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Biomedical subjects

R C Hickson

Publications and source records attributed to R C Hickson.

71 records · Page 4Linked to original sources
PubMed1979

Effect of training on hormonal responses to exercise in competitive swimmers.

The effects of 9 weeks of training on responses of plasma hormones to swimming were studied in eight competitive swimmers who had not trained for several months. Two types of swimming tests were used: (1) 200 yd, a high intensity, exhausting type of exercise in which maximal effort was required both before and after training, and (2) 1000 yd, a pace type of exercise in which subjects swam as fast as possible prior to training and at the same rate after training. Plasma levels of glucagon increased and of insulin decreased during 1000 yd of swimming, but were not altered by 200 yd of swimming. No training effects were apparent in responses of plasma insulin and glucagon to these shortterm, high intensity exercise tests. During the 1000 yd swim, plasma adrenaline was 0.8 ng/ml before vs. 0.1 ng/ml after training. Plasma noradrenaline response decreased from 3.4 to 1.2 ng/ml as a result of training. In the 200 yd swim, adrenaline, but not noradrenaline, was lower after training.

Adolescent↗
PubMed1979

Effect of endurance exercise training on plasma pancreatic polypeptide concentration during exercise.

The effect of exercise on human pancreatic polypeptide (hPP) levels was evaluated in five subjects preceding and following a conditioning program. During 90 min of exercise, the plasma concentration of hPP rose to a peak value five times higher than the resting level. After 2 mo of endurance exercise training, exercising at the same absolute work load resulted in only a twofold increase in hPP levels. Even at a higher work load, plasma hPP levels were significantly lower than the values observed prior to conditioning. These results show that plasma hPP concentrations rise during exercise and the magnitude of this response is significantly lower after 2 mo of endurance exercise training.

Adult↗
PubMed1979

Development and regression of exercise-induced cardiac hypertrophy in rats.

Adult female rats were exercised by daily swimming. All the increase in heart weight induced by the exercise occurred within 14 days and averaged 30%. The half times of the increases in heart weight and total protein content were about 4.5 days, whereas that of cytochrome c, which was used as a mitochondrial marker, was 6.5 days. The total amounts of DNA and of hydroxyproline in the heart, which were used to evaluate the degree of connective tissue hyperplasia, increased only slightly (8% and 10%, respectively). Other animals were subjected to the same swimming program for 21 days. Groups of rats were killed at various time intervals after stopping exercise. Heart weight, total protein content, and total cytochrome c content decreased rapidly initially, with 60% of the total regression of hypertrophy occurring during the first week. Thereafter, heart weight fell more gradually toward the sedentary control value. The hydroxyproline content of the heart, which was increased 10%, did not decrease during the regression of the hypertrophy.

Animals↗
PubMed1979

Training-induced changes in hormonal and metabolic responses to submaximal exercise.

Plasma glucagon and catecholamines increase during prolonged submaximal exercise, but the magnitude of the increase is less in endurance-trained individuals than in untrained subjects. We have studied the rapidity at which this adaptation occurs. Six initially untrained healthy subjects exercised vigorously (on bicycle ergometers and by running) 30-50 min/day, 6 days/wk, for 9 wk. Prior to the beginning of training and at 3-wk intervals thereafter, participants were subjected to 90-min bicycle ergometer test work loads that elicited 58 +/- 2% of the subjects' initial maximal oxygen consumption. The major proportion of the training-induced decrement in plasma glucagon and catecholamine responses to exercise was seen after 3 wk of training. We conclude that the hormonal component of the training adaptation occurs very early in the course of a vigorous endurance training program.

Adult↗
PubMed1979

Disappearance of norepinephrine from the circulation following strenuous exercise.

