Oxygen uptake during swimming in a hypobaric hypoxic environment

Summary The purpose of this study was to determine oxygen uptake O₂) at various water flow rates and maximal oxygen uptake ( O_2max) during swimming in a hypobaric hypoxic environment. Seven trained swimmers swam in normal [N; 751 mmHg (100.1 kPa)] and hypobaric hypoxic [H; 601 mmHg (80.27 kPa)] environments in a chamber where atmospheric pressure could be regulated. Water flow rate started at 0.80 m · s^–1 and was increased by 0.05 m· s^–1 every 2 min up to 1.00 m · s^–1 and then by 0.05 m · s^–1 every minute until exhaustion. At submaximal water flow rates, carbon dioxide production ( CO₂), pulmonary ventilation ( _E) and tidal volume (V _T) were significantly greater in H than in N. There were no significant differences in the response of submaximal O₂, heart rate (f _c) or respiratory frequency (f _R) between N and H. Maximal _E,f _R,V _T,f _c blood lactate concentration and water flow rate were not significantly different between N and H. However, VO_2max under H [3.65 (SD 0.11) l · min^–1] was significantly lower by 12.0% (SD 3.4) % than that in N [4.15 (SD 0.18) l · min^–1] . This decrease agrees well with previous investigations that have studied centrally limited exercise, such as running and cycling, under similar levels of hypoxia.     

Independence of ventilation and blood lactate responses during graded exercise

The effect of power output increment, based on an increase in pedal rate, on blood lactate accumulation during graded exercise is unknown. Therefore, in the present study, we examined the effect of two different rates of power output increments employing two pedal rates on pulmonary ventilation and blood lactate responses during graded cycle ergometry in young men. Males (n=8) with an mean (SD) peak oxygen uptake of 4.2 (0.1) 1·min^–1 served as subjects. Each subject performed two graded cycle ergometer tests. The first test, conducted at 60 rev· min^–1, employed 4 min of unloaded pedaling followed by a standard power output step increment (SI) of 60 W every 3rd min. The second test, conducted at 90 rev·min^–1, employed 4 min of unloaded pedaling followed by a high power output step increment (HI) of 90 W every 3rd min. Venous blood was sampled from a forearm vein after 5 min of seated rest, 4 min of unloaded pedaling, and every 3rd min of graded exercise. Peak exercise values for heart rate, oxygen uptake ( O₂), and ventilation ( _E) were similar (P > 0.05) for SI and HI exercise, as was the relationship between _E and O₂, and between _E and carbon dioxide production ( CO₂). However, the relationship between blood lactate concentration and O₂ was dissimilar between SI and HI exercise with blood lactate accumulation beyond the lowest ventilatory equivalent of oxygen, and peak exercise blood lactate concentration values significantly higher (P < 0.05) for SI [12.8 (2.6) mmol·l^–1] compared to HI [8.0(1.9) mmol·l^–1] exercise. Our findings demonstrate that blood lactate accumulation and _E during graded exercise are dissociated. Blood lactate accumulation is influenced by the rate of external power output increment, while _E is related to O₂ and CO₂.     

Relationships of the anaerobic threshold with the 5 km, 10 km,and 10 mile races

Summary The purpose of present study was to assess the relationship between anaerobic threshold (AT) and performances in three different distance races (i.e., 5 km, 10 km, and 10 mile). AT, O₂ max, and related parameters for 17 young endurance runners aged 16–18 years tested on a treadmill with a discontinuous method. The determination of AT was based upon both gas exchange and blood lactate methods. Performances in the distance races were measured within nearly the same month as the time of experiment. Mean AT- O₂ was 51.0 ml·kg^–1·min^–1 (2.837 l·min^–1), while O₂ max averaged 64.1 ml·kg^–1·min^–1 (3.568 l·min^–1). AT-HR and %AT (AT- O₂/ O₂ max) were 174.7 beats·min^–1 and 79.6%, respectively. The correlations between O₂ max (ml·kg^–1·min^–1) and performances in the three distance races were not high (r=–0.645, r=–0.674, r=–0.574), while those between AT- O₂ and performances was r=–0.945, r=–0.839, and r=–0.835, respectively. The latter results indicate that AT- O₂ alone would account for 83.9%, 70.4%, and 69.7% of the variance in the 5 km, 10 km, and 10 mile performances, respectively. Since r=–0.945 (5 km versus AT- O₂) is significantly different from r=–0.645 (5 km versus O₂ max), the 5 km performance appears to be more related to AT- O₂ than VO₂ max. It is concluded that individual variance in the middle and long distance races (particularly the 5 km race) is better accounted for by the variance in AT- O₂ expressed as milliliters of oxygen per kilogram of body weight than by differences in O₂ max.     

