Title

Effect of exercise-induced hypohydration on body temperature and cycling time trial performance in the heat with adequate facing wind speed

Date of Award

1-1-2008

Degree Type

Thesis

Degree Name

Master of Science

School

School of Exercise, Biomedical and Health sciences

Faculty

Faculty of Computing, Health and Science

Abstract

"Background: Laboratory studies have shown during prolonged exercise that 2-3% dehydration can lead to greater increases of body temperature and cardiovascular work, altered metabolic function, and impaired exercise performance, compared to when no fluid deficit occurs. However, previous studies were conducted in relatively windless environments (i.e. wind speeds <12.9 km.h-1), whereas outdoors wind speeds may be five-fold greater during cycling, for example. Evaporative and convective cooling occurs more effectively when wind speeds are high, consequently physiological strain associated with dehydration is attenuated. Thus, 2-3% dehydration may not impair, cycling, performance when wind speeds are high. Previous studies have used oral rehydration, diuretics, or food and fluid restriction to manipulate hydration status; with these methods subjects can guess their hydration status based on how much they drink and/or how much they urinate. With intravenous infusion therapy, however, subjects cannot estimate how much fluid they lose and gain through drinking and urinating. Thus, IV infusion, compared to the other techniques, should minimize any preconceived assumptions about the effects of dehydration on performance. Purpose: Therefore, the purpose of this thesis was to investigate the effect of hydration status on cycling time trial performance in the heat when subjects were blinded to their hydration status using different levels of intravenous saline re-infusion and adequate facing wind speed. Methods: Ten endurance-trained male cyclists performed a combination of cycling and walking in the heat (37°C, 40% rh) until they lost 3% of their body mass. In a subject-blinded and randomly counterbalanced order, subjects were reinfused with a volume of saline so that they were either 0%, -2% or -3% of their starting body mass, and then completed a 25 km cycling time trial in the heat (33°C, 40% rh; wind speed 32 kmh1) Performance variables, heart rate, rectal temperature, haematocrit and perceptual variables were monitored. Results: Rectal temperature was significantly higher (38.91 ± 0.25°C vs. 38.61 ± 0.32°C; P<0.05) in the latter portion of the time trial in the -3% condition vs. the euhydrated condition. However, time to complete the time trial, heart rate, and all perceptual variables were not significantly different between trials. Calculated plasma volume change following the time trial was also significantly greater in the euhydrated vs. - 2% and -3% trials (16.4 ± 10.6% vs. 3.3 ± 9.0% and 3.3 ± 7.5%; P<0.05). Conclusion: The present study has shown that hydration status had no influence on 25 km cycle time trial performance in the heat under conditions of adequate facing wind speed. While core temperature was significantly higher in the -3% versus euhydrated conditions and plasma volume change was significantly greater in the euhydratcd vs. -2% and -3% trials, no other physiological variables were different between conditions. Suggesting that during a 25 km time trial cyclists can tolerate dehydration as high as -3% with no associated decrements in performance. " "Background: Laboratory studies have shown during prolonged exercise that 2-3% dehydration can lead to greater increases of body temperature and cardiovascular work, altered metabolic function, and impaired exercise performance, compared to when no fluid deficit occurs. However, previous studies were conducted in relatively windless environments (i.e. wind speeds <12.9 km.h-1), whereas outdoors wind speeds may be five-fold greater during cycling, for example. Evaporative and convective cooling occurs more effectively when wind speeds are high, consequently physiological strain associated with dehydration is attenuated. Thus, 2-3% dehydration may not impair, cycling, performance when wind speeds are high. Previous studies have used oral rehydration, diuretics, or food and fluid restriction to manipulate hydration status; with these methods subjects can guess their hydration status based on how much they drink and/or how much they urinate. With intravenous infusion therapy, however, subjects cannot estimate how much fluid they lose and gain through drinking and urinating. Thus, IV infusion, compared to the other techniques, should minimize any preconceived assumptions about the effects of dehydration on performance. Purpose: Therefore, the purpose of this thesis was to investigate the effect of hydration status on cycling time trial performance in the heat when subjects were blinded to their hydration status using different levels of intravenous saline re-infusion and adequate facing wind speed. Methods: Ten endurance-trained male cyclists performed a combination of cycling and walking