Showing papers on "Exercise physiology published in 1986"

Metabolic changes following eccentric exercise in trained and untrained men

Abstract: The effects of one 45-min bout of high-intensity eccentric exercise (250 W) were studied in four male runners and five untrained men. Plasma creatine kinase (CK) activity in these runners was higher (P less than 0.001) than in the untrained men before exercise and peaked at 207 IU/ml 1 day after exercise, whereas in untrained men the maximum was 2,143 IU/ml 5 days after exercise. Plasma interleukin-1 (IL-1) in the trained men was also higher (P less than 0.001) than in the untrained men before exercise but did not significantly increase after exercise. In the untrained men, IL-1 was significantly elevated 3 h after exercise (P less than 0.001). In the untrained group only, 24-h urines were collected before and after exercise while the men consumed a meat-free diet. Urinary 3-methylhistidine/creatinine in the untrained group rose significantly from 127 mumol/g before exercise to 180 mumol/g 10 days after exercise. The results suggest that in untrained men eccentric exercise leads to a metabolic response indicative of delayed muscle damage. Regularly performed long distance running was associated with chronically elevated plasma IL-1 levels and serum CK activities without acute increases after an eccentric exercise bout.

Plasma aldosterone and sweat sodium concentrations after exercise and heat acclimation

Abstract: This investigation was designed to determine the relationship between the levels of plasma aldosterone and eccrine sweat gland sodium excretion following exercise and heat acclimation. Ten subjects exercised at 45% of their maximal O2 uptake in a hot (40 degrees C), moderately humid (45% relative humidity) environment for 2 h/day on ten consecutive days. Acclimation was verified by significant reductions in exercise heart rate, rectal temperature, and heat storage, as well as significant elevation of resting plasma volume (12%, P less than 0.05) and exercise sweat rate on day 10 compared with day 1 of acclimation. During exercise, the concentration and total content of sodium in sweat as well as plasma aldosterone were significantly decreased from day 1 to day 10. The ratio of sweat sodium reabsorbed to plasma aldosterone concentration was significantly increased from day 1 to day 10 after both 1 and 2 h of exercise. These data indicate that plasma aldosterone concentrations decrease following heat acclimation; and eccrine gland responsiveness to aldosterone, as represented by sweat sodium reabsorption, may be augumented through exercise and heat acclimation.

Perceptual and Physiological Responses during Exercise in Cool and Cold Water

Abstract: This investigation examined the interaction of exposure to cold water stress with both perceived exertion and thermal sensation during exercise. Eight male volunteers performed arm, leg, and combined arm and leg exercise for 45 min. in water at 20 and 26 degrees C. Exercise was performed at a low (n = 7) and a high (n = 8) intensity relative to the ergometer specific peak oxygen uptake (VO2 peak). In general, percent VO2 peak did not differ between types of exercise in either 20 or 26 degrees C water. During low intensity exercise when power output was matched across water temperatures (Tw), percent VO2 peak was greater in 20 degrees C water (52%) compared to 26 degrees C water (42%). Ratings of perceived exertion (RPE) did not differ between Tw. During high intensity exercise when percent VO2 peak was matched across Tw, RPE was lower during exercise in 20 degrees C compared to 26 degrees C. Multiple correlation analyses comparing both final RPE and thermal sensation (TS) with physiological and thermal measures were performed across type of exercise and Tw. RPE was moderately correlated with heart rate (r = 0.68) and ventilation (r = 0.61), whereas very slight relationships were established with TS (r = 0.16), skin and rectal temperatures (r = 0.10 and r = 0.20). TS was moderately correlated with skin and rectal temperatures (r = 0.64 and r = 0.73), whereas low correlations existed between TS and both heart rate (r = 0.32) and ventilation (r = -0.12). These data suggest that the change in oxygen uptake associated with exercise in cold water does not add to the over-all perception of exertion. This perception appears to be related to cardiopulmonary variables rather than thermal measures, whereas thermal sensation is related to thermal measures and not cardiopulmonary variables.

