Here's a report on that strange, common, yet almost unknown ailment we call, not so affectionately, rhabdo
Take these three brief case histories:
1. While attempting to build leg-muscle strength and explosiveness, a rugby player carries out intense sets of squat jumps on a hot day. Suddenly, he slumps to the turf and is rushed to the hospital, where he spends two days in intensive care. Doctors notice that his heart is beating abnormally and find unusually high levels of potassium in his blood.
2. A soccer player trying to get in shape decides to run a series of 100-metre sprints at close to maximal intensity. As he recovers from his eighth sprint, he suddenly falls to the ground unconscious and is taken to casualty, where attending staff detect lofty blood levels of potassium and myoglobin. The athlete is hospitalised for several days and is unable to train for several weeks.
3. A highly fit marathon runner cruises through the race at 6:30 pace for the first 26 miles but then collapses a few feet short of the finish line. Heroic efforts by doctors fail to save his life, and blood tests reveal a potassium concentration of 13 milligrams per litre, about three to four times the normal level.
Why did these athletes collapse, and why were their blood levels of potassium so high? That important electrolyte did not saturate the athletes' blood plasma because of excessive consumption of sports drinks - it came from their own muscles.
The rugby, soccer, and running participants were all suffering from rhabdomyolysis, commonly known as 'rhabdo', a condition in which muscle membranes, which normally act as 'wrappers' around muscle cells and securely enclose the cells' contents, begin to break down.
'Eccentric contractions seem to greatly increase membrane tension, compared to routine muscle shortenings'
No one knows exactly why the membranes begin disintegrating - or why some individuals are more susceptible than others; experts only know which factors increase the risk of rhabdo. Probably, the mechanical strain placed on muscles during athletic activity is enough to breach some membranes, especially if the activity includes what are called 'eccentric' contractions (ones in which muscles attempt to shorten while they are being stretched). Eccentric contractions seem to greatly increase membrane tension, compared to routine muscle shortenings (in the examples given above, squat jumps place severe eccentric stress on the quadriceps muscles, and running puts eccentric stress on the entire leg each time a foot hits the ground).
Once muscle membranes get tattered, the inner contents of the muscle cells begin to pour out into surrounding tissues, and other materials move inward. Potassium, which is normally in high concentration inside muscles, pours out of the muscles into the blood and surrounding tissue spaces, and sodium and calcium tend to flow inward, building up inside the cells. The potassium can peak at such high levels in the blood that heart function is altered; arrhythmia is a common consequence, and eventually the heart may fail completely if potassium levels are not tempered.
Myoglobin is the hidden villain
Under normal circumstances, the extra potassium would be filtered out of the blood by the kidneys, but in rhabdo the kidneys are often too damaged to function normally. It's likely that the kidneys are harmed by the accumulation of a chemical called myoglobin.
Myoglobin is found inside muscle cells, too, where it acts as a kind of storage depot for oxygen. As the muscle membranes break down during rhabdomyolysis, however, myoglobin leaks out along with the potassium and is carried to the kidneys. In the kidneys, myoglobin can break down into a toxic chemical called ferrihaemate which damages kidney cells. The injured kidneys then fail to regulate the incoming high tide of potassium.
Myoglobin's presence in the kidneys can also lead to myoglobinuria (myoglobin in the urine). If you ever develop this condition, you'll know at once that you have it: since myoglobin is dark purple in colour, your urine will look exactly like Coca-Cola.
Who actually gets rhabdo?
Although rhabdo is usually thought to be a rare condition, the truth is that many athletes suffer from a mild version of it from time to time. 'If you've ever had stiff and tender muscles after exercising, you've probably had a slight case of rhabdomyolysis,' notes Marc Rogers, Ph. D., an exercise physiologist at the University of Maryland. Novice exercisers can develop the problem, but so can the most highly trained, accomplished athletes ('Catastrophic Medical Events with Exhaustive Exercise: White Collar Rhabdomyolysis,' Kidney International, vol. 38, pp. 709-719, 1990).
Moderate cases of rhabdo are probably common after triathlons. For example, when 25 triathletes were studied during a triathlon which included 1.25 miles of swimming, 53.5 miles of biking, and 13.5 miles of running, it was found that most of
the participants had unusually high levels of myoglobin in their
blood immediately after the competition, suggesting that muscle-membrane leakage had occurred ('Myoglobinaemia and Endurance Exercise: A Study of Twenty-Five Participants in a Triathlon Competition,' American Journal of Sports Medicine, vol. 12, pp. 113, 1984).
Other studies indicate that rowers and cross-country skiers are susceptible to rhabdo, and some reports have indicated that acute rhabdomyolysis can strike about one out of every 300 military recruits during their first week of training ('Rhabdomyolysis, Myoglobinuria, and Exercise,' Sports Medicine, vol. 6, pp. 93-106, 1988).
Athletes and military recruits aren't the only ones who can suffer from rhabdo. Alcoholics and drug addicts are prone to the condition and can develop an extensive case of rhabdomyolysis just by sleeping for an extended period on one side of the body (the pressure on the 'down' side of the body is apparently enough to trigger muscle problems in these groups of people). Severely injured accident victims often experience rhabdo, too, usually because a crushing injury has damaged muscle cells and caused leakage of cell contents into surrounding tissues.
Strangely enough, a small dose of rhabdomyolysis might actually have a positive effect. Various scientists have speculated that the build-up of calcium inside muscle cells during rhabdo can stimulate increased protein synthesis inside the cells, perhaps producing some of the beneficial adaptations we associate with training (more aerobic enzymes, more contractile proteins, more mitochondria). It's only when too much damage is done and the whole process gets out of control that rhabdo becomes a severe threat to health.