Five subjects who had been training vigorously for 2 mo worked 5 min on the cycle ergometer at 1,480 +/- 100 kpm/min and at 1,920 kpm/min on separate days. Plasma norepinephrine (NE), blood lactate, and heart rate were determined during the postexercise periods. The same subjects were also tested at 1,480 +/- 100 kpm/min after a 2-mo detraining period, when subjects did not train. At 1,920 +/- 80 kpm/min, plasma NE was 4 ng/ml at the end of exercise. The NE concentration increased slightly in the first min postexercise, then decreased with a half-time of 2.8 min between 1 and 11 min postexercise. Detraining for 2 mo did not markedly affect the rate of disappearance of NE in the postexercise period in these five subjects. Between 11 and 30 min postexercise (1,480 +/- 100 kpm/min), heart rate was 25 beats/min higher after detraining, while NE was not significantly different. These data provide evidence that more rapid recovery of heart rate in trained individuals during this period is not likely due to a more rapid recovery from the sympathetic response to exercise.

Adult↗
PubMed1978

Regulation of glycogen resynthesis in muscles of rats following exercise.

Following a strenuous bout of exercise, glycogen repletion occurred most rapidly in the fast-twitch red type of muscle, least rapidly in fast-twitch white, and at an intermediate rate in slow-twitch red muscle. There was a linear correlation between glycogen synthase I activity and the rate of glycogen synthesis in the three types of muscle. This finding helps explain the differences between the rates of glycogen resynthesis in the three muscle types, and supports the view that glycogen synthase activity is the most important factor determining the rate of glycogen synthesis when substrate supply is adequate. There was an inverse correlation between muscle glycogen concentration and percent glycogen synthase I. Plasma insulin concentration was low and norepinephrine and glucagon concentrations were elevated in the postexercise period. The finding that rapid glycogen synthesis occurred despite a hormonal milieu conducive to glycogenolysis provides evidence that a low glycogen concentration is a potent stimulus to glycogen synthesis that overrides the effects of low insulin, and high norepinephrine and glucagon levels.

Animals↗
PubMed1978

Faster adjustment of O2 uptake to the energy requirement of exercise in the trained state.

The purpose of this study was to determine the effect of endurance exercise training on the time course of the increase in VO2 toward steady state in response to submaximal constant load work. Seven men participated in a strenuous program of endurance exercise for 40 min/day, 6 days/wk for 10 wk. Their average VO2max increased from 3.29 liters before training to 4.53 liters at the end of the training program. VO2 was measured continuously on a breath-by-breath basis at work rates requiring 40%, 50%, 60%, or 70% of VO2max before training. After training the subjects were retested both at the same absolute and the same relative work rates. The increases in VO2 toward steady state occurred more rapidly in the trained than in the untrained state both at the same absolute and at the same relative work rates. The finding that O2 uptake rises to meet O2 demand more rapidly in the trained than in the untrained state provides evidence that the working muscles become less hypoxic at the onset of exercise of the same intensity after training.

Adult↗
PubMed1978

Time course of sympathoadrenal adaptation to endurance exercise training in man.

One possible reason for the lower exercise heart rate after endurance exercise training is that the sympathetic drive to the heart is reduced. We have studied the relationship between plasma catecholamines and heart rate during exercise in the course of a 7-wk training program. Six untrained subjects exercised vigorously (on bicycle ergometers and by running) 30--50 min/day for 7 wk. Prior to the beginning of training and at weekly intervals thereafter, participants were subjected to a 5-min strenuous bicycle ergometer test. In the test prior to training, plasma epinephrine increased to 0.5 ng/ml and norepinephrine increased to 3.0 ng/ml. The major proportion of the training-induced decrement in catecholamine response was reached at the end of the 3rd wk when epinephrine increased to 0.17 ng/ml and norepinephrine increased to 1.5 ng/ml in response to the same test. Heart rate during exercise continued to decrease even after the catecholamine response had plateaued, implying that the reduced sympathetic response is not solely responsible for the reduced exercise heart rate.

Adaptation, Physiological↗
PubMed1977

Linear increase in aerobic power induced by a strenuous program of endurance exercise.

