The effects of dietary manipulation upon the respiratory exchange ratio as a predictor of maximum oxygen uptake during fixed term maximal incremental exercise in man

Summary This study examined the effects of dietary manipulation upon the respiratory exchange ratio ( ) as a predictor of maximum oxygen uptake ( ). Seven healthy males performed fixed term maximal incremental treadmill exercise after an overnight fast on three separate occasions. The first test took place after the subjects had consumed their normal mixed diet (45±5% carbohydrate (CHO)) for a period of three days. This test protocol was then repeated after three days of a low CHO diet (3±2% CHO), and again after three days of a high CHO diet (61±5% CHO). Respiratory gases were continuously monitored during each test using an online system. No significant changes in mean exercise oxygen uptake ( ), or maximum functional heart rate (FHR_max) were found between tests. Mean exercise carbon dioxide output ( ) and R were significantly lower than normal after the low CHO diet (bothp<0.001) and significantly higher than normal after the high CHO diet (bothp<0.05). Moreover, compared with the normal CHO diet, the R-time relationship during exercise was at all times significantly (p<0.001) shifted to the right after the low CHO diet, and shifted to the left, being significantly so (p<0.05) over the final 5 min of exercise, after the high CHO diet. As a result, predictions of based on the R-time relationship were similar to recorded after the normal CHO dietary condition (-1.5±1.9%), but higher after the low CHO diet (+14.8±3.9%,p<0.001) and lower after the high CHO diet (–7.0±4.5%,p<0.01). These results indicate that dietary manipulation can significantly affect respiratory gas exchanges during fixed term maximal incremental exercise, and by doing so can significantly influence predictions of based on R.     

Increase in atrial natriuretic peptide in response to physical exercise

Summary Circulating atrial natriuretic peptide (ANP) level was determined during physical exercise to investigate the correlation between changes in ANP level and heart rate increases.Six subjects exercised at a work level of 75% for 30 min, two also performed two successive exercises at 75% while two more exercised for longer at 55% · Plasma ANP levels and heart rate increased in all the exercising subjects. At the end of the exercise, the ANP level fell immediately, suggesting an immediate reduction in ANP secretion by the heart. Pre-exercise values were reached after 30 min. Successive exercises gave the same heart rate related ANP patterns without previous secretory episodes having any effect. These results lead to the conclusion that ANP intervenes in the cardiovascular adjustments to exercise.     

Gastric emptying during walking and running: effects of varied exercise intensity

Summary Gastric emptying is increased during running (50%–70% maximal aerobic uptake, as compared to rest. Whether this increase varies as a function of mode (i. e. walking vs running) and intensity of treadmill exercise is unknown. To examine the gastric emptying characteristics of water during treadmill exercise performed over a wide range of intensities relative to resting conditions, 10 men ingested 400 ml of water prior to each of six 15 min exercise bouts or 15 min of seated rest. Three bouts of walking exercise (1.57 m · s^–1) were performed at increasing grades eliciting 28%, 41% or 56% of . On a seperate day, three bouts of running (2.68 ms^–1) exercise were performed at grades eliciting 57%, 65% or 75% of . Gastric emptying was increased during treadmill exercise at all intensities excluding 75% as compared to rest. Gastric emptying was similar for all intensities during walking and at 57% and 65% during running. However, running at 74% decreased the volume of original drink emptied as compared to all lower exercise intensities. Stomach secretions were markedly less during running as compared to walking and rest. These data demonstrate that gastric emptying is similarly increased during both moderate intensity (8%–65% ) walking or running exercise as compared to resting conditions. However, gastric emptying decreases during high intensity exercise. Increases in gastric emptying during moderate intensity treadmill exercise may be related to increases in intragastric pressure brought about by contractile activity of the abdominal muscles.     

Are indices of free radical damage related to exercise intensity

Summary The possibility that plasma levels of malonaldehyde (MDA) are altered by exercise has been examined. The presence of MDA has been recognized to reflect peroxidation of lipids resulting from reactions with free radicals. Maximal exercise, eliciting 100% of maximal oxygen consumption ( ) resulted in a 26% increase in plasma MDA (P<0.005). Short periods of intermittent exercise, the intensity of which was varied, indicated a correlation between lactate and MDA (r ²=0.51) (p<0.001). Blood lactate concentrations increased throughout this exercise regimen. A significant decrease (10.3%) in plasma MDA occurred at 40% . At 70% plasma MDA was still below resting values, however the trend to an increase in MDA with exercise intensity was evident. At exhaustion, plasma MDA and lactate were significantly greater than at rest. These results suggest, that exhaustive maximal exercise induces free radical generation while short periods of submaximal exercise (i.e. <70% ) may inhibit it and lipid peroxidation.     

