Fluid and Exercise ABSTRACTS

Ab-CME1003Pg000ED 11/4/03 10:22 AM Page 1 ABSTRACTS Abstracts are Too much or too intake can do no harm. The advice was to selected on the replace all water lost through sweating or basis of interest to little — fluid and to consume at least 600 – 1 200 ml/hour. our readers. But, as Noakes points out, there is no evi- Publication does exercise dence for any of these assumptions. But it not suggest an was these now outdated guidelines that endorsement of The recent Tour de France – watched prompted Tour de France commentators content or valida- obsessively by the Editor – brought up a Phil Liggett and Paul Sherwen to assume tion of conclusions. common misconception: that dehydration that Armstrong was dehydrated. is a reason for poor performance in an athlete who does not drink enough dur- Ian Rodger, a cyclist who has worked ing competition. As Lance Armstrong with Tim Noakes, was also glued to the appeared to falter in the first time trial, screen during the time trial in question. being beaten by his arch-rival Jan Ulrich, As Super Sport's own team of commenta- the commentators reported that tors started pontificating on the problems Armstrong had apparently lost 6 kg dur- of dehydration during exercise, he sent ing the event and this obvious dehydra- through the following e-mail, which aptly tion must be the reason for his defeat. sums up the problems and misconcep- tions which still abound around optimal At the same time, the British Medical fluid intake during exercise: 'The inter- Journal1 carried an editorial by Professor minablycited 20% decline in performance Tim Noakes pointing out that advice to due to negligible dehydration is simply runners and cyclists to drink copiously wrong. This dates back to the early days during endurance events can lead to fatal of dehydration research, where experi- hypernatraemic encephalopathy. The arti- mental design bore no relation to com- cle starts by mentioning a recent report petitive cycling. In fact dehydration per se that a participant in the 2002 Boston is less important than core temperature, marathon died from hyponatraemic particularly in conditions of high exercise encephalopathy because she drank exces- intensity and high temperature. sive quantities of a sports drink before Perversely, high dehydration can be said and during the race. Noakes points out to assist performance in heat, because it that from 'antiquity to the late 1960s' ath- means that the cyclist has been able to letes were advised not to drink during maintain high sweat rates and so cool exercise as it was believed that this would himself effectively. This delays the devel- impair performance. In 1969 an incorrect opment of a critical core temperature, title to an article 'The danger of inade- which in turn allows a higher exercise quate water intake during marathon run- intensity. ning' started the debate. In fact, the article did not look at the 42-km marathon, ‘In fact, the most dehydrated cyclists are nor did it identify any dangers. What it often the fastest ones, as they can sustain did show was that the most dehydrated the highest exercise intensity and so sweat athletes won the 32-km races. But, the rate/loss. Obviously, the scenario isn't title sparked a rash of studies, mainly quite that straightforward since, at some funded by a new sports drink industry, point, sweating suppression and heat stor- which culminated in guidelines for ingest- age will occur, inhibiting performance. In ing fluid during exercise. addition, in a very heterogeneous popula- tion, found in a fun ride in extreme heat, These guidelines assume that all weight it is equally possible that a recreational lost during exercise must be replaced cyclist can suffer levels of dehydration (assuming that dehydration is a threat), which will inhibit sweating and progress that the athlete’s thirst underestimates to dangerous hyperthermia'. (Editor’s note: actual fluid requirements during racing, As apparently happened to some in The that a universal guideline is possible Argus Cycle Tour of 2002.) because all athletes are essentially the same, and finally that high rates of fluid 616 CME October 2003 Vol.21 No.10 Ab-CME1003Pg000ED 11/4/03 10:22 AM Page 2 ABSTRACTS The fluid loss experienced by Armstrong was quite doing crossword puzzles, playing board games or possible, according to Rodger. He has measured sweat cards, participating in organised group discussions and rates of up to 5 l/hour in cyclists time-trialling in heat playing musical instruments. They were also examined and humidity. Armstrong would have been pushing regarding 11 physical activities – playing tennis or golf, upwards of 450 watts during his time trial, so would swimming, bicycling, dancing, participating in group probably have been sweating at the same rate. As exercises, playing team games such as bowling, walk- Rodger points out, if you add in the sweat lost during ing for exercise, climbing more than 2 flights of stairs, his warm-up, this easily amounts to a 6-kg weight loss. doing housework and babysitting. Frequency of partic- What Rodger did say was that he was surprised that ipation was reported as daily, several days per week, Armstrong, with his scientific approach to training, did once weekly, monthly, occasionally or never. not use a cooling jacket during his warm-up, which During follow-up which amounted to 2702 person- would have saved his time-trial performance. years, 124 participants developed dementia. By the Lance Armstrong went on to win his 5th consecutive end of the study period, 361 subjects had died, 88 had Tour de France – nothing wrong with his perfor- dropped out and 20 were still active. mance! And Tim Noakes has finally had his suggestion This prospective, 21-year study demonstrates a signifi- that drinking according to your thirst is safe and effec- cant association between a higher level of participation tive accepted by the USA Track and Field Organisation in leisure activities at base line and a decreased risk of (www.usatf.org). dementia, both for Alzheimer’s disease and vascular 1. Noakes TD. BMJ 2003; 327: 113-114. dementia. The investigators identified 3 possible expla- nations for this association. First, the presence of pre- clinical dementia may decrease participation in leisure activities. Second, unmeasured confounding factors Use it or lose it may influence the results. Third, there may be a true causal effect of cognitive activities. The prevention of dementia is a major public health priority, but there is little information on effective pre- The investigators conclude that clinical trials are need- ventitive strategies. There appears to be a relationship ed to define the causal role of participation in leisure between dementia and reduced participation in leisure activities. A recent study reported reduced cognitive activities in midlife as well as between cognitive status declines after cognitive training in elderly persons and participation in leisure activities in old age. without dementia. It may be that the results of this Katzman has proposed that persons with higher edu- study will result in recommendations of participation cational levels are more resistant to the effects of in cognitive activities to reduce the risk of dementia in dementia as a result of having greater cognitive reserve the same way that physical activity is recommended to and increased complexity of neuronal synapses. It may reduce the risk of cardiovascular disease. be that, like education, participation in leisure activi- Verghese J et al. N Engl J Med 2003; 348: 2508 – 2516. ties may lower the risk of dementia by improving con- gnitive reserve. Investigators in a study reported in the New England Journal of Medicine examined the relation between leisure activities and the risk of dementia in a prospective cohort of 469 subjects who still lived in the com- munity and did not have dementia at baseline. During the study, subjects were interviewed with the use of a structured medical history questionnaire and were examined by the study doctors. Functional limi- tations on 10 basic and instrumental activities of daily living were rated on a 3-point scale for each activity, with 1 point indicating ‘no limitation’, 2 indicating ‘does activity with difficulty’ and 3 points indicating ‘unable’. Participants were examined on 6 cognitive activities – reading books or newspapers, writing for pleasure, CME October 2003 Vol.21 No.10 617.

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