Responses of subjects with spinal cord injuries to maximal wheelchair exercise: comparison of discontinuous and continuous protocols

Summary Six male subjects with spinal cord injuries (SCI) participated in this investigation to compare peak values of oxygen uptake ( O₂). heart rate (f _c), ventilation ( _E), respiratory exchange ratio (R) and power output (W) obtained using a discontinuous (DP) and a continuous jump max protocol (JMP) in a maximal wheelchair exercise test on a treadmill. The W increments were achieved by imposing an extra mass upon the wheelchair through a pulley system. The DP involved exercise periods of 3 min separated by 2-min intervals at relative rest. Increments in W consisted of 0.10 or 0.15 W · kg^–1 total mass. During the rest intervals no mass was imposed on the wheelchair. The JMP involved an increase in W each minute. Increments and velocity in the JMP were the same as during the exercise periods for DP. Mean peak values for W [99.5 (SD 13.6) W], O₂ [2.13 (SD 0.27) l · min^–1, standard temperature and pressure, dry], R [1.25 (SD 0.16)] and _E [82.8 (SD 11.2) l · min^–1, body temperature and pressure, saturated] in DP were not different from values observed for W [103.5 (SD 13.1)], O₂ [2.18 (SD 0.31) l · min^–1], R [1.17 (SD 0.16)] and _E [78.9 (SD 16.0) l · min^–1] in the JMP. The only significant difference was observed for f _c: 198 (SD 11) beats · min^–1 in DP and 187 (SD 11) beats · min^–1 in JMP. The higher values for f _c elicited using DP have been discussed. It was concluded that both a DP and a JMP seem to be equally appropriate in determining peak O₂ and peak W in SCI persons. In terms of time saving, JMP would seem to be a more favourable protocol.     

Submaximal working capacity,heart size and body size in boys 8–18 years

Heart diameters, heart volume (HV), PWC ₁₃₀, O₂ at 130 heart rate, and cardiorespiratory reactions during work at 3 kgm·s^–1 were obtained in 237 boys ranging in age from 8–18 years. Results indicate that heart size, PWC ₁₃₀, O₁₃₀, and exercise HR, O₂/HR, and SBP change significantly with age. On the other hand, HV·kg^–1 and work O₂, _E and _E/ O₂ remain rather stable throughout the growth period.Correlation analysis indicates that about 85% of the observed variation in the size of the heart during growth can be accounted for by body weight, while about 70% of the variation in light submaximal working capacity ( O₁₃₀) can be explained by HV alone. Holding age, height and body weight constant by partial correlation procedures yields significant relationships between HV and O₁₃₀ (r = 0.461), and between HV·kg^–1 and O₁₃₀ (r = 0.414). Age, height, weight and size of the heart correlated simultaneously against O₁₃₀ account for 75% of the variance in the dependent variable.It would seem important to suggest the need for study of the interactions between age, size and maturity, in addition to indicators of size and efficiency of the oxygen delivery system, and indices of muscle oxygen utilization efficiency. Such an approach will permit a more definite partitioning of the variance in submaximal aerobic capacity during growth, and would probably yield a more conservative estimate of the relationship between the size of the heart and submaximal working capacity during growth.Abbreviations used HV heart volume - HV·kg^–1 heart volume per kg of body weight - PWC ₁₃₀ physical working capacity in kgm·s^–1 of work at a heart rate of 130·min^–1 - O₁₃₀ oxygen consumption per min at a heart rate of 130·min^–1 - O₂, , _E, _E/ O₂, HR, O₂/HR, SBP oxygen consumption, breathing frequency, expiratory volume, respiratory equivalent, heart rate, oxygen pulse, systolic blood pressure in the third minute of work at 3 kgm·s^–1 - CA chronological age Partially supported by grants from the Kuratorium für die Sportmedizinische Forschung, Federal Republic of Germany and Laval University, Quebec, Canada     