Effect of glucose polymer diet supplement on responses to prolonged successive swimming,cycling and running

Summary Fifteen male endurance athletes were studied to determine the effect of a glucose polymer (GP) diet supplement on physiological and perceptual responses to successive swimming, cycling and running exercise. Thirty min of swimming, cycling and running at 70% , followed by a run to exhaustion at 90% was performed after one week of training under two dietary conditions: 1) GP (230 g of GP consumed daily) and 2) placebo (P, saccharin-sweetened supplement consumed daily). During GP, daily carbohydrate (CHO) intake was higher (p<0.05) by 173 g or 14% of energy intake than during P, but total energy intake was not significantly different. During 90 min of exercise, CHO utilization and blood glucose were significantly higher under GP than P by an average of 20.2% and 14.5%, respectively, but heart rate, ventilation, oxygen uptake, ratings of perceived exertion, and plasma lactate were not different. Run time to exhaustion at 90% was significantly longer by 1.2 min (23%) under GP. The results suggest that a GP diet supplement may be of value during endurance exercise by increasing the availability of CHO.     

Active sulfate reabsorption in the proximal convolution of the rat kidney: Specificity,Na+ and HCO 3 − dependence

Using the standing droplet technique in the proximal convolution and simultaneous microperfusion of the peritubular capillaries, the decrease in luminal sulfate concentration with time and the zero net flux transtubular concentration difference of sulfate ( ) at 45 s was determined — the latter being taken as a measure of the rate of active sulfate reabsorption. Starting with 0.5 mmol/l sulfate in both perfusates the value of 0.35 mmol/l was approached exponentially with a half value time of 4.3 s. The values in the early proximal and late proximal convolution did not deviate from each other. If the Na⁺ concentration in the perfusates was reduced, the approached zero and extrapolated to a slightly negative value (c _i>c _o). When 1 mmol/l ouabain was added to the perfusates decreased by 66% (the latter experiments were performed in the golden hamster which is more sensitive to ouabain than the rat). 1 mmol/l thiosulfate diminished by 68% and 1 mmol/l molybdate by 24%. Omitting or replacing bicarbonate by HEPES or glycodiazine reduced the sulfate reabsorption significantly, while acetazolamide (0.1 mmol/l) and increasing the CO₂-pressure from 4.66 to 14.0 kPa (i.e. 5–15% CO₂) had no effect. SITS 1 mmol/l had no effect on sulfate reabsorption.The data indicate that the sulfate reabsorption is driven by a Na⁺ gradient and inhibited by thiosulfate and molybdate, i.e. molecules which have a similar tetrahedral molecule structure. The sulfate reabsorption depends in an undefined manner on the presence of bicarbonate ions.     

Precision of ventilatory and gas exchange alterations as a predictor of the anaerobic threshold

Summary Anaerobic threshold has been defined as the oxygen uptake ( ) at which blood lactate (La) begins to rise systematically during graded exercise (Davis et al. 1982). It has become common practice in the literature to estimate the anaerobic threshold by using ventilatory and/or gas exchange alterations. However, confusion exists as to the validity of this practice. The purpose of this study was to examine the precision with which ventilatory and gas exchange techniques for determining anaerobic threshold predicted the anaerobic threshold resolved by La criteria. The anaerobic threshold was chosen using three criteria: (1) systematic increase in blood La (AT_La), (2) systematic increase in ventilatory equivalent for O₂ with no change in the ventilatory equivalent for CO₂ ( ), and (3) non-linear increase in expired ventilation graphed as a function of ( ). Thirteen trained male subjects performed an incremental cycle ergometer test to exhaustion in which the load was increased by 30 W every 3 minutes. Ventilation, gas exchange measures, and blood samples for La analysis were obtained every 3rd min throughout the test. In five of the thirteen subjects tested the anaerobic threshold determined by ventilatory and gas exchange alterations did not occur at the same as the AT_La. The highest correlation between a gas exchange anaerobic threshold and AT_La was found for and was r=0.63 (P<0.05). These data provide evidence that the AT_La and do not always occur simultaneously and suggest limitations in using ventilatory or gas exchange measures to estimate the AT_la.     

