Sports Medicine Pearls and Pitfalls (2008)

INTRODUCTION Sports medicine physicians are asked about the stresses of altitude and how to avoid acute mountain sickness (AMS), the malady that can strike skiers, hikers, and team athletes who travel to compete on high. At altitude, compared with sea level, a given work rate requires a higher percentage of V˙O2max, so lowlanders new to high altitude show marked decrements in maximal and submaximal exercise performance (1). At even the moderate altitude of 1-mile high, "aerobic athletes" like runners and cyclists can feel the strain (2), and I think in the "anaerobic sport" of football, players in frequent action late in close games can lose stamina. Game-time tactics (substitutions, longer breaks, and supplemental oxygen) can lessen this problem, as can pre-game tips. I offer practical pearls on avoiding AMS - on going higher in good health. WHAT IS AMS? As athletes go higher, oxygen concentration in the air goes lower, so the body struggles harder to supply oxygen: heart rate and stroke volume increase and breathing is deeper and faster. The increase in ventilation at altitude is immediate, as arterial nerve receptors respond to hypoxemia. This hypoxic ventilatory response (HVR) is largely inborn and highly individual. Athletes with the strongest HVR - the "best breathers" - may adapt faster (3) and avoid AMS. A common symptom of AMS is a throbbing headache, which becomes worse with exertion. This may stem from brain swelling, either from hypoxic dilation of brain blood vessels that increases blood flow into the brain, or from mild accumulation of fluid in brain cells. Other AMS symptoms can include anorexia, nausea or vomiting, fatigue or weakness, dizziness, and insomnia. AMS typically begins 6-12 h after ascent, but can begin sooner, even as early as 1 h. Pitfall: AMS can be a mimic; athletes can mistake it for a "cold" or allergy, food poisoning, the flu, or a hangover. The lack of fever, however, along with the rapid onset yet paucity of clinical signs of viral infection, allergy, or gastroenteritis helps to pinpoint the illness as AMS. PEARLS TO GET HIGH IN GOOD HEALTH Stay Lean and Fit In a survey of some 3000 tourists at Colorado ski resorts, obesity was a risk factor for AMS. A recent study concurs, and suggests why. When obese and nonobese men were studied in an altitude chamber for 24 h, the obese men developed more severe AMS and greater hypoxemia, perhaps from more hypoventilation at night (4). Lack of fitness too is a risk factor for AMS in ski tourists (5). Do Not Rush Up Speed of ascent relates to AMS. In a survey of some 800 mountaineers, AMS was three times more common if they ascended in 1 d versus 5 d (6). Athletes with prior AMS ideally should sleep overnight at moderate altitude before proceeding to higher altitude. Hydrate on High Studies of Everest trekkers tie dehydration to AMS risk (7). Athletes should begin hydrating on the plane, because cabin air is dry and dehydrating. At altitude, insensible water loss is increased, so athletes need more fluid; daily weights can help them maintain balance (2). Start Slow Even though fitness may mitigate AMS, exercise upon arrival can exacerbate it. In a cross-over study, seven men rested or exercised - four 30-min cycling bouts - during the first 6 h after passive ascent to simulated high altitude. Compared with resting, exercising evoked more AMS (8). Even for athletes, then, it pays to start slow, hence a quandary for teams traveling to altitude. Experts say athletes need up to 21 d to compete best (2). This is often impractical. Pitfall: According to myth, if weeks to acclimatize are not possible, it is best to arrive just before the game. Experts pan this as unscientific. Even a few days at altitude can help, especially if athletes can perform some altitude-adjusted intense workouts in the days pregame (2). In a study of young rugby players new to moderate altitude, exercise performance was impaired more at 6 h than at 18 or 47 h after arrival (9). Increase Carbohydrates High-carbohydrate diets, good in general for athletes, are even better at altitude. Experts note an increased reliance upon carbohydrate at altitude (2), and U.S. Army research shows that, compared with fat, metabolizing carbohydrates spurs ventilation to improve oxygenation and performance (10). Avoid Alcohol Alcohol, a diuretic, is dehydrating. The equivalent of only three beers can blunt the ventilation response to moderate altitude (11). Be Wary of Pills and Potions Sleeping pills also inhibit HVR and should be avoided. Aspirin, acetaminophen, or ibuprofen lessen altitude headache, but sumatriptan helps little. Acetazolamide (Diamox) can help prevent AMS (12), but is controversial. Although Diamox increases ventilation, it has irksome side effects (for example, beer tastes flat!) and as a diuretic can theoretically impair performance. Ginkgo biloba does not prevent AMS (13). Experts are skeptical of the efficacy of many purported ergogenic aids for altitude (2). Dexamethasone can help prevent or treat AMS (14), but the gold standard for treating severe AMS is supplemental oxygen and descent. For competing athletes, Diamox or dexamethasone without prior approval could possibly complicate testing for banned drugs. Use Your Head The most vital advice for athletes going to altitude? Use your head! If you don't feel quite right, rest. When in doubt, go no higher. If you get sick, get lower: descend!