knows for sure exactly what does cause muscle soreness. But many scientists now think that the delayed pain is caused by microscopic tears in the muscles when a certain exercise or activity is new or novel. These tiny tears eventually produce inflammation, and corresponding pain, 24 to 36 hours later.
"White blood cells start to repair the damaged muscle after about 12 to 24 hours and they release a number of chemicals which are likely to be involved in the generation of local muscle pain," said Dr. Mark Tarnopolsky, a specialist in neuromuscular disorders at the McMaster University Medical Center in Hamilton, Ontario. "You see damage at the microscopic level immediately after exercise, yet the soreness is usually delayed for about 24 hours and peaks at 48 hours."
The good news is that as these little tears repair themselves, they prepare the muscles to handle the same type of exercise better the next time. "The muscle gets more resilient, meaning the next time you do that same exercise you won't get damaged as much," said Dr. Priscilla Clarkson, a professor of exercise science at the University of Massachusetts and a leading searcher on muscle soreness. "That doesn't mean you are stronger, or mean you can lift more weight. It just means your muscle fibers are likely stronger so they won't tear as easily. Over time they'll build up and become a stronger fiber to lift more weight."
Performing certain exercises can almost guarantee delayed soreness: running, hiking or skiing downhill, for example, and lowering weights -- what weight lifters refer to as "negatives." In these downhill or downward motions, called eccentric muscle actions, the muscle fibers have to lengthen and then contract, "like putting on the brakes," Dr. Clarkson explained. "It's that lengthening-contraction that puts the most strain on the fiber and does the most damage." Of the 600 or so muscles in the human body, about 400 of them are skeletal. The largest of these are the muscles most susceptible to delayed soreness, Dr. Wadler said.
Severe muscle pain that lasts for many days can be a sign of rhabdomyolysis, a disorder that occurs when too much of the muscle protein myoglobin leaks from the muscle cells into the bloodstream, possibly damaging the kidneys. Dark urine, indicating the presence of myoglobin, can be a symptom of rhabdomyolysis, which in very rare cases can lead to renal failure. Running marathons and participating in other endurance events can cause rhabdomyolysis, said Dr. William O. Roberts, president of the American College of Sports Medicine. Other risk factors include being unfit or dehydrated and exercising in high temperatures.
"It's one of the reasons why you want to stay well hydrated if you are going to work your muscles hard," Dr. Roberts said. "Drink enough so that you have good urine output to clear these waste products." In most cases, though, delayed muscle soreness is not serious, and the soreness fades after a day or two of rest. Weight lifters typically work out the lower body one day and the upper body the next to give fatigued muscles a chance to recover. And conditioned athletes, like cyclists and runners, often alternate between easy and hard days of exercise. "Stress-adapt, stress-adapt so you can handle more and more exercise," said Dr. Tarnopolsky. "That's what an athlete strives for."
The results for other strategies for avoiding or recovering more quickly from muscle soreness are mixed. Many active people reach for nonsteroidal anti-inflammatory drugs like Advil or Aleve. While some data suggest that the drugs may work to prevent soreness or alleviate it once it sets in, the degree of reduction in soreness is small, Dr. Clarkson said. Rarely, doctors prescribe the painkillers known as COX-2 inhibitors for short-term muscle soreness. But the drugs, which include Celebrex and Bextra, are more commonly used to treat arthritis.
And all cox-2 inhibitors are under increased scrutiny, after Vioxx was pulled from the market in September. Merck withdrew it after studies found it increased the risk of heart attacks and stroke. Stretching does not prevent muscle soreness, researchers have found, and massage does little to improve recovery after eccentric muscle use, according to a study published in September in The American Journal of Sports Medicine. In the study, researchers in Stockholm found that after participants performed leg exercises to exhaustion, massage treatment did not affect the level or duration of pain, loss of strength or muscle function.
Consuming protein, however, may help. In a report published in the July issue of the journal Medicine & Science in Sports & Exercise, scientists found that trained cyclists who consumed a carbohydrate and protein beverage during and immediately after a ride, were able to ride 29 percent longer during the first ride, and 40 percent longer in a second session than those consuming carbohydrates alone.
"Our findings suggest that the protein-carbohydrate mix enhanced muscle performance and recovery in the later rides," said Dr. Saunders of James Madison, the study's lead author. But further research is necessary. The results of the study may have been influenced by a higher caloric content in the carbohydrate-protein beverage. "There is some evidence that consuming protein and carbohydrates in the immediate period after exercise may decrease subsequent muscle damage, but that research is in its infancy," said Dr. Tarnopolsky. "What has been fairly well established is that eating food in the postexercise period is better than starving.
"The take-home message is if you are training in the evening don't go to bed on an empty stomach. And if you work out in the morning, eat breakfast afterward or make darn sure to take a snack to work." A practical tactic is to try to limit muscle soreness before it takes hold. For that, you need to train the body to get used to downhill or downward motions. "Gradually run or walk down hills more if you are planning to participate in a downhill event, or take an elevator up to the top of a tall building and walk or run down the stairs," Dr. Roberts recommended. Hikers should consider using adjustable poles, which distribute some of the stress on the legs, transferring it to the upper body, when descending steep grades. "I put hiking poles into the hands of every one of my clients and tell them that if they don't like them I'll carry them," said Nate Goldberg, who routinely guides hikes up 14,000-foot peaks in the Sawatch Mountains of Colorado as director of the Beaver Creek Hiking Center. "Very rarely do I get a set of poles back."
Seasoned athletes, it turns out, are no more immune to delayed onset of muscle soreness than neophyte exercisers. "If I asked Lance Armstrong to run down 10 flights of stairs, he'd be very sore," Dr. Clarkson said. "It's all about sport specificity."
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