Cardiorespiratory response to absolute and relative work intensity in untrained men

Twenty young, untrained men performed two tests on cycle ergometer in order to verify whether the kinetics of the cardiorespiratory reactions exhibit any relation to maximal oxygen uptake (VO2max) in the untrained state. On the 1st day, the subjects exercised at work intensities of 50 and 100 W, the increase as a step function, for periods of 10 min each. The next day, they performed exercise at a relative intensity of 50% VO2max for 10 min. Respiratory frequency, tidal volume, minute ventilation (VE), heart rate (HR), stroke volume (SV), and cardiac output (Q) were measured continuously. The SV was measured by impedance plethysmography. All the cardiorespiratory variables increased rapidly at the onset of both absolute and relative intensity of work, with a faster response for Q than for VE. The increase in absolute intensity of work from 50 to 100 W caused a significantly slower cardiorespiratory reaction than at the beginning of exercise. The SV increased by 20 ml during first 20 s of both absolute and relative intensities of work and then began to decrease after 6 and 4 min of the exercise, respectively. The decrease in SV was associated with an increase in HR and a stable value of Q. Acceleration at the beginning of, and deceleration during recovery from, the relative intensity of work for VE, HR, and Q were well correlated with individual levels of VO2max in the tested men. It is concluded that the kinetics of cardiorespiratory reaction to a constant, relative intensity of work is related to VO2max in untrained men, and that the kinetics probably constitute a physiological feature of an individual.     

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).     

Oxygen uptake efficiency slope as a useful measure of cardiorespiratory functional reserve in adult cardiac patients

In this study we aimed to elucidate the validity and usefulness of the oxygen uptake efficiency slope (OUES) in the evaluation of adult cardiac patients. Cardiopulmonary exercise tests were performed on a treadmill by 50 adult patients with chronic heart failure. The OUES was calculated from data for the first 75%, 90%, and 100% of exercise duration. The OUES is derived from the following equation: VO(2)=ax logV(E)+b, where VO(2) is oxygen uptake (ml/kg/min), V(E) is minute ventilation (l/kg/min), and the constant "a" represents OUES. We also determined the ventilatory anaerobic threshold (VAT). The correlation coefficient of the logarithmic curve-fitting model was [mean (SD)] 0.986 (0.009). The OUES could be used to discriminate effectively between New York Heart Association functional classes (P < 0.001). OUES and maximum VO(2) were significantly correlated (r=0.78, P < 0.01). Agreement between the OUES values for the first 90%, 75%, and 100% of the exercise was excellent (intraclass correlation coefficient = 0.99). Our results suggest that OUES is applicable to adult cardiac patients as an objective, effort-independent estimation of cardiorespiratory functional reserve.     

Breathing pattern in highly competitive cyclists during incremental exercise

The purpose of our investigation was to analyse the breathing patterns of professional cyclists during incremental exercise from submaximal to maximal intensities. A group of 11 elite amateur male road cyclists [E, mean age 23 (SD 2) years, peak oxygen uptake (VO2peak) 73.8 (SD 5.0) ml kg(-1) min(-1)] and 14 professional male road cyclists [P, mean age 26 (SD 2) years, (VO2peak) 73.2 (SD 6.6) ml kg(-1) min(-1)] participated in this study. Each of the subjects performed an exercise test on a cycle ergometer following a ramp protocol (exercise intensity increases of 25 W x min(-1)) until the subject was exhausted. For each subject, the following parameters were recorded during the tests: oxygen consumption (VO2), carbon dioxide output (VCO2), pulmonary ventilation (VE), tidal volume (VT), breathing frequency (fb), ventilatory equivalents for oxygen (VE x VO2(-1)) and carbon dioxide (VE x VCO2(-1)), end-tidal partial pressure of oxygen and partial pressure of carbon dioxide, inspiratory (tI) and expiratory (tE) times, inspiratory duty cycle (tI/tTOT, where tTOT is the time for one respiratory cycle), and mean inspiratory flow rate (VT/tI). Mean values of VE were significantly higher in E at 300, 350 and 400 W (P < 0.05, P < 0.05 and P < 0.01, respectively); fb was also higher in E in most moderate-to-maximal intensities. On the other hand, VT showed a different pattern in both groups at near-to maximal intensities, since no plateau was observed in P. The response of tI and tE was also different. Finally, VT/tI and tI/tTOT showed a similar response in both P and E. It was concluded that the breathing pattern of the two groups differed mainly in two aspects: in the professional cyclists, VE increased at any exercise intensity as a result of increases in both VT and fb, with no evidence of tachypnoeic shift, and tE was prolonged in this group at high exercise intensities. In contrast, neither the central drive nor the timing component of respiration seem to have been significantly altered by the training demands of professional cycling.     

