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.     

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.     

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.     

Influence of lifting technique on perceptual and cardiovascular responses to submaximal repetitive lifting

Oxygen consumption ( O₂), heart rate, ventilation and central rating of perceived exertion (RPE) in repetitive lifting while executing squat and stoop techniques were investigated in ten male forestry workers. In all five mass/frequency combinations studied, O₂ was significantly higher for the squat than for the stoop technique. No differences were found in RPE between the techniques. The O₂ and RPE recordings were also related to those obtained during maximal repetitive lifting (same lifting technique) and maximal treadmill running. The O₂ expressed as a percentage of that obtained during maximal repetitive lifting with the same lifting technique was defined as relative aerobic intensity (% O_{2max, lifting}). The % O_{2max, lifting} was not significantly different between the techniques except for the lowest mass lifted (1 kg). This study therefore would support the hypothesis that RPE is more closely related to % O_{2max, lifting} than to absolute aerobic intensity. Related to maximal treadmill running, it was demonstrated for both lifting techniques that relative RPE (percentage of the RPE during maximal running) was more accurate than relative O₂ (percentage of maximal O₂ during maximal running) for determining the % O_{2max, lifting} in repetitive lifting. The study showed that the higher O₂ during squat. lifting compared to stoop lifting was caused by the O₂ expended in lifting and lowering the body rather than the O₂ expended lifting and lowering the external mass. It was concluded that the stoop technique was not superior to the squat technique in terms of central RPE. Based on % O_{2max, lifting}, there may be a rationale for choosing the stoop technique during repetitive lifting with light masses, but not with heavy masses.     

A cycle ergometer test of maximal aerobic power

Summary An indirect test of maximal aerobic power (IMAP) was evaluated in 31 healthy male subjects by comparing it with a direct treadmill measurement of maximal aerobic power ( O₂ max), with the prediction of O₂ max from heart rate during submaximal exercise on a cycle ergometer using åstrand's nomogram, with the British Army's Basic Fitness Test (BFT, a 2.4 km run performed in boots and trousers), and with a test of maximum anaerobic power. For the IMAP test, subjects pedalled on a cycle ergometer at 75 revs·min^–1. The workload was 37.5 watts for the first minute, and was increased by 37.5 watts every minute until the subject could not continue. Time to exhaustion was recorded. Predicted O₂ max and times for BFT and IMAP correlated significantly (p<0.001) with the direct O₂ max: r=0.70, r=0.67 and r=0.79 respectively. The correlation between direct O₂ max and the maximum anaerobic power test was significant (p<0.05) but lower, r=0.44. Although lactate levels after direct O₂ max determination were significantly higher than those after the IMAP test, maximum heart rates were not significantly different. Submaximal O₂ values measured during the IMAP test yielded a regression equation relating O₂ max and pedalling time. When individual values for direct and predicted O₂ max and times for BFT and IMAP were compared with equivalent standards, the percentages of subjects able to exceed the standard were 100, 65, 87, and 87 respectively. These data demonstrate that the IMAP test provides a valid estimate of O₂ max and indicate that it may be a practical test for establishing that an individual meets a minimum standard.     

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.     