in the heat (37°C, 40% rh) until they lost 3% of their body mass. In a subject-blinded and randomly counterbalanced order, subjects were reinfused with a volume of saline so that they were either 0%, -2% or -3% of their starting body mass, and then completed a 25 km cycling time trial in the heat (33°C, 40% rh; wind speed 32 kmh1) Performance variables, heart rate, rectal temperature, haematocrit and perceptual variables were monitored. Results: Rectal temperature was significantly higher (38.91 ± 0.25°C vs. 38.61 ± 0.32°C; P<0.05) in the latter portion of the time trial in the -3% condition vs. the euhydrated condition. However, time to complete the time trial, heart rate, and all perceptual variables were not significantly different between trials. Calculated plasma volume change following the time trial was also significantly greater in the euhydrated vs. - 2% and -3% trials (16.4 ± 10.6% vs. 3.3 ± 9.0% and 3.3 ± 7.5%; P<0.05). Conclusion: The present study has shown that hydration status had no influence on 25 km cycle time trial performance in the heat under conditions of adequate facing wind speed. While core temperature was significantly higher in the -3% versus euhydrated conditions and plasma volume change was significantly greater in the euhydratcd vs. -2% and -3% trials, no other physiological variables were different between conditions. Suggesting that during a 25 km time trial cyclists can tolerate dehydration as high as -3% with no associated decrements in performance. " "Background: Laboratory studies have shown during prolonged exercise that 2-3% dehydration can lead to greater increases of body temperature and cardiovascular work, altered metabolic function, and impaired exercise performance, compared to when no fluid deficit occurs. However, previous studies were conducted in relatively windless environments (i.e. wind speeds <12.9 km.h-1), whereas outdoors wind speeds may be five-fold greater during cycling, for example. Evaporative and convective cooling occurs more effectively when wind speeds are high, consequently physiological strain associated with dehydration is attenuated. Thus, 2-3% dehydration may not impair, cycling, performance when wind speeds are high. Previous studies have used oral rehydration, diuretics, or food and fluid restriction to manipulate hydration status; with these methods subjects can guess their hydration status based on how much they drink and/or how much they urinate. With intravenous infusion therapy, however, subjects cannot estimate how much fluid they lose and gain through drinking and urinating. Thus, IV infusion, compared to the other techniques, should minimize any preconceived assumptions about the effects of dehydration on performance. Purpose: Therefore, the purpose of this thesis was to investigate the effect of hydration status on cycling time trial performance in the heat when subjects were blinded to their hydration status using different levels of intravenous saline re-infusion and adequate facing wind speed. Methods: Ten endurance-trained male cyclists performed a combination of cycling and walking in the heat (37°C, 40% rh) until they lost 3% of their body mass. In a subject-blinded and randomly counterbalanced order, subjects were reinfused with a volume of saline so that they were either 0%, -2% or -3% of their starting body mass, and then completed a 25 km cycling time trial in the heat (33°C, 40% rh; wind speed 32 kmh1) Performance variables, heart rate, rectal temperature, haematocrit and perceptual variables were monitored. Results: Rectal temperature was significantly higher (38.91 ± 0.25°C vs. 38.61 ± 0.32°C; P<0.05) in the latter portion of the time trial in the -3% condition vs. the euhydrated condition. However, time to complete the time trial, heart rate, and all perceptual variables were not significantly different between trials. Calculated plasma volume change following the time trial was also significantly greater in the euhydrated vs. - 2% and -3% trials (16.4 ± 10.6% vs. 3.3 ± 9.0% and 3.3 ± 7.5%; P<0.05). Conclusion: The present study has shown that hydration status had no influence on 25 km cycle time trial performance in the heat under conditions of adequate facing wind speed. While core temperature was significantly higher in the -3% versus euhydrated conditions and plasma volume change was significantly greater in the euhydratcd vs. -2% and -3% trials, no other physiological variables were different between conditions. Suggesting that during a 25 km time trial cyclists can tolerate dehydration as high as -3% with no associated decrements in performance. " "Background: Laboratory studies have shown during prolonged exercise that 2-3% dehydration can lead to greater increases of body temperature and cardiovascular work, altered metabolic function, and impaired exercise performance, compared to when no fluid deficit occurs. However, previous studies were conducted in relatively windless environments (i.e. wind speeds <12.9 km.h-1), whereas outdoors wind speeds may be five-fold greater during