Effects of a 24-h CHO-poor diet on metabolic and hormonal responses during prolonged CHO-loaded leg exercise

This study examined the effects of a pre-experimental period of arm exercise followed by a 24-h carbohydrate (CHO)-poor intake, intended to reduce initial hepatic glycogen levels, on substrate and endocrine responses during prolonged CHO-loaded leg exercise. Seven subjects pedaled a cycle ergometer for 60 min at 62% VO2 max in the two following conditions: 1) after leg CHO loading followed by a 60-min arm exercise and a 24-h CHO-poor diet (CHOL + P), and 2) after leg CHO loading only (CHOL). Greater blood concentrations of fatty acids (1.2 vs 0.9 mEq X L-1), glycerol (0.41 vs 0.20 mmol X L-1), norepinephrine (2.09 vs 1.14 ng X ml-1), and epinephrine (0.38 vs 0.19 ng X ml-1) were observed in the CHOL + P as compared to the CHOL condition at min 60 of exercise. Insulin concentration was significantly (P less than 0.05) lower in the CHOL + P condition at rest and during exercise. There were no significant differences during exercise between the two conditions in blood glucose, lactate, glucagon, and cortisol concentrations. It is concluded that changes in blood glucose concentration do not solely account for metabolic and hormonal adaptations during prolonged leg exercise and that a pre-experimental period of arm exercise and CHO-poor diet, in spite of an increase in leg muscle glycogen, may provide a stimulus for such adaptations. It is suggested that the liver glycogen content may be involved in the regulatory mechanism.

Metabolic and hormonal responses of elite swimmers during a regular training session

Metabolic and hormonal measures of eight elite swimmers were taken at rest and during a regular training session after a prolonged bout of swimming (4560 +/- 68 m) at moderate intensity (MI) and after medium duration-high intensity (HI) swimming exercise (1471 +/- 157 m). MI and HI swims were respectively associated with significant increases in free fatty acids (0.4 at rest to 0.8 and 0.67 microeq . ml-1) glycerol (0.1 to 0.26 and 0.25 mmol . l-1), growth hormone (14 to 65 and 51 ng . ml-1) and norepinephrine (0.5 to 3.9 and 4.1 ng . ml-1). HI contrary to MI swimming was also associated with a significant (p less than 0.01) increase in blood lactate (1.5 to 8.8 mmol . l-1) and epinephrine (0.13 to 0.71 ng . ml-1) concentrations. Glucose, insulin, glucagon, and cortisol concentrations were not changed during the training session. It is concluded that a regular training session in elite swimmers is associated with an increase in lipid utilization, and a modest change in some of the hormones directly involved in the regulation of blood glucose level.

Skeletal muscle and cardiac changes with training in patients with angina pectoris

Cardiovascular and skeletal muscle adaptations were studied before and after 6 mo of physical training in patients with coronary artery disease and exertional angina pectoris. Symptom-limited exercise capacity increased by 41% (470 +/- 30 to 665 +/- 35 kg.m.min-1; n = 29, P less than 0.001) with training as did skeletal muscle succinate dehydrogenase activity (1.75 +/- 0.24 to 3.31 +/- 0.24 IU; n = 23, P less than 0.001) and the areas of muscle fibers (type I from 43.6 +/- 3.3 to 54.4 +/- 3.3 micrometers 2 X 10(2); n = 21, P less than 0.05 and type II from 43.9 +/- 2.4 to 57.2 +/- 5.1 micrometers 2 X 10(2); P less than 0.01). At the same submaximal exercise intensity (mean 355 +/- 100 km.m.min-1), plasma catecholamines (1.31 +/- 0.14 to 1.07 +/- 0.09 ng.ml-1; n = 13, P less than 0.05), heart rate (115 +/- 3 to 97 +/- 3 beats/min; n = 29, P less than 0.001), and systolic blood pressure (171 +/- 4 to 143 +2- 4 mmHg; n = 29, P less than 0.001) were significantly reduced after training. Maximal coronary sinus blood flow (192 +/- 10 to 208 +/- 9 ml.min-1; n = 29, P less than 0.05) and left ventricular oxygen consumption (23.2 +/- 1.5 to 25.8 +/- 1.6 ml.min-1; n = 24, P less than 0.05) were increased by 8 and 11%, respectively, after training. The improvement in exercise capacity with training in patients with exercise is secondary to a reduction in myocardial oxygen requirements during subangina levels of exercise and partly to a small increase in maximal myocardial oxygen consumption. The skeletal muscle adaptations with training were not related to other indices of training such as the reduced exercise heart rate or increased symptom-limited exercise capacity.

