Oxygen uptake kinetics measured at the onset of comfortable self-paced walking in elderly women after hip fracture

The objectives of this study were to (1) evaluate the suitability of “comfortable” self-paced walking as a mode of exercise to study VO₂ kinetics, and (2) to investigate VO₂ kinetics after hip fracture using self-paced walking as the exercise mode. The study took place in a Scottish rehabilitation hospital physiotherapy gymnasium [hip fracture (HF) group] and a Scottish University Gymnasium [young (Y) and healthy elderly (HE) groups]. Fifteen women after HF (median age 81 years) and five Y and five older HE women (median ages 22 and 78 years, respectively) took part in the study. Volunteers completed three repeats of 3 min of “comfortable” self-paced walking on two occasions. The ensemble averaged VO₂ response from walks 2 and 3 on visits 1 and 2 were combined and characterised using nonlinear regression techniques to derive a Mean Response Time (MRT). Self-paced walking was described as “constant-load” exercise (coefficient of variation of lap speeds of ≤6%) in 13 of 15 cases in the HF group on at least one visit (100% of cases in Y and HE groups). Steady-state VO₂ was achieved in 3 min in 8 of HF group on Visit 1 and 10 on Visit 2 (100% of cases in Y and HE groups). MRTs for the HF group (51 s, N = 5, 4 repeats; N = 7, 2 repeats) were significantly higher than the Y and HE groups [Y group 22 s (N = 5, 4 repeats); HE group 36 s (N = 5, 4 repeats)]. Self-paced walking provided a suitable mode of exercise to investigate VO₂ kinetics in frail older women after HF and permitted the first characterisation of VO₂ kinetics in this patient group. This test provides a promising methodology to evaluate rehabilitation efforts in frail individuals.     

Increased strength and decreased flexibility are related to reduced oxygen cost of walking

Purpose was determine effects resistance training/weight loss induced changes in muscular strength and flexibility have on net walking oxygen uptake (netVO₂). Sixty-seven premenopausal women lost 12 kg. Before weight loss subjects were assigned to diet (WL) or diet/3 days per week resistance training (WLRT). Resting energy expenditure, oxygen uptake while walking at 4.84 km h⁻¹ on the flat and up 2.5% grade, isometric knee extension strength, and flexibility of the knee extensors and plantar flexors were measured. Strength increased in WLRT (+36 N) but not in WL (−24 N). NetVO₂ decreased significantly while flat walking (7.3%) and 2.5% grade walking (5.7%) in WLRT, but not in WL. Delta strength was negatively while delta knee extensor and plantar flexor flexibility were positively related to delta netVO₂. Decreases in walking and grade netVO₂ were independently and positively related to increased knee extension strength and decreased knee extensor and plantar flexor flexibility.     

Effect of trunk load on the energy expenditure of treadmill walking and ergometer cycling

Summary Data concerning the effect of trunk loads on the energy expenditure of various activities are scanty and partly conflicting.The energy expenditure of walking (4.5 km hr^–1, 1.5% inclination) and ergometer cycling (60 watt, 60 rpm) was measured in 23 apparently healthy subjects with and without a trunk load of 10% of the body weight. For walking, the increment in energy expenditure per kg of load was 2.55±0.25 watt, while the increment per kg of body weight was 4.01±0.45 watt. For ergometer cycling, the increment per kg of load was 1.12±0.64 while that per kg of body weight was 2.73±0.56 watt.Prediction of energy expenditure for trunk loads has previously been made on the basis of the relation between energy expenditure and body weight. Our data show that this may lead to considerable overestimation.This work was supported by grants from the Danish Medical Research Council and the Danish Natural Science Research Council     

Gender differences during treadmill walking with graded loads: biomechanical and physiological comparisons

