Showing papers on "Exercise physiology published in 1989"

Mechanical influences on long-lasting human muscle fatigue and delayed-onset pain.

Abstract: 1. The influence of three mechanical factors, force, muscle length and passive lengthening, on long-lasting changes in voluntary force generation, the force:frequency relationship and the development of tenderness has been studied in healthy human skeletal muscle. The elbow flexors were used in all studies. The effect of muscle length was also investigated in the quadriceps and adductor pollicis muscles. Eighty maximal voluntary contractions (MVCs) were performed: one contraction, lasting approximately 2 s, every 15 s. The MVC and force:frequency relationships were measured before and immediately after the exercise and, together with an assessment of tenderness, at 24 h intervals thereafter. 2. In a series of experiments designed to investigate the effects of force, eccentric (lengthening) contractions were found to cause greater fatique and delayed-onset muscle pain than either isometric or concentric (shortening) contractions. There were, however, no substantial differences between the effects of isometric and concentric contractions. Changes in MVC took 24-48 h to return to normal while the low-frequency fatigue required 3-4 days to recover. 3. Passive lengthening with a comparable number of movements over the full range had no effect on the force generation of the muscle, nor did it cause any muscle pain. 4. In the series of experiments designed to investigate the effects of length, isometric MVCs were performed at either short or long length and the muscles subsequently tested at an intermediate length. The contractions at long length resulted in greater low-frequency fatigue and pain, despite the fact that they generated less force than those at the short length. 5. The results demonstrate that there is no simple relationship between the force generated during exercise and the development of long-lasting muscle fatigue and pain. Furthermore, there is a length-dependent component in the generation of low-frequency fatigue and muscle pain.

The effect of detraining and reduced training on the physiological adaptations to aerobic exercise training.

Abstract: In previously sedentary individuals, regularly performed aerobic exercise results in significant improvements in exercise capacity. The development of peak exercise performance, as typified by competitive endurance athletes, is dependent upon several months to years of aerobic training. The physiological adaptations associated with these improvements in both maximal exercise performance, as reflected by increases in maximal oxygen uptake (VO2max), and submaximal exercise endurance include increases in both cardiovascular function and skeletal muscle oxidative capacity.

Carnitine and acylcarnitine metabolism during exercise in humans. Dependence on skeletal muscle metabolic state

Abstract: Carnitine metabolism has been previously shown to change with exercise in normal subjects, and in patients with ischemic muscle diseases. To characterize carnitine metabolism further during exercise, six normal male subjects performed constant-load exercise on a bicycle ergometer on two separate occasions. Low-intensity exercise was performed for 60 min at a work load equal to 50% of the lactate threshold, and high-intensity exercise was performed for 30 min at a work load between the lactate threshold and maximal work capacity for the individual. Low-intensity exercise was not associated with a change in muscle (vastus lateralis) carnitine metabolism. In contrast, from rest to 10 min of high-intensity exercise, muscle short-chain acylcarnitine content increased 5.5-fold while free carnitine content decreased 66%, and muscle total carnitine content decreased by 19% (all P less than 0.01). These changes in skeletal muscle carnitine metabolism were present at the completion of 30 min of high-intensity exercise, and persisted through a 60-min recovery period. With 30 min of high-intensity exercise, plasma short-chain and long-chain acylcarnitine concentrations increased by 46% and 23%, respectively. Neither exercise state was associated with a change in the urine excretion rates of free carnitine or acylcarnitines. Thus, alterations in skeletal muscle carnitine metabolism, characterized by an increase in acylcarnitines and a decrease in free and total carnitine, are dependent on the work load and, therefore, the metabolic state associated with the exercise, and are poorly reflected in the plasma and urine carnitine pools.

Effects of 4 h preexercise carbohydrate feedings on cycling performance.

