Higher VO2max Research Articles

Cardiovascular activity during mental stress following vigorous exercise in sportsmen and inactive men

Thirty-six competitive sportsmen and 36 inactive men participated in a two-session experiment. Session 1 involved exercise to exhaustion so as to assess maximal oxygen consumption (VO2 max). In Session 2, both groups were randomized into three experimental conditions: 20 min of exercise at high intensity (70% VO2max) or moderate intensity (50% VO2max) or a light exercise control. Following 30 min of recovery, all subjects performed mental arithmetic and public speech tasks in a counterbalanced order. Cardiovascular, electrodermal, respiratory, and subjective variables were recorded. Sportsmen had higher VO2max, lower body fat, and lower resting heart rate (HR) than inactive men. A postexercise hypotensive response was observed among subjects in the 70% and 50% VO2max conditions, accompanied by baroreceptor reflex inhibition in the 70% condition. Systolic pressure was lower during mental arithmetic and during recovery from the speech task in the high-intensity than in the control group. Diastolic pressure was lower following mental arithmetic in the high-intensity group. No differences in HR reactivity, electrodermal, or respiratory parameters were observed, but baroreceptor reflex sensitivity was inhibited during mental arithmetic. The results are discussed in relation to previous reports of suppressed cardiovascular reactivity to mental stress tests following vigorous exercise and the role of stress-related processes in the antihypertensive response to physical training.

DETERMINANTS OF FIRST & SECOND PHASE INSULIN SECRETION (FPIS, SPIS) IN HEALTHY ADOLESCENTS

Diminished FPIS is proposed to be a metabolic marker in the diagnosis and follow up of prediabetes in trials of intervention to prevent IDDM. However, data are scarce regarding the determinants of insulin secretion in normal children. This study aimed to investigate the relationship of physical fitness (FP) and body composition (BC) to in-vivo insulin secretion during a hyperglycemic clamp in 12 (6M/6F) healthy adolescents (Tanner II-IV). Age was 14.0±0.6 yrs and body mass index (BMI) 19.1±0.5 kg/m2. BC was assessed by bioelectric impedance plethysmography; PF by maximum oxygen consumption (VO2max) during progressive bicycle ergometry; and FPIS (0-10 min) and SPIS (10-120 min) during a 120 min hyperglycemic clamp (+125 mg/dl above fasting plasma glucose). FPIS was 75.1±9.0 μu/ml and SPIS 105.0±9.6 μu/inl. FPIS and SPIS were inversely correlated with VO2max (r=−.60 p=0.02, r=-0.70 p=0.005), with no relationship to BC or % body fat. % body fat showed an inverse relationship (r=−0.53 p-0.04) to insulin sensitivity index. Males had significantly lower % BF, higher VO2max and higher insulin sensitivity compared with females, but no difference in FPIS and SPIS.

Exercise training alters feed efficiency and body composition in iron deficient rats.

Studies of body composition and feed efficiency were conducted on 80 male Sprague-Dawley rats to determine how exercise training alters growth and development in iron deficient animals. Animals were assigned to iron deficient (ID) or control (CN) diets (AIN-76, w/o cellulose), and sedentary (SD) or exercised groups [EX, treadmill running, 4 d.wk-1, 90 min.d-1, 65% maximal oxygen consumption (VO2max), maintained for 6 or 12 wk. The ID diet caused a sustained moderate iron deficiency (Hb 7.2 +/- 0.2 g.dl-1). Iron deficient animals failed to increase maximal oxygen consumption despite the rigorous training program, through training resulted in 25% or 35% higher VO2max in 6- or 12-wk CN rats. At 6 wk, IDEX animals had significantly (33%) lower growth rates than did IDSD animals, which in turn were 22% less than CNs. Overall, exercise did not alter relative amounts of protein in the carcass (% total mass); however, a significant interaction between diet and treatment duration was evident in IDEX animals at 12 wk, who had lower % protein than CNEX-12 or IDSD-6 rats. Training decreased fat 11% in CN at 6 wk but not 12 wk, and 20% in IDs at 12 wk but not 6 wk. Feed efficiency and energy intake were 28% and 12% lower in IDEX animals than CNEX at 6 wk. Training increased caloric intake in CNEX animals but not IDEX animals at 6 and 12 wk. Thus, exercise training exacerbates the poor growth associated with ID through alterations in both food intake and feed efficiency in early phases of training, but adaptation is apparent.

