Use of oxygen uptake recovery curve to predict peak oxygen uptake in upper body exercise

A group of 18 well-trained white-water kayakers performed maximal upper body exercise in the laboratory and during.a field test. Laboratory direct peak oxygen uptake ( ) values were compared, firstly by a backward extrapolation estimation and secondly by an estimation calculated from measured during the first 20 s of exercise recovery. Direct peak correlated with backward extrapolation (r=0.89), but the results of this study showed that the backward extrapolation method tended to overestimate significantly peak by [0.57 (SD 0.31) 1·min^–1 in the laboratory, and 0.66 (SD 0.33) 1·min^–1 in the field,P<0.001]. The measured during the first 20 s of recovery, whether the exercise was performed in the laboratory or in the field, correlated well with the laboratory direct peak (r=0.92 andr=0.91, respectively). The use of the regression equation obtained from field data _2f20s, that is peak ₂=0.23+1.08 _2f20s, gave an estimated peak ₂, the mean difference of which compared with direct peak was 0.22 (SD 0.13) 1·min^–1. In conclusion, we propose the use of a regression equation to estimate peak from a single sample of the gas expired during the first 20 s of recovery after maximal exercise involving the upper part of the body.     

Association between heart rate variability and training response in sedentary middle-aged men

The effect of exercise training on heart rate variability (HRV) and improvements in peak oxygen consumption ( _peak) was examined in sedentary middle-aged men. The HRV and absolute and relative _peak of training (n = 19) and control (n = 15) subjects were assessed before and after a 24-session moderate intensity exercise training programme. Results indicated that with exercise training there was a significantly increased absolute and relative _peak (P < 0.005) for the training group (12% and 11% respectively) with no increase for the control group. The training group also displayed a significant reduction in resting heart rate; however, HRV remained unchanged. The trained subjects were further categorized into high (n = 5) and low (n = 5) HRV groups and changes in _peak were compared. Improvements in both absolute and relative _peak were significantly greater (P > 0.005) in the high HRV group (17% and 20% respectively) compared to the low HRV group (6% and 1% respectively). The groups did not differ in mean age, pretraining oxygen consumption, or resting heart rate. These results would seem to suggest that a short aerobic training programme does not alter HRV in middle-aged men. Individual differences in HRV, however, may be associated with _peak response to aerobic training.     

Prediction of individual oxygen uptake on-step transients from frequency responses

Power-oxygen uptake ( ) frequency responses can be used to predict responses to arbitrary exercise intensity patterns. It is still an open question for which range of exercise intensities such computed response patterns yield valid predictions. In the present study, we determined the power- frequency response of nine sports students by means of pseudo-randomised switching between 20 W and 80 W during upright and supine cycle exercise. Starting from a baseline of 20 W each subject also performed sustained step increases to 40 W, 80 W, 120 W, and 160 W in both positions. The individual step responses were then compared with the expected time-courses predicted on the basis of the individual frequency responses. The comparison showed a close agreement for the 20 W–40 W and 20 W–80 W steps in both positions. With larger step amplitudes the kinetics became increasingly slower than the predicted time course in both positions. During additional ramp tests (10 W · 30 s^–1) whole blood lactic acid concentration [1a^–]_b tended to be higher in the supine position at exercise intensities higher than 160 W. The mean power at 4 mmol · 1^–1 [la^–]_b amounted to 234 (SD 32) W and 253 (SD 44) W (P<5%) in the supine and the upright position, respectively. The maximal oxygen uptake relative to body mass was not found to be significantly different [upright, mean 57 (SD 10) ml · (min · kg)^–1;supine, mean 54 (SD 10) ml · (min · kg)]. These findings would suggest that for a range of mild exercise intensities kinetics are not appreciably influenced by the step amplitude or by cardiovascular changes associated with the upright and the supine position.     