Cardiovascular responses to facial cooling during low and moderate intensity exercise

Summary To investigate the hypothesis that facial cooling (FC) exerts a greater influence on the cardiovascular system at lower versus higher levels of exercise, this study examined the effect of facial cooling [mean (SE): 0 (2)°C at 0.8 m·s^–1 wind velocity] during 30 min low [35% maximum oxygen consumption ( O_2max)] and moderate (70% O_2max) levels of cycle ergometry in the supine position. Five male subjects were assigned in random order to four exercise conditions: (1) FC at 35% O_2max(FC35), (2) no cooling (NFC35), (3) FC at 70% O_2max(FC70), and (4) no cooling (NFC70). Heart rate (f _c), stroke volume (V _s), and cardiac output ( _c) were measured at rest and every 10 min of exercise using impedance cardiography. During FC35, the change in f _c [mean (SE)] was significantly lower (P < 0.05) than NFC35 at 10 [22 (5) vs 31 (3) beats· min^–1], 20 [29 (6) vs 35 (3) beats·min^–1], and 30 [29 (5) vs 38 (4) beats·min^–1] min. No differences in f _c were observed between FC70 and NFC70. Furthermore, FC had no effect on V _s or _cat either exercise intensity. However, when comparing the FC70 and NFC70 conditions, there was a significant main effect (P<0.05) in mean arterial pressure (P _a) response with cooling despite the fact that neither V _s or _cwere different from the NFC70 control. The increase (P < 0.05) in the estimated change in systemic vascular resistance ( _a· _c ^–1) could partly explain the relative rise in _aat FC70. No pressor effect of cooling was observed at 35% O_2max. The results suggest that the FC condition promotes exercise bradycardia at low levels of exercise and exerts a greater pressor response during moderate exercise.     

Oxygen uptake during running as related to body mass in circumpubertal boys: a longitudinal study

Summary To investigate the effect of endurance training on physiological characteristics during circumpubertal growth, eight young runners (mean starting age 12 years) were studied every 6 months for 8 years. Four other boys served as untrained controls. Oxygen uptake ( O ₂) and blood lactate concentrations were measured during submaximal and maximal treadmill running. The data were aligned with each individual's age of peak height velocity. The maximal oxygen uptake ( O _2max; ml · kg^–1 · min^–1) decreased with growth in the untrained group but remained almost constant in the training group. The oxygen cost of running at 15 km · h^–1 ( O ₂₁₅, ml · kg^–1 · min^–1) was persistently lower in the trained group but decreased similarly with age in both groups. The development of O _2max and O ₂₁₅ (1 · min^–1) was related to each individual's increase in body mass so that power functions were obtained. The mean body mass scaling factor was 0.78 (SEM 0.07) and 1.01 (SEM 0.04) for O _2max and 0.75 (SEM 0.09) and 0.75 (SEM 0.02) for O ₂₁₅ in the untrained and trained groups, respectively. Therefore, expressed as ml · kg^–0.75 · min^–1, O ₂₁₅ was unchanged in both groups and O _2max increased only in the trained group. The running velocity corresponding to 4 mmol · 1^–1 of blood lactate ( _la4) increased only in the trained group. Blood lactate concentration at exhaustion remained constant in both groups over the years studied. In conclusion, recent and the present findings would suggest that changes in the oxygen cost of running and O _2max (ml · kg^–1 · min^–1) during growth may mainly be due to an overestimation of the body mass dependency of O ₀₂ during running. The O ₂ determined during treadmill running may be better related to kg^0.75 than to kg¹.     

Cardiopulmonary adjustment and metabolic response to maximal and submaximal physical exercise of boys and girls at different stages of maturity