The effects of aerobic fitness on resting metabolic rate

A cross-sectional study was designed to determine the relationship between aerobic fitness and resting metabolic rate (RMR) in 69 males exhibiting a wide range of aerobic fitness levels (VO2max = 32.8-78.1 mL.kg-1.min-1). The results of this study indicated that RMR was not significantly different between trained and untrained individuals when expressed in kJ.kg fat-free weight-1.hr-1 or using an ANCOVA with fat-free weight as the covariate and RMR as the dependent variable (F ratio = 0.353, P less than 0.70). In addition, this study also failed to support a previously suggested hypothesis that an elevated RMR may only be observed in those individuals exhibiting both high VO2max values and currently training a minimum of 12-16 h/wk. Thus, the results of this study strongly suggest that RMR is independent of both a person's current aerobic level and training status.

Chronic exercise and its hemodynamic influences on resting blood pressure of hypertensive rats

Studies with male spontaneously hypertensive rats (SHR) were initiated to determine the hemodynamic relationships associated with the lower resting caudal artery systolic blood pressure (SBP) of endurance-trained SHR populations. After assignment into nontrained (NT, n = 38) and trained (T, n = 38) groups, the T animals were exercised 5 times/wk on a motor-driven treadmill for 12-16 wk at a moderate intensity that ranged from 40 to 70% of their maximum O2 consumption capacity (VO2max). SBP, VO2max, and treadmill run time were determined before the experimental period began and before the animals were instrumented for hemodynamic measurements. At the end of the study, the T rats exhibited significantly lower SBP (NT = 210 +/- 3, T = 200 +/- 3 mmHg) and significantly higher VO2max (NT = 75 +/- 2, T = 83 +/- 2 ml.min-1.kg-1) and run durations (NT = 11.4 +/- 0.4, T = 14.5 +/- 0.3 min). When the animals were anesthetized for insertion of catheters and microprobes for blood pressure and cardiac output (thermodilution) measurements, the T rats had lower values for body mass, heart rate, mean blood pressure, cardiac output, and cardiac index than the NT rats; however, only the body mass and heart rate differences were statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of Obesity and Physical Fitness to Cardiopulmonary and Metabolic Function in Healthy Older Men

The relationship of obesity and physical fitness (VO2max) to cardiopulmonary and metabolic function was examined in 132 healthy obese, nonsmoking men age 45-79. Obese men with higher VO2max had lower % body fat and waist-to-hip ratio (WHR) than obese men with low VO2max. The obese subjects with high WHR (upper body fat distribution) had higher systolic blood pressure, hyperinsulinemia and impaired glucose tolerance, lower high density lipoprotein cholesterol (HDL-C), and higher triglyceride (TG). VO2max (ml/kg FFM.min) was lower in the older men (r = -0.54, p less than .001), and 32% of the variation was accounted for by age and the one-second forced expiratory volume. Although pulmonary function was normal, 50% of the variability was predicted by age, height, and VO2max or WHR. Glucose tolerance and insulin correlated better with VO2max and indices of body composition than with age, while plasma TG and HDL-C correlated with body composition, not VO2max or age. Thus, while age affects the cardiopulmonary and metabolic function of obese older men, physical inactivity, obesity, and an abdominal body fat distribution (increased WHR) contributed significantly to their reductions in physiological function.

Reaction Time Unchanged in Older Women following Aerobic Training

The effect of aerobic exercise on reaction time in older women was investigated. 14 women (M age = 65 yr.) were carefully screened for health status and lifestyle, then assigned to a random order of the exercise and control groups (ns = 7). Pre- and posttraining tests of aerobic capacity, simple reaction time, and choice reaction time were administered. The exercise group rode a stationary bicycle ergometer for 8 consecutive weeks for 3 35- to 40-min. sessions per week. There were no significant pretraining differences between groups on simple reaction time, choice reaction time, or estimated VO2max. No posttraining differences for simple and choice reaction time were found even though the exercise group had a significantly higher VO2max than the controls. Contrary to some other findings, the data indicate that reaction time may be independent of aerobic training in healthy older women.

女子長距離陸上競技選手の最大酸素摂取量 第２報

Six female long distance runners in the vocational society were evaluated in order to determine their maximal oxygen uptake (VO2max). In addition, VO2max of high school student girls were measured. The examination proved that the vocational group have a higher level VO2max than the student group. It proved that there is a definite relationship between VO2max and ability to run 5000m. High grade VO2max does not always ensure better competitive records, but it is beneficial for a long distance runner.

