Effects of moderate hyperoxia on oxygen consumption during submaximal and maximal exercise

The present study examined the effect of hyperoxia on oxygen uptake (V˙O₂) and on maximal oxygen uptake (V˙O_2max) during incremental exercise (IE) and constant work rate exercise (CWRE). Ten subjects performed IE on a bicycle ergometer under normoxic and hyperoxic conditions (30% oxygen). They also performed four 12-min bouts of CWRE at 40, 55, 70 and 85% of normoxic V˙O_2max (ex1, ex2, ex3 and ex4, respectively) in normoxia and in hyperoxia. V˙O_2max was significantly improved by 15.0 (15.2)% under hyperoxia, while performance (maximum workload, W _max) was improved by only +4.5 (3.0)%. During IE, the slope of the linear regression relating V˙O₂ to work rate was significantly steeper in hyperoxia than in normoxia [10.80 (0.88) vs 10.06 (0.66) ml·min^–1·W^–1]. During CWRE, we found a higher V˙O₂ at ex1, ex2, ex3 and ex4, and a higher V˙O₂ slow component at ex4 under hyperoxia. We have shown that breathing hyperoxic gas increases V˙O_2max, but to an extent that is difficult to explain by an increase in oxygen supply alone. Changes in metabolic response, fibre type recruitment and V˙O₂ of non-exercising tissue could explain the additional V˙O₂ for a given submaximal work rate under hyperoxia. Electronic Publication     

Influence of body mass on maximal oxygen uptake: effect of sample size

Basal metabolic rate is scaled to body mass to the power of 0.73, and we evaluated whether a similar scaling applies when the O₂ transport capacity of the body is challenged during maximal exercise (i.e. at maximal O₂ uptake, V˙O _2max). The allometric relationship between V˙O _2max and body mass (y=a · x ^b, where y is V˙O _2max and x is body mass) was developed for 967 athletes representing 25 different sports, with up to 157 participants in each sport. With an increasing number of observations, the exponent approached 0.73, while for ventilation the exponent was only 0.55. By using the 0.73 exponent for V˙O _2max, the highest value [mean (SD)] for the males was obtained for the runners and cyclists [234 (16) ml · kg^−0.73 · min⁻¹], and for the females the highest value was found for the runners [189 (14) ml · kg^−0.73 · min⁻¹]. For the females, aerobic power was about 80% of the value achieved by the males. Scaling may help both in understanding variation in aerobic power and in defining the physiological limitations of work capacity. Accepted: 3 November 2000     

The influence of either no fluid or carbohydrate-electrolyte fluid ingestion and the environment (thermoneutral versus hot and humid) on running economy after prolonged, high-intensity exercise

This study investigated the effects on running economy (RE) of ingesting either no fluid or an electrolyte solution with or without 6% carbohydrate (counterbalanced design) during 60-min running bouts at 80% maximal oxygen consumption (V˙O_2max). Tests were undertaken in either a thermoneutral (22–23°C; 56–62% relative humidity, RH) or a hot and humid natural environment (Singapore: 25–35°C; 66–77% RH). The subjects were 15 young adult male Singaporeans [V˙O_2max = 55.5 (4.4 SD) ml kg⁻¹ min⁻¹]. The RE was measured at 3 m s⁻¹ [65 (6)% V˙O_2max] before (RE1) and after each prolonged run (RE2). Fluids were administered every 2 min, at an individual rate determined from prior tests, to maintain body mass (group mean = 17.4 ml min⁻¹). The V˙O₂ during RE2 was higher (P < 0.05) than that during the RE1 test for all treatments, with no differences between treatments (ANOVA). The mean increase in V˙O₂ from RE1 to RE2 ranged from 3.4 to 4.7 ml kg⁻¹ min⁻¹ across treatments. In conclusion, the deterioration in RE at 3 m s⁻¹ (65% V˙O_2max) after 60 min of running at 80% V˙O_2max appears to occur independently of whether fluid is ingested and regardless of whether the fluid contains carbohydrates or electrolytes, in both a thermoneutral and in a hot, humid environment. Accepted: 30 October 1997     

Changes in blood lactate and respiratory gas exchange measures in sports with discontinuous load profiles

