The purpose of this study was to determine if intravenous fluid rehydration, versus oral rehydration. during a brief period (20 min) differentially affects plasma ACTH, cortisol, and norepinephrine concentrations during subsequent exhaustive exercise in the heat. Following dehydration (DHY) to −4% of body weight, 8 nonacclimated highly trained males (age = 23.5 ± 1.2 years, V̇O2peak = 61.4±0.8 ml · kg · min−1, % body fat = 13.5±0.6%) cycled to exhaustion at 74% V̇O2peak in 36.8 °C on three different occasions. These included: (a) no fluid (NF), where no fluid was provided during the rehydration period; (b) DRINK, where oral rehydration (0.45% NaCl) was provided equal to 50% of the prior DHY; and (c) IV, where intravenous infusion (0.45% NaCl) was provided equal to 50%’ of the prior DHY. Exercise time to exhaustion was not different p = .07) between the DRINK (34.86 ±4.01) and IV (29.48 ± 3.50) trials, but both were significantly p < .05) longer than the NF (18.95 ± 2.73) trial. No differences (p > .05) were found for any of the hormone measures among trials. The endocrine responses at exhaustion were similar regardless of hydration state and mode of rehydration, but rehydration prolonged the exercise time to exhaustion.
Douglas J. Casa, Carl M. Maresh, Lawrence E. Armstrong, Stavros A. Kavouras, Jorge A. Herrera-Soto, Frank T. Hacker Jr., Timothy P. Scheett, and James Stoppani
Darlene A. Sedlock, Man-Gyoon Lee, Michael G. Flynn, Kyung-Shin Park, and Gary H. Kamimori
Literature examining the effects of aerobic exercise training on excess postexercise oxygen consumption (EPOC) is sparse. In this study, 9 male participants (19–32 yr) trained (EX) for 12 wk, and 10 in a control group (CON) maintained normal activity. VO2max, rectal temperature (Tre), epinephrine, norepinephrine, free fatty acids (FFA), insulin, glucose, blood lactate (BLA), and EPOC were measured before (PRE) and after (POST) the intervention. EPOC at PRE was measured for 120 min after 30 min of treadmill running at 70% VO2max. EX completed 2 EPOC trials at POST, i.e., at the same absolute (ABS) and relative (REL) intensity; 1 EPOC test for CON served as both the ABS and REL trial because no significant change in VO2max was noted. During the ABS trial, total EPOC decreased significantly (p < .01) from PRE (39.4 ± 3.6 kcal) to POST (31.7 ± 2.2 kcal). Tre, epinephrine, insulin, glucose, and BLA at end-exercise or during recovery were significantly lower and FFA significantly higher after training. Training did not significantly affect EPOC during the REL trial; however, epinephrine was significantly lower, and norepinephrine and FFA, significantly higher, at endexercise after training. Results indicate that EPOC varies as a function of relative rather than absolute metabolic stress and that training improves the efficiency of metabolic regulation during recovery from exercise. Mechanisms for the decreased magnitude of EPOC in the ABS trial include decreases in BLA, Tre, and perhaps epinephrine-mediated hepatic glucose production and insulin-mediated glucose uptake.
Keith B. Wheeler and Keith A. Garleb
The use of gamma-oryzanol and phytosterols is gaining popularity among various athletic populations. These compounds are being consumed in the belief that they elicit anabolic effects ranging from increased testosterone production and release to stimulating human growth hormone release. However, published scientific studies suggest that these compounds are poorly absorbed. Furthermore, animal studies indicate that when these compounds are injected subcutaneously or intravenously, they induce antianabolic or catabolic activity. Normally, less than 5% of orally consumed phytosterols are absorbed from the Intestinal tract, with the majority being excreted in the feces. Intravenous or subcutaneous injections of gamma-oryzanol in rats have been shown to suppress luteinizing hormone release, reduce growth hormone synthesis and release, and increase release of the catecholamines, dopamine and norepinephrine, in the brain. Although it hasn't been directly measured, this metabolic milieu, if accurate, may actually reduce testosterone production.