In this study, we compared the biomechanical and physiological responses of healthy men and women during bilateral load carriage while they walked on a treadmill at their self-selected velocity. Eleven men mean (SD) maximal oxygen uptake, [V˙O_{2 max} = 56.0 (7.1) ml · kg⁻¹ · min⁻¹] and 11 women [V˙O_{2 max} = 44.6 (7.6) ml · kg⁻¹ · min⁻¹] carried 15-kg and 20-kg loads in random order using a custom-designed load-carriage device. The load supported by each hand was measured by placing strain gauges in each handle of the device. The load supported by the body was calculated as the difference between the load carried and that supported by each hand. Physiological measurements were recorded using standard procedures, and cardiac output was measured by carbon dioxide rebreathing while standing, walking, and during load carriage. Three-way analysis of variance (gender by load by test phase) indicated no significant (P > 0.05) three-way interaction, implying that the overall trend in these responses was similar in men and women. A-priori Scheffe multiple comparisons revealed the following significant (P < 0.05) gender differences during load carriage: (1) women supported a lower proportion of the load with the hands and transferred a greater amount to the body by resting the load against the chest, (2) the oxygen uptake increased by a greater amount in the women compared with men and exceeded the ventilatory threshold during the 20-kg walk in women, and (3) the cardiovascular stress, as indicated by the percentage of maximal heart rate and rate pressure product (product of heart rate and systolic blood pressure), was significantly higher in women compared with men during both of the load-carriage walks. These observations suggest that when carrying absolute loads of 15 kg and 20 kg, women are more susceptible to fatigue and are at a greater risk of cardiovascular complications than men. Accepted: 18 June 1999     

Effects of gradient and load carried on human haemodynamic responses during treadmill walking

This study examined the effects of different loads carried and gradients, on haemodynamic and cardiovascular responses during 45 min of treadmill walking. A group of 20 male endurance-trained athletes [mean maximal oxygen uptake 61.4 (SD 4) ml · kg⁻¹ · min⁻¹] volunteered for this study. The subjects took part in three separate trials. The first involved a backpack weighing 25 kg , the second a 35 kg backpack, and the third trial, unladen, while walking on a treadmill at a speed of 5 km · h⁻¹. The subjects began walking on the treadmill with the randomized load at 0% gradient. After 15 min, the gradient was increased by 5% every 15 min for a total of 45 min. The order of the loads carried was randomized among subjects. No significant differences were noted for all the variables measured attributable to loads between 25 kg and 35 kg. However, significant (P < 0.05) differences were seen for all variables each time the gradient was increased. Cardiac output increased from 11.4 (SD 0.6) l · min⁻¹ at 0% to 13.6 (SD 0.8) l · min⁻¹ at 5% and to 17.6 (SD 1.3) l · min⁻¹ at 10% carrying the 35 kg load. Similarly, lactic acid concentrations in the blood increased from 2.8 (SD 0.2) to 3.1 (SD 0.6) and to 5.3 (SD 1.3) mmol · l⁻¹, respectively. Similar changes were observed for all variables while carrying the 25 kg load. In addition, steady states in oxygen uptake and other physiological variables were obtained throughout the course of the tests. These data suggest that during isodynamic exercise, one of the main factors determining metabolic and haemodynamic responses will be the change in gradient and to a lesser extent, the mass of the load carried. Accepted: 12 May 2000     

Energy cost of running in similarly trained men and women

Summary The energy demand of running on a treadmill was studied in different groups of trained athletes of both sexes. We have not found any significant differences in the net energy cost (C) during running (expressed in J·kg⁻¹·m⁻¹) between similarly trained groups of men and women. For men and women respectively in adult middle distance runnersC=3.57±0.15 and 3.65±0.20, in adult long-distance runnersC=3.63±0.18 and 3.70±0.21, in adult canoeistsC=3.82±0.34 and 3.80±0.24, in young middle-distance runnersC=3.84±0.18 and 3.78±0.26 and in young long-distance runnersC=3.85±0.12 and 3.80±0.24. This similarity may be explained by the similar training states of both sexes, resulting from the intense training which did not differ in its relative intensity and frequency between the groups of men and women. A negative relationship was found between the energy cost of running and maximal oxygen uptake expressed relative to body weight (for menr=−0.471,p<0.001; for womenr=−0.589,p<0.001). In contrast, no significant relationship was found in either sex between the energy cost of running and . We conclude therefore that differences in sports performance between similarly trained men and women are related to differences in . The evaluation ofC as an additional characteristic during laboratory tests may help us to ascertain, along with other parameters, not only the effectiveness of the training procedure, but also to evaluate the technique performed.     

