An improved estimation of mean body temperature using combined direct calorimetry and thermometry

The conventional method used to estimate the change in mean body temperature (dMBT) is by taking X% of a body core temperature and (1−X)% of weighted mean skin temperature, the value of X being dependent upon ambient temperature. This technique is used widely, despite opposition from calorimetrists. In the present paper we attempt to provide a better method. Minute-by-minute changes in dMBT, as assessed using calorimetry, and 21 (20 if esophageal temperature was unavailable) various regional temperatures (dRBTs), as assessed using thermometry, including 6 subcutaneous measures, were collected from 7 young male adults at 6 calorimeter temperatures. Since a calorimeter measures only changes in heat storage, which can be converted to dMBT, all body temperatures are expressed as changes from the reasonably constant pre-exposure temperatures. The following three aspects were investigated. (1) The prediction of dMBT from the 21 (or 20) dRBTs with multi-linear regression analysis (MLR). This yields two results, model A with rectal temperature (dT _re) alone, and model B with dT _re and esophageal temperature (dT _es). (2) The prediction of dMBT from dT _re with or without dT _es and 13 skin surface temperatures combined to one weighted mean skin temperature (dTˉ _sk), using MLR. This results in models C and D. Six more models (E–J) were added, representing the above two sets in various combinations with four factors. (3) The conventional method calculated with four values for X. Model A predicted better than 0.3 °C in 70% of the cases. Model I was the best amongst the models with 13 weighted skin temperatures (better than 0.3 °C in 60% of the cases). The conventional method was erratic. Accepted: 14 January 2000     

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     

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     

Specificity of treadmill and cycle ergometer tests in triathletes, runners and cyclists

The objective of this study was to evaluate the viability of using a single test in which cardiorespiratory variables are measured, to establish training guidelines in running and/or cycling training activities. Six triathletes (two females and four males), six runners (two females and four males) and six males cyclists, all with 5.5 years of serious training and still involved in racing, were tested on a treadmill and cycle ergometer. Cardiorespiratory variables [e.g., heart rate (HR), minute ventilation, carbon dioxide output (V˙CO₂)] were calculated relative to fixed percentages of maximal oxygen uptake (V˙O_2max; from 50 to 100%). The entire group of subjects had significantly (P < 0.05) higher values of V˙O_2max on the treadmill compared with the cycle ergometer [mean (SEM) 4.7 (0.8) and 4.4 (0.9) l · min⁻¹, respectively], and differences between tests averaged 10.5% for runners, 6.1% for triathletes and 2.8% for cyclists. A three-way analysis of variance using a 3 × 2 × 6 design (groups × tests × intensities) demonstrated that all factors yielded highly significant F-ratios (P < 0.05) for all variables between tests, even though differences in HR were only 4 beats · min⁻¹. When HR was plotted against a fixed percentage of V˙O_2max, a high correlation was found between tests. These results demonstrate that for triathletes, cyclists and runners, the relationship between HR and percentage of V˙O_2max, obtained in either a treadmill or a cycle ergometer test, may be used independently of absolute V˙O_2max to obtain reference HR values that can be used to monitor their running and/or cycling training bouts. Received: 3 November 1998 / Accepted: 29 July 1999     

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     

Time to exhaustion during severe intensity running: response following a single bout of interval training

 The primary aim of this study was to examine any change in performance caused by a fatiguing interval training session (TS). A secondary aim of this study was to examine the change in oxygen uptake (V˙O₂) during moderate and severe intensity running, and the relationship with the change in performance. Seven male runners [mean age 24 (SD 6) years, height 1.79 (SD 0.06) m, body mass 67.9 (SD 7.6) kg, maximal oxygen uptake (V˙O_2max) 4.14 (SD 0.49) l · min⁻¹] were studied. The V˙O₂ during moderate and severe intensity running and running performance were studied immediately prior to, 1 h following, and 72 h following TS. The TS was performed on a treadmill, and consisted of six bouts of 800 m at 1 km · h⁻¹ below the velocity at V˙O_2max (v _V˙ O_2max), with 3-min rest intervals. Performance was also assessed at 1 km · h⁻¹ below v _V˙ O_2max, in the form of time to exhaustion (t _lim). The V˙O₂ and heart rate (f _c) were assessed both during the severe intensity performance trial, and the moderate intensity run at 50% v _V˙ O_2max. Whilst a significant change was observed in running performance and the V˙O₂ during both moderate and severe intensity running prior to and following TS, no relationship was observed between the magnitude of change in these variables. At 1 h following TS, t _lim had decreased by 24%, V˙O₂ during moderate intensity running had increased by 2%, and the difference in V˙O₂ between 2 min 45 s and the end of severe intensity running had increased by 91% compared with values recorded prior to TS. At 1 h following TS, ƒ_c had also increased significantly during moderate intensity running by 5% compared to the value recorded prior to TS. These findings demonstrated that TS resulted in a reduction in performance, and that the relationship between running performance and V˙O₂ during running may be altered under conditions of prolonged fatigue. Accepted: 16 September 1999     

