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.     

Le métabolisme non lié à l'activité musculaire est fonction de {\text{FA}}_{{\text{CO}}_{\text{2}} } et de la température

Summary Metabolic variations as a function of and as a function of temperature are studied in curarized, artificially ventilated cats. Metabolic rate is measured in terms of O₂ uptake and CO₂ production. Measures are taken for variations of 4–7% and for temperatures between 42 and 21°C. The results are presented in the form of graphs. Metabolism decreases when increases and increases when temperature increases. The shape of the curve obtained when values for metabolic rate are plotted as a function of temperature, depends upon the ventilation which acts by determining the magnitude of .     

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.     

A model for studying the distortion of muscle oxygen uptake patterns by circulation parameters

Summary The transmission of muscle oxygen uptake patterns to the pulmonary site is a basically nonlinear process during unsteady state exercise. We were mainly interested in three questions concerning the dynamic relationship between power input and pulmonary output: 1. To what extent can linear system analysis be applied? 2. What is the relative influence of muscle on pulmonary as compared to other parameters such as muscle perfusion kinetics? 3. To what extent does pulmonary reflect muscle ? Investigations were performed by means of a mathematical model including a muscle compartment and two serial, flow-varying time delays. The non-exercising parts of the body were. incorporated as one term for perfusion and one for . Parameters were adjusted so as to represent a reference state of aerobic exercise while monofrequent sinusoidal changes in aerobic metabolism were used as forcing signals. The following answers were derived from the simulations: 1. Non-linear distortions of the signals are negligible provided that analyses are not driven too far into the higher frequency range (periods shorter than about 1 min). 2. Variations of muscle kinetics have greater effects on pulmonary than changes of perfusion kinetics or venous volume. This finding applies irrespective of whether or not pulmonary closely reflects muscle 3. Small differences in the time constants for muscle perfusion and muscle are a major prerequisite if pulmonary , kinetics are to be taken as correct estimates of muscle kinetics. High basal muscle perfusion, small perfusion changes and small venous volumes between muscle and lungs are further factors reducing dynamic distortions of the muscle signal.     

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.     

Exercise-induced changes in blood ammonia levels in humans

Summary Five male and two female subjects each performed a maximal aerobic capacity ( ) test, and two to four submaximal aerobic exercise bouts (requiring approximately 50 and 80% of the individual's measured ) on a motor-driven treadmill. Pre-exercise resting oxygen uptakes ( ) and heart rates were determined and a venous blood sample drawn prior to each work session. These same measurements were repeated at 4, 15, 30, and 45 min of the resting recovery period that followed each exercise experiment. Additionally, at the 30th min of each 45-min submaximal exercise, another peripheral venous blood sample was drawn following determination of and heart rate. In all blood samples, the hematocrit and concentrations of ammonia, lactate, pyruvate, glucose, hemoglobin, and total plasma proteins were measured.A significant exponential relationship was observed betwen blood ammonia levels and for all sample periods (pre-exercise rest, exercise, and post-exercise recovery). Peripheral venous blood ammonia levels were significantly correlated with levels of pyruvate and lactate, as these latter substrates exhibited a similar exponential relationship with as was observed with ammonia.This work was supported in part by the Air Force Office of Scientific Research, Air Force Systems Command, Grant AFOSR 73-2455 and by the National Institutes of Health, Grant NIH HD00235-6     

Respiratory response to arterial H+ at different levels of arterialP_{{\text{CO}}_{\text{2}} } during hyperoxia or hypoxia

Summary Experiments were carried out in 12 dogs anesthetized with halothane of constant alveolar concentration (mean: 0.89%). The ventilatory response to arterial with hyperoxia was determined in metabolic acidosis (by infusion of 0.5 N HCl solution). The ventilatory response to arterial with constant hypoxia (about 50 mm Hg arterial ) was determined in both metabolic acidosis and alkalosis (by infusion of 1 M NaHCO₃ solution).The arterial H⁺-ventilation response curve was obtained at different constant levels of by simultaneous analysis of the -H⁺ diagram and the -ventilation response curve. Ventilation in hyperoxia was largely dependent on if acid-base balance was near normal, but became independent of and dependent on arterial H⁺ as this increased. It was postulated that this was partly due to the negative interaction between and H⁺. The H⁺-ventilation response curves showed the same pattern in hypoxia, but only on the alkalotic side. However, with hypoxia in the range of normal to acidotic condition, control of ventilation was mainly dependent on H⁺ and independent of ; this implies an interaction between hypoxia and H⁺ at the peripheral chemoreceptors.     