Eight subjects exercised for 40 min/day, 6 days/wk for 10 wk. For 3 days/wk they performed six 5-min intervals of bicycling on an ergometer against a resistance that elicited VO2 max, separated by 2-min intervals of exercise requiring 50-60% of Vo2 max. On the alternate 3 days, they ran as far as they could in 40 min. Our purpose was to obtain information regarding the time course and magnitude of the increase in Vo2 max and endurance that occur in response to strenuous exercise when the training stimulus is kept approximately constant relative to maximum aerobic capacity. Average Vo2 max increased 5% (P less than 0.05) during the 1st wk. Endurance, Vo2 max, and time to attainment of peak heart rate all increased linearly during the 10 wk. The average weekly increase in Vo2 max was 0.12 l/min. The total increase in Vo2 max averaged 16.8 ml/kg per min (44%). Four of the eight subjects attained Vo2 max levels approaching or exceeding 60 ml/kg per min. It appears from these results that aerobic work capacity can increase more rapidly and to a greater extent in response to training than has generally been thought.

Adult↗
PubMed1977

Effect of training on the response of plasma glucagon to exercise.

This study was undertaken to determine whether the increase in plasma glucagon concentration that occurs in response to prolonged exercise is modified by endurance exercise training. Eight subjects participated in an exercise program, consisting of running and bicycling, 4 days/wk for 10 wk. The training program resulted in an average increase in VO2 max of 18%. The average increase in plasma glucagon during a 60-min long bicycle exercise test that required 60% of the subjects' VO2 max was 107+/-28 pg/ml, from 116+/-14 pg/ml at rest to 223+/-37 pg/ml after 60 min of exercise, prior to training. After training the same absolute work rate resulted in an increase in plasma glucagon of only 20+/-6 pg/ml, from 125+/-20 to 145+/-16 pg/ml (P less than 0.02). A similar blunting of the glucagon response to exercise was seen during work of the same relative intensity after training. Plasma insulin concentration decreased from 18.1+/-2.5 to 7.6+/-1.6 muunits/ml during the 60 min of exercise before training. A similar decrease in insulin concentration was seen at the same relative work rate after training. However, the decrease in plasma insulin at the same absolute work rate, from 18.5+/-3.0 to 12.5+/-1.8 muunits/ml, was significantly smaller after training (P less than 0.05).

Adult↗
PubMed1977

Effects of increased plasma fatty acids on glycogen utilization and endurance.

The purpose of this study was to test the hypothesis that increased availability of fatty acids could increase endurance by slowing the rate of glycogen depletion. Rats were given corn oil by stomach tube, and 3 h later an injection of heparin was given to raise their plasma free fatty acids (FFA). The rats with raised FFA were able to run approximately 1 h longer than otherwise comparable control animals before becoming exhausted (181 +/- 8 vs. 118 +/- 8 min, P less than 0.001). At the point of exhaustion, both groups were hypoglycemic and had low muscle glycogen concentrations. The fall in blood glucose occurred less rapidly in the animals with raised FFA; these rats also had significantly higher blood glycerol and beta-hydroxybutyrate concentrations than the controls. Glycogen concencentration decreased less rapidly in all three types of skeletal muscle and in liver in the animals with raised FFA than in the controls. We conclude that increased availability of fatty acids delays the development of exhaustion in rats subjected to prolonged running. It appears likely that the carbohydrate-sparing effect of fatty acids is largely responsible for the increase in endurance.

Animals↗
PubMed1976

Effects of an anabolic steroid and sprint training on selected histochemical and morphological observations in rat skeletal muscle types.