This study compares two different sport events (orienteering = OTC; tennis = TEC) with discontinuous load profiles and different activity/recovery patterns by means of blood lactate (LA), heart rate (HR), and respiratory gas exchange measures (RGME) determined via a portable respiratory system. During the TEC, 20 tennis-ranked male subjects [age: 26.0 (3.7) years; height: 181.0 (5.7) cm; weight: 73.2 (6.8) kg; maximal oxygen consumption (V˙O₂max): 57.3 (5.1) ml·kg⁻¹·min⁻¹] played ten matches of 50 min. During the OTC, 11 male members of the Austrian National Team [age: 23.5 (3.9) years; height: 183.6 (6.8) cm; weight: 72.4 (3.9) kg; V˙O₂max: 67.9 (3.8) ml·kg⁻¹·min⁻¹] performed a simulated OTC (six sections; average length: 10.090 m). In both studies data from the maximal treadmill tests (TT) were used as reference values for the comparison of energy expenditure of OTC and TEC. During TEC, the average V˙O₂ was considerably lower [29.1 (5.6) ml^·kg^−1·min⁻¹] or 51.1 (10.9)% of VO₂max and 64.8.0 (13.3)% of V˙O₂ determined at the individual anaerobic threshold (IAT) on the TT. The short high-intensity periods (activity/recovery = 1/6) did not result in higher LA levels [average LA of games: 2.07 (0.9) mmol·l⁻¹]. The highest average V˙O₂ value for a whole game was 47.8 ml·kg^−1·min⁻¹ and may provide a reference for energy demands required to sustain high-intensity periods of tennis predominately via aerobic mechanism of energy delivery. During OTC, we found an average V˙O₂ of 56.4 (4.5) ml·kg⁻¹·min⁻¹ or 83.0 (3.8)% of V˙O₂max and 94.6 (5.2)% of V˙O₂ at IAT. In contrast to TEC, LA were relatively high [5.16 (1.5) mmol·l⁻¹) although the average V˙O₂ was significantly lower than V˙O₂ at IAT. Our data suggest that portable RGEM provides valuable information concerning the energy expenditure in sports that cannot be interpreted from LA or HR measures alone. Portable RGEM systems provide valuable assessment of under- or over-estimation of requirements of sports and assist in the optimization and interpretation of training in athletes. Electronic Publication     

The influence of prior cycling on biomechanical and cardiorespiratory response profiles during running in triathletes

The aim of the present study was to determine the effects of 40 km of cycling on the biomechanical and cardiorespiratory responses measured during the running segment of a classic triathlon, with particular emphasis on the time course of these responses. Seven male triathletes underwent four successive laboratory trials: (1) 40 km of cycling followed by a 10-km triathlon run (TR), (2) a 10-km control run (CR) at the same speed as TR, (3) an incremental treadmill test, and (4) an incremental cycle test. The following ventilatory data were collected every minute using an automated breath-by-breath system: pulmonary ventilation (V˙ _E, l · min⁻¹), oxygen uptake (V˙O₂, ml · min⁻¹ · kg⁻¹), carbon dioxide output (ml · min⁻¹), respiratory equivalents for oxygen (V˙ _E/V˙O₂) and carbon dioxide (V˙ _E/V˙CO₂), respiratory exchange ratio (R) respiratory frequency (f, breaths · min⁻¹), and tidal volume (ml). Heart rate (HR, beats · min⁻¹) was monitored using a telemetric system. Biomechanical variables included stride length (SL) and stride frequency (SF) recorded on a video tape. The results showed that the following variables were significantly higher (analysis of variance, P < 0.05) for TR than for CR: V˙O₂ [51.7 (3.4) vs 48.3 (3.9) ml · kg⁻¹ · min⁻¹, respectively], V˙ _E [100.4 (1.4) l · min⁻¹ vs 84.4 (7.0) l · min⁻¹], V˙ _E/V˙O₂ [24.2 (2.6) vs 21.5 (2.7)] V˙ _E/V˙CO₂ [25.2 (2.6) vs 22.4 (2.6)], f [55.8 (11.6) vs 49.0 (12.4) breaths · min⁻¹] and HR [175 (7) vs 168 (9) beats · min⁻¹]. Moreover, the time needed to reach steady-state was shorter for HR and V˙O₂ (1 min and 2 min, respectively) and longer for V˙ _E (7 min). In contrast, the biomechanical parameters, i.e. SL and SF, remained unchanged throughout TR versus CR. We conclude that the first minutes of the run segment after cycling in an experimental triathlon were specific in terms of V˙O₂ and cardiorespiratory variables, and nonspecific in terms of biomechanical variables. Accepted: 7 July 1997     

Maximal oxygen uptake during field running does not exceed that measured during treadmill exercise

