Naloxone effect on ANP in trained and untrained rats.

1. The effect of a dose of naloxone (1 mg.kg-1 b.w.) on peripheral (plasma, atria) and central (hypothalamus, hypophysis) levels of atrial natriuretic peptide (ANP) was investigated in the rat. 2. In control rats, an acute subcutaneous dose of naloxone produced no significant change in plasma ANP, but a decrease (NS) in atrial ANP concentration. 3. In physically conditioned animals, naloxone produced a significant decrease in atrial ANP levels. Receptor sensitivity may thus be involved in this differential response. 4. In hypothalamus and hypophysis, no effect on ANP concentrations was seen after a high dose of naloxone whether in control or in physically conditioned animals, suggesting peripheral and central ANP might be differently regulated, at least after chronic endurance physical training.     

Effect of diazepam treatment on metabolic indices in trained and untrained rats

Exercise training, like diazepam, is commonly employed as a means of reducing anxiety. Both diazepam and exercise training have been shown to modify carbohydrate and lipid metabolism as well as influence calcium metabolism in skeletal muscle. As receptor binding and thereby efficacy of diazepam has been demonstrated to be modulated by the lipid environment of the receptor, and changes in calcium levels can affect a number of intracellular signalling pathways, we sought to determine if the interaction of both chronic diazepam and exercise training would modify selected metabolic indices in an animal model. For this purpose, muscle and liver glycogen, blood glucose and plasma free fatty acids (FFA) were measured in sedentary, exercise trained and exercise trained, acutely exhausted animals. Alterations in lipid and carbohydrate metabolism were observed in all experimental groups. Diazepam treatment alone exerts metabolic consequences, such as elevated muscle glycogen and plasma FFA and depressed blood glucose levels, which are similar to those observed with exercise training. When animals are acutely exercised to exhaustion, however, differences appear, including a reduced rise in plasma FFA, which suggests that long-term diazepam treatment does influence exercise metabolism, possibly as a result of effects on the sympatho-adrenal system.     

Alpha and beta adrenergic sensitivity in trained and untrained albino rats.

The effects on the blood pressure and heart rate responses of different adrenergic stimulants (norepinephrine, sympathomim, epinephrine and isoproterenol) and blocking agents (phenoxybenzamine and propranolol) were studied in control (N=55) and exercising (N=52) albino rats under anaesthesia. The test rats exercised by regular swimming for 10-14 weeks. Alpha stimulation and beta blocking produced smaller responses while alpha blocking and beta stimulation were followed by greater changes after training as compared with the control animals. The assumption of a modified adrenergic receptor sensitivity could not be substantiated by the results; the observations indicate rather a complex change in the autonomous regulation following regular physical exercise.     

Exercise intensity: effect on postexercise O2 uptake in trained and untrained women

Despite many reports of long-lasting elevation of metabolism after exercise, little is known regarding the effects of exercise intensity and duration on this phenomenon. This study examined the effect of a constant duration (30 min) of cycle ergometer exercise at varied intensity levels [50 and 70% of maximal O2 consumption (VO2max)] on 3-h recovery of oxygen uptake (VO2). VO2 and respiratory exchange ratios were measured by open-circuit spirometry in five trained female cyclists (age 25 +/- 1.7 yr) and five untrained females (age 27 +/- 0.8 yr). Postexercise VO2 measured at intervals for 3 h after exercise was greater (P less than 0.01) after exercise at 50% VO2max in trained (0.40 +/- 0.01 l/min) and untrained subjects (0.39 +/- 0.01 l/min) than after 70% VO2max in (0.31 +/- 0.02 l/min) and untrained subjects (0.29 +/- 0.02 l/min). The lower respiratory exchange ratio values (P less than 0.01) after 50% VO2max in trained (0.78 +/- 0.01) and untrained subjects (0.80 +/- 0.01) compared with 70% VO2max in trained (0.81 +/- 0.01) and untrained subjects (0.83 +/- 0.01) suggest that an increase in fat metabolism may be implicated in the long-term elevation of metabolism after exercise. This was supported by the greater estimated fatty acid oxidation (P less than 0.05) after 50% VO2max in trained (147 +/- 4 mg/min) and untrained subjects (133 +/- 9 mg/min) compared with 70% VO2max in trained (101 +/- 6 mg/min) and untrained subjects (85 +/- 7 mg/min).     

Effects of swimming exercise on red blood cell rheology in trained and untrained rats.