Effects of improvement in aerobic power on resting insulin and glucose concentrations in children

In this study we determined the influence of improving aerobic power (V˙O_2max) on basal plasma levels of insulin and glucose of 11- to 14-year-old children, while accounting for body fat, gender, pubertal status, and leisure-time physical activity (LTPA) levels. Blood samples were obtained from 349 children after an overnight fast and analyzed for plasma insulin and glucose. Height, mass, body mass index (BMI), and sum of skinfolds (Σ triceps + subscapular sites) were measured. LTPA levels and pubertal status were estimated from questionnaires, and V˙O_2max was predicted from a cycle ergometry test. Regardless of gender, insulin levels were significantly correlated (P = 0.0001) to BMI, skinfolds, pubertal stage, and predicted V˙O_2max, but were not related to LTPA levels. Fasting glucose levels were not correlated to measures of adiposity or exercise (LTPA score, V˙O_2max) for females; however, BMI and skinfolds were correlated for males (P < 0.006). The children then took part in an 8-week aerobic exercise program. The 60 children whose V˙O_2max improved (≥3 ml · kg⁻¹ · min⁻¹) had a greater reduction in circulating insulin than the 204 children whose V˙O_2max did not increase −16 (41) vs −1 (63) pmol · l⁻¹; P = 0.028. The greatest change occurred in those children with the highest initial resting insulin levels. Plasma glucose levels were slightly reduced only in those children with the highest insulin levels whose V˙O_2max improved (P < 0.0506). The results of this study indicate that in children, adiposity has the most significant influence on fasting insulin levels; however, increasing V˙O_2max via exercise can lower insulin levels in those children with initially high levels of the hormone. In addition, LTPA does not appear to be associated with fasting insulin status, unless it is sufficient to increase V˙O_2max. Accepted: 2 June 1999     

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

In this study we aimed to elucidate the validity and usefulness of the oxygen uptake efficiency slope (OUES) in the evaluation of adult cardiac patients. Cardiopulmonary exercise tests were performed on a treadmill by 50 adult patients with chronic heart failure. The OUES was calculated from data for the first 75%, 90%, and 100% of exercise duration. The OUES is derived from the following equation: V˙O₂=a× logV˙ _E+b, where V˙O₂ is oxygen uptake (ml/kg/min), V˙ _E is minute ventilation (l/kg/min), and the constant “a” represents OUES. We also determined the ventilatory anaerobic threshold (VAT). The correlation coefficient of the logarithmic curve-fitting model was [mean (SD)] 0.986 (0.009). The OUES could be used to discriminate effectively between New York Heart Association functional classes (P < 0.001). OUES and maximum V˙O₂ were significantly correlated (r=0.78, P < 0.01). Agreement between the OUES values for the first 90%, 75%, and 100% of the exercise was excellent (intraclass correlation coefficient = 0.99). Our results suggest that OUES is applicable to adult cardiac patients as an objective, effort-independent estimation of cardiorespiratory functional reserve. Accepted: 7 September 1998     

In humans the oxygen uptake slow component is reduced by prior exercise of high as well as low intensity