Abstract: This study determined the effects of consuming three different amounts of liquid carbohydrate 4 h before exercise on the metabolic responses during exercise and on exercise performance. Four hours before exercise subjects consumed either 45 (L) or 156 (M) g of carbohydrate in isocaloric feedings and either 0 (P) or 312 (H) g of carbohydrate. Interval cycling was undertaken for 95 min, followed by a performance trial. Blood glucose had reached basal 1 h after all feedings; blood insulin had reached basal 3 h after ingestion of P, L, and M but was still 84% higher for H at the start of exercise. During exercise insulin averaged 48% higher for H than P. Blood glucose decreased 16% during exercise for P, L, and M, whereas for H there was a transient drop the first 15 min of exercise, after which glucose increased and remained constant throughout exercise. More carbohydrate oxidation occurred during exercise for H vs P, whereas results were similar for L and M. Ingestion of H improved performance by 15% as compared with P, whereas performance was similar for L and M. These results indicate that, despite elevated insulin at the start of and during exercise, consumption of 312 g of carbohydrate 4 h before moderately intense prolonged exercise can improve performance, perhaps via an enhancement of carbohydrate oxidation.

Systemic and forearm vascular resistance changes after upright bicycle exercise in man.

Abstract: 1. Blood pressure, cardiac function and forearm blood flow following voluntary maximal upright bicycle exercise were studied in thirteen normal volunteers in a cross-over design against a control day. 2. After exercise there was a short-lived (5-10 min) increase in systolic blood pressure, peak aortic blood velocity and aortic acceleration suggesting a persistence of the positive inotropic influence of exercise. 3. Systemic vasodilation, which was seen immediately exercise stopped, lasted at least 60 min. This was associated with a reduction in diastolic blood pressure for the whole hour. After 30 min systolic blood pressure was also reduced. Heart rate and cardiac output were still significantly elevated and systemic vascular resistance still reduced at 60 min post-exercise. 4. A non-exercising limb vascular bed (forearm) showed a marked vasodilation for 1 h after predominately leg exercise indicating the presence of a vasodilatory influence affecting vascular beds other than the exercising muscle groups.

Gastric emptying during exercise: effects of heat stress and hypohydration.

Abstract: To determine the effects of acute heat stress, heat acclimation and hypohydration on the gastric emptying rate of water (W) during treadmill exercise, ten physically fit men ingested 400 ml of W before each of three 15 min bouts of exercise (treadmill, ∼50% $$\dot V_{{\text{O}}_{{\text{2max}}} } $$ ) on five seperate occasions. Stomach contents were aspirated after each exercise bout. Before heat acclimation (ACC), experiments were performed in a neutral (18°C), hot (49°C) and warm (35°C) environment. Subjects were euhydrated for all experiments before ACC. After ACC, the subjects completed two more experiments in the warm (35°C) environment; one while euhydrated and a final one while hypohydrated (-5% of body weight). The volume of ingested water emptied into the intestines at the completion of each exercise bout was inversely correlated (P<0.01) with the rectal temperature (r=-0.76). The following new observations were made: 1) exercise in a hot (49°C) environment impairs gastric emptying rate as compared with a neutral (18°C) environment, 2) exercise in a warm (35° C) environment does not significantly reduce gastric emptying before or after heat acclimation, but 3) exercise in a warm environment (35° C) when hypohydrated reduces gastric emptying rate and stomach secretions. Reductions in gastric emptying appear to be related to the severity of the thermal strain induced by an exercise/heat stress.

Early dynamics of O2 uptake and heart rate as affected by exercise work rate.

Abstract: The kinetics of O2 uptake (Vo2) and heart rate (HR) in response to constant work rate exercise have been characterized as two phases, an immediate response as the result largely of abrupt hemodynam...

Exercise intolerance, lactic acidosis, and abnormal cardiopulmonary regulation in exercise associated with adult skeletal muscle cytochrome c oxidase deficiency.

