Showing papers on "Exercise physiology published in 1984"

Adaptations of skeletal muscle to endurance exercise and their metabolic consequences

Abstract: Regularly performed endurance exercise induces major adaptations in skeletal muscle. These include increases in the mitochondrial content and respiratory capacity of the muscle fibers. As a consequence of the increase in mitochondria, exercise of the same intensity results in a disturbance in homeostasis that is smaller in trained than in untrained muscles. The major metabolic consequences of the adaptations of muscle to endurance exercise are a slower utilization of muscle glycogen and blood glucose, a greater reliance on fat oxidation, and less lactate production during exercise of a given intensity. These adaptations play an important role in the large increase in the ability to perform prolonged strenuous exercise that occurs in response to endurance exercise training.

Exercise physiology: Human bioenergetics and its applications

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Metabolic recovery after exercise and the assessment of mitochondrial function in vivo in human skeletal muscle by means of 31P NMR.

Abstract: It has been suggested that the rate of phosphocreatine resynthesis after exercise is an index of mitochondrial oxidative metabolism in intact muscle. To investigate this hypothesis, the time courses of metabolite recovery following mild and more severe dynamic exercise of human forearm muscle were compared by means of 31P NMR. Severe exercise resulted in greater net hydrolysis of phosphocreatine and greater intracellular acidosis than light exercise. The rate of phosphocreatine resynthesis was significantly slower during recovery from the more severe exercise. To explain this it was noted that, as a consequence of the high activity of creatine kinase in the sarcoplasm, the [phosphocreatine] at any time is a function of the intracellular pH. Calculations demonstrate that the difference between rates of phosphocreatine recovery after the two exercise protocols was primarily determined by the rates of recovery of the intracellular pH to normal rest values. It is concluded that the calculated rate of recovery of the cytosolic free [ADP] to its pre-exercise concentration may provide a more specific measure of mitochondrial oxidative activity.

The effect of exercise training on human hypertension: a review.

Abstract: Numerous sources of information in both the medical and exercise physiology areas state that exercise training lowers blood pressure at rest and during submaximal exercise in normotensive and hypertensive individuals. Based on these statements, the medical community is currently recommending regular exercise as a non-pharmacological therapy for reducing blood pressure in hypertensive patients. The purpose of this review was to assess the existing literature in this area to determine whether a basis exists for this recommendation. Our findings indicate that most of the studies reviewed reported modest reductions in blood pressure (means less than or equal to 10 mmHg) at rest and during submaximal exercise after training. However, even the modest reductions in blood pressure reported in these studies must be interpreted with caution because of numerous methodological shortcomings and inadequate study design, most notably the omission of non-exercising hypertensive control groups. Therefore, the evidence available at the present time is inadequate to recommend exercise training as a non-pharmacological therapy in hypertension.

Differentiated ratings of perceived exertion and various physiological responses during prolonged upper and lower body exercise

Abstract: This study examined whether prolonged exercise employing upper or lower body muscle groups led to significant alterations in three differentiated ratings of perceived exertion (RPE). Multiple regression analyses were used to identify those physiological responses which accounted for the greatest variability in these three RPE. Nine volunteer males performed 60 min of arm crank and cycle exercise at similar absolute and at similar relative exercise intensities. There were no significant differences (P>0.05) between arm and leg exercise for oxygen uptake (\(\dot V_{{\text{O}}_{\text{2}} }\)) during the absolute tests (~ 1.60 l·min−1) or during the relative tests (~ 60% peak\(\dot V_{{\text{O}}_{\text{2}} }\)). The RPE included local RPE (muscle and joint exertion), central RPE (ventilatory and circulatory exertion), and overall RPE. During the absolute tests, the final means for all three RPE were lower (P 0.05) were found during the relative tests between arm and leg exercise for any of the three RPE. Local RPE was generally higher than central RPE. The various physiological responses accounted for more (total) variance in all three RPE for arm than leg exercise (absolute and relative arm exercise: median R2=0.99; absolute and relative leg exercise: median R2=0.75). Lactate and the ventilatory equivalent of oxygen made the greatest contribution to R2. These data suggest that RPE may be more closely related to relative exercise intensity, and perceptual cues may be more readily monitored from smaller muscle masses such as the upper body. Further, steady-state RPE was not attained during prolonged upper body exercise.

Skeletal muscle metabolism of sea-level natives following short-term high-altitude residence.

