{"id":988,"date":"2011-02-21T21:17:15","date_gmt":"2011-02-21T20:17:15","guid":{"rendered":"http:\/\/stg-blogs.bmj.com\/bjsm\/?p=988"},"modified":"2011-02-21T21:17:15","modified_gmt":"2011-02-21T20:17:15","slug":"debating-weight-change-and-performance-in-marathon-runners-armstrong-johnson-and-munoz-guest-blog-e-letter","status":"publish","type":"post","link":"https:\/\/stg-blogs.bmj.com\/bjsm\/2011\/02\/21\/debating-weight-change-and-performance-in-marathon-runners-armstrong-johnson-and-munoz-guest-blog-e-letter\/","title":{"rendered":"Debating weight change and performance in marathon runners: Armstrong, Johnson, and Munoz guest blog (e-letter)"},"content":{"rendered":"

We write to present alternative interpretations of the data published<\/tt> by Zouhal and colleagues, in the BJSM article:\u00a0Inverse relationship between percentage body weight change and finishing time in 643 forty-two-kilometre marathon runners<\/a>\"\"
\n<\/strong><\/tt><\/p>\n

The Abstract states that \"... these \u00a0data are <\/tt>not compatible with laboratory-derived data suggesting that BW [body <\/tt>weight] loss greater than 2% during exercise impairs athletic <\/tt>performance.\" \u00a0We agree, but not for the reason proposed in this paper. <\/tt><\/p>\n

<\/tt>Figure 2, which is critical to the findings of this publication, presents <\/tt>an intra-individual group relationship; laboratory studies regarding the <\/tt>influence of dehydration on exercise performance utilize an individual as <\/tt>his\/her own control. \u00a0The cross-sectional trend in Figure 2, which arose <\/tt>from a single field study, should not be equated with a randomized, <\/tt>controlled, repeated measures experimental design.<\/tt><\/p>\n

On the basis of Figure 2, the text states, \"... lesser degrees of <\/tt>body weight loss were associated with longer race finishing times...\" and <\/tt>the discussion section implies cause-and-effect. However, statistical <\/tt>correlation neither implies causation nor warrants a principle. \u00a0Figure 2 <\/tt>also includes noteworthy exceptions. \u00a0Three runners (upper left quadrant) <\/tt>lost approximately 4 - 7% of body weight (i.e., 2.9 - 5.1 kg, based on a <\/tt>prerace body weight of 72.2 kg) but finished with times &gt;300 min; and <\/tt>three runners (lower right quadrant) gained 2 - 3% of body weight (i.e., <\/tt>1.4 - 2.2 kg) but finished with times approximating 180 min. <\/tt><\/p>\n

\"\"<\/tt><\/p>\n

Further, per<\/tt>cent body weight change accounted for only 4.7% of the variance in race <\/tt>time (r2 = 0.047). \u00a0We believe that this relationship is weak because <\/tt>endurance exercise performance is influenced by training, diet, <\/tt>psychological state, years of experience, age, and numerous other factors <\/tt>which interact in complex ways 2. \u00a0Further, the 2009 Mont Saint-Michel <\/tt>marathon was run in air temperatures ranging from 9 to 16?C (Table 1). \u00a0In<\/tt> a hot environment, runners who drink less (i.e., 6% of runners lost 6 - 8%<\/tt> body weight loss, see Fig. 1) increase their risk of exertional heat <\/tt>exhaustion and heatstroke 4. \u00a0This medical advice is noticeably absent, as<\/tt> a qualification to the concept that \"the fastest runners lost the most <\/tt>weight.\"<\/tt><\/p>\n

\"\"<\/p>\n

Three other factors likely complicated the relationship between body <\/tt>weight change (%) and race time (min). \u00a0Firstly, approximately 78% of the <\/tt>643 runners lost weight. \u00a0Sweat loss, of course, was part of their total <\/tt>body water deficits, but was not considered in the interpretation of <\/tt>
\nFigure 2. \u00a0Similarly, we note that pre-race excretion is not mentioned. <\/tt>This would amplify reported body weight changes because runners void <\/tt>bladder and bowl as the race start nears. \u00a0Body weight was measured <\/tt>between 90 and 60 min before the race, and thus weight loss due to pre-<\/tt>race elimination of urine and feces was unknown in Figure 2. \u00a0Thirdly, we <\/tt>examined numerous online photos of competitors in the 2009 Mont Saint-<\/tt>Michel marathon. \u00a0On the basis of our previous experiences at marathon <\/tt>events, we expected that front runners would wear less clothing than slow <\/tt>runners. \u00a0This trend was evident. \u00a0Thus sweat-soaked clothing, which had <\/tt>been dry at the starting line, represented an additional unmeasured <\/tt>component of the body weight variance in Figure 2.<\/tt><\/p>\n