Abstract: A 27-yr-old woman with lifelong severe exercise intolerance manifested by muscle fatigue, lactic acidosis, and prominent symptoms of dyspnea and tachycardia induced by trivial exercise was found to have a skeletal muscle respiratory chain defect characterized by low levels of reducible cytochromes a + a3 and b in muscle mitochondria and marked deficiency of cytochrome c oxidase (complex IV) as assessed biochemically and immunologically. Investigation of the pathophysiology of the exercise response in the patient revealed low maximal oxygen uptake (1/3 that of normal sedentary women) in cycle exercise and impaired muscle oxygen extraction as indicated by profoundly low maximal systemic arteriovenous oxygen difference (5.8 ml/dl; controls = 15.4 +/- 1.4, mean +/- SD). The increases in cardiac output and ventilation during exercise, normally closely coupled to muscle metabolic rate, were markedly exaggerated (more than two- to threefold normal) relative to oxygen uptake and carbon dioxide production accounting for prominent tachycardia and dyspnea at low workloads. Symptoms in our patient are similar to those reported in other human skeletal muscle respiratory chain defects involving complexes I and III, and the exaggerated circulatory response resembles that seen during experimental inhibition of the mitochondrial respiratory chain. These results suggest that impaired oxidative phosphorylation in working muscle disrupts the normal regulation of cardiac output and ventilation relative to muscle metabolic rate in exercise.

Exercise-training protocols for astronauts in microgravity

Abstract: The question of the composition of exercise protocols for use by astronauts in microgravity is unresolved. Based on our knowledge of physical working requirements for astronauts during intra- and extravehicular activity and on the findings from bed-rest studies that utilized exercise training as a countermeasure for the reduction of aerobic power, deterioration of muscular strength and endurance, decrements in mood and cognitive performance, and possibly for bone loss, two exercise protocols are proposed. One assumes that, during microgravity, astronaut exercise physiological functions should be maintained at 100% of ground-based levels; the other assumes that maximal aerobic power in flight can be reduced by 10% of the ground-based level. A recommended prescription for in-flight prevention or partial suppression of calcium (bone) loss cannot be written until further research findings are obtained that elucidate the site, the magnitude, and the mechanism of the changes. Hopefully these proposed exercise prescriptions will stimulate further research and discussion resulting in even more efficient protocols that will help ensure the optimal health and well-being of our astronauts.

Epidural anaesthesia and cardiovascular responses to static exercise in man.

Abstract: 1. In human subjects, sustained static contractions of the knee extensors were performed in one leg with the same absolute (10% of the initial maximal voluntary contraction) and relative (30% of the maximal voluntary contraction immediately prior to the static exercise) intensities before and during epidural anaesthesia. Epidural anaesthesia reduced strength to 62 +/- 8% of the control value and partially blocked sensory input from the working muscles. During contractions performed with the same relative force, the increases in mean arterial pressure and heart rate were greater during control contractions than during epidural anaesthesia. During contractions at the same absolute force, there was no significant difference in magnitude of cardiovascular responses between control contractions and contractions performed during epidural anaesthesia. 2. The metabolic role in the exercise pressor reflex was assessed by applying an arterial leg cuff 10 s before cessation of exercise and through the following 3 min of recovery. Although mean arterial pressure and heart rate decreased immediately after cessation of exercise, application of the arterial occlusion cuff resulted in higher post-exercise mean arterial pressure and heart rate values. Control and epidural mean arterial pressures during arterial occlusion were not significantly different. 3. The results of this study suggest that the reflex neural mechanism rather than the intended effort (central command) is important in determining the blood pressure and heart rate responses to static exercise in man. That is, when epidural anaesthesia diminishes sensory feedback and produces muscular weakness, central command does not determine the cardiovascular response. This conclusion, however, is opposite to that derived from experiments with partial neuromuscular blockade which demonstrated the importance of central command in determining the cardiovascular response to static exercise (Leonard, Mitchell, Mizuno, Rube, Saltin & Secher, 1985). Taken together, these two studies are complementary and support the concept that both central and reflex neural mechanisms play roles in regulating arterial blood pressure and heart rate during static exercise in man.

Temperature regulation during upper body exercise: able-bodied and spinal cord injured.