The effect of exercise intensity and duration on salivary immunoglobulin A.

Two experiments were performed to examine salivary immunoglobulin A (s-IgA) responses to varying levels of exercise intensity and duration. For experiment 1, 9 college men (mean age, SD = 23.56, 1.64 years) completed treadmill runs of 15, 30, and 45 min at approximately 60% of maximum oxygen consumption (VO2max). For experiment 2, 9 other college men (mean age, SD = 23.67, 2.0 years) ran for 20 min at approximately 50, 65 and 80% of VO2max. Unstimulated salivary samples were collected before, and immediately, 1 and 2 h after the exercise. Samples were assayed for s-IgA using an enzyme-linked immunosorbent assay. Mean s-IgA levels did not change significantly (P greater than 0.05) at any of the post-exercise collection times when compared to pre-exercise levels. The results of this investigation indicated that running at intensities of 50-80% of VO2max and for durations of 15-45 min did not affect s-IgA levels.     

The relationship between anaerobic threshold and electromyographic fatigue threshold in college women

The purpose of this study was to investigate the relationship between anaerobic threshold (Th(an)) and muscle fatigue threshold (EMGFT) as estimated from electromyographic (EMG) data taken from the quadriceps muscles (vastus lateralis) during exercise on a cycle ergometer. The subjects in this study were 20 female college students, including highly trained endurance athletes and untrained sedentary individuals, whose fitness levels derived from their maximal oxygen consumption ranged from 24.9 to 62.2 ml.kg-1.min-1. The rate of increase in integrated EMG (iEMG) activity as a function of time (iEMG slope) was calculated at each of four constant power outputs (350, 300, 250, 200 W), sufficiently high to bring about muscle fatigue. The iEMG slopes so obtained were plotted against the exercise intensities imposed, resulting in linear plots which were extrapolated to zero slope to give an intercept on the power axis which was in turn interpreted as the highest exercise intensity sustainable without electromyographic evidence of neuromuscular fatigue (EMGFT). The Th(an) was estimated from gas exchange parameters during an incremental exercise test on the same cycle ergometer. The mean results indicated that oxygen uptake (VO2) at Than was 1.39 l.min-1, SD 0.44 and VO2 at EMGFT was 1.33 l.min-1, SD 0.57. There was no significant difference between these mean values (P greater than 0.05) and there was a highly significant correlation between VO2 at Than and VO2 at EMGFT (r = 0.823, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Adrenergic regulation of HSL serine phosphorylation and activity in human skeletal muscle during the onset of exercise

Skeletal muscle hormone-sensitive lipase (HSL) activity is increased by contractions and increases in blood epinephrine (EPI) concentrations and cyclic AMP activation of the adrenergic pathway during prolonged exercise. To determine the importance of hormonal stimulation of HSL activity during the onset of moderate- and high-intensity exercise, nine men [age 24.3 +/- 1.2 yr, 80.8 +/- 5.0 kg, peak oxygen consumption (VO2 peak) 43.9 +/- 3.6 ml x kg(-1) x min(-1)] cycled for 1 min at approximately 65% VO2 peak, rested for 60 min, and cycled at approximately 90% VO2 peak for 1 min. Skeletal muscle biopsies were taken pre- and postexercise, and arterial blood was sampled throughout exercise. Arterial EPI increased (P < 0.05) postexercise at 65% (0.45 +/- 0.10 to 0.78 +/- 0.27 nM) and 90% VO2 peak (0.57 +/- 0.34 to 1.09 +/- 0.50 nM). HSL activity increased (P < 0.05) following 1 min of exercise at 65% VO2 peak [1.05 +/- 0.39 to 1.78 +/- 0.54 mmol x min(-1) x kg dry muscle (dm)(-1)] and 90% VO2 peak (1.07 +/- 0.24 to 1.91 +/- 0.62 mmol x min(-1) x kg dm(-1)). Cyclic AMP content also increased (P < 0.05) at both exercise intensities (65%: 1.52 +/- 0.67 to 2.75 +/- 1.12, 90%: 1.85 +/- 0.65 to 2.64 +/- 0.93 micromol/kg dm). HSL Ser660 phosphorylation (approximately 55% increase) and ERK1/2 phosphorylation ( approximately 33% increase) were augmented following exercise at both intensities, whereas HSL Ser563 and Ser565 phosphorylation were not different from rest. The results indicate that increases in arterial EPI concentration during the onset of moderate- and high-intensity exercise increase cyclic AMP content, which results in the phosphorylation of HSL Ser660. This adrenergic stimulation contributes to the increase in HSL activity that occurs in human skeletal muscle in the first minute of exercise at 65% and 90% VO2 peak.     

