摘要:

GORDON, N. F., J. P. VAN RENSBURG, D. P. VAN DEN HEEVER, N. B. KALLIATAKIS, and D. P. MYBURGH. Effect of dual β-blockade and calcium antagonism on endurance performance.Med. Sci. Sports Exerc., Vol. 19, No. 1, pp. 1–6, 1987. The effect of oral clinically used doses of propranolol, atenolol, nifedipine, propranolol + nifedipine, and atenolol + nifedipine on endurance performance and ventilatory responses to graded treadmill testing was studied in 12 healthy physically active men. Maximal exercise duration was reduced by propranolol (8.5%,P< 0.001) and its combination with nifedipine (11.1%,P< 0.001), and to a lesser degree by atenolol (3.2%, 0.05 <P< 0.1), nifedipine (2.1%,P< 0.05), and atenolol + nifedipine (3.9%,P< 0.01). Exercise duration and heart rate (HR) and ventilatory responses to maximal exercise were equivalent with a β-blockade reduced the HR and oxygen uptake, nifedipine accentuated the HR but did not alter ventilation, and all drugs modified the relative oxygen uptake corresponding to 85% of the maximal HR. Physiologic responses to submaximal exercise during combination therapy were similar to those during β-blockade alone. This study concludes that, in physically active men, nifedipine induces a small impairment of maximal performance, but does not accentuate the reduction in effort tolerance resulting from β-blockade. Furthermore, HR and ventilatory responses to exercise during combined β-blockade and calcium antagonism can be predicted from those during β-blockade alone.

ISSN:0195-9131    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

LOCKETTE, W., R. MCCURDY, S. SMITH, and O. CARRETERO. Endurance training and human α2-adrenergic receptors on platelets.Med. Sci. Sports Exerc., Vol. 19, No. 1, pp. 7–10, 1987. Trained endurance athletes have a smaller rise in blood pressure, heart rate, and catecholamine response to stress when compared to an untrained, control population. Since pre-synaptic α2-adrenergic receptors modulate the control of epinephrine release from nerve terminals, and since platelets are used as models of monoaminergic neurons, we investigated changes in the number and affinity binding of α2-adrenergic receptors on platelets from endurance athletes and a sedentary population using the radiolabeled ligand yohimbine. We found, compared to a control, sedentary population, trained athletes had a 45% increase in the number of platelet α2-adrenergic receptors (338 ± 39 receptors/platelet vs 233 ± 25 receptors/platelet,P< 0.05) with no change in the dissociation constant (2.53 nM ± 0.2 vs 2.24 nM ± 0.2, NS) or the ED50concentration for the competitive displacement of 2.5 nM yohimbine by epinephrine (2.8 x 10-6M vs 3.34 x 10-6M, NS). The increase in α2-adrenergic receptors found in athletes may explain their decreased catecholamine response and concomitant physiologic responses to exertion.

ISSN:0195-9131    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

SQUIRE, J. M., M. M. MYERS, and R. FRIED. Cardiovascular responses to exercise and stress in the borderline hypertensive rat.Med. Sci. Sports Exerc. Vol. 19, No. 1, pp. 11–16, 1987. This report demonstrates the effect of voluntary exercise in attenuating increases in heart rate (HR) caused by chronic stress in an animal model of stress-induced hypertension, the borderline hypertensive rat (BHR). Exercise training also protected against the hypertensive effects of stress in 16-wk-old, but not 10-wk-old animals. In the first experiment, adult borderline hypertensive rats were subjected to 1 wk of signaled shock followed by 6 wk of signaled, unsignaled, or no shock. Half of these animals also had free access to a running wheel. Blood pressure (BP) and HR were measured before and after treatments by the tail cuff method. Exercise was found to significantly attenuate the rise in BP by 56% and HR by over 100%, as compared to non-exercised animals. In a second study, borderline hypertensive rats were subjected daily to anticipation of shock or handling for 6 wk. Half of these animals could exercise voluntarily. BP and HR, measured weekly under light ether anesthesia, increased over time due to both stressors alone. Exercise attenuated stress-induced increases in HR by 50%, but did not attenuate BP. These studies demonstrate that voluntary exercise can reliably attenuate increases in HR regardless of age or concurrent stress, but the protective effects of exercise on stress-induced hypertension may interact with the age of the subject.