Effect of training on the rating of perceived exertion at the ventilatory threshold

Summary The purpose of this study was to determine the effect of training on the rating of perceived exertion (RPE) at the ventilatory threshold. College students were assigned to either training (n=17) or control (n=10) groups. Trainers completed 18 interval training sessions (five × 5 min cycling at 90–100% ) and 8 continuous training sessions (40 min running or cycling) in 6 weeks. Pre- and post-training, cardiorespiratory, metabolic, and perceptual variables were measured at the ventilatory threshold during graded exercise tests on a cycle ergometer. Ventilatory threshold was that point above which increased abruptly relative to work rate. Post-training means of trained and control subjects were compared using analysis of covariance, with pre-training values as covariates. Following training, the adjusted means for the trained subjects were significantly greater (p<0.05) than for controls for (6%), and for work rate (20%), (23%), and % (13%) at the ventilatory threshold. However, adjusted means for RPE at the ventilatory threshold were not significantly different (2%). Both before and after training, exercise at the ventilatory threshold was perceived as somewhat hard to hard (RPE=13–15) by both groups. The relationship between RPE and % was altered by training, with trained subjects having a lower RPE at a given % . It is concluded that RPE at the ventilatory threshold is not affected by training, despite that after training the ventilatory threshold occurs at a higher work rate and is associated with higher absolute and relative metabolic and cardiorespiratory demands.     

Energy sources in alpine skiing (giant slalom)

Summary The energy cost of a giant slalom event was measured in eight skiers of national level. The lap lasted on average 82 s. was measured during the first, the second and the last third of the lap in different trials and also during recovery from a complete lap. Blood lactate was measured at the end of a lap. From the data obtained it was possible to calculate that: a) , as measured during the lap, would correspond at steady state to 80% of the of the subjects; b) the total metabolic power delivered during the lap should be equal to about 72ml O₂·kg^–1·min^–1, corresponding to 120% of of the subjects. Considering the short duration of the trial and the power output delivered during maximal efforts on a bicycle ergometer, it appears that the giant slalom is not a very high energy demanding event.Preliminary results of this work have been presented at the XXII. World Congress on Sport Medicine, Vienna 1982     

The effect of one-legged sprint training on intramuscular pH and nonbicarbonate buffering capacity

Summary To determine the effect of one-legged sprint training on muscle pH and nonbicarbonate buffering capacity (BC), 9 subjects completed 15 to 20 intervals at 90 RPM, 4 days a week for 7 weeks on a bicycle ergometer adapted for one-legged pedaling. Needle biopsies from the vastus lateralis and blood samples from an antecubital vein were taken at rest and twice during recovery (1 and 4 minutes) from a 60 s one-legged maximal power test on a cycle ergometer. pH one minute after exercise in both the trained and untrained legs following the training period was not different but both were higher than before training. BC increased from 49.9 to 57.8 mol HCl×g^–1×pH^–1 after training (p<0.05). Blood lactate levels after exercise were significantly higher for the trained leg when compared to the untrained leg after sprint training. Peak and average power output on the 60 s power test increased significantly after training. One-legged aerobic power ( ) significantly increased in the untrained and trained legs. Two-legged also improved significantly after training. These data suggest that nonbicarbonate buffering capacity and power output can be enhanced with one-legged sprint training. Also, small but significant improvements in were also observed.     

The effects of cigarette smoking on maximal oxygen consumption and selected physiological responses of elite team sportsmen

Summary The acute and chronic effects of cigarette smoking on selected physiological responses were determined in seven well-trained non-smokers and seven well-trained habitual smokers. Non-smokers and smokers did not differ significantly with respect to maximal oxygen consumption ( ). The acute effect of smoking two cigarettes immediately prior to a graded exercise stress test on a treadmill ergometer did not significantly alter the of either group. However, the time taken for non-smokers to reach exhaustion decreased significantly (F=5.381, P<0.05) by a mean of 0.64 min. Smokers recorded lower scores for forced vital capacity (FVC) and forced expiratory volume in the 1st s exhalation (FEV₁) than non-smokers. Only the mean FVC of smokers recorded 5 min post-exercise was significantly altered by pre-exercise smoking. No differences were found between the resting heart rates (HR) of non-smokers and smokers. Smoking two cigarettes significantly (F=44.720, P<0.01) increased the mean resting HR of smokers and non-smokers by 15.8 beats·min^–1 and 15.6 beats·min^–1 respectively. No alteration to the exercise HR of either group was found under smoking conditions of the tests.     