Perceived exertion and gas exchange after calcium and beta-blockade in atrial fibrillation

Nine male patients (mean age 65 yr) with chronic atrial fibrillation underwent maximal exercise testing during placebo, beta-adrenergic (celiprolol, 600 mg), or calcium (diltiazem, 30 or 60 mg four times daily) channel blockade. The results were analyzed to determine which factors most closely related to ratings of perceived exertion (RPE) during exercise. Heart rate (HR), blood pressure (BP), oxygen uptake (VO2), minute ventilation (VE), and carbon dioxide production (VCO2) were evaluated at rest, 3.0 mph/0% grade, the gas exchange anaerobic threshold (ATge), 80% of placebo maximal O2 uptake, and maximal exercise. Both beta-adrenergic and calcium channel blockade significantly reduced heart rate and systolic blood pressure relative to placebo; these effects were more profound during beta-adrenergic blockade and as exercise progressed. Correlation coefficients and estimates of slope were derived for changes in RPE during exercise vs. changes in HR, VO2, VE, and VCO2 during the three treatments (r = 0.76 to 0.92, P less than 0.001). Although RPE was significantly correlated with HR during placebo and diltiazem therapy (r = 0.45, P less than 0.01), this was not the case during beta-adrenergic blockade (r = 0.31, NS). Slope of the regression lines between RPE and VO2, VE, and VCO2 did not differ between the three treatments. Slope of the regression lines between RPE and HR differed only during calcium channel blockade. Because the presence of atrial fibrillation and beta-adrenergic blockade altered the associations between RPE, VO2, and HR, these results suggest that VE is more closely related to RPE than the other parameters.     

Metabolic and cardioventilatory responses during a graded exercise test before and 24 h after a triathlon

Previous studies have reported respiratory, cardiac and muscle changes at rest in triathletes 24 h after completion of the event. To examine the effects of these changes on metabolic and cardioventilatory variables during exercise, eight male triathletes of mean age 21.1 (SD 2.5) years (range 17-26 years) performed an incremental cycle exercise test (IET) before (pre) and the day after (post) an official classic triathlon (1.5-km swimming, 40-km cycling and 10-km running). The IET was performed using an electromagnetic cycle ergometer. Ventilatory data were collected every minute using a breath-by-breath automated system and included minute ventilation (V(E)), oxygen uptake (VO2), carbon dioxide production (VCO2), respiratory exchange ratio, ventilatory equivalent for oxygen (V(E)/VO2) and for carbon dioxide (V(E)/VCO2), breathing frequency and tidal volume. Heart rate (HR) was monitored using an electrocardiogram. The oxygen pulse was calculated as VO2/HR. Arterialized blood was collected every 2 min throughout IET and the recovery period, and lactate concentration was measured using an enzymatic method. Maximal oxygen uptake (VO2max) was determined using conventional criteria. Ventilatory threshold (VT) was determined using the V-slope method formulated earlier. Cardioventilatory variables were studied during the test, at the point when the subject felt exhausted and during recovery. Results indicated no significant differences (P > 0.05) in VO2max [62.6 (SD 5.9) vs 64.6 (SD 4.8) ml x kg(-1) x min(-1)], VT [2368 (SD 258) vs 2477 (SD 352) ml x min(-1)] and time courses of VO2 between the pre- versus post-triathlon sessions. In contrast, the time courses of HR and blood lactate concentration reached significantly higher values (P < 0.05) in the pre-triathlon session. We concluded that these triathletes when tested 24 h after a classic triathlon displayed their pre-event aerobic exercise capacity, bud did not recover pretriathlon time courses in HR or blood lactate concentration.     