Abstract: This paper will consider human thermoregulatory response differences between upper and lower body exercise In addition, the thermoregulatory problems of spinal cord injured individuals are examined For able-bodied individuals, the rise in core temperature is independent of the skeletal muscle mass employed and dependent upon the metabolic rate during exercise The avenues of heat exchange, however, are different for individuals performing upper body as opposed to lower body exercise During upper body exercise, there is a greater dry heat loss from the torso; however, no additional heat loss (as compared to lower body exercise) occurs from the exercising arms If an individual performs upper body exercise in cold water, there will be a greater heat loss and susceptibility to hypothermia than during lower body exercise A spinal cord injury impairs one's ability to thermoregulate because of: (a) loss of autonomic nervous system control for vasomotor and sudomotor responses in the areas of the insensate skin; (b) a reduced thermoregulatory effector response for a given core temperature; and (c) a loss of skeletal muscle pump activity from the paralyzed limbs As a result, a spinal cord injured person has a reduced ability to tolerate thermal extremes and to perform aerobic exercise Surprisingly little research, however, has focused on the ability of the disabled to thermoregulate during exercise Recent data suggest that rectal temperature measurements may underestimate the thermal burden imposed on wheelchair athletes during competition

High-intensity exercise performance is not impaired by low intramuscular glycogen

Abstract: The purpose of this study was to evaluate the effects of glycogen availability on short-term, high-intensity exercise performance. Eight males completed performance evaluation tasks (PET) consisting of maximum isokinetic strength and endurance, isometric strength, and electrically evoked force of the leg extensors, twice during each of two conditions. On day 1 (D1) of the control condition (C) subjects performed the PET, followed by strenuous exercise designed to deplete glycogen stores of the leg extensors. After consuming a mixed diet for 48h (days 2 and 3) they performed the PET again on day 4 (D4). The experimental condition (E) was identical to C, except that a strictly controlled low carbohydrate diet was consumed during Days 2 and 3. Biopsies from the vastus lateralis before the PET on D4 confirmed differences between conditions in intramuscular glycogen (426 +/- 43 vs 153 +/- 60 mmol glucose units.kg-1 d.w. for C and E respectively, P less than 0.001). Results obtained from the PET were not different between conditions on D4, nor within conditions when D1 and D4 were compared. Resting blood glucose, hematological variables indicative of hydration and acid-base status, and post PET blood lactate were similar for all trials. It is concluded that short-term, high-intensity exercise performance of glycogen depleted leg extensors is not impaired.

Cardiovascular responses to upper body exercise in normals and cardiac patients.

Abstract: This review summarizes and contrasts the cardiovascular responses elicited during dynamic upper body exercise (UBE) with those associated with lower body exercise (LBE). Information was obtained from studies which utilized arm-crank and/or cycle ergometers. At any given submaximal oxygen uptake (VO2), cardiac output (Q) is similar for UBE and LBE; however, heart rate (HR) is higher and stroke volume (SV) lower during UBE. Peripheral resistance and systolic and diastolic blood pressure are greater during UBE. Maximal Q, HR, SV, workload, and VO2 are less for UBE. As observed with healthy individuals, cardiac patients experience greater physiological stress for any given VO2 during UBE. UBE offers a satisfactory but perhaps not equivalent alternative to LBE for evaluation of angina and ischemic responses to exercise. The central and peripheral responses to either upper or lower body exercise appear to be independent of the muscle mass but directly related to the ergometer specific relative exercise intensity. The control mechanisms which govern these responses appear to be a centrally mediated activation of medullary centers coupled with a chemoreflex arising in the exercising skeletal muscle.

Aerobic exercise training programs for the upper body.