Validity of a velodrome test for competitive road cyclists

The aim of this study was to evaluate the validity of a velodrome field test consisting of repeated rides of 2,280 m, with an initial speed of 28 km·h^–1 and increments of 1.5 km·h^–1 interspersed with 1-min recovery periods until exhaustion. A group of 12 male competitive road cyclists performed maximal cycling tests under velodrome and laboratory conditions. Velodrome oxygen uptake ( O₂) and power output were estimated using equations previously published. Physiological responses to the two tests were compared. Relationships between performance in the velodrome and physiological parameters measured in the laboratory were studied. Maximal power output, heart rate and O₂ were similar in the velodrome and the laboratory [372 (SD 50) vs 365 (SD 36) W, 195 (SD 8) vs 196 (SD 9) beats·min^–1 and 4.49 (SD 0.56) vs 4.49 (SD 0.46) l·min^–1, respectively], while maximal velodrome blood lactate concentration was significantly higher [13.5 (SD 2.1) vs 11.8 (SD 3.1) mmol·l^–1]. Velodrome heart rate was higher at submaximal exercise intensities representing 40%, 50% and 60% of maximal aerobic power, and velodrome blood lactate concentration was also higher at 60%, 70% and 80% of maximal aerobic power. The laboratory parameter that showed the highest correlation with the maximal cycling speed in the velodrome was maximal oxygen uptake ( O_2max) expressed per unit of body mass (r = 0.93). In addition, the accuracy of different methods of estimation of the metabolic cost of cycling, rolling resistance, air resistance coefficients and O_2max were compared. Significant differences were found. In conclusion, the present results indicated the validity of a velodrome test used to estimate maximal aerobic parameters of competitive road cyclists, as long as the estimation is made using established equations. When road cyclists are tested in the laboratory, physiological values should be expressed per unit of body surface area or body mass, to predict more accurately the cyclist's performance level under specific field conditions.     

Physiological characteristics of young well-trained swimmers

Summary The purpose of this study was to describe body composition, muscular strength, pulmonary function, and aerobic capacity of young swimmers, after 6 years of training. Twelve male members of a competitive swim team, ranging in age from 13 to 16 years, served as subjects. Each subject was measured on 2 separate days at approximately the same time of day on each occasion. On day one, body composition, muscular strength, TLC, FVC, FEV_1.0, FRC, RV, and resting DL_c0 were determined. On day 2, height, weight, E max Hr max, and O₂ max were measured. Results indicated that children who train to swim competitively: (1) are lower than average in percent body fat (10.8%) as determined by hydrostatic weighing, (2) are muscularly fit as indicated by the Oregon Cable-Tension Strength Test, and (3) have cardiorespiratory capacities which are greater than one would expect to see in untrained youth of similar ages.     

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.     

Mean arterial pressure,O2-uptake,and muscle force time during dynamic and rhythmic-static exercise in men with high percentages of fast- and slow-twitch fibers

Summary The influence of different percentages of slow-twitch (ST) and fast-twitch (FT) fibers in vastus lateralis on the relationship between mean arterial pressure (MAP) and O₂-uptake ( O₂) with muscle force time (MIpm, ⁶⁰₀ p×t) exerted on the pedal during upright cycling, or during rhythmic isometric contraction (RIC) (only one subject) was studied in three high percent ST men (average 78% ST) (ST group), and in three high percent FT men (average 75% FT) FT group). MAP, or MIpm, was higher and had a steeper linear regression in the FT group than in the ST group at or against the same absolute O₂ during cycling at 60 rpm, or 100 rpm. The relationship between MAP and MIpm, however, was almost the same between both in the FT and ST group, or between both at 60 and 100 rpm. During RIC the slope (y/x) of the linear regression line between MAP and MIpm was close to that during cycling, whereas the slope of O₂ vs. MIpm was much lower. In conclusion, the variations in fiber population in working muscle do not seem to have any effect on MAP. MAP increases with MIpm independent of fiber population and/or fitness ( O₂ max).     

Role of decreased carbohydrate oxidation on slower rises in ventilation with increasing exercise intensity after training

In these studies, we examined whether the rightward shift in steady-state minute ventilation ( _E) versus O₂ uptake curves after training is more closely linked to the reduced CO₂ production from carbohydrate oxidation (CHO_OX) after training than to the attenuated increase in blood lactate concentration. Steady state _E values and gas exchange were measured in eight previously sedentary men who underwent exercise tests of 60 W + 40 W every 6 min before and after a 9 week training programme of cycling approximately 40 min a day. Following training, the slower rises in _E with increasing exercise intensities were associated with a reduced reliance on CHO_OX, (P < 0.01). Both before and after training, _E values in litres per minute rose as a linear _E = 18 · CHO_OX + 14, function of rates of CHO_OX in grams per minute (r = 0.99), irrespective of a marked shift to the right in arterialized venous blood lactate concentration versus CHO_OX curves following training (P < 0.01). Thus, slower increases in steady-state _E values with increasing exercise intensities following endurance training appeared to be more closely linked to the decreased reliance on CHO_OX than to the attenuated increase in blood lactate concentration.     

