Effect of hydration state on strength, power, and resistance exercise performance

PURPOSE: Although many studies have attempted to examine the effect of hypohydration on strength, power, and high-intensity endurance, few have successfully isolated changes in total body water from other variables that alter performance (e.g., increased core temperature), and none have documented the influence of hypohydration on an isotonic, multiset, multirepetition exercise bout typical of resistance exercise training. Further, no investigations document the effect of hypohydration on the ability of the central nervous system to stimulate the musculature, despite numerous scientists suggesting this possibility. The purposes of this study were to examine the isolated effect of hydration state on 1) strength, power, and the performance of acute resistance exercise, and 2) central activation ratio (CAR). METHODS: Seven healthy resistance-trained males (age = 23 +/- 4 yr, body mass = 87.8 +/- 6.8 kg, body fat = 11.5 +/- 5.2%) completed three resistance exercise bouts in different hydration states: euhydrated (EU), hypohydrated by approximately 2.5% body mass (HY25), and hypohydrated by approximately 5.0% body mass (HY50). Investigators manipulated hydration status via exercise-heat stress and controlled fluid intake 1 d preceding testing. RESULTS: Body mass decreased 2.4 +/- 0.4 and 4.8 +/- 0.4% during HY25 and HY50, respectively. No significant differences existed among trials in vertical jump height, peak lower-body power (assessed via jump squat), or peak lower-body force (assessed via isometric back squat). CAR tended to decrease as hypohydration increased (EU = 95.6 +/- 4.9%, HY25 = 94.0 +/- 3.1%, HY50 = 92.5 +/- 5.1%; P = 0.075, eta(p)(2) = 0.41). When evaluated as a function of the percentage of total work completed during a six-set back squat protocol, hypohydration significantly decreased resistance exercise performance during sets 2-3 and 2-5 for HY25 and HY50, respectively. CONCLUSION: These data indicate that hypohydration attenuates resistance exercise performance; the role of central drive as the causative mechanism driving these responses merits further research.     

Pre-exercise carbohydrate status influences carbohydrate-mediated attenuation of post-exercise cytokine responses

Most studies investigating the effects of acute carbohydrate (CHO) ingestion on post-exercise cytokine responses have involved fasted athletes. This study characterised the effects of acute CHO beverage ingestion preceded by consumption of a CHO-containing pre-exercise meal. Sixteen highly-trained male cyclists/triathletes (age: 30.6 +/- 5.6 y; V O (2max): 64.8 +/- 4.7 ml . kg . min (-1) [mean +/- SD]) undertook two cycle ergometry trials involving randomised consumption of a 10 % CHO beverage (15 mL . kg (-1) . hr (-1)) or water (H (2)O). Trials were undertaken 2 h after a breakfast providing 2.1 g CHO . kg (-1) body mass (BM) (48 kJ . kg (-1) BM) and consisted of 100 min steady state cycle ergometry at 70 % V O (2max) followed by a time trial of approximately 30 min duration. Blood samples were collected pre-, post- and 1 h post-exercise for measurement of Interleukin (IL)-6, IL-8, IL-10 and IL-1ra. Time-trial performance was not substantially different between CHO and H (2)O trials (4.5 %, p = 0.42). Neither IL-6 nor IL-8 responses were substantially reduced in the CHO compared to the H (2)O trial. There was a substantial reduction in IL-10 (32 %, p = 0.05) and IL-1ra (43 %, p = 0.02) responses at 1 h post-exercise with CHO compared to H (2)O ingestion. In conclusion, the previously shown attenuating effects of CHO ingestion during exercise on cytokine responses appear reduced when athletes consume a CHO-containing pre-exercise meal.     