Age-associated blood glucose levels during exercise in female swimmers

Summary The purpose of this study was to determine whether age-associated alterations in blood glucose levels occur during exercise. In addition, blood lactate and fitness levels ( ) were examined to ascertain if these factors influenced the age-related responses. Sixty-four female masters swimmers (25–75 years) were classified into either a well trained (WT) or recreational trained (RT) group and exercised on a treadmill to . data confirmed our classification of WT and RT swimmers based on activity levels. There were no differences in post-absorptive blood glucose and lactate levels across age and fitness. Significant age-related effects on blood glucose levels during exercise (p<0.01) but no fitness effect were revealed by ANOVA. Within the first or second exercise stage all age groups demonstrated a significant decline in blood glucose (6.3 to 14.1%). A hyperglycemic response was observed during recovery in all age groups with the exception of the over 60 (60+) group. The 60+ group exhibited lower blood glucose levels compared to all other age groups during exercise commencing with the second exercise stage. There were no significant differences in glucose levels among any of the other age groups during exercise or recovery. There were no age-related differences in maximal or recovery lactates. These data indicate that there is an alteration of blood glucose homeostasis during exercise in females over 60 years of age.     

Ventilatory response during incremental exercise tests in weight lifters and endurance cyclists

Summary The effect of a progressively increasing work rate (15 W·min^–1) up to exhaustion on the time course of O₂ uptake ( ), ventilation ( ) and heart rate (HR) has been studied in weight lifters (WL) in comparison to endurance cyclists (Cycl) and sedentary controls (Sed). and were measured as average value of 30-s intervals by a semiautomatic open circuit method. was 2.55±0.33; 4.29±0.53 and 2.86±0.19·min^–1 in WL, Cycl and Sed respectively. With time and work rate, while and HR increased linearly, changed its slope at two levels. The 1st change occured at a work load corresponding to a mean (± SD) of 1.50±0.26; 1.93±0.34; and 1.23±0.14 l·min^–1 in WL, Cycl, and Sed respectively. values corresponding to the second change of slope were 2.18±0.32 in WL; 3.48±0.53 in Cycl and 2.17±0.28 l·min^–1 in Sed. The first change of slope might be the consequence of the different readjustment of on-response and hence of early lactate in the different subjects. The second change seems to be comparable to the conventional anaerobic threshold and is achieved in all subjects when vs time slope is 7–10 l·min^–1/min of exercise.This work has been supported in part by a grant from the Italian National Research Council (CNR)     

Sex differences in endurance capacity and metabolic response to prolonged,heavy exercise

Summary In order to test for possible sex differences in endurance capacity, groups of young, physically active women (n=6) and men (n=7) performed bicycle ergometer exercise at 80% and 90% of their maximal oxygen uptakes ( ). The groups were matched for age and physical activity habits. At 80% the women performed significantly longer (P<0.05), 53.8±12.7 min vs 36.8±12.2 min, respectively (means ± SD). Mid-exercise and terminal respiratory exchange ratio (R) values were significantly lower in women, suggesting a later occurrence of muscle glycogen depletion as a factor in their enhanced endurance. At 90% the endurance times were similar for men and women, 21.2±10.3 min and 22.0±5.0 min, respectively. The blood lactate levels reached in these experiments were only marginally lower (mean differences 1.5 to 2 mmol·l^–1) than those obtained at , suggesting high lactate levels as a factor in exhaustion. The changes in body weight during the 80% experiments and the degree of hemoconcentration were not significantly different between men and women.     