Modern ergometric equipment enables the simulation of laboratory maximal oxygen uptake (V˙O_2max) testing in the field. Therefore, it was investigated whether the improved event specificity on the track might lead to higher V˙O_2max measurements in running. Identical protocols were used on the treadmill and on the track (speed was indicated by a computer-driven flashing light system). Ambulatory measurements of gas exchange were carried out throughout both tests, which were executed in randomized order. There were no significant differences (P=0.71) in V˙O_2max between treadmill [4.65 (0.51) ml·min^–1] and field tests [4.63 (0.55) ml·min^–1]. However, the test duration differed significantly (P<0.001) by approximately 5%: treadmill 691 (39) s; field test 727 (42) s. With the exception of maximum heart rate (HR_max; significantly higher in the field with P=0.02) all criteria for the degree of effort were similar between the two tests. However, the difference in HR_max at less than 2 beats·min^–1, was practically negligible. Submaximal measurements of oxygen uptake and minute ventilation were significantly higher on the treadmill (P<0.001 for both parameters). In summary, field tests with incremental running protocols do not result in higher V˙O_2max measurements compared to laboratory treadmill exercise. A better running economy on the track results in higher maximal velocities and longer exercise durations being sustained. The determination of V˙O_2max is not a reasonable application for ambulatory gas exchange measurements because laboratory values are not surpassed. Electronic Publication     

The effect of training in male prepubertal and pubertal monozygotic twins

Nine male pairs of monozygotic twins aged 11–14 years, height 147 (7.6) cm and body mass 39.7 (9.6) kg, participated in this study. Twin zygocity was tested using morphological, dermatoglyphic and hematologic methods, and Tanner's five stages were used for the evaluation of biological maturation. One twin from each pair undertook training for 6 months, three times a week, with running at 85–120% of the lactate anaerobic threshold (LT). Anthropometrics, determination of maximum O₂ uptake (V˙O_2max), LT and maximal blood lactate concentration ([La]_max) was carried out before, during and after training. No significant difference existed between the trained twins and their untrained brothers before training. After training, the trained twins increased their V˙O_2max (per kg body mass) by 10.6% and their LT by 18.2% (P<0.01), reaching values that differed significantly from those of their untrained brothers [57.5 (3.6) ml·kg⁻¹·min⁻¹ vs 55.4 (3.3) ml·kg⁻¹·min⁻¹ and 13.4 (1.1) km·h⁻¹ vs 12.7 (1.1) km·h⁻¹, respectively]. In addition, in the trained twins relative body fat was reduced (P<0.05) from 17.8 to 16.2% and their somatotype altered significantly (decrease of endomorphy and mesomorphy and increase of ectomorphy), while in the untrained twins there was no change in these parameters. Both groups of twins significantly increased their absolute V˙O_2max after the 6 months of training, the trained by 14,9% [from 2.08 (0.43) to 2.37 (0.45) l·min⁻¹] and the untrained by 10.5% [from 2.10 (0.41) to 2.32 (0.47) l·min⁻¹], but no difference was registered between them. A comparison of the intrapair changes in V˙O_2max of prepubertal and pubertal twins showed an influence of training in the prepubertal (19.3% vs 5.2%) but not in the pubertal twins (12.7% vs 13.1%). Using analysis of variance, the relative importance of training, heredity and their interaction was evaluated to be 20%, 70% and 10%, respectively, for the change in body fat, 35%, 45% and 20%, respectively, for the change in relative V˙O_2max and 25–30%, 50–60% and 15–20%, respectively, for the change in LT. In conclusion, training during pubertal growth can favour aerobic power (depending on body composition) as well as aerobic capacity, but it has no effect on absolute V˙O_2max. Genetic control seems to have a strong effect on the extent of adaptations, and the genotype—training interaction explains a small, but prominent part of them. Electronic Publication     

Effect of prior heavy arm and leg exercise on V˙O<Subscript>2</Subscript> kinetics during heavy leg exercise