Changes in skeletal muscle oxygenation during incremental exercise measured with near infrared spectroscopy

To determine the change in muscle oxygenation in response to progressively increasing work rate exercise, muscle oxyhemoglobin + oxymyoglobin saturation was measured transcutaneously with near infrared spectroscopy in the vastus lateralis muscle during cycle ergometry. Studies were done in 11 subjects while gas exchange was measured breath-by-breath. As work rate was increased, tissue oxygenation initially either remained constant near resting levels or, more usually, decreased. Near the work rate and metabolic rate where significant lactic acidosis was detected by excess CO₂ production (lactic acidosis threshold, LAT), muscle oxygenation decreased more steeply. As maximum oxygen uptake ( ) was approached, the rate of desaturation slowed. In 8 of the 11 subjects, tissue O₂ saturation reached a minimum which was sustained for 1–3 min before was reached. The LAT correlated with both the (r = 0.95,P < 0.0001) and the work rate (r = 0.94,P < 0.0001) at which the rate of tissue O₂ desaturation accelerated. These results describe a consistent pattern in the rate of decrease in muscle oxygenation, slowly decreasing over the lower work rate range, decreasing more rapidly in the work rate range of the LAT and then slowing at about 80% of , approaching or reaching a minimum saturation at .     

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.     

Factors which alter the relationship between ventilation and carbon dioxide production during exercise in normal subjects

The slope of the linear relationship between ventilation and carbon dioxide production has been thought to indicate that is one of the major stimuli to . A group of 15 normal subjects undertook different incremental treadmill exercise protocols to explore the relationship between and . An incremental protocol using 1 instead of 3-min stages of exercise resulted in an increase in the to ratio [26.84 (SEM 1.23) vs 31.08 (SEM 1.36) (P < 0.008) for the first stage, 25.24 (SEM 0.86) vs 27.83 (SEM 0.91) (P < 0.005) for the second stage and 23.90 (SEM 0.86) vs 26.34 (SEM 0.81) (P = 0.001) for the third stage]. Voluntary hyperventilation to double the control level of during exercise resulted in an increase in the to slope [from 21.3 (SEM 0.71) for the control run to 35.1 (SEM 1.2) for the hyperventilation run (P < 0.001)]. Prolonged hyperventilation (5 min) during exercise at stage 2 of the Bruce protocol resulted in a continuted elevation of and the slope. A steady state of and metabolic gas exchange can only be said to have been present after at least 3 min of exercise. Voluntary hyperventilation increased the slope of the relationship between and . End-tidal carbon dioxide fell, but remained within the normal range. These results would suggest that a non-carbon dioxide factor may have been responsible for the increase we found in during exercise, and that factors other than increased dead space ventilation can cause an increased ventilation to slope, such as that seen in some pathophysiological conditions, such as chronic heart failure.     

Ventilatory control studied with circulatory occlusion during exercise recovery

Summary Mechanisms involved in the control of pulmonary ventilation were studied in seven male subjects following 6 min of exercise on a cycle ergometer at 98w. Circulation to the legs was occluded by thigh cuffs (27 kPa) during the last 15 s of exercise and the subsequent 4 min of recovery. Respiratory gas exchange and the tidal partial pressures of O₂ and CO₂ were measured breathby-breath. The results were compared to control studies without occlusion. There was a significant increase in both systolic and diastolic blood pressures during occluded recovery. Following occlusion systolic pressure remained elevated while diastolic pressure returned to control values. Occlusion during recovery caused hyperventilation during the first 1.5 min after exercise as evidenced by significantly higher , P_ETO₂, and lower P_ETCO₂. Following the release of the cuffs P_ETCO₂, , and heart rate all increased significantly above control values, while P_ETO₂ decreased. P_ETCO₂ rose abruptly 14.5±0.9 s after the release of the cuffs. Marked increases inV _E and heart rate were seen, and occurred 30.8±1.5 s and 12.8±1.3 s, respectively, after cuff release. The 16.3±1.4 s lag between the increase in P_ETCO₂ and after occlusion suggests that the ventilatory response to a sudden load of hypercapnic blood is not mediated by a pulmonary chemoreceptor. Other receptors, probably the peripheral chemoreceptors, appear to be responsible for hypercapnic hyperventilation.     

Effect of diet on human muscle weakness following prolonged exercise

Summary The effect of altering muscle glycogen on the ability of skeletal muscle to generate voluntary and electrically evoked isometric force following prolonged exercise has been investigated in five healthy male subjects. Measurements from the triceps surae were made at rest, and before and after prolonged exercise (uphill walking) at approximately 75% in low muscle glycogen (low CHO) and high muscle glycogen (high CHO) conditions.The results showed that before exercise there was no change in maximal twitch tension ( ), maximal tetanic tension at frequencies of 10 (P_o10), 20 (P_o20) and 50 Hz (P_o50), and maximal voluntary contraction (MVC) in low and high CHO compared with normal. The loss of force during a 2 min electrically evoked fatigue test at rest was found to be higher (p<0.05) in low CHO and lower (p<0.05) in high CHO than normal.Following the prolonged exercise, muscle weakness was produced in both low and high CHO conditions, but was found to be significantly greater in the low CHO condition for the measurements of P_o10 (p<0.01), P_o20 (p<0.05) and MVC (p<0.05).It is concluded that changes in muscle glycogen alone do not alter the isometric force generating capacity of human muscle, but when combined with prolonged exercise low muscle glycogen enhances exercise-induced muscle weakness.     