Energy cost of swimming of elite long-distance swimmers

The aim of this study was: (1) to assess the energy cost of swimming (C_s, kJ km^–1) in a group of male (n=5) and female (n=5) elite swimmers specialised in long-distance competitions; (2) to evaluate the possible effect of a 2-km trial on the absolute value of C_s. C_s was assessed during three consecutive 400-m trials covered in a 50-m pool at increasing speeds (v₁, v₂, v₃). After these experiments the subjects swam a 2-km trial at the 10-km race speed (v_2km) after which the three 400-m trials were repeated at the same speed as before (v₅=v₁, v₆=v₂, v₇=v₃). C_s was calculated by dividing the net oxygen uptake at steady state by the corresponding average speed (v, m s^–1). was estimated by using back extrapolation technique from breath-to-breath recorded during the first 30 s of recovery after each test. C_s increased (from 0.69 kJ m^–1 to 1.27 kJ m^–1) as a function of v (from 1.29 m s^–1 to 1.50 m s^–1), its values being comparable to those measured in elite short distance swimmers at similar speeds. In both groups of subjects the speed maintained during the 2-km trial (v_2km) was on the average only 1.2% faster than of v₂ and v₆ (P>0.05), whereas C_s assessed at the end of the 2-km trial (v_2km) turned out to be 21±26% larger than that assessed at v₂ and v₆ (P<0.05); the average stroke frequency (SF, cycles min^–1) during the 2-km trial turned to be about 6% (P<0.05) faster than that assessed at v₂ and v₆. At v₅, C_s turned out to be 19±9% (P<0.05) and 22±27% (0.1<P=0.05) larger than at v₁ in male and female subjects (respectively). SF was significantly faster (P<0.05, in male subjects) and the distance per stroke (Ds=v/SF) significantly shorter (P<0.05) in female subjects at v₅ and v₆ than at v₁ and v₂. These data suggest that the increase of C_s found after the 2-km trial was likely related to a decrease in propelling efficiency, since the latter is related to the distance per stroke.     

Energy cost and energy sources of a ballet dance exercise in female adolescents with different technical ability

This study evaluated energy cost and energy sources of a ballet exercise (grand adage) in young female dancers with different technical ability, and then related the energy sources to the subject’s and anaerobic threshold (IAT). Twenty-five dancers (13–16 years) were divided into two different technical ability groups: low-level (n = 13) and high-level (n = 12). The overall energy requirement of dance exercise (VO_2eq) was obtained by adding the amount of VO₂ during exercise above resting (aerobic source or VO_2ex) to the VO₂ up to the fast component of recovery (anaerobic alactic source or VO_2al) and to the energy equivalent of peak blood lactate accumulation (anaerobic lactic source or ) of recovery. VO_2eq of exercise amounted to 81 ± 10 and 94 ± 9 ml kg⁻¹ in low-level and high-level groups, respectively. VO_2ex represented the higher fraction (65 ± 4% and 77 ± 5%) in low-level and high-level groups, respectively, of VO_2eq in both the groups. In the low-level group the remaining fractions were: 23 ± 2 % for VO_2al and 12 ± 1% for . In high-level group the remaining fractions were: 18 ± 2 % for VO_2al and 4 ± 1% for . Between two groups, significant differences were found in VO_2ex (P < 0.01), (P < 0.01), and VO_2al (P < 0.05). IAT was 55 and 60% of for low-level and high-level dancers, respectively. Low-level dancers performed more exercise above IAT than high-level. For these reasons, it should be better to define exercise intensity according to the IAT parameter and not only to      