Abstract: Sufficient data are available to support the inclusion of upper body or combined arm-leg training in a comprehensive physical conditioning program. There is now evidence to suggest that initial fitness, as well as the intensity, frequency, and duration of training, may be important variables in determining the extent of cross-training benefits from the legs to the arms, and vice versa. Nevertheless, the limited degree of transfer of training benefits from one set of limbs to another appears to discount the practice of emphasizing leg training alone. Aerobic exercise programs for the upper body may yield significant central (Q and SV) and peripheral (a-vO2 difference) adaptations to support improvements in peak oxygen uptake (VO2peak) during arm and leg work, especially in subjects who are initially unfit, with the more dominant effects specific to the upper extremities. Finally, an arm exercise prescription that is based on the maximal heart rate derived from leg testing may result in an inappropriately high target heart rate for arm training. Workloads (kg.m.min-1) considered appropriate for leg training will generally need to be reduced by 50-60% for arm training.

Physiologic Responses to Treadmill and Water Running

Abstract: In brief: The physiologic responses to running on a treadmill and to running in water while wearing a buoyant vest were compared in seven uninjured runners. Ventilation, oxygen uptake, and respiratory quotient were significantly higher during treadmill running, whereas heart rate and perceived exertion were not significantly different for the two forms of exercise. Water running elicited a 36% lower metabolic cost than treadmill running despite the athletes' efforts to maintain a similar level of exertion. The results suggest that water running may help lessen the rate of deconditioning of injured athletes who must suspend their regular forms of exercise, but they fail to show that the metabolic cost of water running is significantly greater than that of treadmill running.

Hypothalamic-pituitary-adrenal responses to short-duration high-intensity cycle exercise

Abstract: beta-Endorphin (beta-EP), adrenocorticotropin (ACTH), and cortisol plasma concentrations were examined before and after maximal exercise at four intensities [36, 55, 73, and 100% of maximal leg power (MLP)] by means of a computerized cycle ergometer. All intensities were greater than those eliciting peak O2 uptake for the individual subjects. Blood samples were collected at rest, immediately after exercise, and at 5 and 15 min postexercise. Significant (P less than 0.05) increases were observed at 36% MLP for beta-EP and ACTH immediately after exercise and at 5 and 15 min postexercise. Plasma cortisol increased at 36% MLP at 15 min postexercise. Blood lactate significantly increased at all postexercise collection points for exercise intensities of 36, 55, and 73% MLP and at 5 min postexercise for 100% MLP. beta-EP concentrations at 36% MLP were significantly correlated (r = 0.75) with capillary density (mm-2), and cortisol concentrations at 36% MLP were significantly correlated (r = 0.89) with percentage of type II muscle fibers. No other significant relationships were observed. These data show that brief, high-intensity exercise up to maximal power production results in a nonlinear response pattern in peripheral blood hormone concentrations. Furthermore, blood lactate levels do not appear to be related to hypothalamic-pituitary-adrenal hormone plasma concentrations at high exercise intensities.

The physiological effects of aerobic dance. A review.

Abstract: Aerobic dance exercise is currently one of the most commonly practised adult fitness activities. The majority of the research pertaining to this form of exercise supports its application as a valid cardiovascular training alternative, especially for adult females if performed according to the American College of Sports Medicine (ACSM) guidelines. If, however, the participant is interested in modifying body composition, training frequency, duration, or efforts toward caloric restriction may need to be increased or altered beyond those employed in the aerobic dance training investigations. The amount of energy expended during a bout of aerobic dance can vary dramatically according to the intensity of the exercise. 'Low intensity' dance exercise is usually characterised by less large muscle activity and/or less lower extremity impact, and music of slower tempo. Dance exercise representative of this variety requires a cost of approximately 4 to 5 kcal/minute. Several trials, however, have shown that vigorous 'high intensity' aerobic dance which entails using the large muscle groups can require 10 to 11 kcal/minute. The associated training outcomes could be affected by such differences in dance exercise intensity and style.

Metabolic and hormonal responses during exercise at 20 degrees, 0 degrees and -20 degrees C.

