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 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

On two occasions, six well-trained, male competitive triathletes performed, in random order, two experimental trials consisting of either a timed ride to exhaustion on a cycle ergometer or a run to exhaustion on a motor-driven treadmill at 80% of their respective peak cycling and peak running oxygen (VO2 max) uptakes. At the start of exercise, subjects drank 250 ml of a 15 g.100 ml-1 w/v [U-14C]glucose solution and, thereafter, 150 ml of the same solution every 15 min. Despite identical metabolic rates [VO2 3.51 (0.06) vs 3.51 (0.10) 1.min-1; values are mean (SEM) for the cycling and running trials, respectively], exercise times to exhaustion were significantly longer during cycling than running [96 (14) vs 63 (11) min; P < 0.05]. The superior cycling than running endurance was not associated with any differences in either the rate of blood glucose oxidation [3.8 (0.1) vs 3.9 (0.4) mmol.min-1], or the rate of ingested glucose oxidation [2.0 (0.1) vs 1.7 (0.2) mmol.min-1] at the last common time point (40 min) before exhaustion, despite higher blood glucose concentrations at exhaustion during running than cycling [7.0 (0.9) vs 5.8 (0.5) mmol.l-1; P < 0.05]. However, the final rate of total carbohydrate (CHO) oxidation was significantly greater during cycling than running [24.0 (0.8) vs 21.7 (1.4) mmol C6.min-1; P < 0.01]. At exhaustion, the estimated contribution to energy production from muscle glycogen had declined to similar extents in both cycling and running [68 (3) vs 65 (5)%]. These differences between the rates of total CHO oxidation and blood glucose oxidation suggest that the direct and/or indirect (via lactate) oxidation of muscle glycogen was greater in cycling than running.
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PMID:Fuel kinetics during intense running and cycling when fed carbohydrate. 889 98

The effect of two different light intensities (dim, 50 lux and bright, 5,000 lux) on handgrip exercise in a climatic chamber (26 degrees C, 60% relative humidity) were studied in eight female subjects, aged 20-24 years. The subjects were in either the dim or bright light from 1000 hours to 1800 hours. They were then in 50 lux from 1800 hours to 2200 hours in complete darkness from 2200 hours to 0600 hours (sleep), and again in 50 lux from 0600 hours to 0800 hours. They were instructed to perform handgrip exercise with a hand ergometer until the occurrence of exhaustion from 0600 hours. The influence of dim and bright intensities during the previous daytime on the number of contractions was compared. The main findings were firstly that the mean number of contractions was 766.63 SEM 43.28 in dim and 864.5 SEM 54.76 in bright intensities (P < 0.01), and secondly that rectal temperatures were slightly but significantly lower in the bright than in the dim intensities. The reason for the reduced number of contractions in dim was discussed in terms of the establishment of a higher set-point in the core temperature in dim.
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PMID:Influence of two different light intensities during daytime on endurance performance of handgrip exercise. 891 23

We studied the changes in the anti-oxidant capacity of tissues, such as heart, liver, and blood in male and female rats, as a parameter for evaluating oxidative stress after either a prolonged (210 min) or an exhausting bout of swimming. Furthermore, we also investigated exercise-induced changes in the electrophysiological properties, measured in vitro, of papillary muscle fibres. Small decreases of anti-oxidant capacities after prolonged exercise [0.10 (SEM 0.04) in heart, 0.43 (SEM 0.19) in liver, 0.22 (SEM 0.05) in blood] and greater decreases after exhausting exercise [0.23 (SEM 0.04) in blood] were found in tissues from the male rats. For the female rats, similar changes were found only in the blood [0.11 (SEM 0.07) and 0.35 (SEM 0.06) for prolonged and exhausting exercise respectively]. Liver and heart anti-oxidant capacity remained unchanged after prolonged exercise, while after exhausting swimming it underwent a decrease almost the same as found in the male rats, though the swimming time to exhaustion (endurance capacity) was much greater [706 (SEM 10) min and 444 (SEM 32) min for the females and males, respectively]. The duration of the action potential, recorded from papillary muscle fibres, underwent changes related to the decreases in heart anti-oxidant capacity. In fact, the action potential duration (APD) was shorter only in preparations from the male rats after prolonged exercise, but in all preparations after exhausting exercise. After such exercise, the APD was similar for the male and female rats [37.1 (SEM 3.4) ms and 37.0 (SEM 3.6) ms, respectively]. Such a pattern was independent of stimulation frequency, since it was found substantially unchanged when the frequency was increased from 1 to 5 Hz. We concluded that the different susceptibilities to the effects of physical exercise, exhibited by tissues from these male and female rats might have been related to different capacities to oppose oxidative stress effectively.
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PMID:Effect of exercise on tissue anti-oxidant capacity and heart electrical properties in male and female rats. 891 24

