Laboratory ACTES, (EA 3596: Department of Physiology), Faculty of Physical Activity and Sports, University of Guadeloupe, Pointe à Pitre, France; Laboratory CNEP (EA 4242), University of New Caledonia, Nouméa, New Caledonia.
Athlete Health and Performance Research Centre, Aspetar, Qatar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
PLoS One. 2014 Apr 24;9(4):e96145. doi: 10.1371/journal.pone.0096145. eCollection 2014.
Growth hormone (GH) may stimulate water loss during exercise by activating sweating. This study investigated GH secretion and water loss during sequential cycling and running, taking postural changes into account. The two exercise segments had similar durations and were performed at the same relative intensity to determine their respective contributions to water loss and the plasma volume variation noted in such trials. Eight elite triathletes first performed an incremental cycle test to assess maximal oxygen consumption. Then, the triathletes performed one of two trials in randomized order: constant submaximal cycling followed by treadmill running (C1-R2) or an inversed succession of running followed by cycling (R1-C2). Each segment of both trials was performed for 20 minutes at ∼75% of maximal oxygen consumption. The second trial, reversing the segment order of the first trial, took place two weeks later. During cycling, the triathletes used their own bicycles equipped with a profiled handlebar. Blood sampling (for GH concentrations, plasma viscosity and plasma volume variation) was conducted at rest and after each segment while water loss was estimated from the post- and pre-measures. GH increases were significantly lower in R2 than C2 (72.2±50.1 vs. 164.0±157 ng x ml(-1) x min(-1), respectively; P<0.05). Water loss was significantly lower after C1-R2 than R1-C2 (1105±163 and 1235±153 ml, respectively; P<0.05). Plasma volume variation was significantly negative in C1 and R1 (-6.15±2.0 and -3.16±5.0%, respectively; P<0.05), not significant in C2, and significantly positive for seven subjects in R2 (4.05±3.1%). We concluded that the lower GH increases in R2 may have contributed to the smaller reduction in plasma volume by reducing sweating. Moreover, this lower GH response could be explained by the postural change during the transition from cycling to running. We recommend to pay particular attention to their hydration status during R1 which could limit a potential dehydration during C2.
生长激素（GH）可能通过激活出汗来刺激运动时的水分流失。本研究考虑到姿势变化，调查了连续骑自行车和跑步时 GH 的分泌和水分流失。这两个运动段具有相似的持续时间，并以相同的相对强度进行，以确定它们各自对水损失和血浆体积变化的贡献，这些试验中观察到了这种变化。8 名精英铁人三项运动员首先进行递增式自行车测试以评估最大摄氧量。然后，运动员以随机顺序进行两种试验之一：恒定亚最大强度自行车骑行后进行跑步机跑步（C1-R2）或相反的顺序跑步后进行自行车骑行（R1-C2）。两种试验的每个段持续 20 分钟，约为最大摄氧量的 75%。第二项试验在第一项试验的段序颠倒后两周进行。在自行车运动中，运动员使用配备有轮廓把手的自己的自行车。在休息时和每个段结束时进行血液采样（用于测量 GH 浓度、血浆粘度和血浆体积变化），并根据后测和前测来估计水分流失。R2 中的 GH 增加明显低于 C2（分别为 72.2±50.1 和 164.0±157ng x ml(-1) x min(-1)；P<0.05）。C1-R2 后的水分流失明显低于 R1-C2（分别为 1105±163 和 1235±153ml；P<0.05）。C1 和 R1 中的血浆体积变化显著为负（分别为-6.15±2.0 和-3.16±5.0%；P<0.05），C2 中不显著，R2 中 7 名受试者显著为正（4.05±3.1%）。我们得出结论，R2 中较低的 GH 增加可能通过减少出汗导致血浆体积减少较小。此外，这种较低的 GH 反应可以通过从自行车骑行到跑步的过渡期间的姿势变化来解释。我们建议在 R1 期间特别注意他们的水合状态，这可能会限制 C2 期间潜在的脱水。