The aim of the study was to examine to what extent prior high- or low-intensity cycling, yielding the same amount of external work, influenced the oxygen uptake (V˙O₂) slow component of subsequent high-intensity cycling. The 12 subjects cycled in two protocols consisting of an initial 3 min period of unloaded cycling followed by two periods of constant-load exercise separated by 3 min of rest and 3 min of unloaded cycling. In protocol 1 both periods of exercise consisted of 6 min cycling at a work rate corresponding to 90% peak oxygen uptake (V˙O_2peak). Protocol 2 differed from protocol 1 in that the first period of exercise consisted of a mean of 12.1 (SD 0.8) min cycling at a work rate corresponding to 50% V˙O_2peak. The difference between the 3rd min V˙O₂ and the end V˙O₂ (ΔV˙O₂₍₆₋₃₎) was used as an index of the V˙O₂ slow component. Prior high-intensity exercise significantly reduced ΔV˙O₂₍₆₋₃₎. The ΔV˙O₂₍₆₋₃₎ was also reduced by prior low-intensity exercise despite an unchanged plasma lactate concentration at the start of the second period of exercise. The reduction was more pronounced after prior high- than after prior low-intensity exercise (59% and 28%, respectively). The results of this study show that prior exercise of high as well as low intensity reduces the V˙O₂ slow component and indicate that a metabolic acidosis is not a necessary condition to elicit a reduction in ΔV˙O₂₍₆₋₃₎. Accepted: 8 July 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     

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 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     

Estimation of %V˙O2 reserve from heart rate during arm exercise and running

The purpose of the present investigation was to examine the relationship between the percent heart rate reserve (%HRR) in arm exercise and the corresponding percent oxygen uptake (V˙O₂) reserve, and to compare this relationship to that occurring in running. Fourteen male physical education students took part in the study. Each subject performed a maximal running exercise test and a maximal arm cycling test. The subjects also performed three submaximal exercise bouts (in both exercise modes) at 30%, 60% and 80% of their HRR. The subjects were monitored for their heart rate (HR) at rest, maximal HR (HR_max), HR at submaximal work loads, maximal V˙O₂ (V˙O_2max), V˙O₂ at rest and V˙O₂ at submaximal loads. For each subject, load and exercise mode, %HRR and %V˙O₂ reserve were calculated (from HR_max and V˙O_2max as measured during running and arm cycling) and the relationship between the two was evaluated. The main finding of the present investigation is that the prediction of %V˙O₂ reserve in arm cycling from %HRR is grossly overestimated when calculated from HR_max and V˙O_2max measured during running. The prediction is better but still overestimated when calculated from HR_max and V˙O_2max measured during arm cycling. The findings indicate a better prediction of %V˙O₂ reserve from %HRR for running than for arm exercise. These findings should be taken into consideration when prescribing the target HR for arm training. Accepted: 24 July 2000     

Determinants of 2,000 m rowing ergometer performance in elite rowers

This study examined the physiological determinants of performance during rowing over 2,000 m on an ergometer in finalists from World Championship rowing or sculling competitions from all categories of competion rowing (19 male and 13 female heavyweight, 4 male and 5 female lightweight). Discontinuous incremental rowing to exhaustion established the blood lactate threshold, maximum oxygen consumption (V˙O_2max) and power at V˙O_2max; five maximal strokes assessed maximal force, maximal power and stroke length. These results were compared to maximal speed during a 2,000 m ergometer time trial. The strongest correlations were for power at V˙O_2max, maximal power and maximal force (r=0.95; P<0.001). Correlations were also observed for V˙O_2max (r=0.88, P<0.001) and oxygen consumption (V˙O₂) at the blood lactate threshold (r=0.87, P=0.001). The physiological variables were included in a stepwise regression analysis to predict performance speed (metres per second). The resultant model included power at V˙O_2max, V˙O₂ at the blood lactate threshold, power at the 4 mmol·l^–1 concentration of blood lactate and maximal power which together explained 98% of the variance in the rowing performance over 2,000 m on an ergometer. The model was validated in 18 elite rowers, producing limits of agreement from –0.006 to 0.098 m·s^–1 for speed of rowing over 2,000 m on the ergometer, equivalent to times of –1.5 to 6.9 s (–0.41% to 1.85%). Together, power at V˙O_2max, V˙O₂ at the blood lactate threshold, power at 4 mmol·l^–1 blood lactate concentration and maximal power could be used to predict rowing performance. Electronic Publication     