Response of muscle protein turnover to insulin after acute exercise and training

Abstract: To determine whether the enhanced insulin-sensitivity of glucose metabolism in muscle after acute exercise also extends to protein metabolism, untrained and exercise-trained rats were subjected to an acute bout of exercise, and the responses of protein synthesis and degradation to insulin were measured in epitrochlearis muscles in vitro. Acute exercise of both untrained and trained rats decreased protein synthesis in muscle in the absence or presence of insulin, but protein degradation was not altered. Exercise training alone had no effect on protein synthesis or degradation in muscle in the absence or presence of insulin. Acute exercise or training alone enhanced the sensitivities of both protein synthesis and degradation to insulin, but the enhanced insulin-sensitivities from training alone were not additive to those after acute exercise. These results indicate that: a decrease in protein synthesis is the primary change in muscle protein turnover after acute exercise and is not altered by prior exercise training, and the enhanced insulin-sensitivities of metabolism of both glucose and protein after either acute exercise or training suggest post-binding receptor events.

Factors affecting changes in muscle glycogen concentration during and after prolonged exercise.

Abstract: Muscle glycogen concentration decreases continuously during prolonged severe exercise. The rate of depletion increases with increasing exercise intensity. During heavy exercise at 65-75% of VO2 max, time till exhaustion correlates with the pre-exercise muscle glycogen concentration and exhaustion coincides with empty glycogen stores. A substantial number of type I fibres are depleted within 60 min of mild exercise (43% of VO2 max). These results suggest that glycogen depletion may contribute to muscle fatigue even during light exercise. When glycogen depletion becomes present in an increasing number of type I fibres, glycogen breakdown occur in an increasing number of type II fibres, indicating that these fibres take over more of the force development. It is well documented that a high carbohydrate diet is a prerequisite for a rapid post-exercise muscle glycogen resynthesis. Recent studies indicate that there is an increasing rate of glycogen resynthesis with increasing oral glucose intake up to a certain level. A further increase in glucose intake gives no further increase in the rate of resynthesis. However, glucose infusion is reported to induce a 2-3 times higher rate of resynthesis. This higher rate of resynthesis may be caused by the higher blood glucose concentration which can occur during glucose infusion. Preliminary results indicate that muscle glycogen is resynthesized at equal rates when the blood glucose concentration is kept at the same level, irrespective of whether the glucose is administered orally or by infusion. Muscle glycogen resynthesis seems to be slower during fructose ingestion than glucose ingestion.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise Responses after Inactivity

Abstract: The exercise response after bed rest inactivity is a reduction in the physical work capacity and is manifested by significant decreases in oxygen uptake. The magnitude of decrease in maximal oxygen intake V(dot)O2max is related to the duration of confinement and the pre-bed-rest level of aerobic fitness; these relationships are relatively independent of age and gender. The reduced exercise performance and V(dot)O2max following bed rest are associated with various physiological adaptations including reductions in blood volume, submaximal and maximal stroke volume, maximal cardiac output, sceletal muscle tone and strength, and aerobic enzyme capacities, as well as increases in venous compliance and submaximal and maximal heart rate. This reduction in physiological capacity can be partially restored by specific countermeasures that provide regular muscular activity or orhtostatic stress or both during the bed rest exposure. The understanding of these physiological and physical responses to exercise following bed rest inactivity has important implications for the solution to safety and health problems that arise in clinical medicine, aerospace medicine, sedentary living, and aging.

Lack of Influence of the Menstrual Cycle on Blood Lactate.

Abstract: In brief: Some female athletes report that i their performance varies between phases of the menstrual cycle, and some may use oral contraceptives to modify their cycles. To determine if energy metabolism varies across the cycle, the author examined the response of blood lactate to 60 minutes of moderate-intensity, steady-state exercise during the beginning (early follicular phase) and near the end (midluteal phase) of the menstrual cycle. Lactate increased during exercise in both phases, but it did not differ significantly between phases. The author concluded that the menstrual cycle exerts no effect on blood lactate concentration during moderate-intensity, steady-state exercise.

Coagulability and Rheology: Hematologic Benefits From Exercise, Fish, and Aspirin. Implications for Athletes and Nonathletes.

Abstract: In brief: Physical activity makes the blood more fluid and less likely to clot. The healthy hematologic adaptations to exercise (enhanced fibrinolysis, expanded plasma volume, decreased hematocrit, increased red cell deformability, and decreased blood viscosity) seem to enhance the delivery of oxygen and decrease the risk of thrombosis. Regular exercise, then, by changing the blood, may offer the elite athlete enhanced performance and the general population reduced risk of heart attack. Increased amounts of fish in the diet and-for selected persons-low-dose aspirin, may be useful antithrombotic adjuncts to exercise.