The respiratory system as an exercise limiting factor in normal trained subjects

Recently, we have shown that an untrained respiratory system does limit the endurance of submaximal exercise (64% peak oxygen consumption) in normal sedentary subjects. These subjects were able to increase breathing endurance by almost 300% and cycle endurance by 50% after isolated respiratory training. The aim of the present study was to find out if normal, endurance trained subjects would also benefit from respiratory training. Breathing and cycle endurance as well as maximal oxygen consumption (VO2max) and anaerobic threshold were measured in eight subjects. Subsequently, the subjects trained their respiratory muscles for 4 weeks by breathing 85-160 l.min-1 for 30 min daily. Otherwise they continued their habitual endurance training. After respiratory training, the performance tests made at the beginning of the study were repeated. Respiratory training increased breathing endurance from 6.1 (SD 1.8) min to about 40 min. Cycle endurance at the anaerobic threshold [77 (SD 6) %VO2max] was improved from 22.8 (SD 8.3) min to 31.5 (SD 12.6) min while VO2max and the anaerobic threshold remained essentially the same. Therefore, the endurance of respiratory muscles can be improved remarkably even in trained subjects. Respiratory muscle fatigue induced hyperventilation which limited cycle performance at the anaerobic threshold. After respiratory training, minute ventilation for a given exercise intensity was reduced and cycle performance at the anaerobic threshold was prolonged. These results would indicate the respiratory system to be an exercise limiting factor in normal, endurance trained subjects.     

Muscle recruitment patterns regulate physiological responses during exercise of the same intensity

On different days, 10 men performed 30-min sessions of cycling at 50-55% of their peak oxygen uptake (VO(2)); one at 40 rpm and another at 80 rpm. Rectal temperature, heart rate (HR), mean arterial pressure (MAP), plasma lactate, glucose, insulin, and cortisol were measured before exercise, during the 15th and 30th min of exercise, and at 5 and 10 min postexercise. Rating of perceived exertion (RPE) was assessed 15 and 30 min into exercise. Electromyography established cadence-specific different intensities of quadriceps activation during cycling. At minute 30 of exercise and 5 min postexercise, HR was significantly (P < 0.05) greater at 40 rpm than at 80 rpm. MAP remained elevated longer after the 40-rpm than after the 80-rpm bout. Similarly, exercise-induced increases in plasma lactate persisted longer after the 40-rpm bout. Cortisol levels were elevated only at 40 rpm. RPE was higher during the slower cadence. These data indicated that the more pronounced muscle activation pattern associated with pedaling at 40 rpm resulted in greater physiological and psychophysiological stress than that observed at 80 rpm even though VO(2) was the same.     

Training effects of cross-country skiing and running on maximal aerobic cycle performance and on blood lipids

Two experiments were carried out to compare the cardiorespiratory and metabolic effects of cross-country skiing and running training during two successive winters. Forty-year-old men were randomly assigned into skiing (n = 15 in study 1, n = 16 in study 2), running (n = 16 in study 1 and n = 16 in study 2) and control (n = 17 in study 1 and n = 16 in study 2) groups. Three subjects dropped out of the programme. The training lasted 9-10 weeks with 40-min exercise sessions three times each week. The training intensity was controlled at 75%-85% of the maximal oxygen consumption (VO2max) using portable heart rate metres and the mean heart rate was 156-157 beats.min-1 in the training groups. In the pooled data of the two studies the mean increase in the VO2max (in ml.min-1.kg-1) on a cycle ergometer was 17% for the skiing group, 13% for the running group and 2% for the control group. The increase in VO2max was highly significant in the combined exercise group compared to the control group but did not differ significantly between the skiing and running groups. The fasting serum concentrations of lipoproteins and insulin did not change significantly in any of the groups. These results suggested that training by cross-country skiing and running of the same duration and intensity at each session for 9-10 weeks improved equally the cardiorespiratory fitness of untrained middle-aged men.     

Slow upward drift of VO2 during constant-load cycling in untrained subjects

The oxygen uptake kinetics during constant-load exercise when sitting on a bicycle ergometer were determined in 7 untrained subjects by measuring breath-by-breath VO2 during continuous exercise to volitional exhaustion (mean endurance time = 1160 +/- 172 s) at a pedal frequency of 70 revolutions.min-1. The power output, averaging 189.5 W, was set at 82.5% of that eliciting the individual VO2max during a 5 min incremental exercise test. Throughout the exercise period, the VO2 kinetics could be appropriately described by a two-component exponential equation of the form: VO2(t) = Ya[1 - exp(-kat)] + Yb[1 - exp(-kbt)] where VO2 is net oxygen consumption and t the time from work onset. VO2 measured at the end of exercise was close to VO2max (98% VO2max) and the mean values of Ya, ka, Yb and kb amounted to 1195 ml O2.min-1, 0.034 s-1, 1562 ml O2.min-1, and 0.005 s-1 respectively. The initial rate of increase in VO2 predicted from the above equation is slower than that calculated, for the same work intensity, on the basis of the data obtained by Morton (1985) in trained subjects. For t greater than 480 s, however, the two models yield substantially equal results.     