Nutritional status and physical fitness of elderly sportsmen

The nutritional status of elderly sportsmen has not been reported on, neither has the nutritional balance nor the precise relationship between nutritional status and physical fitness been detailed for this population. Thus, group of 18 sportsmen [age 63 (SD 4.5) years] was monitored by weighing their food during a 6-day period. Macro nutrient, mineral and vitamin content was derived from tables. Daily energy expenditure (DEE) and sport activity (DSA) were quantified over a 7-day period using a questionnaire. Physical fitness was assessed by maximal oxygen uptake (V˙O_2max) measurements. The DEE was 11 429 (SD 1890) kJ · day⁻¹. The DSA corresponded to 38% of DEE and V˙O_2max to 35.9 (SD 6.1) ml · min⁻¹ · kg⁻¹. When compared with French recommended dietary allowances (RDA) intakes were higher for energy (+24%), macro nutrients, and most minerals and vitamins. Despite high energy intakes, some subjects had mineral and vitamin deficits. Energy intakes were significantly related to intakes of magnesium, phosphorus, iron, vitamins B2, B6, C and to V˙O_2max, but not to age. Stepwise regressions indicated that vitamin C intake was the only determinant to have a relationship with V˙O_2max. Thus, most elderly sportsmen had higher nutritional status than RDA, although some had mineral and vitamin deficits. It is therefore suggested that elderly sportsmen should be encouraged to consume food with higher mineral and vitamin contents. Accepted: 17 June 1997     

V˙E and V˙CO2 remain tightly coupled during incremental cycling performed after a bout of high-intensity exercise

The purpose of the present study was to determine whether the linear relationship between CO₂ output (V˙CO₂) and pulmonary ventilation (V˙ _E) is altered during incremental cycling performed after exercise-induced metabolic acidosis. Ten untrained, female subjects performed two incremental cycling tests (15 W · min⁻¹ up to 165 W) on separate days. One incremental exercise test was conducted without prior exercise, whereas the other test was preceded by a 1-min bout of maximal cycling. The ventilatory equivalent for O₂ (V˙ _E/V˙O₂) was only elevated above control values at 15–60 W during incremental cycling performed after high-intensity exercise. In contrast, the ventilatory equivalent for CO₂ (V˙ _E/V˙CO₂) was significantly increased above control levels at nearly every work stage of incremental work (all except 165 W). Hyperventilation relative to V˙CO₂ was confirmed by the significantly lower end-tidal CO₂ tension (P _ETCO₂) obtained throughout the incremental cycling that was performed after high-intensity exercise (except at 165 W). V˙ _E and V˙CO₂ were significantly correlated under both treatment conditions (r > 0.99; P < 0.001). Moreover, both the slope and y-intercept of the linear regression were found to be significantly elevated during the incremental cycling performed after high-intensity cycling compared to control conditions (P < 0.01). The increase in the slope of the V˙ _E-V˙CO₂ relationship during incremental exercise performed under these conditions does not represent an uncoupling of V˙ _E from V˙CO₂, but could be accounted for by the significantly lower P _ETCO₂ observed during exercise. Accepted: 20 June 1997     

Gas exchange responses to continuous incremental cycle ergometry exercise in primary pulmonary hypertension in humans

In patients suffering from primary pulmonary hypertension (PPH), a raised pulmonary vascular resistance may limit the ability to increase pulmonary blood flow as work rate increases. We hypothesised that oxygen uptake (V˙O₂) may not rise appropriately with increasing work rate during incremental cardiopulmonary exercise tests. Nine PPH patients and nine normal subjects performed symptom-limited maximal continuous incremental cycle ergometry exercise. Mean peak V˙O₂ [1.00 (SD 0.22) compared to 2.58 (SD 0.64) l · min⁻¹] and mean V˙O₂ at lactic acidosis threshold [LAT, 0.73 (SD 0.17) compared to 1.46 (SD 0.21 · l) ml · min⁻¹] were much lower in patients than in normal subjects (both P < 0.01, two-way ANOVA with Tukey test). The mean rate of change of V˙O₂ with increasing work rate above the LAT [5.9 (SD 2.1) compared to 9.4 (SD 1.3) ml · min⁻¹ · W⁻¹, P < 0.01)] was also much lower in patients than in normal subjects [apparent δ efficiency 60.3 (SD 38.8)% in patients compared to 31.0 (SD 4.9)% in normal subjects]. The patients displayed lower mean values of end-tidal partial pressure of carbon dioxide than the normal subjects at peak exercise [29.7 (SD 6.8) compared to 42.4 (SD 5.8) mmHg, P < 0.01] and mean oxyhaemoglobin saturation [89.1 (SD 4.1) compared to 93.6 (SD 1.8)%, P < 0.05]. Mean ventilatory equivalents for CO₂ [49.3 (SD 11.4) compared to 35.0 (SD 7.3), P < 0.05] and O₂ [44.2 (SD 10.7) compared to 29.9 (SD 5.1), P < 0.05] were greater in patients than normal subjects. The sub-normal slopes for the V˙O₂-work-rate relationship above the LAT indicated severe impairment of the circulatory response to exercise in patients with PPH. The ventilatory abnormalities in PPH suggested that the lung had become an inefficient gas exchange organ because of impaired perfusion of the ventilated lung. Accepted: 17 April 2000     