Red blood cell (RBC) mechanical properties were investigated after swimming exercise in trained and untrained rats. A group of rats was trained for 6 wk (60 min swimming, daily), and another group was kept sedentary. Blood samples were obtained either within 5 min or 24 h after 60 min swimming in both groups. In the untrained rats, the RBC aggregation index decreased to 2.60 +/- 0.4 immediately after exercise from a control value of 6.73 +/- 0.18 (P < 0.01), whereas it increased to 13.13 +/- 0.66 after 24 h (P < 0.01). RBC transit time through 5-microm pores increased to 3.53 +/- 0.16 ms within 5 min after the exercise from a control value of 2.19 +/- 0. 07 ms (P < 0.005). A very significant enhancement (166%) in RBC lipid peroxidation was detected only after 24 h. In the trained group, the alterations in all these parameters were attenuated; there was a slight, transient impairment in RBC deformability (transit time = 2.64 +/- 0.13 ms), and lipid peroxidation was found to be unchanged. These findings suggest that training can significantly limit the hemorheological alterations related to a given bout of exercise. Whether this effect is secondary to the training-induced reduction in the degree of metabolic and/or hormonal perturbation remains to be determined.     

The effect of dropping height on jumping performance in trained and untrained prepubertal boys and girls

Plyometric training in children, including different types of jumps, has become common practice during the last few years in different sports, although there is limited information about the adaptability of children with respect to different loads and the differences in performance between various jump types. The purpose of this study was to examine the effect of gender and training background on the optimal drop jump height of 9- to 11-year-old children. Sixty prepubertal (untrained and track and field athletes, boys and girls, equally distributed in each group [n = 15]), performed the following in random order: 3 squat jumps, 3 countermovement jumps (CMJs) and 3 drop jumps from heights of 10, 20, 30, 40, and 50 cm. The trial with the best performance in jump height of each test was used for further analysis. The jump type significantly affected the jump height. The jump height during the CMJ was the highest among all other jump types, resulting in advanced performance for both trained and untrained prepubertal boys and girls. However, increasing the dropping height did not change the jumping height or contact time during the drop jump. This possibly indicates an inability of prepubertal children to use their stored elastic energy to increase jumping height during drop jumps, irrespective of their gender or training status. This indicates that children, independent of gender and training status, have no performance gain during drop jumps from heights up to 50 cm, and therefore, it is recommended that only low drop jump heights be included in plyometric training to limit the probability of sustaining injuries.     

Maximal vascular leg conductance in trained and untrained men

Lower leg blood flow and vascular conductance were studied and related to maximal oxygen uptake in 15 sedentary men (28.5 +/- 1.2 yr, mean +/- SE) and 11 endurance-trained men (30.5 +/- 2.0 yr). Blood flows were obtained at rest and during reactive hyperemia produced by ischemic exercise to fatigue. Vascular conductance was computed from blood flow measured by venous occlusion plethysmography, and mean arterial blood pressure was determined by auscultation of the brachial artery. Resting blood flow and mean arterial pressure were similar in both groups (combined mean, 3.0 ml X min-1 X 100 ml-1 and 88.2 mmHg). After ischemic exercise, blood flows were 29- and 19-fold higher (P less than 0.001) than rest in trained (83.3 +/- 3.8 ml X min-1 X 100 ml-1) and sedentary subjects (61.5 +/- 2.3 ml X min-1 X 100 ml-1), respectively. Blood pressure and heart rate were only slightly elevated in both groups. Maximal vascular conductance was significantly higher (P less than 0.001) in the trained compared with the sedentary subjects. The correlation coefficients for maximal oxygen uptake vs. vascular conductance were 0.81 (trained) and 0.45 (sedentary). These data suggest that physical training increases the capacity for vasodilation in active limbs and also enables the trained individual to utilize a larger fraction of maximal vascular conductance than the sedentary subject.     

Oxygen dissociation curves in trained and untrained subjects.

Oxygen dissociation curves (ODC) in whole blood and organic phosphate concentrations in red cells were determined in 10 highly trained male athletes (TR), 6 semitrained subjects (ST) who played sports regularly at low intensities and 8 untrained people (UT). In all groups standard ODCs (37 degrees C, pH 7.40, PCO2 approximately 43 Torr) at rest and after a short exhaustive exercise were nearly identical, but PO2 values measured immediately after blood sampling and corrected to standard conditions tended to fall to the right of the in vitro ODC. Elevated P50 in the physically active [28.65 +/- 1.4 Torr (3.81 +/- 0.18 kPa) in ST, 28.0 +/- 1.1 Torr (3.73 +/- 0.15 kPa) in TR, but 26.5 +/- 1.1 Torr (3.53 +/- 0.15 kPa) in UT] were partly caused by different [DPG] (11.9 +/- 1.3 mumol/GHb in UT, 13.3 +/- 1.5 mumol/GHb in TR, 13.8 +/- 2.2 mumol/gHb in ST). There were remarkable differences in the shape of the curves between the groups. The slope "n" in the Hill plot amounted to 2.65 +/- 0.12 in UT, 2.74 +/- in ST and 2.90 +/- 0.11 in the TR (2 p against UT less than 0.001), leading to an elevated oxygen pressure of about 2 Torr (0.27 kPa) at 20% saturation and an augmented oxygen extraction of 5--7 SO2 at a PO2 of about 15 Torr (2kPa), which might be favorable at high workloads. The reason for the phenomenon could be an increased amount of young red cells in the blood of TR, caused by exercise induced hemolysis.     