Plasma catecholamines and response to exercise in 6-hydroxydopamine-treated dogs

Plasma catecholamine (CA; picograms per millilitre) concentrations were measured simultaneously with heart rate (HR, beats per minute) during short-duration exercise, and with plasma glucose, lactate, and free fatty acid (FFA) concentrations (millimoles per litre) during long-duration exercise, in control dogs (N-dogs) and in sympathectomized dogs (S-dogs) with 6-hydroxydopamine (50 mg X kg-1). At rest, higher plasma CA in S-dogs (690 +/- 90 vs. 320 +/- 60) was associated with higher HR (126 +/- 3 vs. 90 +/- 5), plasma glucose (6.4 +/- 0.2 vs. 5.1 +/- 0.2), lactate (2.9 +/- 0.2 vs. 1.6 +/- 0.2), and FFA concentrations (1.08 +/- 0.11 vs. 0.81 +/- 0.11). During short-duration exercise a normal HR response in S-dogs (226 +/- 9 vs. 228 +/- 8) was dependent upon larger than normal plasma CA values (4280 +/- 680 vs. 1990 +/- 360). Metabolic adjustments to long-duration exercise were impaired in S-dogs as evidenced by the higher plasma glucose and lactate concentrations (8.2 +/- 0.5 and 5.5 +/- 0.3 vs. 6.4 +/- 0.4 and 4.6 +/- 0.3) and the lower plasma FFA concentration (0.66 +/- 0.16 vs. 1.20 +/- 0.09). These occurred despite a normal plasma CA response in S-dogs (6850 +/- 1450 vs. 8740 +/- 1680). Following chemical sympathectomy the adrenal medulla can compensate to ensure an adequate heart rate response to short-duration exercise, but not to ensure adequate metabolic adjustments to prolonged exercise.

Left ventricular dimensions following training in young and middle-aged men

To document the effects of endurance training upon left ventricular dimensions, an echocardiographic examination was performed on 11 young (19 +/- 1 years) and 13 middle-aged (40 +/- 3 years) subjects before and after a 20-week endurance training program. The maximal working capacity was increased by 28% and 27% in young and in middle-aged subjects, respectively. Following training, the left ventricular posterior wall and septal thickness in diastole were unchanged both in young (10.1 +/- 0.2 mm and 9.0 +/- 0.2 mm, pre-; 10.1 +/- 0.2 mm and 9.3 +/- 0.3 mm, post-) and in middle-aged subjects (10.0 +/- 0.3 mm and 10.2 +/- 0.3 mm, pre-; 9.7 +/- 0.2 mm and 10.1 +/- 0.2 mm, post-); the left ventricular end-diastolic internal diameter was unchanged in middle-aged subjects (47.8 +/- 0.9 mm, pre-; 48.1 +/- 1.0 mm, post-) but was significantly increased in young subjects (47.8 +/- 1.0 mm, pre-; 49.9 +/- 1.0 mm, post-) (P less than 0.05). These data could suggest that the left ventricular adaptation to training decreases with age. However, the decrease in resting heart rate observed in young subjects (68 +/- 3 to 60 +/- 2 beats X min-1) (P less than 0.05) but not in middle-aged subjects (63 +/- 3 and 65 +/- 3 beats X min-1) could also increase diastolic filling time and explain the small left ventricular end-diastolic enlargement found in the young subjects.