Changes in the concentrations of thiobarbituric acid-reactive substances (TBARS), an index of lipid peroxidation in liver, heart and soleus muscle, were studied in trained (T) and untrained (U) rats throughout a period of 48-72 h following running until exhaustion. Creatine kinase (CK) concentration in serum was also determined. The running time till exhaustion in group T was significantly longer than in group U [174.5 (SEM 9.8) vs 92.7 (SEM 8.3) min, P < 0.01]. In group U TBARS concentration in investigated tissues increased significantly (P < 0.01) after exercise with the peak values observed 3 h after running. The postexercise increase in the TBARS concentration persisted longer in the soleus muscle (48 h) than in the liver or heart (3 h). A postexercise increase of TBARS was observed in group T only in the liver. The influence of training on the TBARS content depended on the kind of tissue. The TBARS concentrations in the liver at rest and immediately after the exercise were lower in group U than in group T. In contrast, TBARS concentrations in the heart and soleus muscle were higher in group U than in group T. The exercise resulted, in both groups, in a rise of serum CK concentration, peak values being observed 3 h following the exercise. Postexercise concentrations of CK were considerably lower in group T than in group U [3 h postexercise: 1740 (SEM 170) vs 2750 (SEM 231) U.l-1 P < 0.01]. A positive correlation (r = 0.66, P < 0.05) between TBARS content in muscle and serum CK concentration was found only in group U. The results obtained indicated that the generation of lipid peroxidation products in the soleus muscle was intensified for a relatively long time after the exercise. Endurance training decreased the susceptibility of tissues to the action of free radicals. However, this influence of training was more pronounced in the heart and soleus muscle than in the liver.
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PMID:Changes in concentrations of tissue free radical marker and serum creatine kinase during the post-exercise period in rats. 895 95

Performance of intense dynamic exercise in highly trained athletes is associated with a reduced arterial haemoglobin saturation for O2 (SaO2) and lower arterial PO2 (PaO2). We hypothesized that compared with upright exercise, supine exercise would be accompanied by a smaller reduction in SaO2 because of a lower maximal O2 uptake (VO2max) and/or a more even ventilation-perfusion distribution. Eight elite bicyclists completed progressive cycle ergometry to exhaustion in both positions with concomitant determinations of ventilatory data, arterial blood gases and pH. During upright cycling VO2max averaged 75 +/- 1.6 mL O2 min-1 kg-1 (+/-SEM) and it was 10.6 +/- 1.7% lower during supine cycling (P < 0.001). Also the maximal pulmonary and alveolar ventilation were lower during supine cycling (by 15 +/- 2% and 21 +/- 3%, respectively; P < 0.001) which related to a 0.8 +/- 0.1 L lower tidal volume (P < 0.001). In all subjects and independent of work posture PaO2 and SaO2 decreased from rest to exhaustion (from 99 +/- 3 to 82 +/- 2 Torr and 98.1 +/- 0.2 to 95.2 +/- 0.4%, respectively; P < 0.001); alveolar-arterial PO2 difference increased from 6 +/- 2 to 37 +/- 3 Torr in both body positions. At exhaustion arterial PCO2 was lower in upright than in supine (33.4 +/- 0.6 vs. 35.9 +/- 0.9 Torr; P < 0.01), suggesting a greater relative hyperventilation in upright. Arterial pH was similar in upright and supine at rest (both 7.41 +/- 0.01) and at exhaustion (7.31 +/- 0.01 vs. 7.32 +/- 0.01, respectively). We conclude that despite a lower Vo2max and supposedly an improved ventilation-perfusion distribution, altering body position from upright to supine does not influence arterial O2 desaturation during intense exercise.
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PMID:Reduced arterial O2 saturation during supine exercise in highly trained cyclists. 897 Dec 53