Abstract: The influence of short-term high-altitude (HA) residence on intramuscular pH and skeletal muscle enzyme activity of sea-level (SL) residents was investigated. Vastus lateralis muscle samples were obtained by biopsy from rested subjects (n = 5) at SL (50 m) and on the 18th day of HA residence (4,300 m) for determination of glycogen phosphorylase, hexokinase, malate dehydrogenase, and total lactate dehydrogenase activities. A second group of subjects (n = 6) performed cycle exercise of the same absolute intensity (mean +/- SE = 195 +/- 5 W) at SL and on the 15th day of residence at HA. Before and immediately after exercise, vastus lateralis muscle samples were obtained for the determination of intramuscular pH, and venous blood was obtained for determination of lactate concentration. The first group of subjects showed no significant changes in skeletal muscle enzyme activity after 18 days at HA. The second group of subjects were instructed to exercise for exactly 30 min, and all but one could complete the entire bout at SL. However, at HA, none could continue 30 min, and time to exhaustion (mean +/- SE) was 11.9 +/- 1.6 min. Resting intramuscular pH was not significantly different after HA residence as compared to SL. The fall in intramuscular pH was less with exercise on day 15 at HA than during SL exercise. Likewise, the increase in blood lactate concentration with exercise at HA was less than at SL. These data indicate that, after 15-18 days of HA residence, limitations in exercise performance are not due to inordinate intramuscular acidosis or to changes in the activity of glycolytic and oxidative enzymes.

The effect of exercise training on glycogen, glycogen synthase and phosphorylase in muscle and liver

Abstract: It is thought that exercise training in both man and the rat results in a protective effect against the depletion of carbohydrate stores during exercise (glycogen-sparing). However there has been no comprehensive study of the effects of training on glycogen anabolic and catabolic enzymes with liver or muscle. The aim of this study was to examine whether changes in these enzymes occur and whether these changes may provide an explanation for the glycogen-sparing which results from exercise training.

Effects of Talking on Exercise Tolerance

Abstract: Two studies determined the effects of responding to questions on heart rate (HR), rating of perceived exertion (RPE), and time to voluntary exhaustion on a graded treadmill walking/running test in naive college students. The first study used 16 (8 female and 8 male) volunteers; each subject was tested both without talking and while responding to 3 questions during each exercise stage. The second study had independent groups (n = 10 females each): (1) no talking during the early exercise stages (two walking stages), but answering questions during the later (running) stages until exhaustion, and (2) answering questions during the walking stages, but not talking during the running stages. Differences between groups (.10 level) were determined by two-way ANOVA (talking/no talking; gender) and t test for independent groups, respectively. There were no gender/treatment interactions. Exercise tolerance, HR, and RPE were generally not affected by the tester asking subjects questions about subjects' physi...

Metabolic and Cardiovascular Responses of Children during Prolonged Physical Activity.

Abstract: Metabolic and cardiovascular responses during 45 minutes of continuous moderate intensity exercise were investigated in 11 children, 8–11 years of age. Maximal oxygen consumption ( max) was determined by a treadmill test and was used to set the workload for the prolonged 45-minute exercise test at 50% max. Oxygen consumption, pulmonary ventilation, and central and peripheral circulatory measures were monitored for two-minute intervals at six selected points (min 4, 11, 18, 29, 36, 43) during the exercise period. Oxygen consumption during the first measurement period was 0.92 l/min and was significantly higher (p < .05) than the five subsequent time periods which averaged 0.88l/min. The respiratory exchange ratio decreased (p < .05) after the second measurement period from 0.90 to 0.86. Pulmonary ventilation did not change significantly, although breathing rate and tidal volume significantly (p < .05) increased by 9.1% and decreased by 8.3%, respectively. Changes in cardiac output, measured by the...

Effect of Physical Work and Sleep Loss on Recovery Sleep

Abstract: : The effect of exercise and sleep loss on sleep was studied in four groups of young, physically fit, well-trained U.S. Marine Corps male volunteer subjects. In the first study, Study 1, ten pairs of Marines were observed. One member of each pair was assigned to an exercise routine and walked on a treadmill in full combat gear at a speed that induced an elevated heart rate corresponding to 30% of the individual's VO2 max. Exercise periods lasted half an hour per hour for two 17-hr long periods of continuous work, designated CW1 and CW2. The two CW episodes were separated by a 3-hr nap. Individuals assigned the exercise routine spent the second half of each hour in the CW period performing cognitive tasks using a computer terminal. The remaining member of each pair was assigned to a non-exercise, 'control' routine. Study 1 consisted of two routines and data on the participants and were grouped as follows: (1) 'Nap/Exercise', and (2) 'Nap/No Exercise.' In a second study, Study 2, eight pairs of Marines participated. In Study 2 the experimental protocol was identical with Study 1 with the exception that neither the exercising subject nor the control subject were permitted to nap between CW1 and CW2.