ISSN:0195-9131    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

KAUFMAN, F. L., R. L. HUGHSON, and J. P. SCHAMAN. Effect of exercise on recovery blood pressure in normotensive and hypertensive subjects.Med. Sci. Sports Exerc. Vol. 19, No. 1, pp. 17–20, 1987. The effects of dynamic exercise on the acute recovery blood pressure (BP) were studied in normotensive and hypertensive subjects. Three groups [eight normotensives, age 19 to 29 yr (N1); eight normotensives, age 35 to 62 yr (N2); and eight hypertensives, age 44 to 57 yr (H)] were tested over three separate sessions. The first two sessions were for familiarization with the protocol and test procedures. Resting systolic BP decreased (P<0.01) in all groups from sessions 1 to 3: N1 = 126 to 121 mm Hg; N2 = 127 to 120; H = 155 to 142. Resting diastolic BP decreased (P< 0.05) in the N1 and H groups from 77 to 73 and 98 to 95 mm Hg, respectively. On the third day, each subject followed the protocol of Wilcox et al. (8) of 15 min of seated rest, five 10-min periods of treadmill walking with a 3-min rest between each period, and 60 min of seated recovery. Exercise was performed at 67% of estimated maximal heart rate. In all three groups, significant (P< 0.05) reductions in both systolic BP (N1 = −12 ± 1; N2 = −10 ± 2; H = −12 ± 3) and diastolic BP (N1 = −5 ± 2; N2 = −5 ± 1; H = −7 ± 2) occurred from pre-exercise rest to post-exercise rest. Systolic BP remained lower following 60-min recovery (P< 0.02), while diastolic BP returned to pre-exercise levels in all three groups. No between-group differences were observed in the magnitude of reduction of BP post-exercise. It is concluded that studies of BP responses to exercise should ensure a stable baseline of pre-exercise rest in order to prevent over-estimation of the BP reducing effects of exercise.

ISSN:0195-9131    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

MCKEEVER, K. H., W. A. SCHURG, S. H. JARRETT, and V. A. CONVERTINO. Exercise training-induced hypervolemia in the horse.Med. Sci. Sports Exerc., Vol. 19, No. 1, pp. 21–27, 1987. The purpose of this study was to determine if a chronic hypervolemia would accompany endurance exercise training in the horse. Six mature previously inactive horses were utilized for this study. During the 5-wk experiment, five of the horses were trained for 14 d on a treadmill ergometer at a constant treadmill speed of 5.6 km·hr-1and a constant grade of 12.5% for graduated lengths of time. One horse was trained by lunging at a trotting pace in a round pen. Following training, plasma volume increased by 4.7 1 (29.1%,P< 0.05). Although the rate of daily water intake did not change during the training period, 24-h urine output decreased by an average of 3.51· d-1(-24.5%,P< 0.05). Resting glomerular filtration rate and the rate of sodium clearance were not altered by training. However, urea, potassium, and osmotic clearance were decreased by training (P< 0.05) while free water clearance was increased (P< 0.05). Resting plasma aldosterone and arginine vasopressin concentrations were not altered by training. Plasma potassium concentration was significantly decreased (P< 0.05) following the 2 wk of training. These data would appear to suggest that renal control mechanisms affecting water reabsorption via the re-absorption of urea and osmotically active substances other than sodium provide the primary route for the traininginduced hypervolemia seen in horses.