cycling, for example. Evaporative and convective cooling occurs more effectively when wind speeds are high, consequently physiological strain associated with dehydration is attenuated. Thus, 2-3% dehydration may not impair, cycling, performance when wind speeds are high. Previous studies have used oral rehydration, diuretics, or food and fluid restriction to manipulate hydration status; with these methods subjects can guess their hydration status based on how much they drink and/or how much they urinate. With intravenous infusion therapy, however, subjects cannot estimate how much fluid they lose and gain through drinking and urinating. Thus, IV infusion, compared to the other techniques, should minimize any preconceived assumptions about the effects of dehydration on performance. Purpose: Therefore, the purpose of this thesis was to investigate the effect of hydration status on cycling time trial performance in the heat when subjects were blinded to their hydration status using different levels of intravenous saline re-infusion and adequate facing wind speed. Methods: Ten endurance-trained male cyclists performed a combination of cycling and walking in the heat (37°C, 40% rh) until they lost 3% of their body mass. In a subject-blinded and randomly counterbalanced order, subjects were reinfused with a volume of saline so that they were either 0%, -2% or -3% of their starting body mass, and then completed a 25 km cycling time trial in the heat (33°C, 40% rh; wind speed 32 kmh1) Performance variables, heart rate, rectal temperature, haematocrit and perceptual variables were monitored. Results: Rectal temperature was significantly higher (38.91 ± 0.25°C vs. 38.61 ± 0.32°C; P<0.05) in the latter portion of the time trial in the -3% condition vs. the euhydrated condition. However, time to complete the time trial, heart rate, and all perceptual variables were not significantly different between trials. Calculated plasma volume change following the time trial was also significantly greater in the euhydrated vs. - 2% and -3% trials (16.4 ± 10.6% vs. 3.3 ± 9.0% and 3.3 ± 7.5%; P<0.05). Conclusion: The present study has shown that hydration status had no influence on 25 km cycle time trial performance in the heat under conditions of adequate facing wind speed. While core temperature was significantly higher in the -3% versus euhydrated conditions and plasma volume change was significantly greater in the euhydratcd vs. -2% and -3% trials, no other physiological variables were different between conditions. Suggesting that during a 25 km time trial cyclists can tolerate dehydration as high as -3% with no associated decrements in performance. " "Background: Laboratory studies have shown during prolonged exercise that 2-3% dehydration can lead to greater increases of body temperature and cardiovascular work, altered metabolic function, and impaired exercise performance, compared to when no fluid deficit occurs. However, previous studies were conducted in relatively windless environments (i.e. wind speeds <12.9 km.h-1), whereas outdoors wind speeds may be five-fold greater during cycling, for example. Evaporative and convective cooling occurs more effectively when wind speeds are high, consequently physiological strain associated with dehydration is attenuated. Thus, 2-3% dehydration may not impair, cycling, performance when wind speeds are high. Previous studies have used oral rehydration, diuretics, or food and fluid restriction to manipulate hydration status; with these methods subjects can guess their hydration status based on how much they drink and/or how much they urinate. With intravenous infusion therapy, however, subjects cannot estimate how much fluid they lose and gain through drinking and urinating. Thus, IV infusion, compared to the other techniques, should minimize any preconceived assumptions about the effects of dehydration on performance. Purpose: Therefore, the purpose of this thesis was to investigate the effect of hydration status on cycling time trial performance in the heat when subjects were blinded to their hydration status using different levels of intravenous saline re-infusion and adequate facing wind speed. Methods: Ten endurance-trained male cyclists performed a combination of cycling and walking in the heat (37°C, 40% rh) until they lost 3% of their body mass. In a subject-blinded and randomly counterbalanced order, subjects were reinfused with a volume of saline so that they were either 0%, -2% or -3% of their starting body mass, and then completed a 25 km cycling time trial in the heat (33°C, 40% rh; wind speed 32 kmh1) Performance variables, heart rate, rectal temperature, haematocrit and perceptual variables were monitored. Results: Rectal temperature was significantly higher (38.91 ± 0.25°C vs. 38.61 ± 0.32°C; P<0.05) in the latter portion of the time trial in the -3% condition vs. the euhydrated condition. However, time to complete the time trial, heart rate, and all perceptual variables were not significantly different between trials. Calculated plasma volume change