The aim of the present study was to examine the effect of prior exercise at a remote site on the V˙O₂ kinetics during subsequent heavy cycle exercise using a model that allowed us to discriminate between the V˙O₂ fast and slow component responses. Ten male subjects completed a constant-load exercise of 6 min cycling at 90% of the V˙O₂peak in three conditions: without prior exercise (LE-C), after heavy cycling exercise (6 min at 90% of the V˙O₂peak) (LE-L) and after heavy arm-cranking exercise (6 min at 90% of the arm V˙O₂peak) (LE-A). Subjects performed four repetitions of each exercise protocol, separated by at least 1 day. V˙O₂ was measured on a breath-by-breath basis and V˙O₂ kinetics were determined with a biexponential model. There were no significant differences in the V˙O₂ fast component parameters between LE-C, LE-L and LE-A. However, the V˙O₂ slow component amplitude was significantly reduced in LE-L and LE-A compared to LE–C, but the reduction was less pronounced in LE-A [the value of the V˙O₂ slow exponential term at the end of exercise, A ₂′, was 657 (SD 200) ml^.min^–1 in LE-C versus 384 (SD 136) ml^.min^–1 in LE-L and 551 (SD 169) ml^.min^–1 in LE-A; P<0.05]. The results of this study demonstrate that prior heavy arm exercise alters V˙O₂ kinetics during cycling exercise by reducing the V˙O₂slow component amplitude, though this reduction is smaller than the reduction observed following prior heavy leg exercise. These data indicate that the primary factor causing changes in the V˙O₂ kinetics is probably located in the involved muscle. Electronic Publication     

Low frequency of the "plateau phenomenon" during maximal exercise in elite British athletes

A plateau in oxygen consumption (V̇O₂) has long been considered the criterion for maximal effort during an incremental exercise test. But, surprisingly, the termination of a maximum exercise test often occurs in the absence of a V̇O₂ plateau. To explain this inconsistency, some have proposed that an oxygen limitation in skeletal muscle occurs only in elite athletes. To evaluate this hypothesis, we determined the frequency with which the "plateau phenomenon" developed in a group of elite male and female athletes. Fifty subjects performed a continuous incremental treadmill test to measure maximal oxygen consumption (V̇O_2max). Treadmill velocity increased by 0.31 m s⁻¹ until the respiratory exchange ratio (R) reached 1.00. Thereafter the treadmill gradient increased by 1% each minute until exhaustion. The V̇O_2max was the highest V̇O₂ sustained for 60 s. Three criteria were used to determine maximal efforts: (1) a plateau in the V̇O₂, defined as an increase of less than 1.5 ml kg⁻¹ min⁻¹; (2) a final R of 1.1 or above; (3) a final heart rate (HR) above 95% of the age-related maximum. Mean V̇O_2max exceeded 65 ml kg⁻¹ min⁻¹ in both groups. The criteria for R and HR were satisfied by 72% of males and 56% females, and 55% of males and 69% of females, respectively. In contrast a V̇O₂ plateau was identified in only 39% of males and 25% of females. These findings refute the twin arguments: (1) that the absence of a "plateau phenomenon" results from an inadequate motivational effort in poorly trained athletes and (2) that the "plateau phenomenon" and a consequent skeletal muscle anaerobiosis occur only in athletes with the highest V̇O_2max values.     

Oxygen uptake kinetics during moderate,heavy and severe intensity "submaximal" exercise in humans: the influence of muscle fibre type and capillarisation

The purpose of the present study was to test the hypothesis that muscle fibre type influences the oxygen uptake (V˙O₂) on-kinetic response (primary time constant; primary and slow component amplitudes) during moderate, heavy and severe intensity sub-maximal cycle exercise. Fourteen subjects [10 males, mean (SD) age 25 (4) years; mass 72.6 (3.9) kg; V˙O_2peak 47.9 (2.3) ml kg⁻¹ min⁻¹] volunteered to participate in this study. The subjects underwent a muscle biopsy of the vastus lateralis for histochemical determination of muscle fibre type, and completed repeat 'square-wave' transitions from unloaded cycling to power outputs corresponding to 80% of the ventilatory threshold (VT; moderate exercise), 50% (heavy exercise) and 70% (severe exercise) of the difference between the VT and V˙O_2peak. Pulmonary V˙O₂ was measured breath-by-breath. The percentage of type I fibres was significantly correlated with the time constant of the primary V˙O₂ response for heavy exercise (r=−0.68). Furthermore, the percentage of type I muscle fibres was significantly correlated with the gain of the V˙O₂ primary component for moderate (r=0.65), heavy (r=0.57) and severe (r=0.57) exercise, and with the relative amplitude of the V˙O₂ slow component for heavy (r=−0.74) and severe (r=−0.64) exercise. The influence of muscle fibre type on the V˙O₂ on-kinetic response persisted when differences in aerobic fitness and muscle capillarity were accounted for. This study demonstrates that muscle fibre type is significantly related to both the speed and the amplitudes of the V˙O₂ response at the onset of constant-load sub-maximal exercise. Differences in contraction efficiency and oxidative enzyme activity between type I and type II muscle fibres may be responsible for the differences observed. Electronic Publication     