Abstract: This study was designed to clarify the effects of cold air exposure on metabolic and hormonal responses during progressive incremental exercise. Eight healthy males volunteered for the study. Informed consent was obtained from every participant. The following protocol was administered to each subject on three occasions in a climatic chamber in which the temperature was 20 degrees, 0 degree or -20 degrees C with relative humidity at 60% +/- 1%. Exercise tests were conducted on an electrically braked ergocycle, and consisted of a progressive incremental maximal exercise. Respiratory parameters were continuously monitored by an automated open-circuit sampling system. Exercise blood lactate (LA), free fatty acids (FFA), glucose levels, bicarbonate concentration (HCO-3), acid-base balance, plasma epinephrine (E) and norepinephrine (NE) were determined from venous blood samples obtained through an indwelling brachial catheter. Maximal oxygen uptake was significantly different between conditions: 72.0 +/- 5.4 ml kg-1 min-1 at 20 degrees C; 68.9 +/- 5.1 ml kg-1 min-1 at 0 degree C and 68.5 +/- 4.6 ml kg-1 min-1 at -20 degrees C. Workload, time to exhaustion, glucose levels and rectal temperature decreased significantly at -20 degrees C. Catecholamines and lactate values were not significantly altered by thermal conditions after maximal exercise but the catecholamines were decreased during rest. Bicarbonate, respiratory quotient, lactate and ventilatory thresholds increased significantly at -20 degrees C. The data support the contention that metabolic and hormonal responses following progressive incremental exercise are altered by cold exposure and they indicate a marked decrease in maximal oxygen uptake, time to exhaustion and workload.

Arthritis and Aerobic Exercise: A Review.

Abstract: In brief: Despite increasing evidence that regular aerobic exercise yields many benefits for patients with arthritis, patients often are advised to curtail physical activity. Findings from studies of patients with either rheumatoid arthritis or osteoarthritis who participated in an aerobic exercise program show that the subjects made significant gains in aerobic capacity, functional status, muscle strength, and other aspects of performance. In addition, they improved in subjective aspects that might have a positive impact on quality of life, including pain tolerance, joint pain, mood, and social activity. The authors discuss some questions that remain unanswered and present guidelines for physicians who wish to prescribe aerobic exercise for their arthritis patients.

The role of exercise in preventing osteoporosis

Abstract: Evidence from a variety of sources indicates that exercise can increase the mineral content of bone, raising the expectation that exercise programs may be effective therapy for the treatment of osteoporosis, and the prevention of hip and spinal fractures. Indeed, prospective studies demonstrate that primarily weight-bearing exercise prevents the age-related decline in axial skeletal mass and, in some instances, increases bone mineral content. Optimal changes in the skeleton in response to exercise are seen in those women with adequate intake of dietary calcium. Neither hormonal status nor age appears to preclude the skeletal benefits of exercise. The design of an exercise program must consider the physical condition of the participants, their current levels of activity, their compliance, and the objectives of the program. Generic programs that are not designed for individuals' needs and limitations, and that are not adequately supervised, will result in a high rate of musculoskeletal complications and noncompliance. Unfortunately, additional studies are necessary before we can construct an optimum exercise prescription for bone health which addresses duration, frequency, intensity, and type of exercise. Of concern is the fact that gains in bone mass achieved with exercise are lost following their discontinuation in postmenopausal women, underscoring the concept that the level of physical activity is a major and dynamic determinant of skeletal integrity. Thus, it will be necessary to develop strategies to preserve the gains in skeletal mass achieved through exercise. Finally, before exercise can be promoted for bone health, it will be necessary to demonstrate that such programs can indeed prevent osteoporotic fractures.

Measurement of Cardiac Output in Children during Exercise: A Review

Abstract: Knowledge of cardiac output changes during exercise is helpful for understanding normal exercise physiology and the effect of disease upon exercise performance. There are four noninvasive techniques applicable to measurement of cardiac output in children: Indirect Fick, acetylene rebreathing, electrical bioimpedance, and Doppler. Each technique requires substantial operator experience to obtain reliable and reproducible results.