Human intravascular immunoglobulin responses to exercise-heat and hypohydration

Several investigators have suggested that prolonged exercise and hypohydration alter the intravascular mass of immunoglobulins. Those studies, however, have methodological concerns which make generalizations from their data very tenuous. This study examined the effects of prolonged moderate intensity exercise in the heat and hypohydration on changes in the intravascular mass of immunoglobulins. Five heat-acclimated males attempted two Heat Stress Tests (HSTs). One HST was completed when subjects were euhydrated and the other HST when subjects were hypohydrated (-5% from base line body weight). The HSTs consisted of 30 min of rest in a 20 degrees C antechamber, followed by a 120-min exposure (2 repeats of 15 min rest and 45 min walking) in a hot (35 degrees C, 45% rh) environment. The following observations were made concerning immunoglobulin responses to hypohydration and exercise-heat stress: a) the changes in concentrations (mg.dl-1) of the measured immunoglobulins were often a reflection of changes in the plasma volume; b) hypohydration increased the intravascular mass (g) of the complement enzyme C3 during resting conditions, but did not alter the intravascular mass of IgG, IgA, and IgM, and c) prolonged treadmill exercise in the heat, when either euhydrated or hypohydrated, did not alter the intravascular mass of IgG, IgA, IgM, and C3. These data indicate that the intravascular mass of immunoglobulins does not change during prolonged moderate intensity exercise in the heat, and that hypohydration results in a translocation of C3 to the intravascular space. In addition, these data indicate that immunoglobulins do not provide a stress index for hypohydration.     

Aerobic fitness and the hypohydration response to exercise-heat stress

This study examined the influence that aerobic fitness (VO2 max) had on final heart rate (HR), final rectal temperature (Tre), and total body sweat rate (Msw) when subjects exercised while euhydrated and hypohydrated (-5.0% from baseline body weight). Eight male and six female subjects completed four exercise tests both before and after a 10-d heat acclimation program. The tests were a euhydration and a hypohydration exposure conducted in a comfortable (20 degrees C, 40% rh) and in a hot-dry (49 degrees C, 20% rh) environment. Significant differences were not generally found between the genders for HR, Tre and Msw during the tests. In the comfortable environment, HR, Tre and Msw were not generally significantly correlated (p greater than 0.05) with VO2max. In the hot-dry environment, Tre and VO2max were significantly correlated (r = -0.58) when euhydrated before acclimation. HR was significantly related to VO2max before acclimation when eu- (r = -0.61) and hypohydrated (r = -0.60) as well as after acclimation when eu- (r = -0.57) and hypohydrated (r = -0.67). These data indicate that, when euhydrated in the heat, aerobic fitness provides cardiovascular and thermoregulatory benefits before acclimation, but only cardiovascular benefits after acclimation. However, when hypohydrated in the heat, cardiovascular benefits are present for fit subjects both before and after acclimation, but thermoregulatory benefits are not associated with fitness.     

Effects of pyridostigmine bromide on physiological responses to heat, exercise, and hypohydration.

Five men underwent eight heat stress tests (HSTs) at 35 degrees C, each consisting of four 25-min treadmill walks (35% Vo2max), separated by 5-min rests, in four conditions: 1) 20% relative humidity (rh), subjects euhydrated and drinking ad libitum; 2) 20% rh, euhydrated; 3) 75% rh, euhydrated; and 4) 20% rh, hypohydrated 3% of body weight. In Conditions 2-4 subjects drank during the walks to maintain their pre-HST weight. In each condition we tested subjects once after 30 mg pyridostigmine bromide (PB) by mouth and once after placebo. PB lowered heart rate a mean of 3 beats/min overall, most with hypohydration. PB did not significantly affect rectal temperature (Tre), but reduced the rise in Tre during hypohydrated exercise. In Condition 2, chest skin temperature decreased more during exercise with PB. PB had no significant effect on other skin temperatures, sweating, hematocrit, hemoglobin, total plasma protein, osmolality, ad libitum drinking, rate of O2 uptake, or subject ratings of temperature, discomfort, or exertion. PB thus had little effect on physiological responses to moderate exercise-heat stress.     