Summary Cardiopulmonary and metabolic variables were investigated at maximal and submaximal bicycle ergometer exercises in 41 swimmers of both sexes, 8–18 years old. O₂ max and O₂ max·HR^–1 were higher in boys than in girls and increased with maturity, while O₂ max·kg^–1 and HVE were not influenced by this. The HV increased clearly during this growth period, the pubertal and postpubertal subjects showing 16 and 17% higher values for HV and HV·kg^–1 than those reported in normal schoolchildren populations. During the submaximal exercise at 70% O₂ max the highest HR values were found in the prepubertal group, whilst the lowest were observed in the postpubertal subjects. These findings suggest that a given percentage of O₂ max as a reference unit, is more reliable than a certain HR to obtain comparable results in subjects with different ages.Blood samples were collected before, during, and after the submaximal exercise. Blood glucose and FFA did not differ in relation to the stages of maturity. During exercise, insulin decreased in prepubertal children, did not alter in pubertal adolescents, and increased in postpubertal subjects. The lactate concentration, during exercise, increased in relation to maturity. The same results were found for HGH, but no differences were found with regard to sex. Since the pattern of HGH secretion during exercise is similar to that found after arginine and insulin administration it is assumed that the same mechanism (i.e., sex hormones) triggers the HGH release.Abbreviations HV heart volume - HV·kg^–1 heart volume per kg body weight - HR heart rate - average heart rate during the submaximal exercise - WL work load - W·kg^–1 watts per kg body weight - O₂ max maximal oxygen consumption - 70% O₂ max 70% of maximal oxygen consumption - O₂ max·HR^–1 oxygen pulse - HVE heart volume equivalent (HV/ O₂ max·HR^–1) - FFA free fatty acids - HGH human growth hormone     

Maximal O2 uptake of boys and girls — ages 14–17

Summary White high school girls (n = 120) and boys (n = 120) aged 14–17 years, selected from 9th, 10th, 11th and 12 grades of a northern, midwest U.S. high school performed running exercise on a motor driven treadmill for determinations of maximal O₂ uptake ( O₂ max).The mean O₂ max for all age groups was 40.8±4.0 and 54.7±5.6 ml/kg·min^–1 for girls and boys respectively. The difference in O₂ max across age groups varied only from 40.2–41.2 ml/kg·min^–1 for girls and 54.0–56.3 ml/kg·min^–1 for boys. These differences were not significant (P>0.05). The reported O₂ max data are compared with those reported in other studies for bicycle ergometer and treadmill exercise using similar age groups.     

Effect of hand paddle aids on oxygen uptake during arm-stroke-only swimming

Summary Cardiorespiratory responses during armstroke-only swimming with and without the aid of paddle were compared in seven trained swimmers. Water flow rate was started at 0.80 m · s^–1 and was increased by 0.05 m · s^–1 every 2 min up to 1.00 m · s^–1 Subsequently, the flow rate was increased by 0.05 m · s^–1 every minute until exhaustion. At given submaximal water flow rates, oxygen uptake, heart rate (f _c), pulmonary ventilation ( _E) and respiratory frequency (f _R) during swimming using hands alone (H) were significantly higher than when aided by paddles (P). There were no significant differences in tidal volume (V _T) between H and P. The subjects were able to swim significantly faster using paddles (P<0.05); however, no significant differences between H and P were found in peak oxygen uptake ( O_2peak,f _c, _E,f _R,V _T and the blood lactate concentration at which O_2peak was obtained (P>0.05). These results would suggest that the ability to swim faster with paddles does not depend on higher energy production but may be attributed to higher propelling efficiency.     

Relationship between ventilation and arterial potassium concentration during incremental exercise and recovery

Summary The purpose of this study was to compare the relationship of ventilation ( _E) with pH, arterial concentrations of potassium ([K⁺]_a), bicarbonate ([HCO₃ ^–]_a), lactate ([la]_a), and acid-base parameters which would affect hyperpnoea during exercise and recovery. To assess this relationship, ten healthy male subjects exercised with intensity increasing as a ramp function of 20 W · min^–1 until voluntary exhaustion and they were then allowed a 5-min recovery period. Breath-by-breath gas exchange data, [HCO₃ ^–]_a, pH, [1a]_a, [K⁺]_a and blood gases were determined during both exercise and recovery. Using a linear regression method, the _E/[K⁺]a relationship was analysed during both exercise and recovery. Several interesting results were obtained: a significant relationship between [K⁺]_a and _E was observed during recovery as well as during exercise; the _E at any given values of [K⁺]_a was significantly higher during recovery than during exercise and out of those factors affecting exercise hyperpnoea, only [K⁺]_a had a similar time-course to _E during recovery. Changes in [K⁺]a during recovery were shown to occur significantly faster than _E with an [K⁺]_a time constant of 70.0 s, SD 16.2 as opposed to 105.5 s, SD 10.0 for _E (P < 0.01). These results provided further evidence that [K⁺]_a might play an important role as a substance which can stimulate exercise hyperpnoea as has been suggested by other workers. The present study also showed that during recovery [K⁺]_a contributed significantly to the control of _E.     