ISSN:0195-9131    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

BASSETT, JR., D. R., F. J. NAGLE, S. MOOKERJEE, K. C. DARR, A. V. NG, S. G. VOSS, and J. P. NAPP. Thermoregulatory responses to skin wetting during prolonged treadmill running.Med. Sci. Sports Exerc., Vol. 19, No. 1, pp. 28–32, 1987. We examined the physiological responses to skin wetting during a 120-min level treadmill run to assess whether skin wetting would reduce the dehydration and the increase in core temperature associated with prolonged exercise. Testing was conducted in an environmental chamber (T = 29.5°C, wind velocity = 3 m·sec-1) under two different humidity conditions (33 or 66% relative humidity). Ten male subjects performed two runs in each humidity condition; one served as a control run. The other included spraying the body with 50 ml of water (T = 29.5°C) every 10 min. Spraying had no effect on rectal temperature (Tre), heart rate, oxygen consumption, perceived exertion, sweat loss, or percent change in plasma volume in both the humid and the dry conditions. Spraying produced a significant reduction in mean skin temperature (&OV0374;sk), which increased the (Tre- &OV0374;sk) gradient. At the same time, overall skin conductance (K) was decreased, presumably as a result of cutaneous vasoconstriction due to the low &OV0374;sk. Since heat transfer from the body's core to the skin is expressed by the equation:heat transfer = K x (Tre- &OV0374;sk)the spraying had no effect on heat transfer away from the core, and Treremained unchanged.

ISSN:0195-9131    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

HARGREAVES, M., D. L. COSTILL, W. J. FINK, D. S. KING, and R. A. FIELDING. Effect of pre-exercise carbohydrate feedings on endurance cycling performance.Med. Sci. Sports Exerc., Vol. 19, No. 1, pp. 33–36, 1987. Six men were studied to compare the effects of pre-exercise carbohydrate feedings on endurance performance and muscle glycogen utilization during prolonged exercise. Trials consisted of a cycling ride to exhaustion at 75% maximal oxygen uptake preceded by the ingestion of either 75 g of glucose in 350 ml of water (GLU), 75 g of fructose in 350 ml of water (FRU), or 350 ml of an artificially sweetened and flavored placebo (CON). No differences were observed between trials for oxygen uptake, respiratory exchange ratio, heart rate, or exercise time to exhaustion (CON = 92.7 ± 5.2 min, FRU = 90.6 ± 12.4, and GLU = 92.8 ± 11.3, mean ± SE). Blood glucose was elevated as a result of the GLU feeding, but fell rapidly with the onset of exercise, reaching a low of 4.02 ± 0.34 mmol·1-1at 15 min of exercise. Serum insulin also increased following the GLU feeding but had returned to pre-drink levels by 30 min of exercise. No differences in blood glucose and insulin were observed between. FRU and CON. Muscle glycogen utilization during the first 30 min of exercise (CON = 46.3 ± 8.2 mmol·kg-1wet weight, FRU = 56.3 ± 3.0 mmol·kg-1wet weight, GLU = 50.0 ± 4.9 mmol±kg-1wet weight) and total glycogen use (CON = 93.4 ± 11.1, FRU = 118.8 ± 10.9, and GLU = 99.5 ± 4.3) were similar in the three trials. It was concluded that despite more stable blood glucose and insulin levels in FRU and CON, compared with GLU, no advantage to endurance performance or muscle glycogen utilization during prolonged exercise was provided.

