Skin temperature modifies the impact of hypohydration on aerobic performance.

This study determined the effects of hypohydration on aerobic performance in compensable [evaporative cooling requirement (E(req)) < maximal evaporative cooling (E(max))] conditions of 10 degrees C [7 degrees C wet bulb globe temperature (WBGT)], 20 degrees C (16 degrees C WBGT), 30 degrees C (22 degrees C WBGT), and 40 degrees C (27 degrees C WBGT) ambient temperature (T(a)). Our hypothesis was that 4% hypohydration would impair aerobic performance to a greater extent with increasing heat stress. Thirty-two men [22 +/- 4 yr old, 45 +/- 8 ml.kg(-1).min(-1) peak O(2) uptake (Vo(2 peak))] were divided into four matched cohorts (n = 8) and tested at one of four T(a) in euhydrated (EU) and hypohydrated (HYPO, -4% body mass) conditions. Subjects completed 30 min of preload exercise (cycle ergometer, 50% Vo(2 peak)) followed by a 15 min self-paced time trial. Time-trial performance (total work, change from EU) was -3% (P = 0.1), -5% (P = 0.06), -12% (P < 0.05), and -23% (P < 0.05) in 10 degrees C, 20 degrees C, 30 degrees C, and 40 degrees C T(a), respectively. During preload exercise, skin temperature (T(sk)) increased by approximately 4 degrees C per 10 degrees C T(a), while core (rectal) temperature (T(re)) values were similar within EU and HYPO conditions across all T(a). A significant relationship (P < 0.05, r = 0.61) was found between T(sk) and the percent decrement in time-trial performance. During preload exercise, hypohydration generally blunted the increases in cardiac output and blood pressure while reducing blood volume over time in 30 degrees C and 40 degrees C T(a). Our conclusions are as follows: 1) hypohydration degrades aerobic performance to a greater extent with increasing heat stress; 2) when T(sk) is >29 degrees C, 4% hypohydration degrades aerobic performance by approximately 1.6% for each additional 1 degrees C T(sk); and 3) cardiovascular strain from high skin blood flow requirements combined with blood volume reductions induced by hypohydration is an important contributor to impaired performance.

[1]  Gary W. Mack,et al.  Exercise and Fluid Replacement , 1996 .

[2]  Paul B. Gastin,et al.  Energy System Interaction and Relative Contribution During Maximal Exercise , 2001, Sports medicine.

[3]  Richard R. Gonzalez,et al.  Mechanisms of Heat Exchange: Biophysics and Physiology , 2011 .

[4]  J A Faulkner,et al.  Temperature, skeletal muscle mitochondrial functions, and oxygen debt. , 1971, The American journal of physiology.

[5]  D. Wendt,et al.  Thermoregulation during Exercise in the Heat , 2007, Sports medicine.

[6]  N. Ramanathan,et al.  A NEW WEIGHTING SYSTEM FOR MEAN SURFACE TEMPERATURE OF THE HUMAN BODY. , 1964, Journal of applied physiology.

[7]  J. Leigh,et al.  Lactate efflux from exercising human skeletal muscle: role of intracellular PO2. , 1998, Journal of applied physiology.

[8]  D. B. Dill,et al.  Metabolic reactions to work in the desert. , 1967, Journal of applied physiology.

[9]  Robert Carter,et al.  Hypohydration impairs endurance exercise performance in temperate but not cold air. , 2005, Journal of applied physiology.

[10]  R. Fitts.  Cellular mechanisms of muscle fatigue. , 1994, Physiological reviews.

[11]  R. Meeusen,et al.  Exercise and Brain Neurotransmission , 1995, Sports medicine.

[12]  M. Febbraio,et al.  Effects of heat stress on physiological responses and exercise performance in elite cyclists. , 2000, Journal of science and medicine in sport.

[13]  Peter G. Martin,et al.  Reduced voluntary activation of human skeletal muscle during shortening and lengthening contractions in whole body hyperthermia , 2005, Experimental physiology.

[14]  D. Mitchell,et al.  Brain and abdominal temperatures at fatigue in rats exercising in the heat. , 1998, Journal of applied physiology.