Plasma beta-endorphin immunoreactivity during graded cycle ergometry

The present study was undertaken to define the response of plasma beta-endorphin immunoreactivity (ir-BE) to exercise of increasing intensity. Nineteen healthy males performed continuous exercise for 32 min on a cycle ergometer, comprised of 8-min bouts at %VO2max approximating 25, 50, and 75% of maximal exercise. Venous blood samples were collected before exercise (T = -20 and 0 min), during exercise (T = 8, 16, 24, and 32 min), and in recovery (T = +15, +30 min). Ir-BE in plasma was measured by radioimmunoassay using Immuno Nuclear assay kits. Plasma ir-BE level (pg X ml-1) was not altered from pre-exercise (18.3 +/- 1.3) after 8 min of exercise at 25 and 50% VO2max intensity; however, ir-BE rose significantly after 8 min of 75% VO2max work intensity (27.1 +/- 2.4) and was further elevated at maximal exercise (74.1 +/- 8.6). Ir-BE level remained elevated 15 min (60.9 +/- 8.1) and 30 min (35.2 +/- 5.2) post-exercise. The response pattern was further characterized by a significant (P less than 0.05) inter-individual variation, both at rest and during exercise; also, regression analysis indicated the ir-Be levels attained at maximal exercise were inversely related to the relative VO2max (ml X kg-1 X min-1) of the subject (predicted ir-BE = 248.2 - 3.39 VO2max; r = -0.397, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypohydration and acclimation: effects on hormone responses to exercise/heat stress

This study was designed to assess the effects of hypohydration (-5% body weight) and heat acclimation on plasma cortisol (PC) and growth hormone (GH) responses to exercise (1.34 m X s-1) in a hot-wet (35 degrees C, 79% rh) or hot-dry (49 degrees C, 20% rh) environment. Preacclimation, hypohydration in both the hot-wet and hot-dry environments resulted in significant (p less than 0.05) increments in PC levels during the fourth exercise interval. Acclimation had no effects on PC levels in the euhydrated condition, but in the hot-wet environment there did occur an attenuation of the PC response when hypohydrated. Preacclimation exercise in either the hot-wet or hot-dry environment resulted in significant (p less than 0.05) increments in GH when euhydrated. While the effects of acclimation were inconsistent, hypohydration generally resulted in elevated levels of GH compared to euhydration. We concluded from these studies that hypohydration to -5% of body weight generally elicited elevations in circulating levels of stress hormones, and that acclimation did not effect consistent decrements in these responses.     

Previous-day hypohydration impairs skill performance in elite female field hockey players

The purpose of this study was to determine the effects of 2% hypohydration on skill performance in elite female field hockey players following intermittent exercise in the heat. Eight elite female field hockey players performed 50 min of a field hockey-specific intermittent treadmill running protocol (FHITP) in hot environmental conditions (33 °C, 60% relative humidity) in different hydration states: euhydrated (EUH) and hypohydrated by 2% body mass (HYPO). Hydration status was manipulated via a period (121±10 min) of passive hyperthermia (40 °C, 75% relative humidity) and controlled fluid intake 1 day preceding testing. Ad libitum fluid intake was permitted throughout both trials. Field hockey skill tests were performed pre- and post-FHITP. Skill performance time increased (P=0.029) in the HYPO trial compared with the EUH trial, which may be attributed to an increase in penalty time (P=0.024). Decision-making time increased (P=0.008) in the HYPO trial and was significantly impaired compared with EUH (P=0.016) pre-FHITP. Ad libitum drinking appeared to be sufficient to maintain decision-making performance as no interaction effects were evident post-FHITP. Players who commence match-play in a state of hypohydration may be susceptible to decrements in skill and decision-making performance.     

Acute hormonal responses in elite junior weightlifters.