Effect of toeclip use during cycle ergometry on ventilatory threshold and[Vdot]O2max in trained cyclists and runners

The purpose of this study was to investigate the effects of the use of toeclips on the ventilatory threshold (VT) of cyclists and runners during cycle ergometry. Ten competitive cyclists and ten well-trained runners performed two continuous maximal cycle ergometer tests, once with toeclips and once without toeclips. Respiratory data were collected every 20 s and used to determine VT and VO2 max. For cyclists, the mean (congruent to SEM) oxygen uptake at VT (VO2, VT) was greater during the trial with toeclips (48.8 +/- 1.9 ml kg-1 min-1 and 46.9 +/- 1.9 ml kg-1 min-1 during cycle ergometry with and without toeclips, respectively; p less than 0.05). No significant difference in VO2, VT was noted between trials for runners. The cyclists also demonstrated a higher VO2 max during the trial with toeclips (58.8 +/- 3.0 ml kg-1 min-1) compared to the trial without toeclips (54.4 +/- 2.0 ml kg-1 min-1; p less than 0.05). When expressed relative to VO2 max (%VO2 max) the VT during the toeclip trial for cyclists was significantly decreased (p less than 0.05). These data suggest that the cyclists in this study developed specific adaptations related to the use of toeclips, and the use of toeclips during cycle ergometry is therefore recommended. We recommend that future studies report results with VT expressed in both absolute (VO2) and relative (%VO2 max) terms.

Seasonal variation in cold hardiness and peak rates of cold-induced thermogenesis in the Dark-eyed Junco (Junco hyemalis)

-I used helium-oxygen (heliox) gas mixtures (approximately 79.5% He: 20.5% 02) to study seasonal variation in cold resistance and peak rates of thermogenesis (Vo2 max = maximum oxygen consumption maintained over a 10-min period) in Dark-eyed Juncos (Junco hyemalis). Cold tolerance increased markedly in winter-acclimatized juncos. Heliox temperatures required to induce hypothermia within 90 min in more than 50% of the birds tested were 4?C in summer and -9?C in winter. In winter, Vo2 m.. increased significantly on both a per-bird and mass-specific basis. In summer, Vo2mm,, was 5.78 ml 02/min (20.75 ml 02 g-1 h-'), and 7.39 ml 02/min (23.42 ml 02 gh-1) in winter. Vo2m,, exceeded standard metabolic rate by 6.6 times, and by 6.7-7.2 times in winter. Maximal instantaneous oxygen consumption (Vo2 i = maximal 1-min Vo2) under cold stress did not vary seasonally on either a per-bird or mass-specific basis. Mass loss rates during cold stress did not vary seasonally. Winter increases in V02 ma, and cold tolerance characterize metabolic acclimatization in Dark-eyed Juncos. Received 2 May 1989, accepted 29 January 1990. SMALL birds that overwinter in temperate climates show marked seasonal changes in cold tolerance (Hart 1962, Barnett 1970, Pohl and West 1973, Dawson and Carey 1976, Dawson et al. 1983). Seasonal variation in peak rates of cold-induced thermogenesis (Vo2ma., defined here as maximal Vo2 maintained over 10 min) in these birds has received little attention, mostly because of problems associated with generating experimental temperatures low enough to elicit maximum metabolism. High specific heat helium-oxygen gas mixtures (heliox) facilitate heat loss, and induce V02 max at less extreme temperatures (Rosenmann and Morrison 1974). Consequently, heliox gas mixtures have been used to document winter increases in maximal thermogenic capacity in several mammals, including snowshoe hares (Lepus americanus; Feist and Rosenmann 1975), red-backed voles (Clethrionomys rutilus; Rosenmann et al. 1975), and white-footed mice (Peromyscus leucopus; Wickler 1980). In birds, Dawson and Smith (1986) documented an increased Vo2ma in winter-acclimatized American Goldfinches (Carduelis tristis) from Michigan compared with those acclimatized to spring conditions. Higher VO2max in winter may indicate changes in the metabolic machinery involved in thermogenesis that increase thermogenic capacity and enable small birds to prolong cold resistance. However, it remains unclear whether seasonal variation in maximal thermogenic capacity is widespread among small birds wintering in temperate cli-