[15]  R. Meeusen,et al.  Exercise, fatigue, neurotransmission and the influence of the neuroendocrine axis. , 2003, Advances in experimental medicine and biology.

[16]  Lars Nybo,et al.  Inadequate Cerebral Oxygen Delivery and Central Fatigue during Strenuous Exercise , 2007, Exercise and sport sciences reviews.

[17]  John M. Johnson,et al.  Cardiovascular Adjustments to Heat Stress , 2011 .

[18]  E. Coyle,et al.  Dehydration reduces cardiac output and increases systemic and cutaneous vascular resistance during exercise. , 1995, Journal of applied physiology.

[19]  Lars Nybo,et al.  Cerebral Changes During Exercise in the Heat , 2003, Sports medicine.

[20]  T M McLellan,et al.  Heat acclimation, aerobic fitness, and hydration effects on tolerance during uncompensable heat stress. , 1998, Journal of applied physiology.

[21]  Ronald G. Knowlton,et al.  Thermal and circulatory responses to repeated bouts of prolonged running. , 1979, Medicine and science in sports.

[22]  D. Costill,et al.  Calculation of percentage changes in volumes of blood, plasma, and red cells in dehydration. , 1974, Journal of applied physiology.

[23]  K. Cureton,et al.  Relation of heart rate to percent VO2 peak during submaximal exercise in the heat. , 2003, Journal of applied physiology.

[24]  A. Bartolozzi,et al.  Thermal Responses in Football and Cross-Country Athletes During Their Respective Practices in a Hot Environment. , 2004, Journal of athletic training.

[25]  L. Nybo,et al.  Middle cerebral artery blood velocity is reduced with hyperthermia during prolonged exercise in humans , 2001, The Journal of physiology.

[26]  W L Kenney,et al.  Age alters the cardiovascular response to direct passive heating. , 1998, Journal of applied physiology.

[27]  A. McComas,et al.  Extent of motor unit activation during effort. , 1981, Journal of applied physiology: respiratory, environmental and exercise physiology.

[28]  A. Cymerman,et al.  Intermittent hypoxic exposure does not improve endurance performance at altitude. , 2009, Medicine and science in sports and exercise.

[29]  D. Costill,et al.  Influence of diuretic-induced dehydration on competitive running performance. , 1985, Medicine and science in sports and exercise.

[30]  S C Gandevia,et al.  Reliability of measurements of muscle strength and voluntary activation using twitch interpolation , 1995, Muscle & nerve.

[31]  J. Bligh.  Temperature regulation in mammals and other vertebrates , 1973 .

[32]  J. Davis,et al.  Possible mechanisms of central nervous system fatigue during exercise. , 1997, Medicine and science in sports and exercise.

[33]  M. Sawka,et al.  Does dehydration impair exercise performance? , 2007, Medicine and science in sports and exercise.

[34]  J. Bligh.  MAMMALIAN HOMEOTHERMY : AN INTEGRATIVE THESIS , 1998 .

[35]  Gabrielle Todd,et al.  Hyperthermia: a failure of the motor cortex and the muscle , 2005, The Journal of physiology.

[36]  Lars Nybo,et al.  CNS fatigue and prolonged exercise: effect of glucose supplementation. , 2003, Medicine and science in sports and exercise.

[37]  L. Nybo,et al.  Hyperthermia and central fatigue during prolonged exercise in humans. , 2001, Journal of applied physiology.

[38]  M. Febbraio,et al.  Effect of Temperature on Muscle Metabolism During Submaximal Exercise in Humans , 1999, Experimental physiology.

[39]  B. Falk,et al.  The effect of heat exposure on performance of and recovery from high-intensity, intermittent exercise. , 1998, International journal of sports medicine.

[40]  M. Febbraio,et al.  Limits to Exercise Performance in the Heat , 1998, International journal of sports medicine.

[41]  E R Nadel,et al.  Effect of hydration state of circulatory and thermal regulations. , 1980, Journal of applied physiology: respiratory, environmental and exercise physiology.

[42]  Erich Gnaiger,et al.  Mitochondrial respiration at low levels of oxygen and cytochrome c. , 2001, Biochemical Society transactions.