Endurance Exercise: Normal Physiology and Limitations Imposed by Pathological Processes (Part 1).

Abstract: In brief: Endurance exercise induces significant and rapid changes in many physiological functions To maintain homeostasis, adaptations in the oxygen transport and delivery chain are necessary Increases in minute ventilation and diffusion across the alveolar-capillary membrane enhance oxygenation of blood in the lungs Parallel changes in cardiac output, muscle blood flow, and arteriovenous oxygen difference increase oxygen transport and delivery Pulmonary and cardiovascular diseases can limit oxygen transport and/or delivery, while muscle diseases can impair oxygen delivery

Metabolic regulation in skeletal muscle during exercise : a fish-mammal comparison

Abstract: The aim of the present investigation was to examine the control of anaerobic glycogenolysis in working and fatigued skeletal muscle. The two animals chosen for the study were a teleost fish and the laboratory rat. The rationale behind using a comparative approach to investigate fundamental questions on metabolic control resides in the different abil it ies of each animal to perform exercise, and to their markedly different myofibril lar organization. In the process of defining the hierarchical recruitment of fuel and pathway selection in rainbow trout fast-twitch white skeletal muscle, it was clear that the near-maximal myosin ATPase activity was supported solely by PCr hydrolysis. It was not until the rate and force of contraction decreased that the relative contribution of anaerobic glycogenolysis became Increasingly important. Despite glycogenolysis possessing a lower maximal ATP generating potential than PCr hydrolysis, it has the advantage of being less constrained by time, and is recruited to extend muscle performance, but at submaximal workloads. Demonstration of the same temporal pattern of activation was not attempted for rat skeletal muscle because of complex fiber heterogeneity. The etiology of fatigue after 10 and 30 minutes of burst swimming in trout was due to the near depletion of glycogen In white muscle. Inhibition of anaerobic glycogenolysis was not correlated with l imitations to either the availability of ADP or NAD\ or inhibition of

Metabolism of exercising skeletal muscle during beta1-selective adrenoceptor blockade

Abstract: Concentrations of glycogen, glucose, glucose-6-phosphate and lactate in the lateral vastus muscle were measured in seven subjects before and after dynamic muscle exercise at a work load of 75% of each subject's maximal working capacity, and with and without intravenous administration of the beta 1-selective beta-adrenoceptor blocking agent, atenolol. Pulmonary oxygen uptake was measured during exercise. Heart rate and arterial blood pressure were measured throughout the study. Arterial concentrations of glucose, lactate and free fatty acids were measured at rest and during exercise. The muscle concentration of glycogen and the extent of glycogen depletion with exercise were not influenced by the beta 1-adrenoceptor blocker. Similarly, there was no change in the muscle concentrations of glucose, glucose-6-phosphate and lactate. Heart rate decreased at rest and during exercise. Arterial blood pressure was not influenced by beta-blockade. Pulmonary oxygen uptake decreased by 6.5%. The exercise induced rise in arterial blood concentration of free fatty acids was abolished by beta 1-selective beta-blockade. It is concluded that the decrease in lactate release from exercising muscles during beta 1-adrenoceptor blockade seen in other studies cannot be explained by an impaired breakdown of muscle glycogen. It may be inferred, however, that a reduced availability of free fatty acids in the exercising muscles during beta 1-selective (and non-selective) beta-blockade may enhance the combustion of pyruvic acid and thereby decrease the production of lactate.

Metabolic response to exercise and muscle disease.

Abstract: Physical fitness through exercise is the rage of today. Almost everybody is indulging in various forms of exercise from weight lifting to marathons. These regimens presuppose a normal muscle metabolism. However, a significant number of so-called normals end up with the symptoms of cramps, fatigue, and, in advanced cases, myoglobinuria. Exercise forms the mainstay of rehabilitation of patients with neurologic disorders manifesting as paresis or paralysis, and certain rheumatologic or metabolic problems are also handled via the medium of exercise therapy. It is, thus, imperative that there should be a clear understanding of normal muscle composition and metabolic responses. We will summarize the histology, histochemistry, physiology and metabolic responses of normal muscle to exercise and put this information in perspective in the light of various muscle disorders.