following the time trial was also significantly greater in the euhydrated vs. - 2% and -3% trials (16.4 ± 10.6% vs. 3.3 ± 9.0% and 3.3 ± 7.5%; P<0.05). Conclusion: The present study has shown that hydration status had no influence on 25 km cycle time trial performance in the heat under conditions of adequate facing wind speed. While core temperature was significantly higher in the -3% versus euhydrated conditions and plasma volume change was significantly greater in the euhydratcd vs. -2% and -3% trials, no other physiological variables were different between conditions. Suggesting that during a 25 km time trial cyclists can tolerate dehydration as high as -3% with no associated decrements in performance. " "Background: Laboratory studies have shown during prolonged exercise that 2-3% dehydration can lead to greater increases of body temperature and cardiovascular work, altered metabolic function, and impaired exercise performance, compared to when no fluid deficit occurs. However, previous studies were conducted in relatively windless environments (i.e. wind speeds <12.9 km.h-1), whereas outdoors wind speeds may be five-fold greater during cycling, for example. Evaporative and convective cooling occurs more effectively when wind speeds are high, consequently physiological strain associated with dehydration is attenuated. Thus, 2-3% dehydration may not impair, cycling, performance when wind speeds are high. Previous studies have used oral rehydration, diuretics, or food and fluid restriction to manipulate hydration status; with these methods subjects can guess their hydration status based on how much they drink and/or how much they urinate. With intravenous infusion therapy, however, subjects cannot estimate how much fluid they lose and gain through drinking and urinating. Thus, IV infusion, compared to the other techniques, should minimize any preconceived assumptions about the effects of dehydration on performance. Purpose: Therefore, the purpose of this thesis was to investigate the effect of hydration status on cycling time trial performance in the heat when subjects were blinded to their hydration status using different levels of intravenous saline re-infusion and adequate facing wind speed. Methods: Ten endurance-trained male cyclists performed a combination of cycling and walking in the heat (37°C, 40% rh) until they lost 3% of their body mass. In a subject-blinded and randomly counterbalanced order, subjects were reinfused with a volume of saline so that they were either 0%, -2% or -3% of their starting body mass, and then completed a 25 km cycling time trial in the heat (33°C, 40% rh; wind speed 32 kmh1) Performance variables, heart rate, rectal temperature, haematocrit and perceptual variables were monitored. Results: Rectal temperature was significantly higher (38.91 ± 0.25°C vs. 38.61 ± 0.32°C; P<0.05) in the latter portion of the time trial in the -3% condition vs. the euhydrated condition. However, time to complete the time trial, heart rate, and all perceptual variables were not significantly different between trials. Calculated plasma volume change following the time trial was also significantly greater in the euhydrated vs. - 2% and -3% trials (16.4 ± 10.6% vs. 3.3 ± 9.0% and 3.3 ± 7.5%; P<0.05). Conclusion: The present study has shown that hydration status had no influence on 25 km cycle time trial performance in the heat under conditions of adequate facing wind speed. While core temperature was significantly higher in the -3% versus euhydrated conditions and plasma volume change was significantly greater in the euhydratcd vs. -2% and -3% trials, no other physiological variables were different between conditions. Suggesting that during a 25 km time trial cyclists can tolerate dehydration as high as -3% with no associated decrements in performance. " "Background: Laboratory studies have shown during prolonged exercise that 2-3% dehydration can lead to greater increases of body temperature and cardiovascular work, altered metabolic function, and impaired exercise performance, compared to when no fluid deficit occurs. However, previous studies were conducted in relatively windless environments (i.e. wind speeds <12.9 km.h-1), whereas outdoors wind speeds may be five-fold greater during cycling, for example. Evaporative and convective cooling occurs more effectively when wind speeds are high, consequently physiological strain associated with dehydration is attenuated. Thus, 2-3% dehydration may not impair, cycling, performance when wind speeds are high. Previous studies have used oral rehydration, diuretics, or food and fluid restriction to manipulate hydration status; with these methods subjects can guess their hydration status based on how much they drink and/or how much they urinate. With intravenous infusion therapy, however, subjects cannot estimate how much fluid they lose and gain through drinking and urinating. Thus, IV infusion, compared to the other techniques, should minimize any preconceived assumptions about the effects of dehydration on performance. Purpose: