Comparison of effective body water and body mass changes at three ground speeds during a 164‐km cycling event (707.9)

Abstract

Although body mass change (ΔMb) before and after exercise often is measured to assess dehydration, ΔMb does not represent all water losses and gains. The present field investigation was designed to determine if (a) ΔMb equaled net effective body water change during ultra‐endurance exercise, and (b) ground speed and exercise duration influenced these variables. Thirty‐two experienced male cyclists (35 ‐ 52y) completed a 164‐km event in a hot environment (35ºC), were retrospectively triplet‐matched, and were placed into one of three participant groups (C4.8, C6.3, C9.6; named to match their mean exercise duration, h). Net effective body water loss was computed from measurements (body mass, total fluid intake, urine excreted) and calculations (water evolved and mass loss due to substrate oxidation, solid food mass, respiratory water loss, and sweat loss), including and excluding water bound to glycogen (ΔEBWgly and ΔEBW, respectively). With all cyclists combined, the mean ΔMb (i.e., loss) was greater than that of ΔEBWgly by 1194 ± 213 g (P<.001), was similar to ΔEBW (difference, 0 ± 200 g; P = .21), and was strongly and linearly correlated with both (r2 = .98). Analysis of variance detected no effect of group between C4.8, C6.3 and C9.6 for ΔMb, ΔEBWgly, and ΔEBW. Due to complexity of calculations, we conclude (a) athletes likely will not utilize ΔEBWgly and ΔEBW routinely during training due to their complexity, and (b) ΔMb remains a field‐expedient estimate of net effective body water change.Grant Funding Source: University and Department Internal Funds