Selective enhancement of the cardiac sympathetic response to exercise by anginal chest pain in humans

Abstract: Cardiac and whole body [3H]norepinephrine kinetics were used to evaluate the response of overall and cardiac sympathetic activity to supine bicycle exercise in 31 patients with coronary artery disease (CAD) and in nine normal control subjects (group 1). Of the 31 patients with CAD, 20 developed evidence of myocardial ischemia during exercise (group 2), typical angina occurring in 20 of 20 and ischemic ST segment changes in 13 of 20, whereas 11 patients developed no evidence of ischemia (no chest pain or electrocardiographic changes) (group 3). Exercise resulted in increased total and cardiac NE spillover in all groups of patients. Basal cardiac NE spillover was similar in the three groups (group 1, 5 +/- 1 ng/min; group 2, 8 +/- 1 ng/min; group 3, 7 +/- 2 ng/min; p = NS), but during exercise, cardiac NE spillover was greater in patients who developed angina (group 2, 30 +/- 5 ng/min) than in those who did not (group 1, 17 +/- 2 ng/min; group 3, 17 +/- 2 ng/min; p less than 0.05). The increases in total NE spillover were similar in the three groups. Supine bicycle exercise increases cardiac and overall sympathetic tone in normal control subjects and in patients with CAD. The occurrence of angina selectively enhances the cardiac sympathetic response to exercise. In the absence of angina, patients with CAD and control subjects without CAD have similar sympathetic responses to exercise.

The effect of circumvaginal muscle (CVM) exercise.

Abstract: Circumvaginal muscle (CVM) home training based on principles of exercise physiology were tested on 48 healthy reproductive-age women. The effect of CVM exercise with a resistance device in place, CVM exercise without a device, and no exercise with device in place was studied. After random assignment to home training, CVM assessment was carried out prior to and after 6 weeks of CVM training at home. Each subject served as her own control and change scores of the three groups, on CVM variables were subjected to analysis of variance. Peak maximum pressure (PMP) was significantly different for the three groups. F = 4.56, df = 2.45, p = .016. PMP of exercise without a device was significantly different from the no exercise group (Dunett's test). Analysis of measurement error between- and within-subjects showed that the inherent variability between women was approximately four times larger than the measurement error. The results support the prescription of CVM exercise to hypertrophy the CVM, and indicate that further investigation of the large variance found in the pressure data is needed.

Effect of beta-adrenergic blockade on hormonal responses during continuous and intermittent exercise.

Abstract: The modifying effect on exercise performance and neuroendocrine response of the nonselective beta blocker timolol (10 mg b.i.d. for 5 days) and the beta 1-selective beta blocker metoprolol (100 mg b.i.d. for 5 days) was studied. The hormones studied were growth hormone, prolactin, cortisol, renin, epinephrine, dopamine, and norepinephrine. The response was studied during short-term maximal dynamic exercise, using two different exercise protocols; continuous (n = 11) and intermittent (n = 9) bicycle ergometry, in normal healthy young men. Accumulated work on placebo was nearly identical in the two studies, but was significantly reduced by 10.4% and 6.6% with timolol and by 4.7% and 6.7% with metoprolol, during continuous and intermittent exercise, respectively. During continuous exercise, accumulated work was 5.8% lower (p less than 0.05) with timolol than with metoprolol. The hormonal plasma concentrations of all hormones except renin were higher during continuous exercise than during intermittent exercise. Beta blockade had no effect on baseline hormonal levels, but the response was markedly changed during exercise. Maximum epinephrine, cortisol, and prolactin responses increased after beta blockade; dopamine remained nearly unchanged; while the renin responses were attenuated. Norepinephrine concentrations were slightly increased during continuous exercise by beta blockade and rose in direct proportion to the increase in workload. During intermittent exercise, maximum norepinephrine levels were significantly reduced by beta blockade compared with placebo. Thus the effect of beta 1-selective and nonselective beta receptor blockade on circulating hormones does not seem to explain the reduced exercise capacity following beta blockade.