Hypoxia and training-induced adaptation of hormonal responses to exercise in humans

To establish whether or not hypoxia influences the training-induced adaptation of hormonal responses to exercise, 21 healthy, untrained subjects [26 (2) years, mean (SE)] were studied in three groups before and after 5 weeks' training (cycle ergometer, 45 min· day^–1, 5 days· week^–1). Group 1 trained at sea level at 70% maximal oxygen uptake ( O_2max), group 2 in a hypobaric chamber at a simulated altitude of 2500 m at 70% of altitude O_2max, and group 3 at a simulated altitude of 2500 m at the same absolute work rate as group 1. Arterial blood was sampled before, during and at the end of exhaustive cycling at sea level (85% of pretraining of O_2max). O₂ increased by 12 (2)% with no significant difference between groups, whereas endurance improved most in group 1 (P < 0.05). Training-induced changes in response to exercise of noradrenaline, adrenaline, growth hormone, -endorphin, glucagon, and insulin were similar in the three groups. Concentrations of erythropoietin and 2,3-diphosphoglycerate at rest did not change over the training period. In conclusion, within 5 weeks of training, no further adaptation of hormonal exercise responses takes place if intensity is increased above 70% O_2max. Furthermore, hypoxia per se does not add to the training-induced hormonal responses to exercise.     

Physiological strain due to load carrying in heavy footwear

Summary To determine the effects of wearing heavy footwear on physiological responses five male and five female subjects were measured while walking on a treadmill (4, 5.25, and 6.5 km·h^–1) with different external loads (barefooted, combat boots, and waist pack). While walking without an external load the oxygen uptake, as a percentage of maximal oxygen uptake (% O_2max) of the men increased from 25% O_2max at 4 km·h^–1 to 31% O_2max at 5.25 km·h^–1 and to 42% O_2max at 6.5 km·h^–1. The women had a significantly higher oxygen uptake of 30%, 40%, and 55% O_2max, respectively. In the most strenuous condition, walking at 6.5 km·h^–1 with combat boots and waist pack (12 kg), the oxygen uptake for the men and women amounted to 53% and 75% O_2max, respectively. The heart rate showed a similar response to the oxygen uptake, the women having a heart rate which was 15–40 beats·min^–1 higher than that of the men, depending on the experimental condition. The perceived exertion was shown to be greatly dependent on the oxygen uptake. From the results a regression formula was calculated predicting the oxygen uptake depending on the mass of the footwear, walking speed and body mass. It was concluded that the mass of footwear resulted in an increase in the energy expenditure which was a factor 1.9–4.7 times greater than that of a kilogram of body mass, depending on sex and walking speed.     

Relationship of middle cerebral artery blood flow velocity to intensity during dynamic exercise in normal subjects

Summary Cerebral blood flow has been reported to increase during dynamic exercise, but whether this occurs in proportion to the intensity remains unsettled. We measured middle cerebral artery blood flow velocity (m) by transcranial Doppler ultrasound in 14 healthy young adults, at rest and during dynamic exercise performed on a cycle ergometer at a intensity progressively increasing, by 50 W every 4 min until exhaustion. Arterial blood pressure, heart rate, end-tidal, partial pressure of carbon dioxide (P _ETCO₂), oxygen uptake ( O₂) and carbon dioxide output were determined at exercise intensity. Mean vM increased from 53 (SEM 2) cm · s^–1 at rest to a maximum of 75 (SEM 4) cm · s^–1 at 57% of the maximal attained O₂( O_2max), and thereafter progressively decreased to 59 (SEM 4) cm · s^–1 at O_2max. The respiratory exchange ratio (R) was 0.97 (SEM 0.01) at 57% of O_2maxand 1.10 (SEM 0.01) at O_2max. The P _ETCO₂ increased from 5.9 (SEM 0.2) kPa at rest to 7.4 (SEM 0.2) kPa at 57% of O_2maxand thereafter decreased to 5.9 (SEM 0.2) kPa at O_2max. Mean arterial pressure increased from 98 (SEM 1) mmHg (13.1 kPa) at rest to 116 (SEM 1) mmHg (15.5 kPa) at 90% of O_2max, and decreased slightly to 108 (SEM 1) mmHg (14.4 kPa) at O_2max. In all the subjects, the maximal value of v _m was recorded at the highest attained exercise intensity below the anaerobic threshold (defined by R greater than 1). We concluded that cerebral blood flow as evaluated by middle cerebral artery flow velocity increased during dynamic exercise as a function of exercise intensity below the anaerobic threshold. At higher intensities, cerebral blood flow decreased, without however a complete return to baseline values, and it is suggested that this may have been at least in part explained by concomitant changes in arterial PCO₂.     