Transient oxygen uptake response to exercise characterizes functional capacity of the cardiocirculatory system in patients with chronic heart failure: a random stimulus approach

The transient response of oxygen uptake (V˙O₂) to submaximal exercise, known to be abnormal in patients with cardiovascular disorders, can be useful in assessing the functional status of the cardiocirculatory system, however, a method for evaluating it accurately has not yet been established. As an alternative approach to the conventional test at constant exercise intensity, we applied a random stimulus technique that has been shown to provide relatively noise immune responses of system being investigated. In 27 patients with heart failure and 24 age-matched control subjects, we imposed cycle exercise at 50 W intermittently according to a pseudo-random binary (exercise-rest) sequence, while measuring breath-by-breath V˙O₂. After determining the transfer function relating exercise intensity (W˙) to V˙O₂ and attenuating the high frequency ranges (>6 exercise-rest cycles · min⁻¹), we computed the high resolution band-limited (0–6 cycles · min⁻¹) V˙O₂ response (0–120 s) to a hypothetical step exercise. The V˙O₂ response showed a longer time constant in the patients than in the control subjects [47 (SD 37) and 31 (SD 8) s, respectively, P < 0.05]. Furthermore, the amplitude of the V˙O₂ response after the initial response was shown to be significantly smaller in the patients than in the control subjects [176 (SD 50) and 267 (SD 54) ml · min⁻¹ at 120 s]. The average amplitude over 120 s correlated well with peak V˙O₂ (r = 0.73) and ΔV˙O₂/ΔW˙ (r = 0.70), both of which are well-established indexes of exercise tolerance. The data indicated that our band-limited V˙O₂ step response using random exercise was more markedly attenuated and delayed in the patients with heart failure than in the normal controls and that it could be useful in quantifying the overall functional status of the cardiocirculatory system. Accepted: 6 January 1998     

Oxygen uptake kinetics during horizontal and uphill treadmill running in humans

The aim of this study was to examine the effect of increasing the ratio of concentric to eccentric muscle activation on oxygen uptake (V˙O₂) kinetics during treadmill running. Nine subjects [2 women; mean (SD) age 29 (7) years, height 1.77 (0.07) m, body mass 73.0 (7.5) kg] completed incremental treadmill tests to exhaustion at 0% and 10% gradients to establish the gradient-specific ventilatory threshold (VT) and maximal oxygen uptake (V˙O_2max). Subsequently, the subjects performed repeated moderate intensity (80% of gradient-specific VT) and heavy intensity (50% of the difference between the gradient specific VT and V˙O_2max) square-wave runs with the treadmill gradient set at 0% and 10%. For moderate intensity exercise, there were no significant differences between treadmill gradients for V˙O₂ kinetics. For heavy intensity exercise, the amplitude of the primary component of V˙O₂ was not significantly different between 0% and 10% treadmill gradients [mean (SEM) 2,940 (196) compared to 2,869 (156) ml·min^–1, respectively], but the amplitude of the V˙O₂ slow component was significantly greater at the 10% gradient [283 (43) compared to 397 (37) ml·min^–1; P<0.05]. These results indicate that the muscle contraction regimen (i.e. the relative contribution of concentric and eccentric muscle action) significantly influences the amplitude of the V˙O₂ slow component. Electronic Publication     

The effect of endurance training on the ventilatory response to exercise in elite cyclists