Therefore, the purpose of this thesis was to investigate the effect of hydration status on cycling time trial performance in the heat when subjects were blinded to their hydration status using different levels of intravenous saline re-infusion and adequate facing wind speed. Methods: Ten endurance-trained male cyclists performed a combination of cycling and walking in the heat (37°C, 40% rh) until they lost 3% of their body mass. In a subject-blinded and randomly counterbalanced order, subjects were reinfused with a volume of saline so that they were either 0%, -2% or -3% of their starting body mass, and then completed a 25 km cycling time trial in the heat (33°C, 40% rh; wind speed 32 kmh1) Performance variables, heart rate, rectal temperature, haematocrit and perceptual variables were monitored. Results: Rectal temperature was significantly higher (38.91 ± 0.25°C vs. 38.61 ± 0.32°C; P<0.05) in the latter portion of the time trial in the -3% condition vs. the euhydrated condition. However, time to complete the time trial, heart rate, and all perceptual variables were not significantly different between trials. Calculated plasma volume change following the time trial was also significantly greater in the euhydrated vs. - 2% and -3% trials (16.4 ± 10.6% vs. 3.3 ± 9.0% and 3.3 ± 7.5%; P<0.05). Conclusion: The present study has shown that hydration status had no influence on 25 km cycle time trial performance in the heat under conditions of adequate facing wind speed. While core temperature was significantly higher in the -3% versus euhydrated conditions and plasma volume change was significantly greater in the euhydratcd vs. -2% and -3% trials, no other physiological variables were different between conditions. Suggesting that during a 25 km time trial cyclists can tolerate dehydration as high as -3% with no associated decrements in performance. " "Background: Laboratory studies have shown during prolonged exercise that 2-3% dehydration can lead to greater increases of body temperature and cardiovascular work, altered metabolic function, and impaired exercise performance, compared to when no fluid deficit occurs. However, previous studies were conducted in relatively windless environments (i.e. wind speeds <12.9 km.h-1), whereas outdoors wind speeds may be five-fold greater during cycling, for example. Evaporative and convective cooling occurs more effectively when wind speeds are high, consequently physiological strain associated with dehydration is attenuated. Thus, 2-3% dehydration may not impair, cycling, performance when wind speeds are high. Previous studies have used oral rehydration, diuretics, or food and fluid restriction to manipulate hydration status; with these methods subjects can guess their hydration status based on how much they drink and/or how much they urinate. With intravenous infusion therapy, however, subjects cannot estimate how much fluid they lose and gain through drinking and urinating. Thus, IV infusion, compared to the other techniques, should minimize any preconceived assumptions about the effects of dehydration on performance. Purpose: Therefore, the purpose of this thesis was to investigate the effect of hydration status on cycling time trial performance in the heat when subjects were blinded to their hydration status using different levels of intravenous saline re-infusion and adequate facing wind speed. Methods: Ten endurance-trained male cyclists performed a combination of cycling and walking in the heat (37°C, 40% rh) until they lost 3% of their body mass. In a subject-blinded and randomly counterbalanced order, subjects were reinfused with a volume of saline so that they were either 0%, -2% or -3% of their starting body mass, and then completed a 25 km cycling time trial in the heat (33°C, 40% rh; wind speed 32 kmh1) Performance variables, heart rate, rectal temperature, haematocrit and perceptual variables were monitored. Results: Rectal temperature was significantly higher (38.91 ± 0.25°C vs. 38.61 ± 0.32°C; P<0.05) in the latter portion of the time trial in the -3% condition vs. the euhydrated condition. However, time to complete the time trial, heart rate, and all perceptual variables were not significantly different between trials. Calculated plasma volume change following the time trial was also significantly greater in the euhydrated vs. - 2% and -3% trials (16.4 ± 10.6% vs. 3.3 ± 9.0% and 3.3 ± 7.5%; P<0.05). Conclusion: The present study has shown that hydration status had no influence on 25 km cycle time trial performance in the heat under conditions of adequate facing wind speed. While core temperature was significantly higher in the -3% versus euhydrated conditions and plasma volume change was significantly greater in the euhydratcd vs. -2% and -3% trials, no other physiological variables were different between conditions. Suggesting that during a 25 km time trial cyclists can tolerate dehydration as high as -3% with no associated decrements in performance. "

http://library.ecu.edu.au/record=b1684089


Link to Full Text

Share

 
COinS