Acute exercise has no effect on ghrelin plasma concentrations.

Exercise is a potent, dose-dependent stimulus of growth hormone (GH) secretion. The hypothalamic peptides, GH-releasing hormone (GHRH) and somatostatin are regarded as major regulators of this stimulation. The role of the stomach-derived peptide ghrelin, which has been shown to exert strong GH releasing effects, has not been fully characterized yet. We therefore studied GH and ghrelin plasma concentrations in response to graded levels of exercise in eight healthy young volunteers. After determination of their individual maximal exercise capacity, all individuals underwent a treadmill exercise at 50 %, 70 %, and 90 % of maximum oxygen consumption (VO (2)max) on different days. Maximal GH response to exercise was observed after 40 minutes at 50 % VO (2)max and after 20 minutes at 70 and 90 % VO (2max). GH serum concentrations increased significantly at all three exercise intensities (GH peak concentrations were 5.8 +/- 2.3 ng/ml, 12.0 +/- 3.2 ng/ml, and 9.8 +/- 4.7 ng/ml, respectively). In contrast, ghrelin plasma concentrations remained unchanged at all three workloads. Assuming that the sensitivity of the GH neuroendocrine/metabolic regulation of GH is unaltered, ghrelin does not participate in the regulation of the GH response to exercise in healthy males.     

Effect of previous supramaximal work on lacticaemia during supra-anaerobic threshold exercise

Twelve male and female subjects (eight trained, four untrained) exercised for 30 min on a treadmill at an intensity of maximal O2 consumption (% VO2max) 90.0%, SD 4.7 greater than the anaerobic threshold of 4 mmol.l-1 (Than = 83.6% VO2max, SD 8.9). Time-dependent changes in blood lactate concentration [( lab]) during exercise occurred in two phases: the oxygen uptake (VO2) transient phase (from 0 to 4 min) and the VO2 steady-state phase (4-30 min). During the transient phase, [lab] increased markedly (1.30 mmol.l-1.min-1, SD (0.13). During the steady-state phase, [lab] increased slightly (0.02 mmol.l-1.min-1, SD 0.06) and when individual values were considered, it was seen that there were no time-dependent increases in [lab] in half of the subjects. Following hyperlacticaemia (8.8 mmol.l-1, SD 2.0) induced by a previous 2 min of supramaximal exercise (120% VO2max), [lab] decreased during the VO2 transient (-0.118 mmol.l-1.min-1, SD 0.209) and steady-state (-0.088 mmol.l-1.min-1, SD 0.103) phases of 30 min exercise (91.4% VO2max, SD 4.8). In conclusion, it was not possible from the Than to determine the maximal [lab] steady state for each subject. In addition, lactate accumulated during previous supramaximal exercise was eliminated during the VO2 transient phase of exercise performed at an intensity above the Than. This effect is probably largely explained by the reduction in oxygen deficit during the transient phase. Under these conditions, the time-course of changes in [lab] during the VO2 steady state was also affected.     

A physiological appraisal of aerobic riding in women

The aim of this study was to compare selected acute cardiorespiratory and metabolic effects of exercise on a Fitness Flyer (FF) aerobic rider to those of treadmill (TM) running. Fourteen women, aged 23-35 years, performed incremental exercise tests to exhaustion on the TM and FF. Ratings of perceived exertion (RPE), heart rate (HR), minute ventilation (VE), VO2, and ventilatory equivalent (VEq) were compared in each subject during each phase of the exercise protocols, and blood lactate concentrations were measured before and 2-3 minutes after the exercise tests on the 2 modalities. Peak VO2 was higher (p < 0.05) on the TM than on the FF. Mean submaximal HR and VEq at a given VO2 was, however, higher on the FF than on the TM (p < 0.05). Maximum mean energy expenditure on the FF corresponded with mean energy expenditure on the TM at 8 km.h(-1) at an 18% gradient. Posttest blood lactate concentrations and RPE were higher on the FF than on the TM (p < 0.05). The results indicate that although exercising on an FF elicits less maximal cardiorespiratory response than does TM running, the FF may be better suited to developing local muscle endurance in the thigh muscles.     