The onset of menarche: a late event in pubertal progression to be affected by physical training

Several studies have shown that involvement in certain sports activities could lead to a significant delay in the onset of menarche. It is here emphasized that the latter constitutes a late pubertal event and that research in kinanthropology should now focus on processes underlying menarche. Some findings indeed suggest an influence of certain physical activities upon the maturation rate of endocrine axes which lead to the onset of the first menses.

Plasma catecholamines, heart rate, and cardiac sympathetic activity in exercising dogs

Plasma catecholamines, heart rate, and cardiac sympathetic activity in exercising dogs. Med. Sci. Sports Exercise, Vol. 14, No. 4, pp. 291-285, 1982. The purposes of the study were, 1) to assess the respective roles of locally released norepinephrine in the sinus node and of plasma catecholamines in the control of heart rate during exercise and 2) to verify whether the heart is a source of plasma catecholamines during exercise. Plasma catecholamines (radioenzymatic assay) and heart rate were measured in the last minute of a 5-min exercise period (3.2 km . h-1, 39% slope) in six normal dogs, in six dogs treated with 5 mg . kg-1 sotalol, and in six dogs sympathectomized with 50 mg . kg-1 6-hydroxydopamine. Compared to the exercise heart rate values of the normal dogs (228 +/- 8 beats . min-1) and the sympathectomized dogs (226 +/- 9 beats . min-1), the sotalol-treated dogs had significantly lower rates (148 +/- 6 beats . min-1). However, plasma catecholamine response was higher in the sotalol-treated dogs (7380 +/- 1350 pg . ml-1) and in the sympathectomized dogs (4280 +/- 680 pg . ml-1) than in the normal dogs (1890 +/- 360 pg . ml-1). Since the action of plasma catecholamines on the sinus node is potentiated by denervation hypersensitivity, it is suggested that in exercising normal dogs, heart rate control could be ensured by locally released norepinephrine rather than by plasma catecholamines. Plasma catecholamines were assessed in six normal dogs at rest and at various exercise levels (HR = 90-200 beats . min-1) and in blood sampled simultaneously in the aorta and the coronary sinus. Plasma catecholamines in the coronary sinus and aorta were similar at rest (490 +/- 90 vs 580 +/- 80 pg . ml-1, respectively) and at the low-intensity exercise (710 +/- 140 vs 880 +/- 120 pg . ml-1, respectively). For moderate and severe work loads, plasma catecholamine concentrations in the coronary sinus (960 +/- 160 and 1570 +/- 340 pg . ml-1, respectively) were lower than in the aorta (1380 +/- 260 and 2950 +/- 100 pg . ml-1, respectively). These results suggest that in exercising dogs the heart is not a source of plasma catecholamines.

Plasma norepinephrine response to exercise before and after training in humans

Plasma norepinephrine (NE) concentration was measured by means of a sensitive radioenzymatic assay in blood collected from an antecubital vein in 10 healthy male subjects (37 +/- 2 yr, mean +/- SE). The subjects were evaluated at rest and during exercise before and after a 20-wk training program on bicycle ergometer (three 30-min sessions per week at 80% of maximal heart rate). Following the training program, maximal oxygen uptake increased significantly from 33 +/- 2 to 42 +/- 1 ml . kg-1 . min-1. Resting plasma NE remained unchanged after training (167 +/- 38 before and 185 +/- 29 pg . ml-1 after training). For a given absolute work load (735 +/- 51 kg . m. min-1) the sympathetic nervous response was lower after training as reflected by the decrease in NE concentration (1,371 +/- 286 vs. 687 +/- 64 pg . ml-1). At the same relative work load (heart rate: 158 +/- 5 before and 157 +/- 5 beats . min-1 after training) plasma NE concentration was unchanged after training (1,371 +/- 286 vs. 1,729 +/0 371 pg . ml-1). Results from the present study show that the sympathetic nervous activity is closely linked to the exercise demands and confirm earlier suggestions that it remains constant in relation to the relative work load.