Physical Performance and Carbohydrate Consumption in CF Commandos during a 5-Day Field Trial

Abstract: : This study evaluated the capacity of military personnel to perform maximal exercise before and after 5 days of sustained physical activity. An additional goal was to evaluate whether a carbohydrate supplement to the regular field rations would reduce the extent of any performance impairments. Subjects (Ss) were 29 male volunteers from the Canadian Forces Airborne Regiment. They were allowed 4-5 h sleep each 24h and 45 min per meal, but were otherwise continuously occupied with physically demanding missions in a field environment. Performance tests administered 2 days before and at the end of a the 5-day field trial included evaluations of maximal aerobic power during cycle exercise, anaerobic power, muscular strength and endurance, rate of maximal force development and reaction time. Muscle and blood tissue samples were obtained before and after the trial to clarify the relative contribution of fat and carbohydrate energy stores to meeting the metabolic cost of the field trial. The results demonstrated that the Ss were in a marked negative caloric balance by the end of the field trial. Skeletal muscle glycogen stores were markedly depleted. In association with these changes there were significant impairments at the end of the trial in maximal aerobic power, maximal dynamic strength, and anaerobic power of large muscle groups. These observations have direct implications for mission planning and physical performance expectations of military units involved in sustained operations.

Exercise countermeasures for bed-rest deconditioning

Abstract: The purpose for this 30-day bed rest study was to investigate the effects of short-term, high intensity isotonic and isokinetic exercise training on maintenance of working capacity (peak oxygen uptake), muscular strength and endurance, and on orthostatic tolerance, posture and gait. Other data were collected on muscle atrophy, bone mineralization and density, endocrine analyses concerning vasoactivity and fluid-electrolyte balance, muscle intermediary metabolism, and on performance and mood of the subjects. It was concluded that: The subjects maintained a relatively stable mood, high morale, and high esprit de corps throughout the study. Performance improved in nearly all tests in almost all the subjects. Isotonic training, as opposed to isokinetic exercise training, was associated more with decreasing levels of psychological tension, concentration, and motivation; and improvement in the quality of sleep. Working capacity (peak oxygen uptake) was maintained during bed rest with isotonic exercise training; it was not maintained with isokinetic or no exercise training. In general, there was no significant decrease in strength or endurance of arm or leg muscles during bed rest, in spite of some reduction in muscle size (atrophy) of some leg muscles. There was no effect of isotonic exercise training on orthostasis, since tilt-table tolerance was reduced similarly in all three groups following bed rest. Bed rest resulted in significant decreases of postural stability and self-selected step length, stride length, and walking velocity, which were not influenced by either exercise training regimen. Most pre-bed rest responses were restored by the fourth day of recovery.

Exercise Guidelines for the Elderly (Part 2 of 2).

Abstract: In brief: A properly designed and implemented exercise program for the elderly can have many physical and emotional benefits. Most important, these benefits can allow older persons to maintain an independent, active life-style. However, the program or activity plan must be carefully followed to avoid exercise-related difficulties to which the elderly are prone. Before such a program is begun, the patient should undergo a careful evaluation to show any condition-especially cardiovascular, musculoskeletal, or neurologic-that would preclude exercise or require treatment beforehand. Certain laboratory tests and resting and exercise ECGs should also be performed.

Role of lactic acidosis in the ventilatory response to heavy exercise

Abstract: The purpose of this study was to determine the role of lactic acidosis in the ventilatory response to heavy exercise above anaerobic threshold. Seven subjects ingested either NaHCO3 or CaCO3 at a dose of 300 mg/kg body weight and ran on a motor-driven treadmill at a work load corresponding to 90% of VO2max and above anaerobic threshold for a period of 5 min while minute ventilation and PETCO2 were recorded breath by breath. A total of 10 runs, 5 with CaCO3 and 5 with NaHCO3 in a randomized and blind order, were done in each subject. Statistical analyses of the effects of the chemicals on minute ventilation during the 15 s between min 4.75 and 5 of exercise showed that the differences in ventilation did not reach statistical significance (p greater than 0.05) in 5 of the 7 subjects. Venous pH measurements at the end of exercise revealed a significant increase with NaHCO3 (p much less than 0.05). It is concluded that lactic acidosis is not an essential determinant of ventilatory response to heavy exercise above anaerobic threshold in the majority of the subjects.