Some simple multiple linear regression equations for estimation of maximal aerobic power in healthy indian males

Summary An attempt has been made to evolve some simple multiple linear regression equations for the prediction of max from body weight, time for 3.2 km run and exercise dyspnoeic index (DI_std Ex%). The predictor variables have been selected by examining the product moment correlations of body weight, relative body weight indices, time for 3.2 km run, chest expansion, height, and DI_std Ex% with max, based on data collected on 320 healthy Indian males (17–22 years). It has been observed that body weight, time for 3.2 km run and DI_std Ex% attained maximum correlations with max. Thus, two regression equations with two and three predictor variables have been established in this paper to predict max. The first regression equation yielded a multiple correlation of 0.608 (P<0.001) with a standard error of 0.214 l·min^–1. In this equation, body weight and time for 3.2 km run were considered as significant predictors. To increase the precision of this equation, another multiple linear regression equation based on body weight, time for 3.2 km run and DI_std Ex% as predictors has been developed. This equation yielded a multiple correlation of 0.658 (P<0.001) with a standard error of 0.204 l·min^–1. Applications of these regression equations will be of practical importance to biomedical scientists engaged in the development of a simple procedure for indirect assessment of max, and may serve well as preliminary screening procedures for personnel selection.     

Effects of estrus cycle on thermoregulatory responses during exercise in rats

Summary In female rats, rectal temperature (T _re), tail vasomotor response, oxygen uptake , and carbon dioxide production were measured in proestrus and estrus stages during treadmill running at two different speeds at an ambient temperature (T _a) of 24° C. Experiments were performed at 2.00–6.00 a.m., when the difference inT _re was greatest between the two stages;T _re at rest in the estrus stage was 0.54° C higher than in the proestrus stage. In a mild warm environment, thresholdT _re for a rise in tail skin temperature (T _tail) was also higher in the estrus stage than in the proestrus stage. In contrast, no difference was seen in the thresholdT _re and steady stateT _re at the end of exercise between proestrus and estrus stages. These values were higher at the higher work intensity. was also similar between the two stages, except in the second 5 min after the beginning of exercise, when was greater andT _re rose more steeply in the proestrus stage. These data indicate that deep body temperature during exercise is regulated at a certain level depending on the work intensity and is not influenced by the estrus cycle.This study was supported in part by a Grant-in Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (Grant No. 62480114)     

Energy expenditure and cardiorespiratory responses at the transition between walking and running

We investigated whether the spontaneous transition between walking and running during moving with increasing speed corresponds to the speed at which walking becomes less economical than running. Seven active male subjects [mean age, 23.7 (SEM 0.7) years, mean maximal oxygen uptake ( ), 57.5 (SEM 3.3) ml·kg ^–1·min ^–1, mean ventilatory threshold (VTh), 37.5 (SEM 3) ml·kg ^–1 ·min ^–1] participated in this study. Each subject performed four exercise tests separated by 1-week intervals: test 1, and VTh were determined; test 2, the speed at which the transition between walking and running spontaneously occurs (ST) during increasing speed (increases of 0.5 km·h ^–1 every 4 min from 5 km·h ^–1) was determined; test 3, the subjects were constrained to walk for 4 min at ST, at ST ± 0.5 km·h ^–1 and at ST ± 1 km·h ^–1; and test 4, the subjects were constrained to run for 4 min at ST, at ST±0.5 km·-h ^–1 and at ST±1 km·h ^–1. During exercise, oxygen uptake ( ), heart rate (HR), ventilation ( ), ventilatory equivalents for oxygen and carbon dioxide (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmOvayaaca% WaaSbaaSqaaiaabweaaeqaaOGaai4laiqadAfagaGaamaaBaaaleaa% caqGYaaabeaakiaacYcacaqGGaGaaeiiaiqadAfagaGaamaaBaaale% aacaqGfbaabeaakiaac+caceWGwbGbaiaacaqGdbGaae4tamaaBaaa% leaacaaIYaaabeaaaaa!4240!\[\dot V_{\text{E}} /\dot V_{\text{2}} ,{\text{ }}\dot V_{\text{E}} /\dot V{\text{CO}}_2 \]), respiratory exchange ratio (R), stride length (SL), and stride frequency (SF) were measured. The results showed that: ST occurred at 2.16 (SEM 0.04) m·s ^–1; , HR and speed at ST were significantly lower than the values measured at VTh (P< 0.001, P< 0.001 and P< 0.05, respectively); changed significantly with speed (P< 0.001) but was greater during running than walking below ST (ST minus 1 km·h ^–1, P< 0.001; ST minus 0.5 km·h ^–1, P< 0.05) with the converse above ST (ST.plus 1 km·h ^–1, P<0.05), whereas at ST the values of were very close [23.9 (SEM 1.1) vs 23.7 (SEM 0.8) ml·kg ^–1 · min ^–1 not significant, respectively, for walking and running]; SL was significantly greater during walking than running (P<0.001) and SF lower (P<0.001); and HR and were significantly greater during running than walking below ST (ST minus 1 km·h ^–1, P<0.01; ST minus 0.5 km·h ^–1, P{<0.05) with the converse above ST (ST plus 1 km·h ^–1, P·< 0.05), whereas no difference appeared for and R between the two types of locomotion. We concluded from this study that ST corresponded to the speed at which the energy expenditure of running became lower than the energy expenditure of walking but that the mechanism of the link needed further investigation.     