The influence of body weight on energy expenditure during walking on a road and on a treadmill

Summary 4 oxygen consumptions were measured on 8 subjects (varying in weight from 54.4–66.1 kg) at each of 3 speeds of walking (3.2, 4.8 and 6.4 km/hr) both on a treadmill and a road. Correlations between weight and oxygen consumption of 0.76–0.96, were significant at the 0.1% level of significance, at all three speeds on both treadmill and road. The relationship between body weight and oxygen consumption is linear and is markedly affected by speed. The slope of the linear regression lines of oxygen consumption on body weight increased hyperbolically with an increase in speed. Mean oxygen consumptions at 3.2 and 4.8 km/hr were significantly higher on the road but not at 6.4 km/hr. Curves of O₂ consumption/speed are non-linear and are markedly affected by body weight; both the intercept on the vertical axis and slope increases linearly with body weight.     

Body mass,temperature and cost of walking in polar bears

Body temperatures and oxygen consumption of three sub-adult polar bears (Ursus maritimus) during treadmill exercise are presented. Comparisons are also made with results from prior studies of polar bear locomotion. The increase in body temperature and the metabolic cost were unexpectedly high, particularly in young animals. An equation describing the cost of locomotion versus body mass shows a negative, and apparently linear relationship. A significant correlation between body temperature and oxygen consumption may permit the use of body temperature telemetry to estimate activity metabolism of free-ranging polar bears.     

The effect of short and long duration exercise on serum erythropoietin concentrations

Summary The effects of short and long duration exercise on serum erythropoietin concentrations [EPO]_s were studied in seven male cross-country skiers of national team standard and eight male marathon runners, respectively. The short duration exercise was performed as 60 min of cycling at an intensity of 80%–95% of maximal heart rate. Arterial blood oxygen saturations monitored by pulse-oximetry remained unchanged throughout exercise. The partial pressure of O₂ at which haemoglobin was half-saturated with O₂ calculated from forearm venous blood gas tension and blood O₂ saturation, and the erythrocyte 2,3-diphosphoglycerate did not change significantly during the exercise. Blood lactate concentrations were increased at the end of exercise [from 1.3 (SEM 0.1) to 3.6 (SEM 0.3) mmol · 1^–1]. The [EPO]_s determined (by enzyme-linked immunosorbent assay) pre-exercise, 5 min, 6 h, 19 h, and 30 h after the exercise were unchanged [from 16.1 (SEM 2.6) to 19.1 (SEM 3.2), 17.9 (SEM 3.0), 17.0 (SEM 2.5), and 18.6 (SEM 2.9) U·l^–1, respectively]. The [EPO]_s were not correlated to the earlier parameters. The long duration exercise consisted of habitual training, a 3 week break from training followed by 2 and 4 weeks of re-training. The [EPO]_s, body fat (BF), and serum free-testosterone concentrations determined at the end of each period remained unchanged. The maximal oxygen uptakes were decreased after the break from training and increased during retraining (P=0.04). Body mass (m _b) increased after the break in training (P=0.02). The [EPO]_s were correlated to BF,r=0.42,P=0.02;m _b,r=0.45,P=0.01; and free-testosterone concentrations,r=0.44,P=0.01. Thus, short and long-duration exercise had no direct influence on [EPO]_s; but relationships among [EPO]_s, free-testosterone concentrations and body composition were noted.     

Energy Expenditure is Affected by Rate of Accumulation of Sleep Deficit in Rats

Study Objectives:

Short sleep is a putative risk factor for obesity. However, prolonged total sleep deprivation (TSD) leads to negative energy balance and weight loss in rodents, whereas sleep-restricted humans tend to gain weight. We hypothesized that energy expenditure (V̇O₂) is influenced by the rate of accumulation of sleep deficit in rats.