The effect of different rates of fluid ingestion on heart rate, rectal temperature, plasma electrolytes, hormones and performance was examined during prolonged strenuous exercise conducted at 21 degrees C. Seven well-trained males (24 +/- 1 yr; 68.6 +/- 2.9 kg; VO2 peak = 4.69 +/- 0.17 L min-1; mean +/- SEM) cycled for 2 h at 69 +/- 1% VO2 peak while receiving either no fluid replacement (NF), a volume of water estimated to prevent body weight loss (FR-100 = 2.32 +/- 0.10 L 2 h-1) or 50% of this volume (FR-60 = 1.16 +/- 0.05 L 2 h-1). The 2-h exercise bout was followed by a ride to exhaustion at a workload estimated to be 90% VO2 peak. After 2 h of exercise, NF was associated with a 3.2 +/- 0.1% weight loss, while FR-50 and FR-100 resulted in losses of 1.8 +/- 0.1 and 0.1 +/- 0.1%, respectively. Compared with FR-100, heart rate and rectal temperature were elevated (P < 0.05) during the second hour of exercise in NF, with FR-50 intermediate. Reductions in plasma volume during exercise were greater in NF and FR-50, compared with FR-100 and plasma sodium concentration was elevated in NF, decreased slightly in FR-100, with FR-50 intermediate. Plasma renin activity, aldosterone and atrial natriuretic peptide increased to similar extents in the three trials. Plasma vasopressin remained unchanged for FR-100, increased for NF, with intermediate values for FR-50. Exercise time to exhaustion at 90% VO2-peak was longer in FR-100 (328 +/- 93 s) than NF (171 +/- 75 s) with FR-50 (248 +/- 107 s) not significantly different from either FR-100 or NF. In conclusion, the responses of heart rate, rectal temperature, plasma sodium, and vasopressin during, and performance following, prolonged cycling exercise conducted at 21 degrees C are related to the amount of fluid ingested (i.e. the degree of dehydration).
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PMID:Influence of ingested fluid volume on physiological responses during prolonged exercise. 920 41

The aim of the present prospective longitudinal study was to investigate the hormonal response in overtrained athletes at rest and during exercise consisting of a short-term exhaustive endurance test on a cycle ergometer at an intensity 10% above the individual anaerobic threshold. Over a period of 19+/-1 months, 17 male endurance athletes (cyclists and triathletes; age 23.4+/-1.6 yr; VO2max. 61.2+/-1.8 mL x min(-1) x kg(-1); means+/-SEM) were examined five times on two separate days under standardized conditions. Short-term overtraining states (OT, N=15) were primarily induced by an increase of frequency of high-intensive bouts of exercise or competitions without increase of the total amount of training. OT was compared with normal training states intraindividually (NS, N=62). During OT, the time to exhaustion of the exercise test was significantly decreased by 27% on average. At rest and during exercise, the concentrations in plasma and the nocturnal excretion in urine of free epinephrine and norepinephrine were not significantly changed during OT. At physical rest, the concentrations of (free) testosterone, cortisol, luteinizing hormone, follicle-stimulating hormone, adrenocorticotropic hormone, growth hormone, and insulin during OT were comparable with those during NS. A significantly (P < 0.025) lower maximal exercise-induced increase of the adrenocorticotropic hormone and growth hormone, as well as a trend for a decrease of cortisol (P=0.060) and insulin (P=0.036), was measured. The response of free catecholamines as well as the ergometric performance of an all-out 30-s test was unchanged. Serum urea, uric acid, ferritin, and activity of creatine kinase showed no differences between conditions. In conclusion, the results confirm the hypothesis of a hypothalamo-pituitary dysregulation during OT expressed by an impaired response of pituitary hormones to exhaustive short-endurance exercise.
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PMID:Impaired pituitary hormonal response to exhaustive exercise in overtrained endurance athletes. 952 87