Arterial versus venous blood lactate increase in the forearm during incremental bicycle exercise

Summary Eight male subjects were studied during incremental bicycle exercise. From the forearm, arterial and venous blood lactate concentrations were measured every minute until exhaustion. There was a statistically significant difference (P<0.01) in the points at which the arterial and venous blood lactates began to increase above the resting level. The onset of increase of lactate in arterial blood occurred at 1.00±0.07 l·min^–1 in O₂ (mean ± SEM), which corresponded to 37.0±1.5% of O_2max. Its venous counterpart occurred at 1.50±0.17 l·min^–1 in O₂, 55.0±3.8% of O_2max. The arterio-venous lactate difference became greater after the onset of increase in arterial blood lactate (anaerobic threshold), presumably as consequence of lactate utilization by the forearm muscles.It was concluded that the onset of blood lactate increase differs according to the sites of blood sampling, which should be considered for the interpretation of anaerobic threshold.     

Influence of ageing on aerobic parameters determined from a ramp test

Summary The purpose of this study was to examine the four parameters of aerobic function, the maximum oxygen uptake ( O_2max), ventilation threshold (Th _VE), efficiency, and the effective time constant for oxygen consumption ( 0₂), across age. In particular, the study was designed to observe whether there may be accelerated declines in aerobic function beyond 60 years of age. Seventy-nine sedentary men aged 30–84 years were studied. Each subject performed two maximal cycle ramp function tests, and data were collected on a breath-by-breath basis. The O_2max, from a plateau in 0₂, was achieved in 87% of the subjects using the ramp test. The O_2max showed a significant decrease with increasing age (from linear regression,r = –0.81) at a rate averaging 0.037 l·min^–1·year^–1. The Th _VE also declined with increasing age, but at a slower rate (0.013 l·min^–1·year^–1). The O₂ was significantly increased across the age groups from 69 s for those aged 30–40 years to 98s for those aged 60 years or more. There was no evidence of accelerated decline in these aerobic parameters beyond age 60 years, and there were no differences in efficiency (27.5–29.9%) across age. Although other forcing functions should be used to confirm this characterization of the oxygen kinetics, this slowed response with age would result in greater oxygen deficit and possibly earlier fatigue in response to even light exercise in older individuals.     

Physiological responses of women during lifting exercise

Summary Physiological responses were measured in 7 women subjects who lifted boxes weighing 6.8, 15.9 or 22.7 kg from the floor to a height of 60 cm. After training and establishing the O₂ max, the boxes were lifted for 1 h at 30, 50, and 60% O₂ max. The changes in heart rate, O₂, the integrated EMG during lifting and the loss of isometric hand-grip endurance after lifting were used to assess the development of fatigue. There was no evidence of fatigue at 30% O₂ max but fatigue did exist in some conditions at 50% and in all conditions at 60% O₂ max. It is suggested that fatigue is unlikely to occur while lifting boxes up to 15.9 kg weight at 35–40% O₂ max, i.e., at rates of lifting varying from 5 to 7 times per min.     