To date, no published studies have demonstrated resistance exercise-induced increases in serum testosterone in adolescent males. Furthermore, few data are available on the effects of training experience and lifting performance on acute hormonal responses to weightlifting in young males. Twenty-eight junior elite male Olympic-style weightlifters (17.3 +/- 1.4 yrs) volunteered for the study. An acute weightlifting exercise protocol using moderate to high intensity loads and low volume, characteristic of many weightlifting training sessions, was examined. The exercise protocol was directed toward the training associated with the snatch lift weightlifting exercise. Blood samples were obtained from a superficial arm vein at 7 a.m. (for baseline measurements), and again at pre-exercise, 5 min post-, and 15 min post-exercise time points for determination of serum testosterone, cortisol, growth hormone, plasma beta-endorphin, and whole blood lactate. The exercise protocol elicited significant (p less than or equal to 0.05) increases in each of the hormones and whole blood lactate compared to pre-exercise measures. While not being significantly older, subsequent analysis revealed that subjects with greater than 2 years training experience exhibited significant exercise-induced increases in serum testosterone from pre-exercise to 5 min post-exercise (16.2 +/- 6.2 to 21.4 +/- 7.9 nmol.l-1), while those with less than or equal to 2 years training showed no significant serum testosterone differences. None of the other hormones or whole blood lactate appear to be influenced by training experience.(ABSTRACT TRUNCATED AT 250 WORDS)     

Heat shock protein (HSP-72) levels in skeletal muscle following work in heat

INTRODUCTION: Acute bouts of heat stress and exercise have been shown to independently increase heat shock protein levels; however, the combination of these two stressors on HSP-72 expression in human skeletal muscle has not been established. The purpose of this study was to determine the effect of a bout of exercise in the heat on HSP-72 expression. METHODS: There were eight recreationally active men (Age = 26.4 +/- 3.1 yr, V(O2)peak = 4.01 +/- 0.25 L min(- 1)) who completed two 30-min bouts of cycle ergometry at 75% of V(O2)peak in a hot (39 degrees C; RH 30%) and cold (9 degrees C; RH 61%) environment. Muscle biopsies were obtained from the vastus lateralis prior to, 6 h post, and 24 h post-exercise to measure HSP-72 protein. Core rectal temperature (Tc), average skin temperature (T(SK)), intramuscular temperature (T(IM)), heart rate (HR), oxygen uptake (V(O2)), sweat rate (SR), and plasma cortisol were measured to determine thermal loads. RESULTS: No significant interactions were present between V(O2) (2.80 +/- 0.2 vs. 2.65 +/- 0.1 L min(-1)) or plasma cortisol (27.1 +/- 2 vs. 19.2 +/- 4 microg dl(-1)) when comparing HT and CD. HR (184 +/- 5 vs. 159 +/- 7 bpm), T(IM) (40.7 +/- 0.2 vs. 40.0 +/- 0.2 degrees C), Tc (38.3 +/- 0.2 vs. 37.9 +/- 0.1 degrees C), T(SK) (36.7 +/- 0.2 vs. 29.6 +/- 0.8 degrees C), and SR (2.0 +/- 0.2 vs. 1.2 +/- 0.2 L h(-1)) were significantly greater when comparing HT and CD. HSP-72 was not altered as a result of either treatment (4.04 +/- 0.87 vs. 2.91 +/- 1.58 ng microg(-1) protein for HT and CD at 6 h post-exercise). DISCUSSION: Exercise in the heat produced a greater thermal load than exercise in the cold; however, no significant increases in HSP-72 were seen when comparing hot and cold conditions.     