A method for determining the maximal steady state of blood lactate concentration from two levels of submaximal exercise

The aim of this study was to estimate the characteristic exercise intensity _CL which produces the maximal steady state of blood lactate concentration (MLSS) from submaximal intensities of 20 min carried out on the same day and separated by 40 min. Ten fit male adults [maximal oxygen uptake _max 62 (SD 7) ml · min^–1 · kg^–1] exercisOed for two 30-min periods on a cycle ergometer at 67% (test 1.1) and 82% of _max (test 1.2) separated by 40 min. They exercised 4 days later for 30 min at 82% of _max without prior exercise (test 2). Blood lactate was collected for determination of lactic acid concentration every 5 min and heart rate and O₂ uptake were measured every 30 s. There were no significant differences at the 5th, 10th, 15th, 20th, 25th, or 30th min between , lactacidaemia, and heart rate during tests 1.2 and 2. Moreover, we compared the exercise intensities _CL which produced the MLSS obtained during tests 1.1 and 1.2 or during tests 1.1 and 2 calculated from differential values of lactic acid blood concentration ([1a^–]_b) between the 30th and the 5th min or between the 20th and the 5th min. There was no significant difference between the different values of _CL [68 (SD 9), 71 (SD 7), 73 (SD 6),71 (SD 11) % of _max (ANOVA test,P<0.05). Four subjects ran for 60 min at their _CL determined from periods performed on the same day (test 1.1 and 1.2) and the difference between the [la^–]_b at 5 min and at 20 min ( ([la^–]_b)) was computed. The [la^–]_b remained constant during exercise and ranged from 2.2 to 6.7 mmol · l^–1 [mean value equal to 3.9 (SD 1) mmol · l^–1]. These data suggest that the _CL protocol did not overestimate the exercise intensity corresponding to the maximal fractional utilization of _max at MLSS. For half of the subjects the _CL was very close to the higher stage (82% of _max where an accumulation of lactate in the blood with time was observed. It can be hypothesized that _CL was very close to the real MLSS considering the level of accuracy of [la^–]_b measurement. This study showed that exercise at only two intensities, performed at 65% and 80% of _max and separated by 40 min of complete rest, can be used to determine the intensity yielding a steady state of [la^–1]_b near the real MLSS workload value.     

Physical work capacity in dynamic exercise with differing muscle masses in healthy young and older men