Design and Intervention:

Six Sprague-Dawley rats underwent chronic sleep-restriction (CSR, 6-h sleep opportunity at ZT0-6 for 10 days) and stimulus-control protocols (CON, 12-h sleep opportunity for 10 days, matched number of stimuli) in a balanced cross-over design. Four additional rats underwent TSD (4 days). Sleep was manipulated using a motor-driven walking wheel.

Measurements and Results:

Electroencephalography, electromyography, and body temperature were measured by telemetry, and V̇O₂, by respirometry. Total sleep deficits of 55.1 ± 6.4 hours, 31.8 ± 6.8 hours, and 38.2 ± 2.3 hours accumulated over the CSR, CON, and TSD protocols, respectively. Responses to TSD confirmed previous reports of elevated V̇O₂ and body temperature. These responses were attenuated in CSR, despite a greater cumulative sleep deficit. Rate of rise of O₂ was strongly correlated with rate of accumulation of sleep deficit, above a threshold deficit of 3.6 h·day⁻¹.

Conclusion:

The change in V̇O₂ is affected by rate of accumulation of sleep deficit and not the total sleep loss accrued. Negative energy balance, observed during TSD, is strongly attenuated when brief daily sleep opportunities are available to rats (CSR), despite greater accumulated sleep deficit.

Citation:

Caron AM; Stephenson R. Energy expenditure is affected by rate of accumulation of sleep deficit in rats. SLEEP 2010;33(9):1226-1235.     

Physical fitness,fatigue, and quality of life after liver transplantation

Fatigue is often experienced after liver transplantation. The aims of this cross-sectional study were to assess physical fitness (cardiorespiratory fitness, neuromuscular fitness, body composition) in liver transplant recipients and to explore whether physical fitness is related to severity of fatigue. In addition, we explored the relationship between physical fitness and health-related quality of life. Included were 18 patients 1–5 years after transplantation (aged 48.0 ± 11.8 years) with varying severity of fatigue. Peak oxygen uptake during cycle ergometry, 6-min walk distance, isokinetic muscle strength of the knee extensors, body mass index, waist circumference, skinfold thickness, severity of fatigue, and health-related quality of life were measured. Cardiorespiratory fitness in the liver transplant recipients was on average 16–34% lower than normative values (P ≤ 0.05). Furthermore, the prevalence of obesity seemed to be higher than in the general population (17 vs. 10%). We found no deficit in neuromuscular fitness. Cardiorespiratory fitness was the only fitness component that was related with severity of fatigue (r _s = −0.61 to r _s = -0.50, P ≤ 0.05). Particularly cardiorespiratory fitness was related with several aspects of health-related quality of life (r _s = 0.48 to r _s = 0.70, P ≤ 0.05). Results of our study imply that cardiorespiratory fitness and body composition are impaired in liver transplant recipients and that fitness is related with severity of fatigue (only cardiorespiratory fitness) and quality of life (particularly cardiorespiratory fitness) in this group. These findings have implications for the development of rehabilitation programs for liver transplant recipients.     

Influence of training,sex, age and body mass on the energy cost of running

Summary To highlight the influences of age, sex, body mass (m _b) and running training on the energy cost of running (C _r) young basketball players [38 boys (BB) and 14 girls (BG), aged 14.2 (SD 0.3) and 12.2 (SD 1.9) years, respectively] were selected to be compared to middle-distance runners [27 men (MR) and 14 women (FR) aged 23.7 (SD 3.4) and 23.9 (SD 4.1) years, respectively]. TheC _r was measured during a maximal treadmill test. In each groupC _r and body mass (m _b) and body height were negatively and significantly correlated. A stepwise regression showed that among both the body dimensions measured,m _b was the most important factor in determining the variations ofC _r For the whole group (n=93) the correlation coefficient was 0.72 (P<0.0001). For a givenm _b, there was no significant difference between theC _r of BG, BB and MR: this result would support the hypothesis that the differences inC _r currently attributed to age, running training or sex differences are mainly related tom _b. On the other hand, for a givenm _b, FR showed a significantly lower Cr than the basketball players (P<0.01 for BG and BB) and than MR (P<0.05), thus suggesting that women decrease theirC _r as a response to running training more efficiently than do men.     