Predictors of sweat loss in man during prolonged exercise

Summary Nineteen healthy male subjects, differing in training status and (52±1 ml · min^–1 · kg^–1, mean ±SEM; 43–64 ml · min^–1 · kg^–1, range), exercised for 1 h at an absolute workload of 192±8 W (140–265 W); this was equivalent to 70±1% (66–74%). Each exercise test was performed on an electrically braked cycle ergometer at a constant ambient temperature (22.5±0.0° C) and relative humidity (85±0%). Nude body weight was recorded prior to and after each exercise test. Absolute sweat loss (body weight loss corrected for respiratory weight loss) during each test was 910±82 g (426–1665 g); this was equivalent to 1.3±0.1% (0.7–2.2%) of pre-exercise body weight (relative sweat loss). Weighted mean skin temperature and rectal temperature increased after 5 min of exercise from 30.5±0.3° C and 37.2±0.1° C respectively to 32.5±0.2° C and 38.8±0.1° C respectively, recorded immediately prior to the end of exercise. Bivariate linear regression and Pearson's correlation demonstrated absolute sweat loss was related to (r=0.72,p<0.001), absolute exercise workload (r=0.66,p<0.01), body surface area (r=0.62,p<0.01), weight (r=0.60,p<0.01) and height (r=0.53,p<0.05). Relative sweat loss was related to (r=0.77,p<0.001) and absolute exercise workload (r=0.59,p<0.01). There was no relationship between sweat loss (absolute or relative) and heart rate, skin temperature or rectal temperature. In addition, there was no relationship between rectal temperature or absolute exercise workload or . Stepwise multiple linear regression indicated to be the most important predictor of absolute (r=0.72,F=18.27,p<0.001) and relative (r=0.77,F=24.58,p<0.001) sweat loss in man during prolonged exercise.     

Relationships between skeletal muscle characteristics and aerobic performance in sedentary and active subjects

Summary Forty-eight sedentary and 39 quite active or well-trained men participated in this study. Muscle biopsy samples were taken from the vastus lateralis for the determination of fiber type composition (I, IIa, IIb), fiber type area, and assay of the following enzymes: malate dehydrogenase (MDH), 3-hydroxyacyl CoA dehydrogenase (HADH) and oxoglutarate dehydrogenase (OGDH). Maximal oxygen uptake ( ) was determined with a progressive cycle ergometer test, while endurance performance or maximal aerobic capacity (MAC) was defined as the total work output during a 90-min cycle ergometer test. Correlation analysis revealed no evidence of association between fiber type composition and kg^–1 or MAC kg^–1 in sedentary subjects, while active men exhibited significant correlation between % type I (r=0.52), % type IIb (r=–0.31) and kg^–1. Enzyme activities were not significantly correlated with MAC kg^–1 and kg^–1 in sedentary men while active men exhibited significant correlation for the three enzymes (0.37r0.51) with kg^–1. These results show that the contribution of muscle fiber type and enzyme activities to aerobic performance may be inflated from a statistiscal point of view by the training status heterogeneity of subjects. They also suggest that variation in these muscle characteristics does not account for the individual differences in aerobic performance of subjects who have never trained before. Therefore, the assessment of muscle characteristics is not as useful as originally thought for the detection of individuals with a high potential for endurance performance among untrained subjects.     

Ageing and isokinetic plantar flexion

Summary Isokinetic torques (Cybex II) of the plantar flexors in 25 healthy men were compared at 5 angular velocities (30, 60, 90, 120 and 180° · s^–1). The purposes were to compare plantar flexion torques in young and old subjects, and to determine whether the expected decrease was significantly associated with age, physical activity, or aerobic fitness. Four groups were studied: young (21.7±2.0 years) and older (63.3±2.8 years), active and sedentary. Measurements of height, weight, % body fat, and daily leisure energy expenditure (questionnaire) were determined for each subject. Statistical measures of analysis of variance were used to determine significant differences among groups; product moment correlation and stepwise regression analysis were used to describe the degree of association between the dependent variable of plantar flexion torque and the independent variables at each velocity. A decline in torque was observed as the isokinetic velocity of angular motion increased. Age alone was a significant determinant of plantar flexion torque, whereas at the slowest speed, when was used as an explanatory variable, age was not a significant determinant of torque. At 30° · s^–1 47% of the variance in torque was explained by while at 180° · s^–1 49% of the variance was explained by age.     

