Abstract
Purpose: Hypohydration and hyperhydration are significant disorders of fluid metabolism in endurance performance; however, little relevant data exist regarding multi-stage endurance activities. The aim of the present study was to examine the effect of running seven marathons in 7 consecutive days on selected anthropometric, hematological and biochemical characteristics with an emphasis on hydration status.Methods: Participants included 6 women and 20 men (age 42.6 ± 6.2 years). Data was collected before day 1 (B1) and after day 1 (A1), 4 (A4), and 7 (A7).Results: The average marathon race time was 4:44 h:min (ranging from 3:09 – 6:19 h:min). Plasma sodium, plasma potassium and urine sodium were maintained during the race. Body mass (p < 0.001, η2 = 0.501), body fat (p < 0.001, η2 = 0.572) and hematocrit (p < 0.001, η2 = 0.358) decreased. Plasma osmolality (Posm) (p < 0.001, η2 = 0.416), urine osmolality (Uosm) (p < 0.001, η2 = 0.465), urine potassium (p < 0.001, η2 = 0.507), urine specific gravity (Usg) (p < 0.001, η2 = 0.540), plasma urea (PUN) (p < 0.001, η2 = 0.586), urine urea (UUN) (p < 0.001, η2 = 0.532) and transtubular potassium gradient (p < 0.001, η2 = 0.560) increased at A1, A4, and A7 vs. B1. Posm correlated with PUN at A1 (r = 0.59, p = 0.001) and A4 (r = 0.58, p = 0.002). The reported post-race fluid intake was 0.5 ± 0.2 L/h and it correlated negatively with plasma [Na+] (r = −0.42, p = 0.007) at A4 and (r = −0.50, p = 0.009) at A7. Uosm was associated with UUN at A1 (r = 0.80, p < 0.001), at A4 (r = 0.81, p < 0.001) and at A7 (r = 0.86, p < 0.001) and with Usg (r = 0.71, p < 0.001) at A1, (r = 0.52, p = 0.006) at A4 and (r = 0.46, p = 0.02) at A7.Conclusions: Despite the decrease in body mass, fluid and electrolyte balance was maintained with no decrease in plasma volume after running seven marathons in seven consecutive days. Current findings support the hypothesis that body mass changes do not reflect changes in the hydration status during prolonged exercise.
Highlights
Hypohydration and hyperhydration are significant disorders of fluid metabolism in endurance performance (Hew-Butler et al, 2015)
Exercise-associated hyponatremia (EAH) is a common occurrence among endurance athletes (HewButler et al, 2015) and the incidence of EAH in multi-stage marathons is similar to its incidence in marathons and singlestage ultramarathons (Krabak et al, 2017)
Based upon previous findings from studies investigating multi-stage ultramarathons, we hypothesized that body mass would decrease and our aim was to examine if body mass changes while running marathons for several consecutive days reflect changes in the hydration status of the runners
Summary
Hypohydration and hyperhydration are significant disorders of fluid metabolism in endurance performance (Hew-Butler et al, 2015). In a multi-stage ultramarathon, athletes often compete for several days (Knechtle et al, 2012a), run at a slow pace (Costa et al, 2013), and are at an increased risk of fluid overload (Rüst et al, 2012). In case of excess fluid consumption, an increase in body mass, total body water and a decrease in plasma sodium [Na+] (Hew-Butler et al, 2015) can be expected. EAH occurred during multi-stage races with both increased and stable levels of total body water (Knechtle et al, 2011, 2012a; Rüst et al, 2012; Costa et al, 2013)
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