Endurance running performance in athletes with asthma

Laboratory assessment was made during maximal and submaximal exercise on 16 endurance trained male runners with asthma (aged 35 +/- 9 years) (mean +/- S.D.). Eleven of these asthmatic athletes had recent performance times over a half-marathon, which were examined in light of the results from the laboratory tests. The maximum oxygen uptake (VO2max) of the group was 61.8 +/- 6.3 ml kg-1 min-1 and the maximum ventilation (VEmax) was 138.7 +/- 24.7 l min-1. These maximum cardio-respiratory responses to exercise were positively correlated to the degree of airflow obstruction, defined as the forced expiratory volume in 1 s (expressed as a percentage of predicted normal). The half-marathon performance times of 11 of the athletes ranged from those of recreational to elite runners (82.4 +/- 8.8 min, range 69-94). Race pace was correlated with VO2max (r = 0.863, P less than 0.01) but the highest correlation was with the running velocity at a blood lactate concentration of 2 mmol l-1 (r = 0.971, P less than 0.01). The asthmatic athletes utilized 82 +/- 4% VO2max during the half-marathon, which was correlated with the %VO2max at 2 mmol l-1 blood lactate (r = 0.817, P less than 0.01). The results of this study suggest that athletes with mild to moderate asthma can possess high VO2max values and can develop a high degree of endurance fitness, as defined by their ability to sustain a high percentage of VO2max over an endurance race. In athletes with more severe airflow obstruction, the maximum ventilation rate may be reduced and so VO2max may be impaired. The athletes in the present study have adapted to this limitation by being able to sustain a higher %VO2max before the accumulation of blood lactate, which is an advantage during an endurance race. Therefore, with appropriate training and medication, asthmatics can successfully participate in endurance running at a competitive level.

82 METABOLIC RESPONSES OF DEEP AND SHALLOW WATER RUNNING IN TRAINED RUNNERS

The purpose of this study was to compare the maximal metabolic responses of competitive runners during treadmill running (TMR), deep water running (DWR), and shallow water running (SWR). Seven male and two female members of the Wheaton College varsity cross country team served as subjects. Maximal measures included oxygen consumption (VO2max), respiratory exchange ratio (RER), heart rate (HRmax), and lactic acid (HLA). Repeated-measures ANOVA revealed treadmill running to elicit higher VO2max and HRmax than both water tests (P less than 0.05). VO2max was also greater for SWR than for DWR (P less than 0.05). VO2max values for SWR and DWR were 90.3% and 73.5% of TMR, respectively. HRmax for SWR and DWR were 88.6% and 86% of TMR, respectively. RER and HLA did not differ among tests. These data suggest that shallow water running is capable of eliciting metabolic responses comparable to treadmill running. Shallow water running elicits higher metabolic responses than deep water running.

Dissociation of maximal O2 uptake from O2 delivery in canine gastrocnemius in situ.

To test the hypothesis that maximal O2 uptake (VO2max) can be limited by O2 diffusion in the peripheral tissue, we kept O2 delivery [blood flow X arterial O2 content (CaO2)] to maximally contracting muscle equal between 1) low flow-high CaO2 and 2) high flow-low CaO2 conditions. The hypothesis predicts, because of differences in the capillary PO2 profile, that the former condition will result in both a higher VO2max and muscle effluent venous PO2 (PVO2). We studied the relations among VO2max, PVO2, and O2 delivery during maximal isometric contractions in isolated, in situ dog gastrocnemius muscle (n = 6) during these two conditions. O2 delivery was matched by varying arterial O2 partial pressure and adjusting flow to the muscle accordingly. A total of 18 matched O2 delivery pairs were obtained. As planned, O2 delivery was not significantly different between the two treatments. In contrast, VO2max was significantly higher [10.4 +/- 0.5 (SE) ml.100 g-1.min-1; P = 0.01], as was PVO2 (25 +/- 1 Torr; P less than 0.01) in the low flow-high CaO2 treatment compared with the high flow-low CaO2 treatment (9.1 +/- 0.4 ml.100 g-1.min-1 and 20 +/- 1 Torr, respectively). The rate of fatigue was greater in the high flow-low CaO2 condition, as was lactate output from the muscle and muscle lactate concentration. The results of this study show that VO2max is not uniquely dependent on O2 delivery and support the hypothesis that VO2max can be limited by peripheral tissue O2 diffusion.

Total muscle mitochondrial volume in relation to aerobic capacity of horses and steers.