Exercise plasma catecholamines in dogs: role of adrenals and cardiac nerve endings

The plasma norepinephrine concentration (NE, ng . ml-1) in the pulmonary artery of dogs increased above resting values (0.22 +/- 0.04) for moderate (0.53 +/- 0.06) and severe exercise (1.45 +/- 0.23) and during prolonged exercise of moderate intensity (2.06 +/- 0.14). The plasma epinephrine concentration (E) increased above resting values (0.14 +/- 0.04) for severe exercise only (0.76 +/- 0.10) or when moderate exercise was prolonged (1.81 +/- 0.24). The E response, which appeared greater than that found in humans, is probably related to the species difference in the vasomotor response to exercise between humans and dogs, the latter not being subjected to compensatory vasoconstriction in nonworking areas. The activity of the adrenal medulla is confirmed by the plasma catecholamine (CA) gradient between proximal and distal posterior vena cava at rest (0.20 +/- 0.09) and during short- (0.35 +/- 0.08) and long-duration exercise (1.37 +/- 0.23). On the contrary, the heart is not a source of plasma CA in dogs: coronary sinus CA did not exceed aortic CA at rest and for moderate exercise and was lower than aortic CA for severe exercise (4.80 +/- 0.25 vs. 6.55 +/- 0.76 ng . ml-1).. The sources of plasma NE remain unclear in exercising dogs. Significant amounts of NE may be released by the adrenal medulla.

Prolactinemia in exercising male athletes

8 male collegial athletes were submitted at random to three (55, 70 and 85% of VO2 max) ergocycle exercises of 20-min duration. Venous blood samples were obtained before, during and after ergocycling sessions by antecubital catheterization. Serum prolactin was measured by RIA using specific antiserum. The exercise treatments induced a blood prolactin response proportional to the intensity of the work loads.

Electro- and echocardiographic study of the left ventricle in man after training

Fourteen sedentary middle-aged men underwent a chest X-ray, a 12 lead ECG, a VCG, and an echocardiographic examination prior to and following 5 months of training a moderately severe intensity, on a cycle ergometer. No modification in the X-ray cardiac profile was observed following training. Some electrocardiographic (R wave amplitude in V5 and V6 and Sokolow index: SV1 + RV5 or V6) and vectorcardiographic (maximal QRS vector amplitude, maximal spatial QRS vector, and R wave amplitude) indices of left ventricular hypertrophy were slightly but significantly increased following training. The echocardiographic measurements in diastole (septal and posterior wall thickness, left ventricular internal diameter, and left ventricular mass) were unchanged after training. Results suggest that electrical changes may not provide adequate indications of left ventricular morphological modifications. The lack of echocardiographic evidences of left ventricular hypertrophy suggest that: (1) training does not necessarily induce left ventricular hypertrophy; (2) the large heart sometimes observed in athletes may be the result of a genetic factor or of a prolonged and very intensive training pursued since a very young age, over a number of years; and (3) left ventricular enlargement probably plays a minor role in the increase in aerobic capacity following training.

Plasma catecholamines following low and high doses of ouabain in anesthetized dogs with or without cervical vagotomy

Circulating catecholamine (CA) levels in the aortic blood did not change significantly in anesthetized dogs during a period of 60 min following the rapid intravenous injection of ouabain at a dose of 10 microgram/kg, but they did increase significantly after administration of a dose of 75 microgram/kg. After bilateral cervical vagotomy, the high dose of ouabain caused a greater and earlier elevation in circulating CA levels than in intact animals along with an increased cardiac index and a lower peripheral resistance. These findings suggest the existence of a vagal inhibitory mechanism upon liberation of CA following the administration of ouabain. Although ventricular arrhythmias did occur before the increase in circulating CA, preinjection CA levels were significantly higher in animals presenting ventricular fibrillation, suggesting that a high background adrenergic tone facilitates the production of ventricular arrhythmias by ouabain. Moreover, ventricular tachycardia occurred earlier in vagotomized dogs, in which the immediate elevation of circulating CA could have been a precipitating factor for this type of arrhythmia.