Are there ways to avoid rhabdo?
Can you train and compete in a way which minimises the risk of rhabdomyolysis? Studies are scanty in this area but suggest that as fitness improves and an athlete's training programme becomes more challenging and of longer duration, the likelihood of rhabdo declines. In one study which examined the link between training volume and muscle-membrane damage, three different training programmes were utilised: (1) No training at all for one month, (2) Four miles of running every other day for one month, and (3) Eight miles of running every other day for a month ('Effects of Conditioning on Exertional Rhabdomyolysis and Serum Creatine Kinase after Severe Exercise,' Enzyme, vol. 26, pp. 177-181, 1981).
After the month, all participants in the study were asked to damage their leg muscles by running 14 miles at eight-minute per mile pace. All three training groups experienced increases in blood levels of myoglobin after the 14-mile effort, indicating that some muscle-membrane trauma had indeed occurred.
The smallest rise in myoglobin took place in the eight-mile per day training group, suggesting that increased mileage (and presumably higher fitness) might offer some protection against rhabdo - at least during exertions lasting two to three times as long as one's normal training session. Of course, one must be careful with this conclusion: in some cases, increased training volume might actually increase the risk of rhabdo by placing excessive stress on muscles (it is certainly clear that high-volume, highly fit athletes are not immune to rhabdo). And one might argue that the best shield against rhabdo might be not a mountain of general training but in fact a systematic series of workouts which produce tremendous sport-specific muscular strength. If an athlete is very strong in the specific movements associated with a sport, then protection against muscle damage should be enhanced.
What are the risk factors?
Although no one is exactly sure how rhabdo comes about, there do appear to be risk factors which make it more likely to occur. As mentioned, heavy alcohol consumption seems to heighten the chances of developing rhabdo, as does cocaine usage. A cholesterol-lowering prescription drug called Mevacor (Lovastatin is the generic name) has been linked with rhabdomyolysis, too. Exercising after a recent infection also probably raises the risk of rhabdo. Viral illnesses, for example, can inflame muscle membranes and possibly make their deterioration more likely during exertion.
Being dehydrated can definitely make rhabdo worse. 'If you're dehydrated, blood flow to your kidneys is reduced, so there's more chance of kidney failure and a lack of potassium filtering,' notes Chris McGrew, a sports-medicine physician at the University of New Mexico Hospital. Thus, heavy exertion during warm weather is particularly risky, from a rhabdo standpoint; the strenuous exercise places a heavy strain on the muscles, and the warm weather increases sweating rates, upping the possibility of dehydration. Out-of-shape athletes who begin training seriously in the summer are thus at particular risk; their lack of fitness places more stress on their muscles, and their lack of acclimatisation to the heat raises the risks of heat stress and dehydration. The take-home message here is that initial hot-weather workouts should be kept short and moderate in intensity, and sports drink should be consumed copiously during such exertions. Naturally, eight to 10 glasses of water should be consumed per day.
Strangely enough, only two species of animals - humans and horses - are known to develop rhabdomyolysis, and only MALE humans seem to be susceptible. No one knows why females are immune, although some experts have speculated that decreased total muscle mass and more efficient heat regulation in females may be protective against full-blown rhabdo. It's also possible that the key female sex hormone, oestrogen, has a soothing and stabilising effect on muscle membranes, making it hard to mortally wound them during strenuous exercise.
Unfortunately, rhabdo doesn't announce itself with any hallmark warning signals which could alert you that you were on the verge of developing the condition. Scarily enough, 'people who develop rhabdo might not feel much different than they normally do during hard exertion until shortly before they collapse,' notes McGrew. Some of the athletes who do come down with rhabdo experience fatigue, light-headedness, and muscle tightness and soreness before they are stricken, but these are the same sorts of sensations that all kinds of healthy athletes experience after or towards the end of a very tough workout. As a result, athletes who have died of rhabdo might still be alive if they had cut their exercise short, but they ordinarily would not have had any way of knowing that they were in severe trouble until it was too late.
Rhabdo and endurance runners
Are long-distance runners at particularly high risk of rhabdo? Some studies suggest that they are; in one case following a 99-K ultramarathon, 25 out of 44 runners had excessive quantities of myoglobin in their blood ('Myoglobin, Rhabdomyolysis, and Marathon Running,' Quarterly Journal of Medicine, vol. 188, pp. 463-472, 1978). Nonetheless, marathoning and ultramarathoning appear to be reasonably safe activities. 'To put things into perspective, runners are probably safer running a marathon than they are riding in their cars to and from the event,' notes McGrew.
Careful work by Dr Paul Thompson has shown that in male runners between the ages of 30 and 64, there is about one death for each 800,000 'person-hours' of running or jogging, while in female runners the risk is much lower. That translates into about one death every 10 years in a large event like the London Marathon or about one death every 2192 years for an individual male runner who runs two three-and-a-half hour marathons per week. Thus, marathon running is not risk-free from a rhabdo standpoint, but it is relatively safe. 'Cardiovascular problems and heat injuries kill more runners than rhabdo does,' notes rhabdo-expert McGrew.
So what are the final words? As mysterious as rhabdo is, there are some precautions you can take which should reduce your risk of developing the disorder. You should keep yourself well-hydrated and avoid strenuous exercise during hot weather, especially if humidity is high. You should also stay within your normal limits of exercise; if you usually train for 45 minutes, don't suddenly 'burst out' with a strenuous two-hour exertion, and if you normally work at a moderate intensity with small bits of high-quality exertion, don't suddenly go full-tilt for an extended period of time. Finally, you should keep your workouts light if you have recently had an infectious illness. If you do all these things, your chances of avoiding rhabdo's wrath are very, very good.