Thirst sensations and AVP responses at rest and during exercise-cold exposure

PURPOSE: The purpose of this study was to 1) determine the effect of hypohydration (HYPO) on thirst sensations during moderate exercise in the cold and 2) determine a possible mechanism for a cold-induced decline in thirst. METHODS: In the first phase of the study, eight males walked on four occasions, in T-shirts, shorts, and shoes, at 50% VO2max, for 60 min in either a 4 degrees C (cold) or 27 degrees C (temperate) environment in a state of HYPO or euhydration (EU). In the second phase, nine males in states of EU or HYPO randomly performed four trials consisting of 30 min standing at 27 degrees C, followed by 30 min of standing and 30 min of treadmill exercise at 50% of VO2max, in either 4 degrees C or 27 degrees C air. RESULTS: In phase 1, thirst sensations were lower throughout 60 min of exercise (P < 0.05) in both HYPO and EU conditions during the cold trials. In phase 2, despite elevated plasma osmolality (P < 0.05), perception of thirst and plasma arginine vasopressin [AVP] similarly decreased (P < 0.05) after 30-min standing rest and 30-min exercise in the HYPO-cold trial, compared with the HYPO-temperate, EU-cold, and EU-temperate trials. CONCLUSIONS: When either euhydrated or hypohydrated, cold exposure attenuated thirst by up to 40% at rest and during moderate-intensity exercise. The attenuated thirst when hypohydrated during cold exposure was associated with lower plasma [AVP] despite an elevated plasma osmolality. This decline in thirst and AVP in the cold may be the result of peripheral vasoconstriction, mediating an increase in central blood volume and stimulation of central volume receptors.     

Exercise intensity and erythrocyte 2,3-diphosphoglycerate concentration

The present study examines the acute effects of two different exercise intensities on erythrocyte 2,3-diphosphoglycerate (2,3-DPG) concentration. Thirty-one females (X +/- SD age = 23.7 +/- 3.37 yr; VO2max = 44.3 +/- 5.40 ml X kg-1 X min-1) completed 2 separate 15-min constant load cycling tests at exercise intensities representing 35 and 75% of VO2max. Venous blood was obtained pre-exercise (PRE), immediately post-exercise (POST), 15 min post-exercise (POST15), and 30 min post-exercise (POST30) to determine lactic acid, 2,3-DPG, and hemoglobin concentrations and hematocrit. Significant increases (P less than 0.01) in lactic acid concentration (1.1 +/- 0.14 at PRE to 6.2 +/- 0.48 m X mol-1 X l-1 at POST), 2,3-DPG concentration (1.9 +/- 0.06 at PRE to 2.1 +/- 0.06 mumol X ml-1 at POST), and 2,3-DPG corrected for plasma volume shift (PVC 2,3-DPG) (1.9 +/- 0.06 at PRE to 2.4 +/- 0.07 mumol X ml-1 at POST15) were observed only following the 75% submaximal exercise. At POST30 (75% VO2max) PVC 2,3-DPG and lactic acid remained 5.3 and 97% (P less than 0.05) above baseline, respectively. An exercise intensity effect was observed only in lactic acid response (P less than 0.05) but not in 2,3-DPG (mumol X ml-1 and mumol X g-1 hemoglobin or PVC 2,3-DPG. A significant time-intensity interaction (P less than 0.05) for PVC 2,3-DPG suggests that PVC 2,3-DPG response over time was different between the two exercise intensity levels, with the 75% intensity eliciting a greater increase in PVC 2,3-DPG.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of exercise intensity on serum lipoprotein responses

The purpose of this study was to determine the effect of exercise intensity on lipoprotein responses. Eleven normolipidemic male volunteers (X +/- SD = 23.1 +/- 2.4) participated in the study. The subjects were assessed for VO2max and ventilatory threshold (VT), matched for VO2max and then randomly assigned to one of two groups: Group A, which exercised for 12 minutes at an intensity 15% below VT (n = 5), and Group B, which exercised for 12 minutes at an intensity 15% above VT (n = 6). The lipoprotein measures HDL-C, LDL-C, total cholesterol (TC), and triglycerides (TG) were assessed from blood samples taken pre-exercise and immediately post-exercise as well as one, 24, and 48 hours post-exercise. A 2 X 5 split plot ANCOVA (controlling for pre-exercise values), revealed no significant differences between groups for HDL-C, TC or LDL-C. However, when means were collapsed across groups, TC levels measured immediately post-exercise were significantly higher than those taken 24 and 48 hours post-exercise (168.0, 159.1, and 159.9 mg.dl-1, respectively; p less than 0.05). A significant interaction was found for the TG measurements. For Group A, TG levels were elevated immediately post-exercise, but decreased significantly at the 1 and 24 hours post-exercise sampling, before returning to baseline levels at the 48 hour post-exercise measurement (93.2 +/- 3.1, 69.5 +/- 4.2, 66.8 +/- 6.7 and 99.5 +/- 2.1 mg.dl-1, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of exercise training on salivary immunoglobulin A and cortisol responses to maximal exercise.