The purpose of this study was to investigate the effects of endurance training on the ventilatory response to acute incremental exercise in elite cyclists. Fifteen male elite cyclists [mean (SD) age 24.3 (3.3) years, height 179 (6) cm, body mass 71.1 (7.6) kg, maximal oxygen consumption (V˙O_2max) 69 (7) ml · min⁻¹ · kg⁻¹] underwent two exercise tests on a cycle ergometer. The first test was assessed in December, 6 weeks before the beginning of the cycling season. The second test was performed in June, in the middle of the season. During this period the subjects were expected to be in a highly endurance-trained state. The ventilatory response was assessed during an incremental exercise test (20 W · min⁻¹). Oxygen consumption (V˙O₂), carbon dioxide production (V˙CO₂), minute ventilation (V˙ _E), and heart rate (HR) were assessed at the following points during the test: at workloads of 200 W, 250 W, 300 W, 350 W, 400 W and at the subject's maximal workload, at a respiratory exchange ratio (R) of 1, and at the ventilatory threshold (Th_vent) determined using the V-slope-method. Post-training, the mean (SD) V˙O_2max was increased from the pre-training level of 69 (7) ml · min⁻¹ · kg⁻¹ (range 61.4–78.6) to 78 (6) ml · min⁻¹ · kg⁻¹ (range 70.5–86.3). The mean post-training V˙O₂ was significantly higher than the pre training value (P < 0.01) at all work rates, at Th_vent and at R=1. V˙O₂ was also higher at all work rates except for 200 W and 250 W. V˙ _E was significantly higher at Th_vent and R=1. Training had no effect on HR at all workloads examined. An explanation for the higher V˙O₂ cost for the same work rate may be that in the endurance-trained state, the adaptation to an exercise stimulus with higher intensity is faster than for the less-trained state. Another explanation may be that at the same work rate, in the less-endurance-trained state power is generated using a significantly higher anaerobic input. The results of this study suggest the following practical recommendations for training management in elite cyclists: (1) the V˙O₂ for a subject at the same work rate may be an indicator of the endurance-trained state (i.e., the higher the V˙O₂, the higher the endurance-trained capacity), and (2) the need for multiple exercise tests for determining the HR at Th_vent during a cycling season is doubtful since at Th_vent this parameter does not differ much following endurance training. Accepted: 19 October 1999     

Breathing pattern and exercise endurance time after exhausting cycling or breathing

The aim of the present study was to investigate whether the changes in breathing pattern that frequently occur towards the end of exhaustive exercise (i.e., increased breathing frequency, f _b, with or without decreased tidal volume) may be caused by the respiratory work itself rather than by leg muscle work. Eight healthy, trained subjects performed the following three sessions in random order: (A) two sequential cycling endurance tests at 78% peak O₂ consumption (V˙O_2peak) to exhaustion (A1, A2); (B) isolated, isocapnic hyperpnea (B1) at a minute ventilation (V˙ _E) and an exercise duration similar to that attained during a preliminary cycling endurance test at 78% V˙O_2peak, followed by a cycling endurance test at 78% V˙O_2peak (B2); (C) isolated, isocapnic hyperpnea (C1) at a V˙ _E at least 20% higher than that of the preliminary cycling test and the same exercise duration as the preliminary cycling test, followed by a cycling endurance test at 78% V˙O_2peak (C2). Neither of the two isocapnic hyperventilation tasks (B1 or C1) affected either the breathing pattern or the endurance times of the subsequent cycling tests. Only cycling test A2 was significantly shorter [mean (SD) 26.5 (8.3) min] than tests A1 [41.0 (9.0) min], B2 [41.9 (6.0) min], and C2 [42.0 (7.5) min]. In addition, compared to test A1, only the breathing pattern of test A2 was significantly different [i.e., V˙ _E: +10.5 (7.6) l min⁻¹, and f _b: +12.1 (8.5) breaths min⁻¹], in contrast to the breathing patterns of cycling tests B2 [V˙ _E: −2.5 (6.2) l min⁻¹, f _b: +0.2 (3.6) breaths min⁻¹] and C2 [V˙ _E: −3.0 (7.0) l min⁻¹, f _b: +0.6 (6.1) breaths min⁻¹]. In summary, these results suggest that the changes in breathing pattern that occur towards the end of an exhaustive exercise test are a result of changes in the leg muscles rather than in the respiratory muscles themselves. Accepted: 7 October 1999     

The effect of nitrous oxide-induced narcosis on aerobic work performance

Previous findings of a narcosis-induced reduction in heat production during cold water immersion, as reflected in oxygen uptake (V˙O₂), have been attributed to the attenuation of the shivering response. The possibility of reduced oxygen utilization (V˙O₂) by the muscles could not, however, be excluded. Accordingly, the present study tested the hypothesis that mild narcosis, induced by inhalation of a normoxic gas mixture containing 30% nitrous oxide (N₂O), would affect V˙O₂. Nine male subjects participated in both maximal and submaximal exercise trials, inspiring either room air (AIR) or a normoxic mixture containing 30% N₂O. In the submaximal trials, the subjects exercised at 50% of maximal exercise intensity (W˙ _max ) as determined in the maximal AIR trial. Though the subjects attained the same W˙ _max in the AIR and N₂O trials, maximal V˙O₂ was significantly higher (P < 0.05) during the N₂O condition [58.9 (SEM 3.1) ml · kg^−1 ·min^−l] compared to the AIR condition [55.0 (SEM 2.4) ml · kg⁻¹ · min^−l]. However, the V˙O₂-relative exercise intensity relationship was similar during both maximal AIR and maximal N₂O at submaximal exercise intensities. There were no significant differences in the responses of oesophageal temperature, sweating rate, heart rate and ventilation between AIR and N₂O in the maximal and submaximal tests. It was concluded that the previously reported narcosis-induced reductions in V˙O₂ observed during cold water immersion can be attributed solely to a reduction in the shivering response rather than to decreased oxygen utilization by the muscles. Accepted: 6 February 2000     

