The Different Effects of Fluid with and without Carbohydrate Ingestion on Subjective Responses of Untrained Men during Prolonged Exercise in a Hot Environment

Abstract

SummaryThis study examined the effects of maintaining euhydration by ingesting fluids with or without carbohydrate on subjective responses of untrained men during prolonged exercise in a hot environment. Six healthy untrained subjects completed 90 min of cycling exercises at 55% maximal oxygen consumption (V O 2 max ) in a hot environment (temperature: 28˚C, humidity: 50%) under three different experimental conditions. During the first trial, subjects did not ingest fluids during exercise (dehydration (DH) trial). In the second and third trials, subjects received mineral water (MW) and hypotonic fluid containing carbohydrate (HF), respectively, in amounts equaling their weight loss in the DH trial. At the end of exercise, the overall rating of perceived exertion (RPE-O) was lower in the MW and HF trials than in the DH trial (14.3 Ϯ 1.0 and 13.7 Ϯ 0.6 vs 17.7 Ϯ 1.0, p Ͻ 0.05, respectively). RPEcardiovascular and RPE-legs were lower at the end of exercise in the HF trial compared with the DH trial. V O 2 , heart rate (HR), and rectal temperature increased during exercise in the three trials. At the end of exercise, the drift in V O 2 was lower in the MW and HF trials than in the DH trial (304 Ϯ 41 and 339 Ϯ 40 vs 458 Ϯ 33 mL, p Ͻ 0.05, respectively). HR at the end of exercise in the HF trial was lower than in the DH trial (158 Ϯ 5 vs 173 Ϯ 7 bpm, p Ͻ 0.05). These results suggest that maintaining euhydration during prolonged exercise in untrained men could attenuate RPE-O and that hypotonic electrolyte-carbohydrate solution could attenuate RPE-legs during exercise. Key Words maintaining euhydration, perceived exertion, prolonged exercise, heat exposure Dehydration, hyperthermia and muscle glycogen depletion are the major determinant factors that induce the reduction of performance during prolonged exercise. Fluid ingestion, especially in a hot environment, attenuates hyperthermia and cardiovascular drift ( 1-4 ), and carbohydrate ingestion reduces the rating of perceived exertion (RPE) during prolonged exercise in endurance-trained subjects ( 5-10 ). However, there is no available data about the physiological and subjective benefits of maintaining body water by ingesting fluid with or without carbohydrate supplementation during prolonged submaximal exercise in untrained healthy subjects.Maintaining euhydration by fluid ingestion attenuates cardiovascular strain induced by both hyperthermia and dehydration during prolonged submaximal exercise in the heat ( 2-4 ). Gonzalez-Alonso et al. suggested that despite a marked cardiovascular drift at the 120 min of exercise, corresponding to ~60% maximal oxygen consumption (V O 2 max ) in a dehydration trial, the increase in V O 2 for exercising and nonexercising muscle of the whole body was similar to a euhydration trial ( 2 ). Additionally, it has been demonstrated that during prolonged exercise an increase in carbohydrate availability by carbohydrate supplementation attenuated RPE ( 8 , 9 , 11 ) while fluid ingestion did not attenuate the RPE ( 4 , 12 ). However, these stu...

Effects of Dehydration during Cycling on Skeletal Muscle Metabolism in Females

“…Similar results have been reported in other studies investigating the effects of progressive dehydration on RPE (16,20). It is speculated that hypovolemia associated with exercise dehydration leading to a reduction in brain blood flow may exasperate the displeasure associated with exercising without fiuid leading to greater perceived exertion (18). More simply, it may be that the elevations in Tc, HR, and reduced Pvol in the DEH trial are sensed, and the feedback to the brain results in the greater RPE during exercise at the same relative intensity in a mildly dehydrated state.…”

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

“…In this study, RPE became significantly higher in the DEH trial after only 30 min of cycling when subjects had lost <1% body mass. Similar results have been reported in other studies investigating the effects of progressive dehydration on RPE (Ishijima et al, 2009;McGregor, Nicholas, Lakomy, & Williams, 1999). It is speculated that hypovolumia associated with exercise dehydration leading to a reduction in brain blood flow may exacerbate the sense of effort associated with exercising without fluid leading to greater perceived exertion (Maughan, Shirreffs, & Watson, 2007).…”

The effect of a carbohydrate beverage on the physiological responses during prolonged load carriage

“…These data support the contention that consuming a volume of fluid equal to sweat losses attenuates cardiovascular drift. Ishijima et al (2009) data also suggest that fluid replacement alone (i.e. with no carbohydrate) may reduce _ VO 2 drift, the effect of which was not measured in the present study.…”

“…In addition, body mass changes do not necessarily reflect a measure of hydration status (Maughan et al 2007). Ishijima et al (2009) showed that during 90 min of cycling at 55% _ VO 2max drinking a hypotonic carbohydrate beverage or mineral water equal to the volume of estimated sweat loss (1.92 ± 0.02 L) reduced cardiovascular and _ VO 2 drift compared with no fluid consumption. These data support the contention that consuming a volume of fluid equal to sweat losses attenuates cardiovascular drift.…”