Jonathan Peake, Jeremiah J. Peiffer, Chris R. Abbiss, Kazunori Nosaka, Paul B. Laursen, and Katsuhiko Suzuki
Heat stress might attenuate the effects of carbohydrate on immunoendocrine responses to exercise by increasing endogenous glucose production and reducing the rate of exogenous carbohydrate oxidation. The authors compared the efficacy of carbohydrate consumption on immune responses to exercise in temperate vs. hot conditions.
Ten male cyclists exercised on 2 separate occasions in temperate (18.1 ± 0.4 °C, 58% ± 8% relative humidity) and on another 2 occasions in hot conditions (32.2 ± 0.7 °C, 55% ± 2% relative humidity). On each occasion, the cyclists exercised in a fed state for 90 min at ~60% VO2max and then completed a 16.1-km time trial. Every 15 min during the first 90 min of exercise, they consumed 0.24 g/kg body mass of a carbohydrate or placebo gel.
Neutrophil counts increased during exercise in all trials (p < .05) and were significantly lower (40%, p = .006) after the carbohydrate than after the placebo trial in 32 °C. The concentrations of serum interleukin (IL)-6, IL-8, and IL-10 and plasma granulocyte-colony-stimulating factor, myeloperoxidase, and calprotectin also increased during exercise in all trials but did not differ significantly between the carbohydrate and placebo trials. Plasma norepinephrine concentration increased during exercise in all trials and was significantly higher (50%, p = .01) after the carbohydrate vs. the placebo trial in 32 °C.
Carbohydrate ingestion attenuated neutrophil counts during exercise in hot conditions, whereas it had no effect on any other immune variables in either temperate or hot conditions.
Kazuto Omiya, Yoshihiro J Akashi, Kihei Yoneyama, Naohiko Osada, Kazuhiko Tanabe, and Fumihiko Miyake
The aim of this study was to clarify the mechanism of impaired exercise tolerance in chronic sleep-restricted conditions by investigating variables related to heart-rate (HR) response to sympathetic nervous stimulation. Sixteen healthy men (mean age 21.5 years) were tested in a control state, acute sleep-loss state, and chronic sleeprestricted state. Participants underwent cardiopulmonary exercise testing in each state. Their norepinephrine (NE) concentration was measured before and immediately after exercise. Intracellular magnesium (Mg) concentration was measured in a resting state. Exercise duration was shorter and the ratio of HR response to the percentage increase in NE was higher in the chronic sleep-restricted state than in the control state. Intracellular Mg gradually decreased from control to chronic sleep restriction. There was a negative correlation between peak exercise duration and the ratios of HR response to the rate of increase in NE. Intracellular Mg was positively correlated with the ratios of HR response to the increase in NE both in control and in acute sleep loss. The authors conclude that the impaired exercise tolerance in a chronic sleep-restricted state is caused by hypersensitivity of the HR response to sympathetic nervous stimulation, which showed a compensation for decreased intracellular Mg concentration.
William A. Burgess, J. Mark Davis, William P. Bartoli, and Jeffrey A. Woods
The effects of ingesting a low dose of CHO on plasma glucose, glucoregulatory hormone responses, and performance during prolonged cycling were investigated. Nine male subjects cycled for 165 min at ≈67% peak
Sharon L. Miller, Carl M. Maresh, Lawrence E. Armstrong, Cara B. Ebbeling, Shannon Lennon, and Nancy R. Rodriguez
The interaction of substrates and hormones in response to ingestion of intact proteins during endurance exercise is unknown. This study characterized substrate and hormone responses to supplementation during endurance exercise. Nine male runners participated in 3 trials in which a non-fat (MILK), carbohydrate (CHO), or placebo (PLA) drink was consumed during a 2-hour treadmill >· run at 65% V̇O2max. Circulating levels of insulin, glucagon, epinephrine, norepi-nephrine, growth hormone, testosterone, and cortisol were measured. Plasma substrates included glucose, lactate, free fatty acids, and select amino acids. Except for insulin and cortisol, hormones increased with exercise. While post-exercise insulin concentrations declined similarly in all 3 trials, the glucagon increase was greatest following MILK consumption. CHO blunted the post-exercise increase in growth hormone compared to levels in MILK. Free fatty acids and plasma amino acids also were responsive to nutritional supplementation with both CHO and MILK attenuating the rise in free fatty acids compared to the increase observed in PLA. Correspondingly, respiratory exchange ratio increased during CHO. Essential amino acids increased significantly only after MILK and were either unchanged or decreased in CHO. PLA was characterized by a decrease in branched-chain amino acid concentrations. Modest nutritional supplementation in this study altered the endocrine response as well as substrate availability and utilization following and during an endurance run, respectively.