Ten young (aged 23–30 years) and nine older (aged 54–59 years) healthy men with similar estimated limb muscle volumes performed, in random order, three different types of ergometer exercise tests (one-arm cranking, two-arm cranking, and two-leg cycling) up to the maximal level. Values for work load (WL), peak oxygen consumption , peak heart rate (HR), peak ventilation , respiratory gas exchange ratio (R), recovery blood lactate concentration [La^–], and rating of perceived exertion (RPE) were compared between the age-groups in the given exercise modes. No significant age-related differences in WL, peak , peak HR, R, [La^–], or RPE were found in one-arm or two-arm cranking. During one-arm cranking the mean peak was 1.65 (SD 0.26)1 · min^–1 among the young men and 1.63 (SD 0.10)1 · min^–1 among the older men. Corresponding mean peak during two-arm cranking was 2.19 (SD 0.32)1 · min-1 and 2.09 (SD 0.18)1 · min^–1, respectively. During one-arm cranking peak was higher (P < 0.05) among the older men compared to the young men. During two-leg cycling the young men showed higher values in WL (P < 0.001), peak (P < 0.001), and peak HR (P < 0.001). The mean peak was 3.54 (SD 0.24)1 · min^–1 among the young men and 3.02 (SD 0.20)1 · min^–1 among the older men. Corresponding mean peak HR was 182 (SD 5) beats · min^–1 and 170 (SD 8) beats · min^–1, respectively. During two-leg cycling, peak , R, [La^–], and RPE did not differ between the two age-groups. In summary, the older men with similar sizes of estimated arm and leg muscle volumes as the young men had a reduced physical work capacity in two-leg cycling. In one-arm or two-arm cranking, no significant difference in work capacity was found between the age-groups. These results indicate, that in healthy men, age, at least up to the 6th decade of life, is not necessarily associated with a decline in physical work capacity in exercises using relatively small muscle groups, in which the limiting factors are more peripheral than central.     

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.     

Times to exhaustion at 100% of velocity at\dot V{\text{O}}_{\text{2}} max and modelling of the time-limit / velocity relationship in elite long-distance runners

The aim of this study was to measure running times to exhaustion (Tlim) on a treadmill at 100% of the minimum velocity which elicits _{max max} in 38 elite male long - distance runners _max = 71.4 ± 5.5 ml.kg^–1.min^–1 and _max = 21.8 ± 1.2 km.h^–1). The lactate threshold (LT) was defined as a starting point of accelerated lactate accumulation around 4 mM and was expressed in _max. Tlim value was negatively correlated with _max (r = -0.362, p< 0.05) and _max (r = –0.347, p< 0.05) but positively with LT (%v _max) (r = 0.378, p < 0.05). These data demonstrate that running time to exhaustion at _max in a homogeneous group of elite male long-distance runners was inversely related to _max and experimentally illustrates the model of Monod and Scherrer regarding the time limit-velocity relationship adapted from local exercise for running by Hughson et al. (1984) .     

Effect of an increase in{\text{Hb}}_{{\text{O}}_{\text{2}} } affinity on the calculated capillary recruitment of an isolated rat heart

The effect of an increase in hemoglobin O₂ affinity on myocardial O₂ delivery was studied in a blood perfused working rat heart preparation. In a first series of experiments P₅₀ ( for which saturation is 50%) was lowered by use of carbon monoxide. The heart was alternatively perfused with the blood sample of P₅₀=32 mm Hg and the blood sample of P₅₀=17 mm Hg. O₂ capacity of both samples was kept the same by appropriate hemodilution. In a second serie of experiments change of P₅₀ was obtained by the use of adult human erythrocytes containing hemoglobin creteil with a P₅₀ of 13.6 mm Hg. As P₅₀ decreased from 25 to 10 mm Hg, coronary sinus ( ) diminished from 26±2 to 18±2 mm Hg (–29±2%), coronary sinus O₂ content ( ) increased by 15±3%, myocardial oxygen consumption did not change significantly. The percentage of increase of coronary flow was 23±4%.Analysis of these results with a simple mathematical model of O₂ delivery suggest that increase in affinity is corrected by a simultaneous increase in coronary flow and capillary recruitment.This study was supported by contracts 74-7-0274 from D.G.R.S.T., 76-1-1755 from I.N.S.E.R.M. and a grant from the University of Paris VII     

Circadian variations in plasma renin activity,catecholamines and aldosterone during exercise in women