Much text concerns drinking, biological signals and thirst, however <\/tt>none of these variables were measured during the present study. \u00a0Thus it <\/tt>is invalid and speculative to state, \"... athletes will not wilfully (sic) <\/span><\/tt>ignore their thirst when fluid is available in excess...\", or to state, <\/tt>\"... the only conclusion can be that these 'dehydrated' athletes were <\/tt>drinking according to their innate biological signals...\" \u00a0What evidence <\/tt>supports these statements besides a range of body weight change? \u00a0It is <\/tt>widely appreciated that athletes ignore innate biological signals (e.g., <\/tt>pain, fatigue, perceived exertion) during competition, to optimize <\/tt>performance. \u00a0This issue is further complicated by the fact that thirst <\/tt>sensation and drinking behavior are influenced by numerous host factors <\/tt>(e.g., stomach distention, plasma osmolality, oropharyngeal reflexes), the <\/span><\/tt>environment, and fluid characteristics (e.g., saltiness, sweetness) 3. <\/tt>
\nTherefore it is impossible, from the data of Zouhal et al. 1, to formulate <\/span><\/tt>substantiated conclusions about the relationship between body weight <\/tt>change and thirst, or between performance and thirst.<\/tt><\/p>\n

Fluid overload and illness are considered in the Introduction and <\/tt>Discussion sections. \u00a0However, these concepts are misplaced, in that <\/tt>neither symptomatic exertional hyponatremia (EHS) nor fluid intake were <\/tt>reported for any of these 643 runners, including those who gained 3 - 4% <\/tt>
\nof body weight (2.2 - 2.9 kg, Fig. 2). \u00a0Because the data of this paper <\/tt>focus on performance, not illness, and because &gt; 90% of participants <\/tt>did not gain weight, we believe that the following question is more <\/tt>relevant to competitors, \"Is finish time faster or slower when a runner is<\/tt>
\nmildly dehydrated (1 - 2% body weight loss) than when she\/he is severely <\/tt>dehydrated (&gt;5% body weight loss)?\" \u00a0It is impossible for group trends <\/tt>(Fig. 2, Tables 3 and 4) to answer this question. <\/tt><\/p>\n

Finally, the interpretations of Tables 3 and 4 (which present the <\/tt>same concept, in reverse order) fail to consider differences between the <\/tt>fastest and slowest runners. \u00a0Exercise intensity and duration affect the <\/tt>volume of fluid consumed during a race. \u00a0Front runners (i.e., those who <\/tt>
\nfinish 42.1 km in 160 min) experience a high ventilation rate (e.g., <\/tt>&gt;120 L\/min) that precludes consuming water, out of concern for <\/tt>inhalation and coughing; they also are conscious of time spent at aid <\/tt>stations. \u00a0In contrast, back-of-the-pack runners typically spend more time<\/tt>
\nat aid stations, drink more often, walk during part of the race, and have <\/tt>a greater requirement for exogenous carbohydrate (i.e., 30 - 60 g*h-1, <\/tt>mostly in fluids 5) because they are on the course for more than 5 h. <\/tt>Thus, we believe that an alternative interpretation (i.e., \"During a <\/tt>marathon, fast runners drink less than slow runners.\") is superior to the <\/tt>published conclusion, \"body weight loss during a marathon race may be <\/tt>ergogenic\".<\/tt><\/p>\n

Lawrence E. Armstrong, Ph.D., FACSM<\/tt>
\nEvan C. Johnson, M.A.<\/tt>
\nColleen X. Munoz, M.S.<\/tt><\/p>\n

REFERENCES<\/tt><\/p>\n

1. \u00a0Zouhal H, Groussard C, Minter G, et al. Inverse relationship <\/tt>between percentage body weight change and finishing time in 643 forty-two <\/tt>kilometere marathon runners. Br J Sports Med, published online December <\/tt>15, 2010 as 10.1136\/bjsm.2010.074641.<\/tt><\/p>\n

2. \u00a0Leyk D, Erley O, Gorges W, et al. \u00a0Performance, training and <\/tt>lifestyle parameters of marathon runners aged 20-80 years: Results of the <\/tt>PACE-study. Int J Sports Med 2009;30:360-365.<\/tt><\/p>\n

3. \u00a0Johnson AK. The Sensory Psychobiology of Thirst and Salt <\/tt>Appetite. Med Sci Sports Exerc 2007;39:1388-1400.<\/tt><\/p>\n

4. \u00a0Armstrong LE, Casa DJ, Millard-Stafford M, et al. \u00a0American <\/tt>College of Sports Medicine position stand: Exertional heat illness during <\/tt>training and competition. \u00a0Med Sci Sports Exerc 2007;39:556-572.<\/tt><\/p>\n

5. \u00a0Coyle EF. (1999). Physiological determinants of endurance <\/tt>exercise performance. J Sci Med Sport 1999;2:181-189.<\/tt><\/p>\n

Conflict of Interest: <\/span><\/tt>None declared<\/tt><\/p>\n","protected":false},"excerpt":{"rendered":"

We write to present alternative interpretations of the data published by Zouhal and colleagues, in the BJSM article:\u00a0Inverse relationship between percentage body weight change and finishing time in 643 forty-two-kilometre marathon runners The Abstract states that “… these \u00a0data are not compatible with laboratory-derived data suggesting that BW [body weight] loss greater than 2% during […]<\/p>\n

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