Effects of prolonged exercise at a similar percentage of maximal oxygen consumption in trained and untrained subjects

Six trained male cyclists and six untrained but physically active men participated in this study to test the hypothesis that the use of percentage maximal oxygen consumption (%VO2max) as a normalising independent variable is valid despite significant differences in the absolute VO2max of trained and untrained subjects. The subjects underwent an exercise test to exhaustion on a cycle ergometer to determine VO2max and lactate threshold. The subjects were grouped as trained (T) if their VO2max exceeded 60 ml.kg-1.min-1, and untrained (UT) if their VO2max was less than 50 ml.kg-1.min-1. The subjects were required to exercise on the ergometer for up to 40 min at power outputs that corresponded to approximately 50% and 70% VO2max. The allocation of each exercise session (50% or 70% VO2max) was random and each session was separated by at least 5 days. During these tests venous blood was taken 10 min before exercise (- 10 min), just prior to the commencement of exercise (0 min), after 20 min of exercise (20 min), at the end of exercise and 10 min postexercise (+ 10 min) and analysed for concentrations of cortisol, [Na+], [K+], [Cl-], glucose, free fatty acid, lactate [la-], [NH3], haemoglobin [Hb] and for packed cell volume. The oxygen consumption (VO2) and related variables were measured at two time intervals (14-15 and 34-35 min) during the prolonged exercise tests. Rectal temperature was measured throughout both exercise sessions. There was a significant interaction effect between the level of training and exercise time at 50% VO2max for heart rate (fc) and venous [la-].(ABSTRACT TRUNCATED AT 250 WORDS)     

Diurnal variations in ventilatory and cardiorespiratory responses to submaximal treadmill exercise in females

Diurnal variations in ventilatory and cardiorespiratory responses to submaximal treadmill exercise were analysed in 11 eumenorrhoeic women and in 10 women using monophasic oral contraceptives. Subjects performed submaximal treadmill exercise at three intensities averaging 7, 8, and 9 km x h(-1), each for 4 min at 0800, 1300 and 1700 hours, assigned randomly on 3 separate days. Rectal temperature was measured before (T(rec(b))) and after (T(rec(a))) exercise. Cardiac frequency (f(c)), ventilation (V(E)), oxygen uptake (VO(2)), carbon dioxide output (VCO(2)), and respiratory exchange ratio (R) were assessed in the last minute of each stage of the exercise. Both T(rec(b)) and T(rec(a)) increased from 0800 to 1700 hours (P < 0.001). For a given submaximal work rate, VO(2) and VCO(2) were higher in the afternoon compared to the morning. Similarly, R was increased at 1700 hours compared to 0800 hours during the recovery period following exercise (P < 0.05). However, V(E) did not vary significantly during the day at any of the running intensities. No significant interactions (group x time of day) were observed in any of the studied parameters. In contrast to ventilation, the VO(2) and VCO(2) of the females during submaximal exercise were both affected by the time of day, without any differences between eumenorrhoeic women and users of oral contraceptives.     

The relationship of plasma ammonia and lactate concentrations to perceived exertion in trained and untrained women

The purpose of this study was to investigate the covariance between perceived exertion (recorded using Borg's category-ratio scale CR-10) and the relative oxygen uptake, and lactate and ammonia concentrations in blood from a peripheral vein. Ratings of perceived exertion (RPE) at 25%, 50%, 75% and 90% maximal oxygen uptake and lactate and ammonia concentrations were compared in well-trained women distance runners (n = 22) and untrained women (n = 10). Ammonia concentrations in peripheral venous blood were significantly correlated with RPE (P less than 0.05), both in the trained and untrained women. Differences between the trained and untrained subjects occurred when the ammonia concentration increased to 148 mumol.l-1 in both groups investigated; similarly, the mean RPE correlated significantly with the lactate concentration (P less than 0.05), both in the trained and untrained women and there was a difference in RPE between groups when lactate concentration in the blood had risen to 4.4 mmol.l-1. It would seem that the correlation of blood ammonia and lactate concentrations with RPE during exercise could be a useful indicator of the development of fatigue.