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.     

Ventilation studied with circulatory occlusion during two intensities of exercise

Summary Our purpose was to study the possible role of a pulmonary chemoreceptor in the control of ventilation during exercise. Respiratory gas exchange was measured breath-by-breath at two intensities of exercise with circulatory occlusion of the legs. Eight male subjects exercised on a cycle ergometer at 49 and 98 W for 12 min; circulation to the legs was occluded by thigh cuffs (26.7 kPa) for two min after six min of unoccluded exercise. PETCO₂ and decreased and PETO₂ increased significantly during occlusion at both workloads. Occlusion elicited marked hyperventilation, as evidenced by sharp increases in , and . A sudden sharp increase in PETCO₂ was seen 12.3±0.5 and 6.5±1.2 s after cuff release in all subjects during exercise at 49 and 98 W, respectively. At 49 W a post-occlusion inflection in was seen in 7 subjects 21.1±5.8 s after the PETCO₂ inflection. Three subjects showed an inflection in at 98 W 23.3±7.5 s after the PETCO₂ inflection. There were significant increases in PETCO₂, and after cuff release. mirrored better than , post occlusion. On the basis of a significant lag time between inflections in PETCO₂ and following cuff release, it is concluded that the influences of a pulmonary CO₂ receptor were not seen.     

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.     

Are oxygen uptake kinetics at the onset of exercise speeded up by local metabolic status in active muscles?

To assess the rate-limiting factor of oxygen uptake ( ) kinetics at the onset of exercise, six healthy male sedentary subjects performed repeated one-legged constant-load cycle exercise. The one-legged constant-load exercise test consisted of two 5-min periods of pedalling at an exercise intensity of 50 W, with a 5-min rest between periods (these exercise periods, i.e. first and second exercises, were performed by the same leg). The exercise was then repeated using the other leg. In addition, two-legged incremental exercise was investigated to establish whether kinetics were affected by slower heart rate kinetics. The incremental exercise test consisted of two-legged pedalling first with the cycle unloaded as a warm-up for 5 min followed by 50-W exercise for 5 min. The exercise intensity was then increased to 100 W for 5 min. During exercise, gas exchange parameters were determined by the breath-by-breath method and cardiac output ( ) was determined continuously by an impedance technique with a computer-based automated system. To determine the kinetics of heart rate (HR), and , a best fit procedure was employed using least-squares criteria with a time delay, except during the initial increase. During the one-legged constant-load exercise test, kinetics were significantly accelerated by repeated exercise using the same leg. On the other hand, when the exercise was changed to the other leg, kinetics were significantly slower, although kinetics continued to be faster. During the incremental exercise test, although the HR response was slower at the transition from 50-W to 100-W exercise than at the transition from warm-up to 50-W exercise, there were no significant changes in kinetics. These findings suggest that kinetics may be affected by metabolic conditions in the muscle, but not by blood flow ( and/or HR) kinetics.     

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)     

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.     

Changes in ventilation at the start and end of moderate and heavy exercise of short and long duration

Summary These experiments examined the effect of exercise intensity and duration on the magnitude of the abrupt change in ventilation at the start ( ) and end ( ) of exercise. Five subjects performed constant load treadmill exercise at 50% and 80% of their maximum oxygen consumption ( ) for 6 and 10 min while inspiring atmospheric air. The subjects also completed additional exercise tests at 80% for 10 min while inspiring an oxygen-enriched gas mixture. During each exercise trial ventilation was measured breath-by-breath. The and were determined by using non-linear curve-fitting techniques. The results showed that was greater at the start of the 80-% exercise tests compared to the 50-% tests and that at each level of exercise was greater than . The results also demonstrated that was inversely related to the intensity and duration of exercise. Furthermore, the was not altered subsequent to the inspiration of oxygen-enriched air. These findings have led us to postulate that the stimulus responsible for is reduced during exercise and that the degree of reduction is related to the intensity and duration of exercise. In addition, it was concluded that these changes might occur independently of peripheral chemoreceptor activity.     

