Eichner, E. Randy MD, FACSM
Noted epidemiologist John Ioannidis (8) claims that most published research findings are false. By his analysis, 80% of nonrandomized studies and 10% to 25% of randomized trials turn out to be wrong. He views science as a noble but low-yield endeavor (5). Other researchers claim Ioannidis is wrong. Analyzing more than 5300 P values from some 77,000 articles published from 2000 to 2010 in 5 esteemed medical journals, Jager and Leek (9) found that only 14% of published studies are wrong. Of course, their findings too have been debated. In the debate, a fish story was cited, a published study that makes you laugh and think. Researchers put a salmon in a functional magnetic resonance imaging machine and saw brain activity. But the salmon was dead. Frozen, in fact. Talk about pitfalls. The dead salmon was a red herring (2). This study won the Ignobel Prize in Neuroscience (18).
In any case, most researchers agree that many published studies are flawed and time proves them wrong. After all, this is how science works. It advances in baby steps; if wrong at first, ideally, it self-corrects in time. We keep trying. With that in mind, I cover below some answers and questions from recent studies in sports medicine.
How Many Paths to Hyponatremia?
Exercise-associated hyponatremia (EAH) was studied in five 161-km ultramarathons in northern California (7). The definitions of hyponatremia and hydration status were from Noakes et al. (12); one author of this new study was previously with Noakes et al. This new study differs from Noakes et al. To quote: “Simply stated, EAH was associated more commonly with overhydration in the work of Noakes et al., and more commonly associated with dehydration in the present work” (7).
Overall, 5 races in 5 years, dehydration (body weight loss of >3%) was common, nearly 19% of 887 runners, but weight change varied from an 8% loss to a 10% gain. EAH was seen in 15% of 669 runners. But it was uncommon (<5%) in the cooler years and common (up to 50%) in the two hottest years, when far more with EAH were dehydrated (55%) than overhydrated (8%). EAH was generally mild. Of the 13 with “clinically significant EAH” (serum or plasma sodium <129 mmol·L−1), more were dehydrated than overhydrated, and none was critically ill (7).
The authors speculate that their different results may stem from longer, hotter races than most of the events compiled by Noakes et al. (12), and that sweat sodium loss (not measured) could contribute to their high incidence of EAH with dehydration.
Is this new study a wind shift? Noakes et al. (12) focus on overdrinking. They say that “EAH can be prevented by insuring that athletes do not drink to excess during exercise,” that “loss of sodium due to profuse sweating plays only a minor role, if any, in the pathogenesis of EAH” (1), and “case proven” for EAH as due to overdrinking (13). But this new study may agree with the wag who claims that “salty sweat” is one of the six paths to hyponatremia (3). Even the wag agrees, however, that overdrinking seems the culprit in the fatal EAH cases in athletes. It seems fatal EAH in athletes is on the wane, or at least, I hope so.
If the Shoe Fits
Foot pronation is believed to predispose to running injuries, so the “right shoes” are touted as key in prevention. For two to three decades, shoe companies have sold neutral or stability shoes for neutral feet, cushioned shoes for high-arched supinating feet, and motion control shoes for plantus overpronating feet. Recent studies cast doubt on this custom. For example, a survey of the medical literature found no good research trials and concluded that selling shoe type by foot type is not evidence based (16). Also a randomized controlled trial of different shoes for women training for a half marathon found that motion control shoes increased the risk of injury — even in highly pronated runners — more than stability or neutral shoes (17). Maybe, regarding feet, shoes, and injuries, science is creeping up on marketing.
Now comes a novel study that adds fuel to the science fire. In a 1-year prospective study, Danish researchers enlisted 947 novice runners, evaluated foot posture, and gave them neutral running shoes. During the study, 252 (27%) were injured. But pronators had fewer injuries than those with other foot postures. This study contradicts the belief that moderate foot pronation increases the risk of injury in neutral shoes (11).
One limitation of this study is that few had highly pronated feet, so it did not resolve whether highly pronated feet are more prone to injury than neutral feet. Another limitation was mileage run. No breakdown clarifies who ran how far, but during 1 year of follow-up, the 947 runners ran a total of just over 200,000 miles until “injury or censoring.” Nearly 200 were censored, but when they were censored is unclear. All told, it seems these novice runners, on average over the 1-year follow-up, ran only about 5 miles·wk−1. Running injuries are multifactorial and diverse. They vary by gender, age, body weight, prior injury, weekly mileage, training pace, racing habits, and other factors. If you run only 5 miles·wk−1, does it really matter what shoes you buy? Do we need science to protect us from marketing? Maybe runners should just buy the shoes that feel the most comfortable.
It Is Not the Heat; It Is the Intensity
When all else is equal, it is harder to sprint a given distance in a given time when it is hot than not. In other words, top performance falls off in the heat. For example, when 8 young men cycled to exhaustion at ambient temperatures of 39°F, 51°F, 69°F, and 87°F, exercise duration was longest (94 min) at 51°F and shortest (52 min) at 87°F (6). Ditto for humidity: When 8 men cycled to exhaustion at 86°F but at different relative humidity (24%, 40%, 60%, or 80%), the exercise time was significantly shorter at the 2 highest relative humidity (10).
You might expect, then, that a soccer game would evoke more rhabdomyolysis on a hot day than a cool day. If so, you would be wrong. In a recent study, 17 semiprofessional soccer players took part in a competitive game on a fairly cool day (70°F) and on a very hot day (109°F). During the games, the average heart rate was similar (158 to 160 beats·min−1), as was dehydration (just <2%), but higher muscle (104.5°F) and core (103°F) temperatures were attained in the “hot” game. In the hot game, however, the players ran 7% less and cut high-intensity running by 26%. As they heated up, they slowed down.
The result? Muscle damage was milder after the hot game. Rises in plasma myoglobin and serum creatine kinase were generally modest, but lesser after the hot game. And recovery of sprint performance was faster (back to baseline in 24 h) after the hot game. So in the hot game, compared to the more intense “cool” game, muscles got hotter but had less damage, and players got hotter but had faster recovery (14).
The moral? The toll can be from intensity more than heat. This applies to recent outbreaks of team rhabdomyolysis in sports. A section on rhabdomyolysis will be in the next National Collegiate Athletic Association (NCAA) Sports Medicine Handbook. It also applies to death from exertional sickling in athletes and soldiers with sickle cell trait (4,15).
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Copyright © 2013 by the American College of Sports Medicine.