The relative influence of body characteristics on humid heat stress response

The present study was designed to determine the relative importance of individual characteristics such as maximal oxygen uptake ( O_2max), adiposity, DuBois body surface area (A _D), surface to mass ratio (A _D: mass) and body mass, for the individual's reaction to humid heat stress. For this purpose 27 subjects (19 men, 8 women), with heterogeneous characteristics ( O_2max 1.86–5.28 1 · min^–1; fat% 8.0%–31.9%; mass 49.8–102.1 kg; A _D 1.52–2.33 m²) first rested (30 min) and then exercised (60 W for 1 h) on a cycle ergometer in a warm humid climate (35°C, 80% relative humidity). Their physiological responses at the end of exercise were analysed to assess their relationship with individual characteristics using a stepwise multiple regression technique. Dependent variables (with ranges) included final values of rectal temperature (T _re 37.5–39.0°C), mean skin temperature (T _sk 35.7–37.5°C), body heat storage (S 3.2–8.1 J · g^–1), heart rate (HR 100–172 beat · min^–1), sweat loss (397–1403g), mean arterial blood pressure (BP_a, 68–96 mmHg), forearm blood flow (FBF, 10.1–33.9 ml · 100ml^–1 · min^–1) and forearm vascular conductance (FVC = FBF/BP_a, 0.11–0.49 ml · 100 ml^–1 · min^–1 · mmHg^–1). The T _re, T _sk and S were (34%–65%) determined in the: main by ( O_2max), or by exercise intensity expressed as a percent age of O_2max (% O_2max). For T _re, A _D: mass ratio also contributed to the variance explained, with about half the effect of ( O_2max), For T _sk, fat% contributed to the variance explained with about two-third the effect of O_2max. Total body sweat loss was highly dependent (50%) on body size (A _D or mass) with regular activity level having a quarter of the effect of body size on sweat loss. The HR, similar to T _re, was determined by O_2max (48%–51%), with less than half the effect of A _D or A _D :mass (20%). Other circulatory parameters (FBF, BP_a, FVC) showed little relationship with individual characteristics ( < 36% of variance explained). In general, the higher the ( O_2max), and/or the bigger the subject, the lower the heat strain observed. The widely accepted concept, that body core temperature is determined by exercise intensity expressed as % O_2max and sweat loss by absolute heat load, was only partially supported by the results. For both variables, other individual characteristics were also shown to contribute.     

Cardiac output in paraplegic subjects at high exercise intensities

Summary The purpose of this investigation was to compare cardiac output ( _c ) in paraplegic subjects (P) with wheelchair-confined control subjects (C) at high intensities of arm exercise. At low and moderate exercise intensity _c was the same at a given oxygen uptake ( O₂) in P and C. A group of 11 athletic male P with complete spinal-cord lesions between T6 and T12 and a group of 5 well-matched athletic male C performed maximal arm-cranking exercise and submaximal exercise at 50%, 70% and 80% of each individual's maximal power output (W_max) . Maximal O₂ ( O_2max) was significantly lower, O_2max per kilogram body mass was equal and maximal heart rate (f _c) was significantly higher in P compared to C. At O₂ of 1.3, 1.5 and 1.7 1-min^–1, and for P 65%–90% of the O_2max, _c was not significantly different between the groups, although, _c in P was achieved with a significantly lower stroke volume (SV) and a significantly higherf _c. Although the SV was lower in P, it followed the same pattern as SV in C during incremental exercise, i.e. an increase in SV until about 45%W _max and thereafter a stable SV. The similar _c at a given O₂ in both groups indicated that, even at high exercise intensities, circulation in P can be considered isokinetic with a complete compensation byf _c for a lower SV.     

A new approach to assessing maximal aerobic power in children: the Odense School Child Study

Summary In two experiments maximal aerobic power calculated from maximal mechanical power (W _max) was evaluated in 39 children aged 9–11 years. A maximal multi-stage cycle ergometer exercise test was used with an increase in work load every 3 min. In the first experiment oxygen consumption was measured in 18 children during each of the prescribed work loads and a correction factor was calculated to estimate using the equation . An appropriate increase in work rate based on height was determined for boys (0.16 W · cm^–1) and girls (0.15 W · cm^–1) respectively. In the second experiment 21 children performed a maximal cycle ergometer exercise test twice. In addition to the procedure in the first experiment a similar exercise test was performed, but without measurement of oxygen uptake. Calculated correlated significantly (p<0.01) with those values measured in both boys (r=0.90) and girls (r=0.95) respectively, and the standard error of estimation for (calculated) on (measured) wass less than 3.2%. Two expressions of relative work load (% and %W _max) were established and found to be closely correlated. The relative work load in % could be predicted from the relative work load in % W _max with an average standard error of 3.8%. The data demonstrate that calculated based on a maximal multi-stage exercise test provides an accurate and valid estimate of