The relationship between maximal oxygen consumption rate (VO2max) and mitochondrial content of skeletal muscles was examined in horses and steers (n = 3 each). Samples of the heart left ventricle, diaphragm, m. vastus medialis, m. semitendinosus, m. cutaneous thoracicus and m. masseter, as well as samples of muscles collected in a whole-body sampling procedure, were analyzed by electron microscopy. VO2max per kilogram body mass was 2.7 x greater in horses than steers. This higher VO2max was in proportion to the higher total volume of mitochondria in horse versus steer muscle when analyzed from the whole-body samples and from the locomotor muscle samples. In non-locomotor muscles, total mitochondrial volume was greater in horses than steers, but not in proportion to their differences in VO2max. The VO2max of the mitochondria was estimated to be close to 4.5 ml O2.ml-1 mitochondria in both species. It is concluded that in a comparison of a highly aerobic to a less aerobic mammalian species of similar body size, a higher oxidative potential may be found in all muscles of the more aerobic species. This greater oxidative potential is achieved by a greater total volume of skeletal muscle mitochondria.

Altitudinal and seasonal effects on aerobic metabolism of deer mice.

I compared the maximal aerobic metabolic rates (VO2max), field metabolic rates (FMR), aerobic reserves (VO2max-FMR), and basal metabolic rates (BMR) of wild and recently captured deer mice from low (440 m) and high (3800 m) altitudes. To separate the effects of the thermal environment from other altitudinal effects, I examined mice from different altitudes, but similar thermal environments (i.e., summer mice from high altitude and winter mice from low altitude). When the thermal environment was similar, VO2max, FMR, and aerobic reserve of low and high altitude mice did not differ, but BMR was significantly higher at high altitude. Thus, in the absence of thermal differences, altitude had only minor effects on the aerobic metabolism of wild or recently captured deer mice. At low altitude, there was significant seasonal variation in VO2max, FMR, and aerobic reserve, but not BMR. BMR was correlated with VO2max, but not with FMR. The significant positive correlation of BMR with VO2max indicates a cost of high VO2max, because higher BMR increases food requirements and energy use during periods of thermoneutral conditions.

Cardio-respiratory fitness of young and older active and sedentary men.

Physiological profiles are described for 30 healthy young (20-31 years) and 30 healthy older (50-62 years) men. Half of the individuals in each group reported that during the previous five years they participated frequently in strenuous physical exercises; the other half reported sedentary lifestyles. A treadmill exercise test was used to determine maximal aerobic power (VO2 max). Heart rate and blood pressure were measured during rest, maximal exercise and recovery. The active older men demonstrated significantly lower resting heart rates, lower resting systolic and diastolic blood pressures, higher VO2 max, lower maximal exercise diastolic blood pressure and lower recovery heart rates than the age-matched sedentary men. Compared with the young sedentary men, the older active men had lower resting heart rates and higher VO2 max, walked longer on the treadmill, had lower recovery heart rates and weighed less. Older active men also had higher VO2 max levels than young sedentary men. In summary, physiological profiles of the older active men more closely resembled profiles of active men who were 30 years younger than those of older sedentary men. These results emphasize the range of benefits associated with exercise.

Physiology of Alpine skiing.

Physiological profiles of elite Alpine skiers reveal the importance of muscular strength, anaerobic power, anaerobic endurance, aerobic endurance, coordination, agility, balance, and flexibility. On-hill snow training and dryland training programmes should focus on the elevation of these fitness components. Physical characteristics of elite skiers reveal an average height and body mass. Today, successful skiers are taller and heavier than their predecessors. Slalom skiers tend to be leaner than skiers in other events while the downhill racers are the heaviest. Elite skiers have strong legs when peak torque is measured during isometric and isokinetic conditions involving knee extension, which may be a specific adaptation since the skier is in a crouched position for a prolonged period when racing. Leg strength correlates significantly with performance in the downhill and giant slalom events. The glycolytic contribution in the slalom and giant slalom events is about 40% of the total energy cost. Following a race, blood lactate concentration averages 9 to 13 mmol/L. A muscle lactate concentration of 24 mmol/kg wet muscle tissue has been reported. Elite skiers have higher lactate values than advanced or novice skiers. The aerobic demands of competitive Alpine skiing may approach (90 to 95%) of the athlete's maximal aerobic power. Maximal heart rate is achieved during the latter part of the race. Elite skiers have a high VO2max. This may reflect their training programme and not the actual demands of the sport. When turning, muscular activity acts to impede blood flow and oxygen delivery. As a consequence, anaerobic metabolism is increased. Glycogen studies show significant utilisation from both slow and fast twitch muscle fibres. Skilled and unskilled skiers differ with respect to glycogen utilisation. Skilled skiers have greater glycogen depletion in the slow twitch fibres compared to unskilled skiers. Muscle glycogen decreases by about 32 mmol/kg wet muscle tissue following a day of ski training. Glycogen depletion may contribute to the injury pattern which peaks toward the end of the ski day. The risk of injury has been estimated at 17 injuries per 1000 skier days. When the severity criterion was an injury causing the skier to miss 3 days of skiing or visit a physician, the risk was 2 injuries per 1000 skier-days.(ABSTRACT TRUNCATED AT 400 WORDS)