The salivary immunoglobulin A (s-IgA) and cortisol responses to maximal exercise were examined in 24 adult males (X +/- SD; 22.1 +/- 3.0 yrs) before and after 10 weeks of run training. The subjects performed an incremental treadmill test to exhaustion and were randomly assigned to one of three groups: control (CON; n = 5), low intensity training (LO; n = 8), or high intensity training (HI; n = 11). Following the ten weeks of training, the subjects performed a second maximal treadmill test. Saliva samples were collected before, as well as immediately and 1 hr following each of the maximal treadmill tests and were analyzed for s-IgA and salivary cortisol. Maximal oxygen consumption (VO2max) increased significantly (p < 0.05) in the LO and HI groups but remained unchanged in the CON group. The s-IgA levels decreased significantly (p < 0.05) immediately post-exercise but returned to pre-exercise levels by one hour recovery. In addition, s-IgA and cortisol levels were not significantly (p > 0.05) correlated at any of the sampling times. These findings indicated that the s-IgA response to maximal exercise was unaffected by moderate (70% of VO2 max) to heavy (86% of VO2max) training (designed to develop cardiorespiratory fitness in healthy non-athletic adults) and independent of salivary cortisol.     

Intermittent running: muscle metabolism in the heat and effect of hypohydration.

PURPOSE: This study reports two studies that investigated the reason for a poorer intermittent supramaximal running performance previously found in the heat (Maxwell et al., The effect of climatic heat stress on intermittent supramaximal running performance in humans. Exp. Physiol. 81:833-845, 1996). The first study tested the hypothesis that it was due to different rates of substrate metabolism. The second study tested whether a greater level of hypohydration led to an earlier exhaustion time. METHODS: A maximal anaerobic running test (MART) was the exercise model used. This involved repeated 20-s runs, each at increasing intensities, with 100 s of passive recovery between runs. RESULTS: In study 1, eight male subjects performed the MART on two occasions at either 32.8+/-0.3 degrees C, 80.5+/-1.6% relative humidity (RH), or 21.3+/-0.4 degrees C, 48.8+/-2.2% RH. Needle biopsy samples were taken from the vastus lateralis muscle before and immediately after the MART. In study 2, 11 male subjects performed the MART in a moderately hypohydrated (HYPO) and euhydrated (EUH) state while in a cool environment. In study 1, performance was significantly worse in the hot compared with the cool environment (138+/-7 vs. 150+/-6 s, respectively, P<0.05). No differences were observed in the change in muscle glycogen (100.3+/-15.1 vs. 107.0+/-15.6 mmol glucosyl units x kg dry muscle(-1)) or muscle lactate (102.9+/-18.2 vs. 100.5+/-16.6 mmol x kg dry muscle(-1)) between the hot and cool environments, respectively. In study 2, performance was worse in the HYPO (148+/-9 s) compared with the EUH (154+/-9 s) trial (P<0.05). CONCLUSIONS: These results indicate that a reduced intermittent supramaximal running performance in the heat is not caused by greater muscle glycogenolysis or lactate accumulation. Further, a poorer intermittent sprinting performance is experienced in a hypohydrated compared with a euhydrated state.     