Physiological correlates of middle-distance running performance

Summary To compare the relative contributions of their functional capacities to performance in relation to sex, two groups of middle-distance runners (24 men and 14 women) were selected on the basis of performances over 1500-m and 3000-m running races. To be selected for the study, the average running velocity ( ) in relation to performances had to be superior to a percentage (90% for men and 88% for women) of the best French achieved during the season by an athlete of the same sex. Maximal O₂ consumption ( _max) and energy cost of running (C_R) were measured in the 2 months preceding the track season. This allowed us to calculate the maximal that could be sustained under aerobic conditions, _a,max. A : _{a, max} ratio derived from 1500-m to 3000-m races was used to calculate the maximal duration of a competitive race for which = _a,max (t a,max) In both groups _a,max was correlated to . The relationships calculated for each distance were similar in both sexes. The C_R [0.179 (SD 0.010) ml · kg^–1 · m^–1 in the women versus 0.177 (SD 0.010) in the men] andt _a,max [7.0 (SD 2.0) min versus 8.4 (SD 2.1)] also showed no difference. The relationships between _max and body mass (m _b) calculated in the men and the women were different. At the samem _b the women had a 10% lower C_R than the men; their lowerm _b thus resulted in an identical C_R. In both groups C_R and _max were strongly correlated (r=0.74 and 0.75 respectively,P<0.01), suggesting that a high level of _max could hardly be associated with a low C_R. These relationships were different in the two groups (P<0.05). At the same _max the men had a higher _a,inax than the women. Thus, the disparity in track performances between the two sexes could be attributed to _max and to the _max/C_R relationships.     

Longitudinal study of the effect of high intensity weight training on aerobic capacity

To investigate the effect of a long-term weight lifting programme characterized by high intensity, low repetition and long rest period between sets on maximal oxygen consumption ( _max) and to determine the advantage of this programme combined with jogging, 26 male untrained students were involved in weight training for a period of 3 years. The _max and body composition of the subjects were examined at beginning, 1 year, 2 years (T₂), and 3 years after (T₃) training. Of the group, 19 subjects performed the weight lifting programme 5 days each week for 3 years (W-group), 4 subjects performed the same weight lifting programme for 3 years with an additional running programme consisting of 2 miles of jogging once a week during the 3rd year (R1-group), and 3 subjects performed the weight lifting programme during the 1st year and the same combined jogging and weight lifting programme as the R1-group during the 2nd and 3rd years (R2-group). The average _max relative to their body mass of the W-group decreased significantly during the 1st year, followed by an insignificant decrease in the 2nd year and a levelling off in the 3rd year. The average _max Of the W-group at T₂ and T₃ was 44.2 and 44.1 ml · kg^–1 · min^–1, respectively. The tendency of _max changes in the R1- and R2-groups was similar to the W-group until they started the jogging programme, after which they recovered significantly to the initial level within a year of including that programme, and they then levelled off during the next year. Lean body mass estimated from skinfold thicknesses had increased by about 8% after 3 years of weight lifting. The maximal muscle strength, defined by total olympic lifts (snatch, and clean and jerk), of these three groups increased significantly and there was no significant difference among the amounts of the increase in the three groups. These results suggested that high intensity weight training combined with jogging could be recommended for weight-trained athletes for developing optimal muscle strength without a concomitant reduction in _max.     

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 .     

Respiratory frequency and the oxygen cost of exercise

Summary Although many studies indicate that the spontaneous breathing frequency minimizes breathing work, the consequences of this for exercise energetics have never been investigated. To see if the spontaneous exercise breathing frequency minimizes oxygen uptake, we compared during treadmill walking (2/3 max) at several alternative frequencies. The alternative frequencies ranged from the lowest sustainable to a frequency twice the spontaneous value. All eight subjects adjusted tidal volume to comfort. Exercise oxygen uptake was constant, independent of breathing frequency. At the same time, minute ventilation rose to be 65% greater at the highest frequency than at the lowest (P<0.01). We then reproduced the various exercise frequencies, tidal volumes, and ventilations during seated isocapnic hyperpnea to measure with locomotory muscles at rest. Once again, oxygen uptake was constant, independent of breathing frequency. We conclude that the spontaneous exercise breathing frequency fails to minimize during either exercise or resting reproduction of exercise ventilation.Supported in part by NIH Grant HL 26351     

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 .     

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