The effects on selected histochemical and morphological parameters of anabolic steroid administration and of high-intensity sprint running, separately, and in combination, were studied in young adult male rats. Dianabol (methandrostenolone) 1 mg/day for 8 weeks had no significant effects on phosphorylase or glycogen staining intensities and on fiber area in skeletal muscles of either trained or sedentary animals. The program of sprint training resulted in significantly decreased intensities of phosphorylase in all ten regions of the gastrocnemius, plantaris, and soleus muscles that were studied. Glycogen localization was significantly increased with training in five regions of the gastrocnemius and plantaris muscles which contained predominantly fast-switch fibers. No changes in fiber area occurred with the training program. We conclude from these results that (a) normal androgen levels in young, healthy male animals are sufficiently high so that the intake of large doses of anabolic steroid does not result in the stimulation of glycogen metabolism or hypertrophy of skeletal muscle; (b) the changes induced by high-intensity, short-duration sprint training suggest that the existing glycolytic capacity of muscle is adequate to supply the muscles energy needs even during the stress of very strenous exercise, and that more fast-twitch fibers were recruited by the exercise regimen than slow-twitch fibers.

Animals↗
PubMed1976

Skeletal muscle enzyme alterations after sprint and endurance training.

Specifically designed programs of sprint and endurance running were used to determine how different types of training affect enzyme activities in selected energy metabolism pathways. Three types of rat skeletal muscle were studied. After 8 wk of training, small but significant decreases in lactate dehydrogenase activity (15%) were found in the soleus and white vastus lateralis muscles of the sprint animals. Decreased levels of phosphoglucomutase and lactate dehydrogenase (approx. 20%) of the white vastus lateralis muscles of the endurance group were observed at the same time. By 16 wk of training, fumarase activity increased approximately twofold in the white vastus muscles and 45% in the soleus and plantaris muscles of the endurance group. Similarly, increased fumarase activity (42%) was seen in the soleus muscles of the sprint group. In all muscles, phosphoglucomutase and lactate dehydrogenase activities generally were lower in the endurance animals than in the control animals. No significant differences were found between the sprint and endurance groups at either or sixteen weeks of training. These results suggest that similar enzyme adaptations occur over time with both types of training.

Adaptation, Physiological↗
PubMed1976

Effects of dianabol and high-intensity sprint training on body composition of rats.

The effects on body composition and organ weights of anabolic steroid administration and of high-intensity sprint running, separately and in combination, were studied in young adult male rats. Dianabol (methandrostenolone) 1 mg/day for 8 weeks had no significant effects on muscle weight or lean body mass in either the trained or the sedentary animals. The program of sprint training resulted in a lower body weight, a lesser percentage of body fat (Runners, 8.5%, vs. sedentary, 13.5% P less than 0.01) and a greater relative lean body mass (runners, 91.5% vs. sedentry, 86.5%, P less than 0.01). We conclude from these results that (a) normal androgen levels in young, healthy male animals are sufficiently high so that the addition of a large dose of anabolic steroid does not result in stimulation of additional muscle growth, and (b) the changes in body composition induced by high-intensity, short-duration sprint training are qualitatively similar to those seen with endurance exercise training.

Adrenal Glands↗
PubMedDate not supplied

Adverse effects of anabolic steroids.

Anabolic steroids are used therapeutically for various disorders and as ergogenic aids by athletes to augment strength, muscular development, and to enhance performance. There is a wide range of concomitant temporary and permanent adverse effects with steroid administration. Several well-documented adverse actions of these hormones may develop rapidly within several weeks or less (i.e. altered reproductive function) or require up to several years of steroid intake (i.e. liver carcinoma). More recent studies indicate that glucose intolerance, insulin resistance, increased cardiovascular disease risk profiles, cerebral dangers, musculoskeletal injuries, prostate cancer, psychosis and schizophrenic episodes, among others, accompany anabolic steroid intake. There is, at present, no evidence to support the claim that athletes are less susceptible to adverse effects than those individuals receiving hormone treatment in a clinical setting. Based on the available information which has accumulated primarily from cross-sectional, short term longitudinal, and case studies, there is a need: (a) to develop a comprehensive battery of specific and sensitive markers of adverse effects, particularly those that would be able to detect the onset of adverse actions; and (b) to conduct controlled long term longitudinal studies in order to fully understand the extensiveness and mechanisms involved in the occurrence of adverse effects.

Anabolic Agents↗