[43]  J. González-Alonso.  Separate and Combined Influences of Dehydration and Hyperthermia on Cardiovascular Responses to Exercise , 1998, International journal of sports medicine.

[44]  José González-Alonso,et al.  Limitations to systemic and locomotor limb muscle oxygen delivery and uptake during maximal exercise in humans , 2005, The Journal of physiology.

[45]  Lars Nybo,et al.  Effects of hyperthermia on cerebral blood flow and metabolism during prolonged exercise in humans. , 2002, Journal of applied physiology.

[46]  L. Nybo,et al.  Effects of marked hyperthermia with and without dehydration on VO(2) kinetics during intense exercise. , 2001, Journal of applied physiology.

[47]  E. Coyle,et al.  Stroke volume decline during prolonged exercise is influenced by the increase in heart rate. , 1999, Journal of applied physiology.

[48]  N. Gledhill,et al.  Endurance athletes' stroke volume does not plateau: major advantage is diastolic function. , 1994, Medicine and science in sports and exercise.

[49]  C B Wenger,et al.  Physiological Responses to Acute Exercise-Heat Stress , 1988 .

[50]  K. Wesseling,et al.  Continuous cardiac output in septic shock by simulating a model of the aortic input impedance: a comparison with bolus injection thermodilution. , 1999, Anesthesiology.

[51]  R A Bruce,et al.  Reductions in cardiac output, central blood volume, and stroke volume with thermal stress in normal men during exercise. , 1966, The Journal of clinical investigation.

[52]  B. Saltin,et al.  Human circulatory and thermoregulatory adaptations with heat acclimation and exercise in a hot, dry environment. , 1993, The Journal of physiology.

[53]  J. V. van Lieshout,et al.  Cerebral blood flow and metabolism during exercise: implications for fatigue. , 2008, Journal of applied physiology.

[54]  José González-Alonso,et al.  Reductions in Systemic and Skeletal Muscle Blood Flow and Oxygen Delivery Limit Maximal Aerobic Capacity in Humans , 2003, Circulation.

[55]  N. Secher,et al.  Cerebral perturbations provoked by prolonged exercise , 2004, Progress in Neurobiology.

[56]  Jane A. Kent-Braun,et al.  Central and peripheral contributions to muscle fatigue in humans during sustained maximal effort , 1999, European Journal of Applied Physiology and Occupational Physiology.

[57]  W. L. Kenney,et al.  Control of skin blood flow during exercise. , 1992, Medicine and science in sports and exercise.

[58]  E. Coyle,et al.  Fluid and fuel intake during exercise , 2004, Journal of sports sciences.

[59]  L. Rowell,et al.  Hepatic clearance of indocyanine green in man under thermal and exercise stresses. , 1965, Journal of applied physiology.

[60]  B. Nielsen,et al.  Muscle blood flow is reduced with dehydration during prolonged exercise in humans , 1998, The Journal of physiology.

[61]  M. Sawka,et al.  Influence of hydration level and body fluids on exercise performance in the heat. , 1984, JAMA.

[62]  Lars Nybo,et al.  Hyperthermia and fatigue. , 2008, Journal of applied physiology.

[63]  M N Sawka,et al.  Thermal and Cardiovascular Strain from Hypohydration: Influence of Exercise Intensity , 1998, International journal of sports medicine.

[64]  W. Saris,et al.  Ingestion of branched‐chain amino acids and tryptophan during sustained exercise in man: failure to affect performance. , 1995, The Journal of physiology.

[65]  R. Maughan,et al.  Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man. , 1997, Medicine and science in sports and exercise.

[66]  L G Pugh,et al.  Rectal temperatures, weight losses, and sweat rates in marathon running. , 1967, Journal of applied physiology.

[67]  Louise M Burke,et al.  American College of Sports Medicine position stand. Exercise and fluid replacement. , 2007, Medicine and science in sports and exercise.

[68]  Samuel N Cheuvront,et al.  Evidence against a 40 degrees C core temperature threshold for fatigue in humans. , 2009, Journal of applied physiology.

[69]  P. Schrauwen,et al.  A new validated endurance performance test. , 2005 .

