Increase in Skeletal-Muscle Glycogenolysis and Perceived Exertion With Progressive Dehydration During Cycling in Hydrated Men

Abstract

This study investigated the effects of progressive mild dehydration during cycling on whole-body substrate oxidation and skeletal-muscle metabolism in recreationally active men. Subjects (N = 9) cycled for 120 min at ~65% peak oxygen uptake (VO2peak 22.7 °C, 32% relative humidity) with water to replace sweat losses (HYD) or without fluid (DEH). Blood samples were taken at rest and every 20 min, and muscle biopsies were taken at rest and at 40, 80, and 120 min of exercise. Subjects lost 0.8%, 1.8%, and 2.7% body mass (BM) after 40, 80, and 120 min of cycling in the DEH trial while sweat loss was not significantly different between trials. Heart rate was greater in the DEH trial from 60 to 120 min, and core temperature was greater from 75 to 120 min. Rating of perceived exertion was higher in the DEH trial from 30 to 120 min. There were no differences in VO2, respiratory-exchange ratio, total carbohydrate (CHO) oxidation (HYD 312 ± 9 vs. DEH 307 ± 10 g), or sweat rate between trials. Blood lactate was significantly greater in the DEH trial from 20 to 120 min with no difference in plasma free fatty acids or epinephrine. Glycogenolysis was significantly greater (24%) over the entire DEH vs. HYD trial (433 ± 44 vs. 349 ± 27 mmol · kg-1 · dm-1). In conclusion, dehydration of <2% BM elevated physiological parameters and perceived exertion, as well as muscle glycogenolysis, during exercise without affecting whole-body CHO oxidation.

Maintaining hydration with a carbohydrate–electrolyte solution improves performance, thermoregulation, and fatigue during an ice hockey scrimmage

“…Only 2 players in the CES trial had a peak Tc greater than 39°C, compared with 8 players in NF. The 0.3°C difference in Tc is lower than the 0.5-0.6°C difference measured in studies of 2% dehydration during steady-state exercise in the laboratory (Logan-Sprenger et al 2012, 2013Baker et al 2007), but similar to the 0.4°C difference measured during a self-paced soccer game (Edwards et al 2007). During the same period that Tc was reaching its peak in the present study, players in the CES trial had increased skating speed and time at high effort.…”

“…Sweat rates in CES and NF were similar, while Tc was lower in CES, suggesting that there was increased heat transfer from the core of the body to the periphery in CES. Logan-Sprenger et al (2012, 2013 reported lower Tc in both men and women while cycling in a temperate environment while staying hydrated with water versus progressive mild dehydration, even though sweat rates were identical. During exercise, the cardiovascular system must provide adequate blood flow to the contracting muscles to maintain the exercise intensity and to the skin for adequate heat dissipation.…”

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

“…More recently, we reported a 24% increase in total muscle glycogen use over 2 h of cycling at 65% VO 2peak in male subjects dehydrated to 2.7% BM loss, with no difference in plasma [EPI] or the energy status of the muscle, but a greater Tc between trials (Logan-Sprenger et al. 2013a). There appears to be at least three potential mechanisms that may account for the upregulated glycogen phosphorylase (PHOS) activity and subsequent glycogen use with dehydration.…”

“…(Logan-Sprenger et al. 2013a, 2013b). However, Tc was significantly greater in DEH subjects with 1–2% BM loss.…”

“…The reality in sport is that the majority of athletes only replace ∼50% of sweat losses during exercise leading to significant fluid deficits, and as a result experiences amplified physiological responses compared to when drinking enough fluid to replace sweat losses (Burke 1997; Krause and Rodrigues-Krause 2011; Logan-Sprenger et al. 2013a, 2013b). …”