Oxygen uptake and blood flow of the lower limb in maximal treadmill and bicycle exercise

Summary The present study was undertaken to compare the effects of maximal treadmill and bicycle exercise on maximum oxygen uptake and blood flow in the lower extremity. Mean maximum oxygen uptake in maximal treadmill exercise was higher than that in bicycle exercise (p<0.001). Mean values and standard errors of blood flow measured immediately after maximal treadmill and bicycle exercise in the thigh were 39.1±4.0 and 44.2±2.8 ml/100 ml·min, the difference not being significant. However, a significant difference in blood flow in the calf measured immediately after both types of exercise was observed (p< 0.001). Blood flow in the thigh immediately after bicycle exercise was significantly higher than that in the calf (p<0.001), whereas the difference between thigh and calf in treadmill exercise was small and statistically not significant. Leg blood flow, the average value of blood flow of the thigh and calf added together, was used as an index of blood flow in the lower extremity. It was found that the leg blood flow was significantly higher on the treadmill than with bicycle exercise (p<0.05). From these results, it is suggested that the lower maximum oxygen uptake observed during bicycle exercise as compared with treadmill exercise seems to be due to a lower blood flow in the lower limb.     

Differentiated perceptions of exertion and energy cost of young women while carrying loads

Summary Differentiated local ratings of perceived exertion from the legs and central ratings from the chest, and oxygen consumption, were determined during load carriage in seven young women. Subjects walked for 6 min at 3.22, 4.83, 6.44, or 8.05 km·h^–1 carrying (1) no load, (2) a load equal to 7.5% of body weight (mean: 4.66 kg) or (3) a load equal to 15% of body weight (mean: 9.32 kg). Thus, each subject underwent 12 separate tests. The external loads were in the form of lead pellets carried in a plastic scuba belt worn around the waist. A differentiation threshold was found at 6.44 km·h^–1 for the 0% and 7.5% loads and at 4.83 km·h^–1 for the 15% load. At speeds below the threshold, the perception of exertion was similar in the legs, chest and overall. At higher speeds, exertion was perceived to be more intense in the legs than overall and less intense in the chest than overall, suggesting that the local legs signal was the dominant factor in shaping the overall sensation of exertion. The oxygen uptake was greater for the 15% load than for either the 0% or 7.5% loads, but was similar for the 0% and 7.5% loads. Findings suggested a critical weight limit for external loads that could be transported without increasing the metabolic cost beyond that required to move the body weight alone. This limit fell between 7.5% and 15% of the body weight. When oxygen uptake was expressed per kg of total weight transported, there was no loss of metabolic efficiency while carrying loads up to 15% of the body weight.     

早期使用前置式踝足矫形器脑卒中偏瘫患者的步行能力和速度

背景：脑损伤和脑卒中存活者有相当部分遗留有足下垂内翻畸形,需要借助于踝足矫形器进行治疗。 目的：探讨早期使用前置式踝足矫形器对脑卒中偏瘫患者步行功能的影响及优势。 方法：回顾分析常熟市第二人民医院2008年6月至2009年10月治疗的54例脑卒中偏瘫患者的临床资料,佩戴前置式踝足矫形器为前置组28例和佩戴后置式踝足矫形器为后置组26例。所有患者进行10 m最大步行速度测试,每天观察两组患者步行功能恢复情况。 结果与结论：所有患者在观察期间,无退出及死亡,前置式踝足矫形器组日常生活能力的Barthel指数评分(60.0±12.9)明显高于后置踝足矫形器组日常生活能力的Barthel指数评分(59.1±10.9),但两组间没有显著差异(P > 0.05),在10 m最大步行速度测试中,前置式踝足矫形器组步行速度(39.6±11.6) m/min较后置踝足矫形器组步行速度(33.0±12.4) m/min明显加快(P < 0.05)。说明前置式踝足矫形器更合适用于脑卒中偏瘫患者改善步行速度。     