Simulated moderate altitude elevates serum erythropoietin but does not increase reticulocyte production in well-trained runners

The purpose of this study was to investigate whether the modest increases in serum erythropoietin (sEpo) experienced after brief sojourns at simulated altitude are sufficient to stimulate reticulocyte production. Six well-trained middle-distance runners (HIGH, mean maximum oxygen uptake, V˙O_2max = 70.2 ml · kg⁻¹ · min⁻¹) spent 8–11 h per night for 5 nights in a nitrogen house that simulated an altitude of 2650 m. Five squad members (CONTROL, mean V˙O_2max = 68.9 ml · kg⁻¹ · min⁻¹) undertook the same training, which was conducted under near-sea-level conditions (600 m altitude), and slept in dormitory-style accommodation also at 600 m altitude. For both groups, this 5-night protocol was undertaken on three occasions, with a 3-night interim between successive exposures. Venous blood samples were measured for sEpo after 1 and 5 nights of hypoxia on each occasion. The percentage of reticulocytes was measured, along with a range of reticulocyte parameters that are sensitive to changes in erythropoiesis. Mean serum erythropoietin levels increased significantly (P < 0.01) above baseline values [mean (SD) 7.9 (2.4) mU · ml⁻¹] in the HIGH group after the 1st night [11.8 (1.9) mU · ml⁻¹, 57%], and were also higher on the 5th night [10.7 (2.2) mU · ml⁻¹, 42%] compared with the CONTROL group, whose erythropoietin levels did not change. After athletes spent 3 nights at near sea level, the change in sEpo during subsequent hypoxic exposures was markedly attenuated (13% and −4% change during the second exposure; 26% and 14% change during the third exposure; 1st and 5th nights of each block, respectively). The increase in sEpo was insufficient to stimulate reticulocyte production at any time point. We conclude that when daily training loads are controlled, the modest increases in sEpo known to occur following brief exposure to a simulated altitude of 2650 m are insufficient to stimulate reticulocyte production. Accepted: 7 October 1999     

Physiological characteristics of elite short- and long-distance triathletes

The purpose of this study was to compare the physiological responses in cycling and running of elite short-distance (ShD) and long-distance (LD) triathletes. Fifteen elite male triathletes participating in the World Championships were divided into two groups (ShD and LD) and performed a laboratory trial that comprised submaximal treadmill running, maximal then submaximal ergometry cycling and then an additional submaximal run. 'In situ' best ShD triathlon performances were also analysed for each athlete. ShD demonstrated a significantly faster swim time than LD whereas V˙O_2max (ml kg^–1 min^–1), cycling economy (W l^–1 min^–1), peak power output ( , W) and ventilatory threshold (%V˙O_2max) were all similar between ShD and LD. Moreover, there were no differences between the two groups in the change (%) in running economy from the first to the second running bout. Swimming time was correlated to (r=–0.76; P<0.05) and economy (r=–0.89; P<0.01) in the ShD athletes. Also, cycling time in the triathlon was correlated to (r=–0.83; P<0.05) in LD. In conclusion, ShD triathletes had a faster swimming time but did not exhibit different maximal or submaximal physiological characteristics measured in cycling and running than LD triathletes. Electronic Publication     

Effect of water ingestion on cardiovascular and thermal responses to prolonged cycling and running in humans: a comparison