Carbohydrate ingestion does not influence the change in energy cost during a 2-h run in well-trained triathletes

The aim of this study was to examine whether the increase in the energy cost of running (C_r), previously reported to occur at the end of a prolonged run, could be influenced by the ingestion of either an artificially sweetened placebo (Pl) or a 5.5% carbohydrate (CHO) solution. Ten well-trained triathletes completed three testing sessions within a 3-week period. The aim of the first session was to determine maximal oxygen uptake (V˙O_{2 max}) and the velocity associated with ventilatory threshold (ν_VT). The second and the third sessions were composed of two submaximal treadmill runs (20 min long, 0% grade, performed at ν_VT), before and after an 80-min overground run, also conducted at ν_VT. During these submaximal tests, the subjects ingested (in a random order) either a Pl or CHO solution prior to the first submaximal run and every 20 min after that. During the first session, ventilatory threshold (VT) occurred at [mean (SD)] 81.2 (2.5)% V˙O_{2 max} and 16.5 (0.6) km · h⁻¹. A significant effect of exercise duration was found on C_r (ΔC_r) at the end of the run, whatever the solution ingested (ΔC_r= 5.7% and 7.01% for CHO and Pl, respectively). A reduction in the respiratory exchange ratio (from 0.98 to 0.90) was observed only at the end of the Pl trial. In this study, C_r seems to be affected only to a minor extent by substrate turnover. Moreover, the increase in the demand for oxygen, estimated from the increase in ventilation, accounted for only a minor proportion of the increase in C_r (11% and 17% for CHO and Pl, respectively). No correlation was found between the changes in C_r and the changes in the other physiological parameters recorded. These results suggest, indirectly, that C_r increases during a 2-h run at 80% V˙O_{2 max} in well-trained subjects can be explained mainly by alterations in neuromuscular performance, which lead to a decrease in muscle efficiency. Accepted: 29 June 1999     

Creatine supplementation alters the response to a graded cycle ergometer test

To determine the effects of creatine supplementation on cardiorespiratory responses during a graded exercise test (GXT) 36 trained adults (20 male, 16 female; 21–27 years old) performed two maximal GXTs on a cycle ergometer. The first GXT was done in a non-supplemented condition, and the second GXT was done following 7 days of ingesting either 5 g creatine monohydrate, encased in gelatin capsules, four times daily (CS, 13 male, 6 female), or the same number of glucose capsules (PL, 7 male, 10 female). CS significantly (P < 0.05) improved total test time [pre-CS=1217 (240) s, mean (std. dev.) versus post-CS=1289 (215) s], while PL administration had no effect (P > 0.05) on total test time [pre-PL=1037 (181) s versus post-PL=1047 (172) s]. In addition, both oxygen consumption (V˙ _O2) and heart rate at the end of each of the first five GXT stages were significantly lower after CS, but were unchanged after PL. Moreover, the ventilatory threshold occurred at a significantly greater V˙ _O2 for CS [pre-CS=2.2 (0.4) l · min⁻¹ or 66% of peak V˙ _O2 versus post-CS=2.6 (0.5) l · min⁻¹ or 78% of peak V˙ _O2; pre-PL=2.6 (0.9) l · min⁻¹ or 70% peak V˙ _O2 versus post-PL=2.6 (1.1) l · min⁻¹ or 68% of peak V˙ _O2]. Neither CS nor PL had an effect on peak V˙ _O2 [pre-CS=3.4 (0.7) l · min⁻¹ versus post-CS=3.3 (0.7) l · min⁻¹; pre-PL=3.7 (1.1) l · min⁻¹ versus post-PL=3.7 (1.1) l · min⁻¹]. Apparently, CS can alter the contributions of the different metabolic systems during the initial stages of a GXT. Thus, the body is able to perform the sub-maximal workloads at a lower oxygen cost with a concomitant reduction in the work performed by the cardiovascular system. Accepted: 20 April 2000     

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