[70]  Albert Gjedde,et al.  Capillary-Oxygenation-Level-Dependent Near-Infrared Spectrometry in Frontal Lobe of Humans , 2007, Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism.

[71]  R. Maughan,et al.  Hyperprolactinaemia During Prolonged Exercise in the Heat: Evidence for a Centrally Mediated Component of Fatigue in Trained Cyclists , 2002, Experimental physiology.

[72]  R. Meeusen,et al.  Acute dopamine/noradrenaline reuptake inhibition enhances human exercise performance in warm, but not temperate conditions , 2005, The Journal of physiology.

[73]  Markus Amann,et al.  Arterial oxygenation influences central motor output and exercise performance via effects on peripheral locomotor muscle fatigue in humans , 2006, The Journal of physiology.

[74]  W F Taylor,et al.  Effect of high local temperature on reflex cutaneous vasodilation. , 1984, Journal of applied physiology: respiratory, environmental and exercise physiology.

[75]  Ross Tucker,et al.  The rate of heat storage mediates an anticipatory reduction in exercise intensity during cycling at a fixed rating of perceived exertion , 2006, The Journal of physiology.

[76]  P. A. Mason,et al.  Exercise in the heat is limited by a critical internal temperature. , 2000, Journal of applied physiology.

[77]  W. Willis,et al.  Mitochondrial function during heavy exercise. , 1994, Medicine and science in sports and exercise.

[78]  B. Nielsen,et al.  Brain activity and fatigue during prolonged exercise in the heat , 2001, Pflügers Archiv.

[79]  B Bigland-Ritchie,et al.  Central and peripheral fatigue in sustained maximum voluntary contractions of human quadriceps muscle. , 1978, Clinical science and molecular medicine.

[80]  M. Febbraio,et al.  Effect of heat stress on muscle energy metabolism during exercise. , 1994, Journal of applied physiology.

[81]  J A Dempsey,et al.  Effects of metabolic hyperthermia on performance during heavy prolonged exercise. , 1974, Journal of applied physiology.

[82]  E. Blomstrand,et al.  Amino acids and central fatigue , 2001, Amino Acids.

[83]  K. Brück,et al.  Body temperature related factors diminishing the drive to exercise. , 1987, Canadian journal of physiology and pharmacology.

[84]  Alan St Clair Gibson,et al.  Evidence for neuromuscular fatigue during high-intensity cycling in warm, humid conditions , 2001, European Journal of Applied Physiology.

[85]  B. Saltin,et al.  Body temperatures and sweating during exhaustive exercise. , 1972, Journal of applied physiology.

[86]  Romain Meeusen,et al.  Central Fatigue , 2006, Sports medicine.

[87]  K. Wesseling,et al.  Fifteen years experience with finger arterial pressure monitoring: assessment of the technology. , 1998, Cardiovascular research.

[88]  L. Mcnaughton,et al.  Effects of Differing Pedalling Speeds on the Power-Duration Relationship of High Intensity Cycle Ergometry , 1996, International journal of sports medicine.

[89]  E. Asmussen,et al.  Body Temperature and Capacity for Work , 1945 .

[90]  S. Shirreffs,et al.  The effect of acute branched-chain amino acid supplementation on prolonged exercise capacity in a warm environment , 2004, European Journal of Applied Physiology.

[91]  M. Sawka,et al.  Prior heat stress: effect on subsequent 15-min time trial performance in the heat. , 2009, Medicine and science in sports and exercise.

[92]  M. Sawka,et al.  Aerobic performance is degraded, despite modest hyperthermia, in hot environments. , 2010, Medicine and science in sports and exercise.

[93]  J. Saboisky,et al.  Exercise Heat Stress does not Reduce Central Activation to non‐exercised Human Skeletal Muscle , 2003, Experimental physiology.

[94]  Ross Tucker,et al.  Impaired exercise performance in the heat is associated with an anticipatory reduction in skeletal muscle recruitment , 2004, Pflügers Archiv.

[95]  B. Bigland-ritchie,et al.  Fatigue of intermittent submaximal voluntary contractions: central and peripheral factors. , 1986, Journal of applied physiology.

[96]  M. Sawka,et al.  Impact of a protective vest and spacer garment on exercise-heat strain , 2008, European Journal of Applied Physiology.