The aim of this investigation was to examine the effect of water ingestion on physiological responses to prolonged cycling (CYC) and running (RUN). A group of 11 men with mean (SEM) maximal oxygen uptake (V˙O_2max) 48.5 (1.8) ml·kg^–1·min^–1 on a cycle-ergometer and 52.1 (2.2) ml·kg^–1·min^–1 on a treadmill (P<0.01) exercised for 90 min on four occasions, twice on each ergometer, at 60% of mode specific V˙O_2max. No fluid was taken (D) in one trial on each ergometer, whereas 60% of fluid losses were replaced by drinking water in the other trial (W). In CYC, water ingestion attenuated the change in cardiac output ( ) and the reduction in stroke volume (ΔSV) [ΔSV: –22.7 (3.8) in D, –10.7 (2.9) ml·beat^–1 in W, P<0.01; : –1.9 (0.5) in D, –0.2 (0.4) l·min^–1 in W at 85 min, P<0.01], but did not affect rectal temperature [T _re at 90 min: 38.8 (0.1)°C in D, 38.7 (0.1)°C in W]. In contrast, fluid replacement reduced hyperthermia in RUN [T _re at 90 min: 39.6 (0.2) in D, 39.1 (0.2)°C in W, P<0.01], and this was linked with a higher skin blood flow [RUN-W 88.9 (8.5), RUN-D 70.7 (8.4)%, P<0.05]. The and ΔSV were also attenuated with water ingestion in this mode of exercise (P<0.05). It is concluded that water ingestion improves physiological function in both cycling and running, but that the underlying mechanism is different in the two modes of exercise. Electronic Publication     

Oxygen kinetics and modelling of time to exhaustion whilst running at various velocities at maximal oxygen uptake

The purpose of this study was to characterise the relationship between running velocity and the time for which a subject can run at maximal oxygen uptake (V˙O_{2 max}), (t _lim V˙O_{2 max}). Seven physical education students ran in an incremental test (3-min stages) to determine V˙O_{2 max} and the minimal velocity at which it was elicited (νV˙O_{2 max}). They then performed four all-out running tests on a 200-m indoor track every 2 days in random order. The mean times to exhaustion t _lim at 90%, 100%, 120% and 140% νV˙O_{2 max} were 13 min 22 s (SD 4 min 30 s), 5 min 47 s (SD 1 min 50 s), 2 min 11 s (SD 38 s) and 1 min 12 s (SD 18 s), respectively. Five subjects did not reach V˙O_{2 max} in the 90% νV˙O_{2 max} test. All the subjects reached V˙O_{2 max} in the runs at 100% νV˙O_{2 max}. All the subjects, except one, reached V˙O_{2 max} in the runs at 120%νV˙O_{2 max}. Four subjects did not reach V˙O_{2 max} in the 140% νV˙O_{2 max} test. Time to achieve V˙O_{2 max} was always about 50% of the time to exhaustion irrespective of the intensity. The time to exhaustion-velocity relationship was better fitted by a 3- than by a 2-parameter critical power model for running at 90%, 100%, 120%, 140% νV˙O_{2 max} as determined in the previous incremental test. In conclusion, t _lim V˙O_{2 max} depended on a balance between the time to attain V˙O_{2 max} and the time to exhaustion t _lim. The time to reach V˙O_{2 max} decreased as velocity increased. The t _lim V˙O_{2 max} was a bi-phasic function of velocity, with a peak at 100% νV˙O_{2 max}. Accepted: 2 February 2000     

Reduced performance of male and female athletes at 580 m altitude

This study examined the effect of mild hypobaria (MH) on the peak oxygen consumption (O_2peak) and performance of ten trained male athletes [ (SEM); O_2peak = 72.4 (2.2) ml · kg⁻¹ · min⁻¹] and ten trained female athletes [O_2peak = 60.8 (2.1) ml · kg⁻¹ · min⁻¹]. Subjects performed 5-min maximal work tests on a cycle ergometer within a hypobaric chamber at both normobaria (N, 99.33 kPa) and at MH (92.66 kPa), using a counter-balanced design. MH was equivalent to 580 m altitude. O_2peak at MH decreased significantly compared with N in both men [− 5.9 (0.9)%] and women [− 3.7 (1.0)%]. Performance (total kJ) at MH was also reduced significantly in men [− 3.6 (0.8)%] and women [− 3.8 (1.2)%]. Arterial oxyhaemoglobin saturation (S_aO₂) at O_2peak was significantly lower at MH compared with N in both men [90.1 (0.6)% versus 92.0 (0.6)%] and women [89.7 (3.1)% versus 92.1 (3.0)%]. While S_aO₂ at O_2peak was not different between men and women, it was concluded that relative, rather than absolute, O_2peak may be a more appropriate predictor of exercise-induced hypoxaemia. For men and women, it was calculated that 67–76% of the decrease in O_2peak could be accounted for by a decrease in O₂ delivery, which indicates that reduced O₂ tension at mild altitude (580 m) leads to impairment of exercise performance in a maximal work bout lasting ≈ 5 min. Accepted: 30 July 1996