Neutrophil degranulation response to 2 hours of exercise in a 30 degrees C environment

INTRODUCTION: Evidence supports an interaction between neuro-endocrine responses to exercise and immune responses to exercise. We hypothesized that prolonged exercise in the heat would evoke a greater stress hormone response and a greater decrease in neutrophil degranulation [lipopolysaccharide (LPS)-stimulated elastase release] than when the same exercise was performed in thermoneutral conditions. METHODS: In counterbalanced order and separated by 7 d, 13 male cyclists cycled for 2 h at 62 +/- 3% VO2max (mean +/- SEM), with ad libitum water intake, on one occasion with heat (HOT: 30.3 degrees C, 76% RH) and on another occasion without (CONTROL: 20.4 degrees C, 60% RH). Venous blood samples were collected at pre-, post-, and 2 h post-exercise. RESULTS: Exercising HR, rating of perceived exertion, rectal temperature, corrected body mass loss, and plasma cortisol at post- and 2 h post-exercise were greater during HOT. A marked neutrophilia was evident at post- and 2 h post-exercise with no difference between trials. LPS-stimulated elastase release per neutrophil decreased post-exercise with no difference between trials (pre-exercise: HOT 189 +/- 20 and CONTROL 210 +/- 32; post-exercise: HOT 127 +/- 18 and CONTROL 136 +/- 29 fg x cell(-1)). There was no effect of exercise or trial on neutrophil CD11b expression (neutrophil activation index) or band cell percentage (neutrophil maturity index). CONCLUSIONS: Prolonged exercise results in a decrease in neutrophil degranulation that is unaffected by performing the exercise in hot conditions despite the increase in physiological stress. Additionally, these data suggest that the decrease in neutrophil degranulation after prolonged exercise is not associated with a change in neutrophil activation or maturity as previously suggested.     

No effect of 5% hypohydration on running economy of competitive runners at 23 degrees C

PURPOSE: Although running economy (RE) is recognized as an integral component of successful endurance performance and is affected by numerous factors, little is known about the influence of body water loss on RE. This investigation examined the effects of hypohydration (HY) on RE and associated physiological responses. METHODS: Ten highly trained collegiate distance runners (mean +/- SD; age, 20 +/- 3 yr; height, 178.5 +/- 6.3 cm; body mass, 66.7 +/- 5.4 kg; VO2max, 66.5 +/- 4.1 mL x kg(-1) x min(-1)) participated in four experiments on separate days, twice in a euhydrated (EU) and twice in a HY state (-5.5 and -5.7% body mass loss achieved during 24 h). At each hydration level, subjects performed one 10-min treadmill run per day (23 degrees C environment), at either 70% VO2max (EU 70% or HY 70%) or 85% VO2max (EU 85% or HY 85%) in a randomized, repeated-measures design. Cardiopulmonary, metabolic, thermal, hormonal, and perceptual variables were measured. RESULTS: No between-treatment differences existed for RE (EU 70%, 46.3 +/- 3.2; HY 70%, 47.2 +/- 3.8; EU 85%, 58.6 +/- 2.8; HY 85%, 58.9 +/- 4.1 mL x kg(-1) x min(-1)), postexercise plasma lactate concentration (EU 70%, 1.9 +/- 0.6; HY 70%, 1.8 +/- 0.6; EU 85%, 6.5 +/- 3.5; HY 85%, 6.4 +/- 3.5 mmol x L(-1)), or rating of perceived exertion. HY resulted in a greater (P < 0.05 to 0.001) heart rate (HR), rectal temperature, and plasma norepinephrine concentration (NE), concurrent with reduced cardiac output, stroke volume, and respiratory exchange ratio. CONCLUSION: HY did not alter the RE or lactate accumulation of endurance athletes during 10 min of exercise at 70 and 85% VO2max. These findings indicate that HY had no effect on RE, but that it increased physiological strain in a 23 degrees C environment.     