Different adaptation patterns of antioxidant system in natives and sojourners at high altitude

Comparative studies on the adaptation pattern of antioxidant status among high altitude natives and acclimatized sojourners are very scanty. The aim of the present study was to compare the differences in antioxidant profile between two groups of active male volunteers, i.e. native highlanders (HAN, n = 66) in their natural hypoxic environment with that of sojourners (SOJ, n = 81) from sea level (SL) after 4 weeks of stay at an altitude of 4560 m. Blood samples of SOJ were collected at SL and HA. Same was collected from HAN once at HA. HAN had significantly higher SOD activity and significantly lower catalase, GPX and GR activities than SOJ at HA. Ratio of GSH/GSSG was also significantly higher in HAN than SOJ at HA. In SOJ, antioxidant profile showed an upregulation after HA stay but it was not effective to reduce the levels of oxidative stress markers. Therefore, it can be stated that lifelong exposure to hypoxia has beneficial adaptive effects on antioxidant system in HAN. Similarly, acclimatization to HA also has beneficial preconditioning effects on antioxidant system in SOJ, but, may not be sufficient to ameliorate oxidative stress completely. Transient increase in metabolic rate due to hypoxia may be a causative factor for excess free radical generation among sojourners at HA.     

Energy cost of front-crawl swimming at supra-maximal speeds and underwater torque in young swimmers

The energy cost of front-crawl swimming (C_s, kJ · m⁻¹) at maximal voluntary speeds over distances of 50, 100, 200 and 400 m, and the underwater torque (T′) were assessed in nine young swimmers (three males and six females; 12–17 years old). C_s was calculated from the ratio of the total metabolic energy (E _s, kJ) spent to the distance covered. E _s was estimated as the sum of the energy derived from alactic (AnAl), lactic (AnL) and aerobic (Aer) processes. In turn, AnL was obtained from the net increase of lactate concentration after exercise, AnAl was assumed to amount to 0.393 kJ · kg⁻¹ of body mass, and Aer was estimated from the maximal aerobic power of the subject. Maximal oxygen consumption was calculated by means of the back-extrapolation technique from the oxygen consumption kinetics recorded during recovery after a 400-m maximal trial. Underwater torque (T′, N · m), defined as the product of the force with which the feet of a subject lying horizontally in water tends to sink times the distance from the feet to the center of volume of the lungs, was determined by means of an underwater balance. C_s (kJ · m⁻¹) turned out to be a continuous function of the speed (v, m · s⁻¹) in both males (C_s=0.603 · 10^{0.228 v} , r ²=0.991; n=12) and females (C_s=0.360 · 10^{0.339 v} , r ²=0.919; n=24). A significant relationship was found between T′ and C_s at 1.2 m · s⁻¹; C_s=0.042T′ + 0.594, r=0.839, n=10, P < 0.05. On the contrary, no significant relationships were found between C_s and T′ at faster speeds (1.4 and 1.6 m · s⁻¹). This suggests that T′ is a determinant of C_s only at speeds comparable to that maintained by the subjects over the longest, 400-m distance [mean (SD) 1.20 (0.07) m · s⁻¹]. Accepted: 25 August 2000     

Response to Submaximal and Maximal Exercise at Different Levels of Carboxyhemoglobin

Five subjects performed submaximal and maximal bicycle and maximal treadmill exercise in normalcy and after carbon monoxide inhalation, giving different levels of carboxyhemoglobin (COHb) in the blood. During maximal treadmill exercise work time on a fixed work load and maximal oxygen uptake were decreased with increasing level of COHb (r = 0.79 and r = 0.85, respectively). Peak blood lactate concentration and pulmonary ventilation were unchanged. Highest measured heart rate was lower in parallell with the increased COHb level compared to control studies. During submaximal work heart rate was increased and oxygen uptake was unchanged at the various levels of COHb. At low submaximal work loads blood lactate concentrations and oxygen deficit was unchanged but increased as work load and COHb-level increased.