Portal de Periódicos da CAPES

Muscle Cramping in the Heat

2018; Lippincott Williams & Wilkins; Volume: 17; Issue: 11 Linguagem: Inglês

10.1249/jsr.0000000000000529

1537-8918

E. Randy Eichner,

High Altitude and Hypoxia

Introduction The United States Open tennis tournament in New York City in 2018 was called “the wettest,” even without much rain. Journalists had fun depicting the “wetness” as coming from “inside out,” as tennis players “drowned in seas of themselves” or “rained on their own parade.” This was because many players were soaked from head to toe in their own sweat. The Open was hot and humid from its start on August 27. Ambient temperatures topped 95 degrees and humidity hovered near 50%. Seven of the first 11 days were played under special rules for extreme heat. On day 2, the eventual champion Novak Djokovic and his opponent Marton Fucsovics sat in ice baths for 10 min between their third and fourth sets, while five men quit their matches, citing heat exhaustion or cramping. In the quarterfinals, John Isner went through 11 shirts and lost up to 10 pounds in a four-set loss, while John Millman, in another loss, changed his entire wardrobe — shirt, shorts, socks, and shoes — as early as midway in the second set, when he was dripping so much sweat that the tennis court became dangerously slippery. So the Open in 2018 was not all fun and games. It was survival of the fittest in the heat. And with climate change on us, we can expect more of the same in the near future. My focus, however, is not on climate change, but on pearls and pitfalls in preventing and treating heat cramping. Muscle Cramping in the Heat Muscle cramping can hobble athletes in the heat. This painful problem can range from vexing to disabling. It can begin with twinges or spasms in a single fatiguing muscle and — especially in the face of “salty sweating,” increasing dehydration, and continued top exertion — can evolve into widespread and sharply painful muscle contractions that can sideline athletes. Heat cramping is common in summer tennis and football, but also occurs in distance cycling and running, as in tropical triathlons, in soccer and beach volleyball, and even in basketball playoff games, as NBA star LeBron James has proven more than once. Heat cramping also has occurred late in ice hockey games, where the macroclimate of the ice rink is cool but the “microclimate” of a heavily-garbed goalie is hot. In fact, heat cramping is better thought of as “sweat cramping.” History of Heat Cramping The term “heat cramping” dates back to the 1880s, to describe the cramping in miners sweating heavily in stifling heat underground in Nevada’s Comstock Lode. Similar muscle cramping occurs in stokers, steelworkers, cane cutters, firemen, roofers, and others who toil in extreme heat. Stokers on ocean ships added seawater to their drinking water to fend off cramps. Heat cramps in coal miners in England were reduced by a saline drink. Harvard researchers studying steelworkers and men who built the Hoover Dam tied heat cramping to loss of salt in sweat, reversed cramping with intravenous saline, and concluded that salt can help prevent heat cramps (1). In field studies, we and others in football and Bergeron in tennis tied heat cramping to heavy, salty sweating (2–4). A 17-year-old football player with cystic fibrosis had disabling cramping during the second half of the games until his heavy, salty sweating was offset via Pedialyte and salt tablets, which cured his heat cramping to the extent that, playing both sides of the line, he finished every game in 2017 (5). In short, several lines of evidence suggest that major muscle cramping in the heat can be caused by loss of salt in sweat, along with dehydration and fatigue. Something New Under the Sun However, there is always something new under the sun. When I last covered cramping, it was the “altered neuromuscular control theory.” The idea was to exploit transient receptor potential (TRP) channels in the mouth and upper GI tract. These channels are sensory transducers of temperature and chemicals. The plan was to stimulate TRP channels to depress generalized efferent neural output. The hope was to end muscle cramping by inhibiting any hyperexcitability of alpha-motor neurons (6). The product was “Hotshot,” by Flex Pharma, Inc. It combines capsaicin, ginger, and cinnamon, to give a “hot-spicy kick” to the TRP channels. It comes in 1.7-ounce vials and is meant to be quaffed pre-workout and/or at the first twinge of cramping. I was skeptical (7). After all, any Hotshot “benefits” were mild at best (6), it was impossible to control for the hot-spicy kick, the placebo effect can be strong in sports medicine, and some say that just a hard pinch of your upper lip “works fast” to end a muscle cramp. Two Flex Pharma researchers liked my “homespun delivery,” but did not like my analysis of the miracles of Hotshot (8). Since then, Hotshot sales have been low and Flex Pharma has lost most of its market value and has cut its work force by more than half. Hotshot seems a long shot. But now CrampsAWAY is new under the sun. It hopes to cash in on cramp-busting by tickling the same TRP channels with “natural food acids” and a strong fruity taste. It may follow Hotshot into the sunset. Yet some “cramp busters” hang on for decades; to wit, Cramp Stop (from New Zealand), an oral spray that “works” just as well as Hotshot and CrampsAWAY, yet being homeopathic, in essence has nothing in it. Will wonders never cease? Salty Solutions Research and debate on causes and cures of exertional muscle cramping will endure. However, for heat cramping in tennis and football, “salty solutions” seem the best bet. Exertional muscle cramping is multifactorial and in some endurance athletes may not stem mainly from salt and water depletion along with fatigue. However, swigging a cocktail of hot spices or fruits for heat cramping is risky business, because it delays proper therapy and fails to treat root causes. It is like disabling your blaring fire alarm and going back to bed. As for salty solutions, Bergeron prevents heat cramping in tennis by adding salt to the diet and to sports drinks at the first twinge of cramping (9). We find the same works in football. Players prone to cramping are urged to salt their food and eat healthful salt-rich foods, such as tomato juice, pretzels, and beef jerky. We add extra salt to their sports drinks on-field. Some teams use salt tablets. Some high school teams add about ¼ tsp table salt to each pint of water for cramp-prone athletes. If a player heat-cramps in a game and fails to respond to rest, stretching, massage, ice, and salt-rich drinks, we can often reverse it fairly quickly with 2 L of normal saline intravenously and sometimes get him back into the same game. A caveat is that treating major heat cramping with lots of plain water and/or hypotonic intravenous fluid poses the risk of hyponatremia. Concluding pearl: For heat cramping in summer sports, seek salty solutions.