Summary Four women were studied at 0400 h and 1600 h to determine if their hormonal and hemodynamic responses to exercise varied with the circadian cycle. Esophageal temperature was measured during rest and exercise (60% peak ; 30 min) in a warm room (T _a=35° C; =1.7 kPa). Venous blood samples were drawn during rest and exercise and hemoglobin concentration (Hb), hematocrit (Hct), plasma osmolality (P _osm), plasma protein concentration (P _p), colloid osmotic pressure (COP), plasma renin activity (PRA), cortisol, aldosterone, norepinephrine (NE) and epinephrine (E) were determined. Changes in plasma volume (PV) were estimated from changes in Hb and Hct. The relative hemoconcentration (–11.2%) was similar at 0400 h and 1600 h, but the absolute PV was smaller at 1600 h than at 0400 h (p=0.03). The responses ofP _osm,P _p and COP to exercise were unaffected by time of day. Although PRA was not different at the two times of day, PRA was 244% greater during exercise at 1600 h, but only 103% greater during exercise at 0400 h. The normal circadian rhythms in plasma aldosterone (p=0.043) and plasma cortisol (p=0.004) were observed. Plasma aldosterone was 57% greater during exercise, while plasma cortisol did not change. The change in E and NE was greater at 0400 h, but this was due to the lower resting values of the catecholamines at 0400 h. These data indicate that time of day generally did not affect the hormonal or hemodynamic responses to exercise, with the exception that PRA was markedly higher during exercise at 1600 h compared to 0400 h.     

Bio-energetic profile in 144 boys aged from 6 to 15 years with special reference to sexual maturation

Summary The effects of growth and pubertal development on bio-energetic characteristics were studied in boys aged 6–15 years (n = 144; transverse study). Maximal oxygen consumption (VO_2max, direct method), mechanical power at (VO_2max ( ), maximal anaerobic power (P_max; force-velocity test), mean power in 30-s sprint (P _30s; Wingate test) were evaluated and the ratios between P_max,P _30s and were calculated. Sexual maturation was determined using salivary testosterone as an objective indicator. Normalized for body massVO_2max remained constant from 6 to 15 years (49 ml· min^–1 · kg^–1, SD 6), whilst P_max andP _30s increased from 6–8 to 14–15 years, from 6.2 W · kg^–1, SD 1.1 to 10.8 W · kg^–1, SD 1.4 and from 4.7 W · kg^–1, SD 1.0 to 7.6 W · kg^–1, SD 1.0, respectively, (P < 0.001). The ratio P_max: was 1.7 SD 3.0 at 6–8 years and reached 2.8 SD 0.5 at 14–15 years and the ratioP _30s: changed similarly from 1.3 SD 0.3 to 1.9 SD 0.3. In contrast, the ratio P_max:P _30s remained unchanged (1.4 SD 0.2). Significant relationships (P < 0.001) were observed between P_max (W · kg^–1),P _30s (W · kg^–1), blood lactate concentrations after the Wingate test, and age, height, mass and salivary testosterone concentration. This indicates that growth and maturation have together an important role in the development of anaerobic metabolism.     

Central hypoxic-hypercapnic interaction in mild hypoxia in man

Hypoxic-hypercapnic interaction in mild hypoxia was studied in 12 healthy males. Steady state ventilatory responses to hypercapnic-hypoxia were obtained as the difference in ventilation between hypoxia (mean values ± S.D. of =7.36±0.20 kPa or of 7.10 ±0.41 kPa) and hyperoxia ( >26.7 kPa) with the same degree of hypercapnia ( 6.12±0.22 kPa). On the other band, withdrawal responses were obtained as the magnitude of depression in ventilation caused by two bicaths of O₂ from the above mentioned hypoxic hypercapnia. Averaged and were 9.57±5.45 and 6.45 ±4.90l/min, respectively, the difference being statistically significant (P<0.01). Furthermore, if we assume the presence of ventilatory depression to be due to tissue fall resulting from an increase in cerebral blood flow caused by hypoxia, the magnitude of central hypoxic-hypercapnic interaction was estimated to be as great as the value of .     

Changes of ventilation and ventilatory response to hypoxia during the menstrual cycle

The relationship between change in hypoxic sensitivity in respiration, defined as increment in ventilation per drop of arterial O₂ saturation , with the phase change from follicular to luteal and those in resting pulmonary ventilation , mean inspiratory flow (V _T/T _I), alveolar partial pressures of CO₂ and O₂ ( and , respectively) and body temperature was studied in 10 women. There was a significant relationship between % increase in hypoxic sensitivity and decrement of resting that occurred in the luteal phase. However, no significant relationships were observed between change in hypoxic sensitivity and those in the remaining parameters studied. The intersubject variation in % increase in resting during the luteal phase was not associated with that in % increase in hypoxic sensitivity. The results indicate that the contribution of increased hypoxic sensitivity to increasing during the luteal phase is variable among subjects. Reasons for the increase in hypoxic sensitivity with hypocapnia are discussed.