Daniela A. Rubin, Diobel M. Castner, Hoang Pham, Jason Ng, Eric Adams, and Daniel A. Judelson
During childhood, varying exercise modalities are recommended to stimulate normal growth, development, and health. This project investigated hormonal and metabolic responses triggered by a resistance exercise protocol in lean children (age: 9.3 ± 1.4 y, body fat: 18.3 ± 4.9%), obese children (age: 9.6 ± 1.3 y, body fat: 40.3 ± 5.2%) and lean adults (age: 23.3 ± 2.4 y, body fat: 12.7 ± 2.9%). The protocol consisted of stepping onto a raised platform (height = 20% of stature) while wearing a weighted vest (resistance = 50% of lean body mass). Participants completed 6 sets of 10 repetitions per leg with a 1-min rest period between sets. Blood samples were obtained at rest preexercise, immediately postexercise and 2 times throughout the 1-hr recovery to analyze possible changes in hormones and metabolites. Children-adult differences included a larger exercise-induced norepinephrine increase in adults vs. children and a decrease in glucagon in children but not adults. Similarities between adults and children were observed for GH-IGF-1 axis responses. Metabolically, children presented with lower glycolytic and increased fat metabolism after exercise than adults did. Obesity in childhood negatively influenced GH, insulin, and glucose concentrations. While adults occasionally differed from children, amount of activated lean mass, not maturation, likely drove these dissimilarities.
Charles J. Hardy and Robert G. McMerray
Ten Type A's and 10 Type B's, as measured by the student version of the JAS and the TASRI, exercised on a cycle ergometer for 20 minutes at light (40% V02max), moderate (60% V02max), and high (80% V02max) intensity exercise to determine A/B differences in psychophysiological responses. The norepinephrine and epinephrine responses of A/B types were similar at the light and moderate intensities. However, at the high intensity, norepmephrine response of Type A's was significantly greater than that of Type B's. Epinephrine responses (p=.ll) evidenced the same, albeit nonsignificant, trend. Oxygen uptake and heart rate data indicated that this amine difference was not a function of differential workloads, suggesting that Type A's had a greater psychophysiological reactivity to high intensity exercise than Type B's. Ratings of perceived exertion were similar for Type A's and B's at all intensities. However, a significant interaction between behavioral pattern and intensity emerged for affect. Interpretation of this interaction indicated that Type A's were more positive than B's at light and moderate intensities, yet at the high intensity exercise A's were more negative than B's. The results of this study suggest that A and B types do differ in their psychophysiological responses during exercise, with A's evidencing more positive affect during light and moderate intensities, yet more negative affect and greater neuroendocrine responses during high intensity exercise than B's.
Douglas Potter and Denis Keeling
The effects of exercise and circadian rhythms on memory function were explored in a group of shift workers (mean age 32 yrs). A variant of the Auditory-Verbal Learning Test was used to test memory for word lists at 9:30 a.m. and 12:30, 3:30, and 6:30 p.m. in a repeated-measures design. Without exercise there was clear evidence of a circadian rhythm in memory performance, with peak performance occurring at 12:30 and poorest performance at 3:30. A brisk 10-min walk followed by a 15- to 30-min recovery period resulted in significant improvement in memory recall at all time periods except 12:30. The results of the AVLT task suggest an improvement in both working memory and long-term memory performance. Rhythmic changes in serotonin, epinephrine, norepinephrine, and acetylcholine levels all affect cortical arousal and cognitive function. Exercise may have resulted in altered levels of these neurotransmitters, increased glucose, oxygen, or nutrient levels, or from temporary changes in growth hormone or brain-derived neurotropic factor levels resulting in increased synaptogenesis and neurogenesis. The physiological basis of this temporary improvement in memory remains to be determined, but this simple behavioral intervention may have widespread application in improving memory function in all sections of the population including children and the elderly.