Effective body water and body mass changes during summer ultra-endurance road cycling

Abstract

Because body mass change (ΔMb) does not represent all water losses and gains, the present field investigation determined if (a) ΔMb equalled the net effective body water change during ultra-endurance exercise and (b) ground speed and exercise duration influenced these variables. Thirty-two male cyclists (age range, 35-52 years) completed a 164-km event in a hot environment, were retrospectively triplet matched and placed into one of three groups based on exercise duration (4.8, 6.3, 9.6 h). Net effective body water loss was computed from measurements (body mass, total fluid intake and urine excreted) and calculations (water evolved and mass loss due to substrate oxidation, solid food mass and sweat loss), including (ΔEBWgly) and excluding (ΔEBW) water bound to glycogen. With all cyclists combined, the mean ΔMb (i.e. loss) was greater than that of ΔEBWgly by 1200 ± 200 g (P = 1.4 × 10(-18)), was similar to ΔEBW (difference, 0 ± 200 g; P = .21) and was strongly correlated with both (R(2) = .98). Analysis of equivalence indicated that ΔMb was not equivalent to ΔEBWgly, but was equivalent to ΔEBW. Due to measurement complexity, we concluded that (a) athletes will not calculate the effective body water calculations routinely and (b) body mass change remains a useful field-expedient estimate of net effective body water change.

A variant within theAQP13ʹ-untranslated region is associated with running performance, but not weight changes, during an Ironman Triathlon

“…The limitations of using body weight changes as a proxy for fluid loss are recognised as a limitation to this study (Tam & Noakes, 2013). As the group of athletes with the greatest relative body weight loss were also likely to have been the most dehydrated, and the results of this study were not used for individual fluid replacement advice, relative body weight change was considered a sufficient indirect measure of gross body fluid changes during the event (Armstrong et al, 2014;Saunders et al, 2006). Although not confirmed in this study, the association of the AQP1 rs1049305 C-allele with exercise-induced body fluid loss observed by Rivera et al (2011) may also provide an indirect explanation of the association with running performance observed both previously and in the current study (Martínez et al, 2009;Rivera et al, 2011).…”

“…Percentage body weight lost or gained was calculated as the difference between the pre-and post-race weights divided by the pre-race weight and expressed as a percentage. Although changes in body weight during exercise are significantly influenced by fuel utilisation and likely overestimate true changes in total body water (Tam & Noakes, 2013), weight changes during the Ironman were nevertheless used as an indirect measure of changes in total body water during the event, as the group of athletes with the greatest percentage weight loss would also, presumably, have been the most dehydrated (Armstrong et al, 2014;Saunders et al, 2006). As previously described (Saunders et al, 2006), triathletes who gained weight during the event were considered to be overhydrated, those who lost between 0% and 3% body weight were considered to be euhydrated, while those who lost more than 3% of their pre-race body 2 C. J. Saunders et al…”

Water Intake, Water Balance, and the Elusive Daily Water Requirement

“…An example of large within-subject variability is also seen in the day-to-day differences of sweat losses that are experienced by athletes [24]. Total sweat loss during sedentary work activity (e.g., 8h of computer programming in an air-conditioned environment) may amount to <0.2 L/24h, whereas the total sweat volume during a 164-km ultradistance cycling event often exceeds 9 L during a 9-h ride [42]. The 24-h human water requirement varies with anthropomorphic characteristics, especially body mass.…”

Distinguishing Low and High Water Consumers—A Paradigm of Disease Risk

“…Although the acute effects of moderate-to-severe dehydration have been extensively studied for over 70 years [22][23][24][25], investigators knew little about LOW prior to 2008 because research reports regarding the consequences of chronic mild dehydration were rare [26,27]. Between the years 1996 and 2003, animal experiments and clinical studies revealed the adverse effects of elevated AVP on kidney diseases, albuminuria and hypertension [28].…”