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.     

Aerobic fitness and body fat of young British males entering the army

Summary Aerobic fitness and percent body fat were measured in a sample of 438 male Army recruits between the ages of 17 and 30 prior to the commencement of training. The sample came from all areas of England and Wales. Aerobic fitness, as represented by maximal oxygen uptake ( O₂ max), was predicted from the Astrand submaximal bicycle heart rate test. Body fat was predicted from four skinfold measurements. Total group means ±SD were: age, 19.5±2.5 years; O₂ max 41.7 ±8.3 ml/kg·min; and body fat, 14.5±4.8% of body weight. O₂ max varied with age, athletic participation and aptitude score. No relationship was found with occupation of parent, prior civilian occupation or smoking severity. When adjusted for methodological differences, O₂ max was slightly below similar Army entrants in Norway and the United States.     

The effects of continuous and interval training in women and men

Summary Fourteen Subjects (6 male, 8 female) participated in a training program upon a bicycle ergometer for 7 weeks. Group CT followed a continuous training regimen 4 days per week at 70% O₂ max. Group IT trained by an interval method at 100% O₂ max. The duration of each training session was assigned so that each subject would complete 10,000 kpm of work per session during the first week. Each subsequent week, the work load was increased 3000 kpm. Pretraining tests included O₂ max, standard 7 min tests at 80% O₂ and 90% O₂, an endurance test at 90%, and an intense anaerobic work bout at 2400 kpm. Variables assessed were O₂, HR, and blood lactic acid concentrations. The mean increase in O₂ max was 5.1 ml/kg min (15%) for both groups with a corresponding increase in maximal lactate of 20 mg-%. The response to the post-training tests was nearly identical for both groups: submaximal heart rate at the same absolute work load declined 17 beats/min (CT) and 15 beats/min (IT), submaximal lactate levels declined significantly, endurance ride duration increased 26 min. Continuous and interval training at 70% and 100% O₂ max respectively produce identical changes in heart rate response, blood lactic acid concentration and O₂ max when the total work load is equated per training session.     

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     

A method for estimating bicarbonate buffering of lactic acid during constant work rate exercise

A method to estimate the CO₂ derived from buffering lactic acid by HCO₃ ^– during constant work rate exercise is described. It utilizes the simultaneous continuous measurement of O₂ uptake ( O₂) and CO₂ output ( CO₂), and the muscle respiratory quotient (RQ_m). The CO₂ generated from aerobic metabolism of the contracting skeletal muscles was estimated from the product of the exercise-induced increase in O₂ and RQ_m calculated from gas exchange. By starting exercise from unloaded cycling, the increase in CO₂ stores, not accompanied by a simultaneous decrease in O₂ stores, was minimized. The total CO₂ and aerobic CO₂ outputs and, by difference, the millimoles (mmol) of lactate buffered by HCO₃ ^– (corrected for hyperventilation) were estimated. To test this method, ten normal subjects performed cycling exercise at each of two work rates for 6 min, one below the lactic acidosis threshold (LAT) (50 W for all subjects), and the other above the LAT, midway between LAT and peak O₂ [mean (SD), 144 (48) W]. Hyperventilation had a small effect on the calculation of mmol lactate buffered by HCO₃ ^– [6.5 (2.3)% at 6 min in four subjects who hyperventilated]. The mmol of buffer CO₂ at 6 min of exercise was highly correlated (r = 0.925, P < 0.001) with the increase in venous blood lactate sampled 2 min into recovery (coefficient of variation = ±0.9 mmol·l^–1). The reproducibility between tests done on different days was good. We conclude that the rate of release of CO₂2 from HCO₃ ^– can be estimated from the continuous analysis of simultaneously measured CO₂, O₂, and an estimate of muscle substrate.     

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.     