The acute effects of exercise duration on serum lipoprotein metabolism

The purpose of this study was to determine the effect of exercise duration on lipoprotein responses. Twenty two normolipidemic male volunteers, ages 19-31 yrs (X +/- SEM = 23.1 +/- 2.94) participated in the study. Each was novice a runner (training less than 5 mi/wk). Subjects were assessed for baseline lipid measures of high density lipoprotein (HDL-C), low density lipoprotein (LDL-C), total cholesterol (TC) and triglycerides (TG). They were then evaluated for VO2max and ventilatory threshold (VT). Later they were matched for VO2max and randomly assigned to one of three groups which exercised for 15, 30 or 45 min respectively at a VO2 20% below VT. Subjects were evaluated again for HDL-C, LDL-C, TC and TG from blood samples taken pre-exercise and immediately post-exercise, as well as 1, 24 and 48 hrs post-exercise. A 3 X 4 split plot ANOVA found no difference for any lipid measure during the baseline period. A 3 X 5 split-plot ANOVA (covarying for pre-exercise measures) and post-hoc comparisons of pre- and post-exercise lipid levels indicated no significant differences occurred for either TC, TG or LDL-C measures (p less than 0.05). With respect to HDL-C, the 30 min group had significantly lower HDL-C at the 24 hr measure than did 45 min group (46.41 +/- 1.70 vs 53.34 +/- 1.73 mg.dl-1 respectively). No other differences were found. These findings indicate exercise duration will have an effect on acute responses of lipoprotein following exercise of low intensity.     

Tennis: a physiological profile during match play.

Heart rate (HR), hematocrit, hemoglobin, blood glucose, and plasma concentrations of lactate, cortisol, and testosterone were monitored in 10 male subjects (Division I, 20.3 +/- 2.5 yrs, VO2max: 58.5 +/- 9.4 ml.kg-1.min-1) during singles tennis and a treadmill test. During the on-court session, HR was 144.6 +/- 13.2 beats.min-1 for the 85 min of play. Plasma lactate rose 50% from a post-warmup value of 1.6 +/- 0.6 mmol.l-1 to 2.3 +/- 1.2 mmol.l-1 during play (p greater than 0.05). Blood glucose slightly decreased (8%, p greater than 0.05) from a pre-exercise value of 4.6 +/- 0.8 mmol.l-1 as a result of the 10-min warmup. This was followed by a 23% rise (p less than 0.05) from 4.2 +/- 1.0 mmol.l-1 to 5.2 +/- 0.6 mmol.l-1, measured after the first 30 min of play. Blood glucose subsequently remained steady at slightly above the pre-exercise value. Plasma cortisol rose (9%, p greater than 0.05) during the warmup and subsequently decreased (p less than 0.05) from a post-warmup value of 558.2 +/- 285.2 nmol.l-1 to 337.1 +/- 173.3 nmol.l-1 (a 40% decrease), and remained decreased during recovery. Plasma testosterone rose 22% (p less than 0.05) from pre-exercise to recovery (13.5 +/- 3.8 nmol.l-1 and 16.5 +/- 2.6 nmol.l-1, respectively). Although tennis is characterized by periods of high-intensity exercise, the overall metabolic response resembles prolonged moderate-intensity exercise.     

Markers of hydration status

This paper reviews the literature, describes and discusses methods by which whole body hydration status can be determined in humans. A method of determining whether or not an individual is hypohydrated is of particular significance in an exercise situation as even moderate levels of hypohydration have a negative impact on exercise performance. Inspection of the published literature indicates that a number of methods have been used to determine hydration status. Body mass changes, urinary indices (volume, colour, protein content, specific gravity and osmolality), blood borne indices (haemoglobin concentration, haematocrit, plasma osmolality and sodium concentration, plasma testosterone, adrenaline, noradrenaline, cortisol and atrial natiuretic peptide), bioelectrical impedance analysis, and pulse rate and systolic blood pressure response to postural change are discussed. The urinary measures of colour, specific gravity and osmolality are more sensitive at indicating moderate levels of hypohydration than are blood measurements of hematocrit and serum osmolality and sodium concentration. Currently no "gold standard" hydration status marker exists, particularly for the relatively moderate levels of hypohydration that frequently occur in an exercise situation. The choice of marker for any particular situation will be influenced by the sensitivity and accuracy with which hydration status needs to be established together with the technical and time requirements and expense involved.