Comparison of incremental and steady state tests of endurance training

Summary To compare the results obtained by incremental or constant work load exercises in the evaluation of endurance conditionning, a 20-week training programme was performed by 9 healthy human subjects on the bicycle ergometer for 1 h a day, 4 days a week, at 70–80% . Before and at the end of the training programme, (1) the blood lactate response to a progressive incremental exercise (18 W increments every 2nd min until exhaustion) was used to determine the aerobic and anaerobic thresholds (AeT and AnT respectively). On a different day, (2) blood lactate concentrations were measured during two sessions of constant work load exercises of 20 min duration corresponding to the relative intensities of AeT (1st session) and AnT (2nd session) levels obtained before training. A muscle biopsy was obtained from vastus lateralis at the end of these sessions to determine muscle lactate. AeT and AnT, when expressed as % , increased with training by 17% (p<0.01) and 9% (p<0.05) respectively. Constant workload exercise performed at AeT intensity was linked before training (60% ) to a blood lactate steady state (4.8±1.4 mmol·l^–1) whereas, after training, AeT intensity (73% ) led to a blood lactate accumulation of up to 6.6±1.7 mmol·l^–1 without significant modification of muscle lactate (7.6±3.1 and 8.2±2.8 mmol·kg^–1 wet weight respectively). It is concluded that increase in AeT with training may reflect transient changes linked to lower early blood lactate accumulation during incremental exercise. Nevertheless, the results obtained at the end of the constant work load exercises were assumed to be independant of these changes, the occurrence of blood lactate accumulation being postulated to reflect a decreased removal from the blood linked to a higher relative work intensity. So, the use of incremental exercise is an incomplete procedure when evaluating endurance training effects.     

The response of runners to arduous triathlon competition

Summary As very few of the competitors in a triathlon are truly specialist in more than one of the three disciplines, high levels of physical (and mental) stress may result during the course of the event. We investigated some of the physiological responses occurring in runners participating in an Iron Man triathlon consisting of canoeing (20 km), cycling (90 km) and running (42 km), in that sequence.Twenty-one male entrants volunteered as subjects for the study. Prior to the competition, maximal oxygen consumption ( ) was determined. Basal venous blood samples were collected on the day prior to the competition and post-exercise venous blood samples were collected within 5 minutes of completion of the race.Serum iron was significantly reduced from a mean basal value of 20.6 mol · l^–1 to a mean value of 8.4 mol · l^–1 after the race. Cortisol levels showed a 3 fold increase after the race. Gross (l · min^–1) and mass standardised (ml · min^–1 · kg^–1) were both negatively correlated to cortisol levels after the race (p<0.05). Total performance time was not related to gross (l · min^–1) but was well correlated to mass corrected (ml · min^–1 · kg^–1).The marked fall in serum iron may have been related to heavy sweating or prelatent iron deficiency. Chronic iron deficiency (without frank anaemia) can impair physical performance, although we were unable to show any significant correlation between serum iron level after the race and time taken to complete the event. The subjects with a lower (ml · min^–1 · kg^–1) had a higher cortisol concentration. In spite of a longer performance time, these subjects were apparently still exposed to greater physiological strain.     

Diffusion-limited gas mixing in the lung and its consequences for transpulmonary gas transport

The ratio of alveolar ventilations of He and SF₆ ( ) was determined in 7 healthy male subjects at rest and at three different levels of exercise on a bicycle ergometer (75, 150 and 225 W). This ratio was calculated from the ratio of the specific ventilations for these gases which were obtained from the decay of the end-tidal partial pressures of He and SF₆ during a simultaneous, multiple-breath washout. In all experiments, for He was larger than for SF₆. On the average, was equal to 1.09, and the mean values of this ratio at rest and at the three levels of exercise were not significantly different. Therefore, the difference in for He and SF₆ increased with increasing work load. Further, we used the mean value obtained for , to calculate the ratio of excretion values (E₁/E₂) for pairs of hypothetical tracer gases with equal blood-gas partition coefficients and with different diffusivities in the gas phase. E₁/E₂ ranged from anity for =0 to about 1.08 for =10. At a given , E₁/E₂ decreased with increasing ventilation-perfusion ratio of the lung. Thus, the difference between the excretion values of light and heavy tracer gases will be most pronounced under rest conditions and for gases that are well soluble in blood.