The effect of dehydration on muscle metabolism and time trial performance during prolonged cycling in males

Abstract

This study combined overnight fluid restriction with lack of fluid intake during prolonged cycling to determine the effects of dehydration on substrate oxidation, skeletal muscle metabolism, heat shock protein 72 (Hsp72) response, and time trial (TT) performance. Nine males cycled at ∼65% VO2peak for 90 min followed by a TT (6 kJ/kg BM) either with fluid (HYD) or without fluid (DEH). Blood samples were taken every 20 min and muscle biopsies were taken at 0, 45, and 90 min of exercise and after the TT. DEH subjects started the trial with a −0.6% BM from overnight fluid restriction and were dehydrated by 1.4% after 45 min, 2.3% after 90 min of exercise, and 3.1% BM after the TT. There were no significant differences in oxygen uptake, carbon dioxide production, or total sweat loss between the trials. However, physiological parameters (heart rate [HR], rate of perceived exertion, core temperature [Tc], plasma osmolality [Posm], plasma volume [Pvol] loss, and Hsp72), and carbohydrate (CHO) oxidation and muscle glycogen use were greater during 90 min of moderate cycling when subjects progressed from 0.6% to 2.3% dehydration. TT performance was 13% slower when subjects began 2.3% and ended 3.1% dehydrated. Throughout the TT, Tc, Posm, blood and muscle lactate [La], and serum Hsp72 were higher, even while working at a lower power output (PO). The accelerated muscle glycogen use during 90 min of moderate intensity exercise with DEH did not affect subsequent TT performance, rather augmented Tc, RPE and the additional physiological factors were more important in slowing performance when dehydrated.

Heat therapy promotes the expression of angiogenic regulators in human skeletal muscle

“…However, this confounding effect seems unlikely given that changes in the expression of angiogenic factors and heat shock proteins were remarkably similar between the LBH and TH protocols (Table 7), even though there is negligible dehydration during localized limb heating. In addition, Logan-Sprenger et al (35) recently reported that mild dehydration induced by overnight fluid restriction had no significant impact on the expression of HSP72 in skeletal muscle in humans. Taken together, these observations indicate that mild dehydration does not seem to impact the expression of angiogenic factors and heat shock proteins in skeletal muscle.…”

Fluid Intake Habits in Type 1 Diabetes Individuals during Typical Training Bouts

“…Proper daily consumption of fluids, principally water, should be encouraged for its health benefits. In general, dehydration may affect the rate of glucose oxidation and glycogen metabolism, increasing carbohydrate needs and potentially increasing the risk of hypoglycaemia [24-27] in individuals with type 1 diabetes. Moreover, low total water intake in people with T2DM acutely impairs blood glucose response during an oral glucose tolerance test [28].…”

Příjem tekutin během vytrvalostního zatížení – pít podle pocitu žízně, ano nebo ne?

“…Rozvíjí se absolutní hypovolemie (pokles plasmatického objemu) zvyšující nároky na srdeční výdej s následnou kompenzací vyšší srdeční frekvencí a relativní hypovolemie (snížení průtoku krve podkožím). Výsledkem zhoršené schopnosti organizmu eliminovat produkované teplo je riziko vzestupu tělesné teploty (teploty jádra), zvýšení hladin katecholaminů a akcentovaná glykogenolýza přispívající k dřívějšímu rozvoji únavy u vytrvalostního zatížení (Logan-Sprenger, Heigenhauser, Jones, & Spriet, 2015). Hypohydratace snižuje výkon, přesáhne-li teplota pokožky 27 °C, a s každým dalším stupněm navíc dochází k poklesu výkonu o 1,5 % (Sawka, Cheuvront, & Kenefick, 2015).…”