[97]  Shawnda Morrison,et al.  Passive hyperthermia reduces voluntary activation and isometric force production , 2004, European Journal of Applied Physiology.

[98]  Thomas Eberl,et al.  Control of mitochondrial and cellular respiration by oxygen , 1995, Journal of bioenergetics and biomembranes.

[99]  M. Sawka,et al.  Branched-chain amino acid supplementation and human performance when hypohydrated in the heat. , 2004, Journal of applied physiology.

[100]  Melissa M. Thomas,et al.  Voluntary muscle activation is impaired by core temperature rather than local muscle temperature. , 2006, Journal of applied physiology.

[101]  G. Lamb,et al.  Point:Counterpoint: Lactic acid accumulation is an advantage/disadvantage during muscle activity , 2006 .

[102]  Claus Jessen,et al.  Effects of brain and trunk temperatures on exercise performance in goats , 1986, Pflügers Archiv European Journal of Physiology.

[103]  E. Coyle,et al.  Water and carbohydrate ingestion during prolonged exercise increase maximal neuromuscular power. , 2000, Journal of applied physiology.

[104]  E. Coyle,et al.  Supine exercise restores arterial blood pressure and skin blood flow despite dehydration and hyperthermia. , 1999, The American journal of physiology.

[105]  W G Hopkins,et al.  Measures of Reliability in Sports Medicine and Science , 2000, Sports medicine.

[106]  P. Lachenbruch,et al.  Design Sensitivity: Statistical Power for Experimental Research. , 1989 .

[107]  D. Jones,et al.  Responses to exercise in the heat related to measures of hypothalamic serotonergic and dopaminergic function , 2003, European Journal of Applied Physiology.

[108]  L. Nybo,et al.  Elevations in core and muscle temperature impairs repeated sprint performance. , 2005, Acta physiologica Scandinavica.

[109]  B. Nielsen,et al.  Metabolic and thermodynamic responses to dehydration‐induced reductions in muscle blood flow in exercising humans , 1999, The Journal of physiology.

[110]  R. Meeusen,et al.  Exercise Performance is not Influenced by a 5-HT Reuptake Inhibitor , 2001, International journal of sports medicine.

[111]  M. Sawka,et al.  Expanded prediction equations of human sweat loss and water needs. , 2009, Journal of applied physiology.

[112]  M. Febbraio,et al.  Effect of ambient temperature on human skeletal muscle metabolism during fatiguing submaximal exercise. , 1999, Journal of applied physiology.

[113]  S. Bailey,et al.  Branched-chain amino acids prolong exercise during heat stress in men and women. , 1998, Medicine and science in sports and exercise.

[114]  Michael N. Sawka,et al.  Thermoregulatory Responses to Acute Exercise‐Heat Stress and Heat Acclimation , 2011 .

[115]  F. Pirnay,et al.  Maximal oxygen consumption in a hot environment. , 1970, Journal of applied physiology.

[116]  E. Coyle,et al.  Stroke volume during exercise: interaction of environment and hydration. , 2000, American journal of physiology. Heart and circulatory physiology.

[117]  F. Jensen,et al.  Influence of body temperature on the development of fatigue during prolonged exercise in the heat. , 1999, Journal of applied physiology.

[118]  P. G. Iatridis,et al.  Human Circulation: Regulation During Physical Stress , 1987 .

[119]  M. Pourcyrous,et al.  Hyperthermia increases cerebral metabolic rate and blood flow in neonatal pigs. , 1988, The American journal of physiology.

[120]  R. Meeusen,et al.  Inhibition of the preoptic area and anterior hypothalamus by tetrodotoxin alters thermoregulatory functions in exercising rats. , 2005, Journal of applied physiology.

[121]  J. Davis,et al.  Serotonin and central nervous system fatigue: nutritional considerations. , 2000, The American journal of clinical nutrition.

[122]  E. Coyle,et al.  Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise. , 1992, Journal of applied physiology.

[123]  J. González-Alonso.  Point: Stroke volume does/does not decline during exercise at maximal effort in healthy individuals. , 2008, Journal of applied physiology.