Specificity of metabolic and circulatory responses to arm or leg interval training

Summary The purpose of this study was to evaluate metabolic and circulatory responses to interval training of legs or arms during steady-state, submaximal cycling. 15 college males cycled on a bicycle ergometer twice with arms (63 and 83 W) and twice with legs (100 and 125 W) before and following 5 weeks of daily interval training. Seven subjects trained with arm cycling and eight with leg cycling. Significant post-training decreases in submaximal oxygen consumption ( O₂), heart rate (HR), and venous blood lactate (LA_v) were noted when cycling with trained and untrained muscles with the magnitude of change significantly greater with trained muscles. These results indicate metabolic and circulatory adaptations to interval training that are mediated centrally and peripherally. With respect to HR, but not O₂, training a larger muscle mass (legs) produced a greater central but lesser peripheral effect whereas the opposite was true for the smaller arm muscles. The data also suggested that the peripheral adaptation involves a common mechanism controlling both HR and LA_v changes with a separate mechanism controlling O₂.Supported by a grant from the Central Ohio Heart Chapter     

The validity of anaerobic threshold determination by a Douglas bag method compared with arterial blood lactate concentration

Summary Using an open circuit system (Douglas bag method), measurement of the anaerobic threshold (AT) was performed on ten healthy male college students during an incremental exercise test on a bicycle ergometer in an attempt to determine the validity of this method as compared with arterial blood lactate AT measurement.Blood samples were taken from either the radial or brachial artery through a Teflon catheter (3 ml/each time) every minute until the subject's maximal exercise tolerance was reached. Blood lactate was analyzed by the enzymatic method.Differences in work rate, O₂, % O_{2 max}, _E, HR, and R at AT _LA (AT determined by the increase in blood lactate) and at AT _GE (gas exchange AT based on the non-linear increases in _E, CO₂, and other respiratory parameters), respectively, were all found to be statistically insignificant. There was a significant correlation (r=0.866, p<0.01) between AT _LA and AT _GE when expressed in O₂ values (l/min). There was also a significant correlation between AT _LA and O_{2 max} (r=0.778, p<0.01). These results indicate that the commonly used Douglas bag method could provide a valid non-invasive measure of anaerobic threshold.     

Femoral to cerebral arterial blood flow redistribution and femoral vein distension during orthostatic tests after 4 days in the head-down tilt position or confinement

The first objective of this study was to confirm that 4 days of head-down tilt (HDT) were sufficient to induce orthostatic intolerance, and to check if 4 days of physical confinement may also induce orthostatic intolerance. Evidence of orthostatic intolerance during tilt-up tests was obtained from blood pressure and clinical criteria. The second objective was to quantify the arterial and venous changes associated with orthostatic intolerance and to check whether abnormal responses to the tilt test and lower body negative pressure (LBNP) may occur in the absence of blood pressure or clinical signs of orthostatic intolerance. The cerebral and lower limb arterial blood flow and vascular resistance, the flow redistribution between these two areas, and the femoral vein distension were assessed during tilt-up and LBNP by ultrasound. Eight subjects were given 4 days of HDT and, 1 month later, 4 days of physical confinement. Tilt and LBNP test were performed pre- and post-HDT and confinement. Orthostatic intolerance was significantly more frequent after HDT (63%) than after confinement (25%, P<0.001). Cerebral haemodynamic responses to tilt-up and LBNP tests were similar pre- and post-HDT or confinement. Conversely, during both tilt and LBNP tests the femoral vascular resistances increased less (P<0.002), and the femoral blood flow reduced less (P<0.001) after HDT than before HDT or after confinement. The cerebral to femoral blood flow ratio increased less after HDT than before (P<0.002) but remained unchanged before and after confinement. This ratio was significantly more disturbed in the subjects who did not complete the tilt test. The femoral superficial vein was more distended during post-HDT LBNP than pre-HDT or after confinement (P<0.01). In conclusion, 4 days of HDT were enough to alter the lower limb arterial vasoconstriction and venous distensibility during tilt-up and LBNP, which reduced the flow redistribution in favour of the brain in all HDT subjects. Confinement did not alter significantly the haemodynamic responses to orthostatic tests. The cerebral to femoral blood flow ratio measured during LBNP was the best predictor of orthostatic intolerance.