[Guided training as a therapeutic measure in the treatment of hyper- and hypotension].

Abstract: The high prevalence of hypertension and orthostatic hypotension is a challenge for both preventive and curative medicine. Physical exercise can be of great therapeutic value in these disturbances of blood pressure regulation. Endurance training has been shown to normalize resting and exercise blood pressure in young borderline hypertensives. Other beneficial effects include a decrease in myocardial oxygen consumption (tension-time index) and plasma adrenaline levels at rest and during exercise and an improvement in left ventricular compliance. This can bei achieved without the risks and expense of long-term drug therapy. When medication is needed for the therapy of hypertension, drug-induced changes in blood pressure reaction and circulatory responses to physical training have to be considered. We found that orthostatic hypotension in otherwise healthy people is often associated with poor general physical condition. In such cases endurance training combined with isometric exercise aimed at increasing leg muscle tone is advisable. However, exercise training as a therapeutic measure has to be prescribed in terms of dose (frequency and duration), intensity and type of exercise. This requires an understanding of exercise physiology, as well as the ability to make a rational selection and evaluation of patients using a graded exercise test.

Endurance Exercise: Normal Physiology and Limitations Imposed by Pathological Processes (Part 2).

Abstract: In brief: Endurance exercise causes rapid changes in physiological and metabolic functions, involving not only the body's oxygen transport system (discussed in part 1 of this article, August 1986, page 94) but also the fuel supply and endocrine systems. The hormonal changes increase glucose delivery by stimulating glycogenolysis and gluconeogenesis in the liver and glycogen utilization in muscles, and also increase free fatty acid delivery by stimulating lipolysis in fat cells. Patients with disorders of muscle energy metabolism may have difficulty performing either brief, intense exercise or prolonged exercise, depending on the disorder. Diseases that cause abnormal hormonal and autonomic responses to exercise include autonomic neuropathy, central Cushing's disease, and diabetes mellitus.

Influence of Body Mass, Morphology and Gender on Thermal Responses During Immersion in Cold Water

Abstract: : This report primarily focuses on the influence of body mass, morphology and gender on thermal and metabolic responses during both rest and exercise after cold-water exposure. A group of male and female subjects (n=4 each) were evaluated that had similar (P0.05) percent body fat and total skinfold, but differed (P0.05) in weight, lean body weight, limb divided by trunk skinfold, surface area A sub D and surface area-to-mass ratio (A sub D/wt. ). During both rest and exercise, testing was conducted at three water temperatures (20, 24 and 28 C) for 1-h. Rectal temperature (T sub re), mean- weighted skin temperature (T sub sk) and metabolic rate (M) were monitored during both rest and exercise. In a second series of experiments, metabolic and thermoregulatory responses of male volunteers differing in body morphology and mass during rest and exercise in water at 26 C were evaluated for 1-h duration. Similar thermoregulatory and metabolic responses were evaluated in these experiments as described above with the addition of esophageal temperature (T sub es) and tissue insulation. In conclusion, when these findings were taken collectively, it would appear that water temperature, body mass, and the exercise type and intensity are more critical factors to be considered in preventing a decline in deep body temperature during cold-water immersion than body fat, surface area-to-mass ratio and gender. We believe, however, that this conclusion is more applicable to individuals at exercise rather than rest during cold-water immersion.

Sleep Deprivation and Exercise Tolerance.

Abstract: : The purpose of this study is to identify the effects of sleep deprivation on the physiological and psychological responses to exercise. Standard techniques in human exercise physiology are utilized. During this year, we found that fragmenting two nights of sleep prior to heavy exercise had no effect on physiological response to that exercise. Heart rate, metabolic rate, and body temperature were identical to control, in contrast to sleepiness and mood disturbance, both of which were significantly elevated. In past work, such psychological effects were correlated with decreased exercise tolerance. Also, we found that a 36 hour sleepless period prior to prolonged mild exercise has no influence on physiological responses to that exercise, though it as well significantly elevated mood disturbance. Because neither form of sleep loss changed stress hormonal levels in subsequent exercise, we conclude that sleep loss of this form is primarily a psychological and not a physiological stress.