ISSN:0195-9131    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

FLYNN, M. G., D. L. COSTILL, J. A. HAWLEY, W. J. FINK, P. D. NEUFER, R. A. FIELDING, and M. D. SLEEPER. Influence of selected carbohydrate drinks on cycling performance and glycogen use.Med. Sci. Sports Exerc., Vol. 19, No. 1, pp. 37–40, 1987. Eight well-trained male cyclists were used to determine the influence of carbohydrate feedings on exercise performance and muscle glycogen use. Two days prior to each trial, the subjects performed a 60-min “depletion ride‘’ at 70% &OV0312;O2max, which was followed by the ingestion of a high carbohydrate diet (∼500 g·-1). During the experimental trials, the men performed 2 h of cycling exercise and consumed 150 ml of 1 of 4 solutions at 24-min intervals. The drinks were: H2O (artificially flavored and sweetened); maltodextrin (5 g·100 ml-1) and fructose (5 g·100 ml-1); maltodextrin (7.7 g·100 ml-1) and high fructose corn syrup (2.3 g·100 ml-1). The amount of work completed during the four trials was not significantly different. Initial glycogen levels were high, and glycogen values were not significantly different at the beginning of exercise or at 90 min (185.35 ± 3.26 and 91.93 ± 3.39, respectively). Blood glucose was greater at 60 min in trial maltodextrin and glucose (5.70 ± 0.36 mmoles·1-1), maltodextrin and high fructose corn syrup (6.05 ± 0.54), and maltodextin and fructose (6.03 ± 0.42), compared to H2O (4.97 ± 0.35) (P< 0.05). Blood glucose remained elevated at 90 min during the maltodextrin and fructose and maltodextrin and high fructose corn syrup trials and at 120 min in the maltodextrin and fructose trial. No differences were observed between trials in blood lactate, serum glycerol, respiratory exchange ratio, or the subjects' perception of effort. These results suggest that, when the initial glycogen levels are elevated, carbohydrate ingestion during exercise does not result in a significant sparing of muscle glycogen or an improvement in cycling performance during 2 h of exercise.

ISSN:0195-9131    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

BROOKS-GUNN, J., M. P. WARREN, and L. H. HAMILTON. The relation of eating problems and amenorrhea in ballet dancers.Med. Sci. Sports Exerc., Vol. 19, No. 1, pp. 41–44, 1987. Exerciseinduced amenorrhea has received considerable attention in the medical literature. The combination of exercise and low body weight is thought to exert synergistic effects in the pathogenesis of amenorrhea, while the role of dieting and eating problems, another possible causative mechanism, has not been examined. A sample of 55 adult dancers in national and regional classical ballet companies was studied; their mean age was 24.7 yr. Fifty-six percent of the dancers had delayed menarche (age 14 or later) and 19% of the sample were currently amenorrheic (5 months or longer). One-third of the dancers reported having had an eating problem (self-reported anorexia nervosa or bulimia). Amenorrhea and reported eating problems were significantly related: 50% of amenorrheics reported anorexia nervosa while 13% of the normals did. In addition, prolonged amenorrhea was significantly related to dieting (as measured by EAT-26 scales, a measure of dieting behavior). As expected, leanness and absolute weight also were related to prolonged amenorrhea. Amenorrhea in this sample of adult dancers was not related to current activity level or age at which training began. Thus, eating problems may be one factor in the pathogenesis of prolonged amenorrhea in certain athletic groups.

ISSN:0195-9131    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

O'TOOLE, M. L. W. D. B. HILLER, L. O. CROSBY, and P. S. DOUGLAS. The ultraendurance triathlete: a physiological profile.Med. Sci. Sports Exerc., Vol. 19, No. 1, pp. 45–50, 1987. To better characterize the athletes who participate in ultraendurance triathlons, 14 triathletes in training for the Hawaii IRONMAN triathlon were studied. A physical and physiological profile was developed from anthropometric measurements and oxygen uptake during maximal exercise on a treadmill, cycle ergometer, and arm ergometer. A comparison of the maximal values among exercise modes and between males and females was made. A comparison of height, weight, and percent body fat of these triathletes with elite athletes from the sports of swimming, cycling, and running showed the physique of triathletes to be most similar to that of cyclists. Oxygen uptake at maximal exercise was, for males and females, respectively: 68.8 ml. kg-1·min-1, 65.9 ml·kg-1·min-1on the treadmill; 66.7 ml·kg-1·min-1, 61.6 ml·kg-1·min-1on the cycle ergometer; and 49.1 ml·kg-1·min-1, 39.7 ml·kg-1·min-1on the arm ergometer. When comparing the highest oxygen uptake attained at maximal exercise in any one of the three exercise modes, the male triathletes are comparable to swimmers, but have a lower aerobic capacity than cyclists or distance runners. The female triathletes studied were able to attain oxygen uptake values greater than those previously reported for female athletes.

ISSN:0195-9131    

出版商:OVID    

年代:1987

数据来源: OVID