Chronic hypoxia has been shown to increase plasma endothelin levels. The current study was undertaken to examine the effect of exercise-induced tissue hypoxia on plasma levels of endothelin-1 (ET-1) and its precursor big endothelin-1 (Big-ET-1). After approval by the local ethical committee an incremental dynamic exercise test was performed in 12 physically trained volunteers (aged 20 to 40 years), using an electrically braked bicycle ergometer. The protocol included a step-wise increase of the workload until a heart rate of 130/min was reached, followed by a maintenance period of 25 min, and a further step-wise increase until exhaustion. Blood was drawn before, at several time points during, and 5 min after termination of the study for determination of ET-1, Big-ET-1, plasma renin activity (PRA), angiotensin converting enzyme (ACE), norepinephrine, epinephrine, and lactate. Lactate levels at baseline were 14.5 +/- 1.6 mg/dL (mean +/- SEM), which increased to 76.5 +/- 4.8 mg/dL at the time of exhaustion (P < .01). Baseline values for ET-1 and Big-ET-1 were 0.264 +/- 0.061 and 0.637 +/- 0.130 fmol/ml, respectively, which remained essentially unaltered throughout the exercise test. PRA was 1.46 +/- 0.45 ng/mL/h before exercise and increased to 3.55 +/- 0.96 ng/mL/h at exhaustion (P < .001). Norepinephrine and epinephrine were also increased at exhaustion. The study demonstrates that exhaustive physical exercise with acute development of pronounced tissue hypoxia--in contrast to chronic hypoxia--does not influence the release of ET-1 or Big-ET-1 or the conversion of the precursor to the active compound. Unlike endothelin, circulating renin and the catecholamines were markedly stimulated by this maneuver.
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PMID:Exhaustive exercise-induced tissue hypoxia does not change endothelin and big endothelin plasma levels in normal volunteers. 971 98

This study investigated the recovery of pancreatic insulin content during human islet isolation prior to and after digestion-filtration, continuous Hanks-Ficoll gradient purification (n = 20), and 3-4 day culture at 22 degrees C (n = 6). The native insulin content varied in a wide range from 28.4 U to 360.8 U/pancreas. After digestion the initially measured average insulin content of 115.8 +/- 20.8 U/pancreas (mean +/- SEM) increased to 264.6 +/- 22.8% (p < 0.001). This increase of insulin during pancreas digestion was attributed to the asymetrical distribution of insulin within the pancreas. Sampling of insulin within the pancreatic caput seemed not to be representative for the insulin content of the complete native organ, because the ratio of insulin per gram tissue within the pancreatic cauda compared to the caput (n = 5) was 2.4 +/- 0.4 (p < 0.05). After purification total insulin recovery was 55.3 +/- 4.8% (p < 0.001). Because recovery of islet equivalent number (IEQ) (83.7 +/- 4.4%) exceeded insulin recovery, insulin/IEQ ratio decreased from 656.8 +/- 70.6 microU/IEQ before purification to 436.4 +/- 58.1 microU/IEQ (p < 0.001) after purification. After 22 degrees C culture (n = 6) recovery of insulin and IEQ was 80.1 +/- 8.1% (p < 0.05) and 92.8 +/- 3.5% (p = NS), respectively. Insulin content per IEQ decreased to 85.8 +/- 6.5% (p < 0.05). This study clearly shows that most of islet insulin is lost during purification. This seems to be caused rather by an amplified insulin release than by the loss of islets itself. This release may facilitate the separation of endocrine and exocrine tissue by gradient centrifugation, but may also accelerate islet exhaustion detrimental for long-term insulin independence.
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PMID:Assessment of intracellular insulin content during all steps of human islet isolation procedure. 978 69

In this study we compared cardiopulmonary responses to upper-body exercise in 12 swimmers, using simulation of the front-crawl arm-pulling action on a computer-interfaced isokinetic swim bench and arm cranking on a modified cycle ergometer. Subjects adopted a prone posture; exercise was initially set at 20 W and subsequently increased by 10 W. min(-1). The tests were performed in a randomised order at the same time of day, within 72 h. The highest (peak) oxygen consumption (VO(2peak)), heart rate (HR(peak)), blood lactate ([la(-)](peak)) and exercise intensity (EI(peak)) were recorded at exhaustion. Mean (SEM) peak responses to simulated swimming were higher than those to arm cranking for VO(2peak) [2.9 (0.2) vs 2.4 (0.1) l x min(-1); P = 0.01], HR(peak) [174 (2) vs 161 (2) beats x min(-1); P = 0.03], and EI(peak) [122 (6) vs 102 (5) W; P = 0.02]. However, there were no significant differences in [la(-)](peak) [9.6 (0.6) vs 8.2 (0.6) mmol x l(-1); P = 0.08]. Thus simulated swimming is the preferred form of dry-land ergometry for the assessment of swimmers.
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PMID:Comparison of cardiopulmonary responses to two types of dry-land upper-body exercise testing modes in competitive swimmers. 1054 26


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