Influence of diet on the storage, mobilization and utilization of energy reserves in trained and untrained rats

The effect of the major dietary energy source (fat or carbohydrate) on some of the adaptations to physical training, particularly body composition and tissue glycogen concentrations, were studied in growing male Wistar rats. Resting liver glycogen concentrations were lower in both trained and sedentary rats fed a high fat diet compared to corresponding rats fed a high carbohydrate (low fat) diet. Trained rats on both diets had higher liver glycogen levels than corresponding sedentary controls. Resting gastrocnemius muscle glycogen concentrations were not influenced by diet or training. Rates of liver and muscle glycogen depletion during a 60-min swim were lower in trained rats but were not influenced by diet. Significant interactions were noted between the dietary energy source and exercise training with respect to body weight gain, body fat content, liver weight and liver glycogen concentrations.     

Plasma lactate and ventilation thresholds in trained and untrained cyclists

Six trained male cyclists and six untrained sedentary men were studied to determine whether the plasma lactate threshold (PLT) and ventilation threshold (VT) occur at the same work rate in both fit and unfit populations. The PLT was determined from a marked increase in plasma lactate concentration ([La]) and VT from a nonlinear increase in expired minute ventilation (VE) during incremental leg-cycling tests; work rate was increased 30 W every 2 min until volitional exhaustion. The trained subjects' mean VO2 max (63.8 ml O2 X kg-1 X min-1) and VT (65.8% VO2 max) were significantly higher (P less than 0.05) than the untrained subjects' mean VO2max (35.5 ml O2 X kg-1 X min-1) and VT (51.4% VO2 max). The trained subjects' mean PLT (68.8% VO2 max) and VT did not differ significantly, but the untrained subjects' mean PLT (61.6% VO2 max) was significantly higher than their VT. The trained subjects' mean peak [La] (10.5 mmol X l-1) did not differ significantly from the untrained subjects' mean peak [La] (11.5 mmol X l-1). However, the time of appearance of the peak [La] during passive recovery was inversely related to VO2 max. These results suggest that variance in lactate diffusion and/or removal processes between the trained and untrained subjects may account in part for the different relationships between the VT and PLT in each population.     

Benefits of caffeine ingestion on sprint performance in trained and untrained swimmers

The influence of specific training on benefits from caffeine (Caf) ingestion was examined during a sprint test in a group of highly trained swimmers (T) and compared with the response of a group of untrained occasional swimmers (UT). Seven T and seven UT subjects swam freestyle two randomly assigned 2 x 100 m distances, at maximal speed and separated by 20 min of passive recovery, once after Caf (250 mg) and once after placebo (Pla) ingestion. Anaerobic capacity was assessed by the mean velocity (meters per second) during each 100 m and blood was sampled from the fingertip just before and 1, 3, 5, 7, and 9 min after each 100 m for resting and maximal blood lactate concentration ([la-]b,max) determination. The [la-]bmax was significantly enhanced by Caf in both T and UT subjects (P less than 0.01). However, only T subjects exhibited significant improvement in their swimming velocity (P less than 0.01) after Caf or any significant impairment during the second 100 m. In light of these results, it appears that specific training is necessary to benefit from the metabolic adaptations induced by Caf during supramaximal exercise requiring a high anaerobic capacity.     

Effect of food intake on exercise fatigue in trained and untrained subjects

The effects of carbohydrate and fat intake on exercise-induced fatigue was investigated in 30 untrained--(VO2max of 40.6 +/- 2.7 ml X kg-1 X min-1) and 24 trained-subjects (VO2max of 52.3 +/- 2.7 ml X kg-1 X min-1) performing a 34 km march with a 25 kg backpack. Marching time was 8 1/2 h and 6 1/3 h in the untrained and trained-subjects respectively. The subjects were divided into 3 dietary groups. One group had free access to sugar cubes, the second group was offered almonds and the third one served as a control. Triglyceride levels decreased by 65 mg X dl-1 in untrained, and by 115 mg X dl-1 in trained subjects, while blood glucose remained at normal levels. In the untrained subjects, ingestion of almonds delayed the subjective sensation of exhaustion, while 50% of the controls and the sugar consuming subjects complained of exhaustion. The data suggest that ingestion of food containing fat delays exercise induced exhaustion or fatigue to a greater extent than does carbohydrate ingestion.