Characteristics and performance of male citizen cross-country ski racers.

Forty-three male citizen or recreational cross-country (X-C) ski racers (aged 31 +/- 4.4 years) were tested to determine their weight (BW) and percent body fat (BF), maximal oxygen uptake (VO2max), quadriceps (Quad), hamstrings (Ham) and upper body (UBS) isokinetic strength (60 degrees, 180 degrees, 240 degrees/s), and Quad endurance. In addition, skiers filled out a questionnaire to determine their skiing experience and to see what other activities they participated in. All these variables were run through a stepwise regression procedure to see which characteristics best predicted performance in a 10 km X-C ski race. The relatively high VO2max of 56.6 ml O2/kg/min and low BF of 10.1% indicate this group to be a very fit subset of the general population. All the skiers were active in other sports on a year-round basis. Of the variables studied, UBS, VO2max, and Quad strength were all significant determinants of 10 km race performance, yielding a multiple R of 0.78. Quad endurance, Ham strength, BW, BF, and experience did not significantly contribute toward the prediction of performance. It is felt that a proper training program for the citizen X-C skier should strive to maximize upper body strength as well as one's aerobic capacity.

Physical fitness and other individual factors relating to the shiftwork tolerance of women.

Maximal oxygen consumption (VO2max), muscle strength (MS) and physical activity were compared to age, shiftwork experience, morningness, personality traits and social factors intervening in the shiftwork tolerance of 128 women. The subjects were nurses and nursing aids working irregular shifts in a hospital. Neuroticism was the most powerful negative factor connected to higher fatigue and various symptoms of the subjects. High VO2max and good MS were, on the other hand, the most important positive factors connected to lower fatigue and musculoskeletal symptoms and better sleep quality of the subjects. In different shifts, fatigue, sleep length and quality were influenced most by morningness. It is concluded that physical fitness is an important individual factor explaining the variations of shiftwork tolerance in women.

Cardiovascular and respiratory responses in Thoroughbred horses during treadmill exercise.

Six detrained Thoroughbred horses performed incremental treadmill tests. Maximal oxygen uptake (VO2max) was measured during exercise by analysis of expired gas. The relationships between oxygen consumption (VO2) and work rate, heart rate (HR), cardiac output (Q), stroke volume (SV) and arteriovenous oxygen content difference [C(a-v)O2] were examined during submaximal and maximal exercise. The relative contributions of blood flow and extraction of oxygen from muscle capillaries were assessed during exercise at VO2max. Mean VO2max was 129.7 +/- 2.9 (mean +/- S.E.M.) ml kg-1 min-1, which occurred at a mean speed of 8.0 ms-1, with the treadmill set at a slope of 10%. At VO2max the mean HR was 222 +/- 7 beats min-1. Maximal Q was 534 +/- 22 ml kg-1 min-1 and mean SV was 2.4 +/- 0.1 ml kg-1. Mean C(a-v)O2 was 24.5 +/- 1.2 ml 100 ml-1 blood. Linear relationships were found between VO2 and work rate, HR, Q and C(a-v)O2. Stroke volume did not increase significantly during exercise. Increasing metabolic rate during exercise was associated with linear increases in arterial haemoglobin concentration and oxygen content, and decreases in arterial oxygen partial pressures and haemoglobin saturation. We conclude that the relatively high VO2max in the detrained Thoroughbred racehorse is dependent on the generation of a large C(a-v)O2, despite development of hypoxaemia and haemoglobin desaturation, during strenuous exercise.