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.     

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.     

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     

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.     

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.     

Pulmonary gas exchange and ventilatory responses to brief intense intermittent exercise in young trained and untrained adults

To investigate pulmonary gas exchange and ventilatory responses to brief intense intermittent exercise and to study the effects of physical fitness on thes responses, nine trained and nine untrained healthy male subjects aged 18–33 years performed the force-velocity (F-) exercise test. This test consisted of 6-s sprints against increasing braking forces (F) separated by 5-min recovery periods. Oxygen uptake ( ), carbon dioxide output ( CO₂), and ventilation _E) were continuously measured during the test and the magnitudes of their responses to the sprints were then calculated.For all subjects CO₂ increased rapidly after beginning the sprints, and the peaks of the responses (F = 13.4;P < 0.001), end of recovery values (F = 6.5;P < 0.01), and O₂ magnitudes of response (F = 12.4;P < 0.001) rose significantly with the repetition of the sprints. The O₂ magnitudes of response correlated with the corresponding sprint power outputs (r = 0.55;P < 0.001) and with the sprint repetitions (r = 0.51,P < 0.001). The CO₂ (F = 7.1;P < 0.01) and {ie442-8} (F = 5.0;P < 0.01) peaks of response increased with the initial load incrementation, then stabilized when the subjects attained peak power output. End of recovery CO₂ (F = 18.0;P < 0.001) and _E (F = 14.1;P < 0.001) values rose with increasingF. TheF- peak O₂, CO₂, _E, tidal volume and respiratory frequency responses attained 53%, 40%, 44%, 66%, and 82% of the peak values measured at exhaustion of maximal graded exercise, respectively.Trained and untrained subjects had the same first sprint power output and braking, force. Nevertheless, the trained subjects had higher O₂ peaks (F = 35.2;P < 0.001) and CO₂ magnitudes of response (F = 30.0;P < 0.001) than the untrained subjects for all sprints. The higher peak O₂ values represented similar percentages of maximal oxygen uptake in the trained and untrained subjects. In summary, the present study showed that in brief intense intermittent exercise, i.e. theF- test, the O₂, CO₂, and ventilatory responses in young subjects were submaximal with respect to the peak values attained at exhaustion of maximal graded exercise. The CO₂ magnitude of response increase was related to the power output rise in the corresponding sprints and to the repetition of sprints. Moreover, the trained subjects presented higher CO₂ peaks and magnitudes of response to the sprints than the untrained subjects.     

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.     

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.     

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.     

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.     

Skeletal muscle determinants of maximum aerobic power in man

Summary The interrelationship between whole body maximum O₂ uptake capacity ( O_{2 max}), skeletal muscle respiratory capacity, and muscle fiber type were examined in 20 physically active men. The capacity of homogenates of vastus lateralis muscle biopsy specimes to oxidize pyruvate was significantly related to O_{2 max} (r=0.81). Correlations of 0.75 and 0.74 were found between % slow twitch fibers (%ST) and O_{2 max}, and between % ST fibers and muscle respiratory capacity, respectively (P<0.01). Multiple correlation analysis (R=0.85) indicated that 72% (R ²=0.72) of the variance in CO_{2 max} could be accounted for by the combined effect of muscle respiratory capacity and the % ST fibers. When the % ST fibers was correlated with O_{2 max}, with the effect of respiratory capacity statistically removed, the relationship became insignificant (r=0.38). These data suggest that muscle respiratory capacity plays an important role in determining O_{2 max}, and that the relationship between % ST fibers and O_{2 max} is due primarily to the high oxidative capacity of this muscle fiber type.This research was supported by NIH grant (HL 20408-02)     

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     

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.     

O2 Uptake in hyperthyroidism during constant work rate and incremental exercise

Summary To investigate the effect of hyperthyroidism on the pattern and time course of O₂ uptake ( O₂) following the transition from rest to exercise, six patients and six healthy subjects performed cycle exercise at an average work rate (WR) of 18 and 20 W respectively. Cardiorespiratory variables were measured breath-by-breath. The patients also performed a progressively increasing WR test (1-min increments) to the limit of tolerance. Two patients repeated the studies when euthyroid. Resting and exercise steady-state (SS) O₂ (ml·kg^–1·min^–1) were higher in the patients than control (5.8, SD 0.9 vs 4.0, SD 0.3 and 12.1, SD 1.5 vs 10.2, SD 1.0 respectively). The increase in O₂ during the first 20 s exercise (phase I) was lower in the patients (mean 89 ml·min^–, SD 30) compared to the control (265 ml·min^–1, SD 90), while the difference in half time of the subsequent (phase 11) increase to the SS O₂ (patient 26 s, SD 8; controls 17 s, SD 8) were not significant (P = 0.06). The OZ cost per WR increment ( O₂/WR) in ml·min^–1·^–1, measured during the incremental period (mean 10.9; range 8.3–12.2), was always within two standard deviations of the normal value (10.3, SD 1). In the two patients who repeated the tests, both the increment of O₂ from rest to SS during constant WR exercise and the O₂/WRs during the progressive exercise were higher in the hyperthyroid state than during the euthyroid state. While both resting and exercise O₂ are increased in the hyperthyroid patients, the O₂ cost of a given increment of WR is within the normal range. However, a small reduction in the O₂ requirement to perform exercise following treatment of the hyperthyroid state suggests a subtle change O₂ cost of muscle work in this disease.     

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.     

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.     

Respiratory gas exchange indices used to detect the blood lactate accumulation threshold during an incremental exercise test in young athletes

Summary The time course of changes in blood lactate concentration and ventilatory gas exchange was studied during an incremental exercise test on a cycle ergometer to determine if the lactate accumulation threshold (LT₂) could be accurately estimated by the use of respiratory indices (VT₂) in young athletes. LT₂ was defined as the starting point of accelerated lactate accumulation. VT₂ was identified by the second exponential increase in _E and the ventilatory equivalent for O₂ uptake with a concomitant nonlinear increase in the ventilatory equivalent for CO₂ output. Twelve trained subjects, aged 18–22 years, participated in this study. The initial power setting was 30 W for 3 min with successive increases of 30 W every minute except at the end of the test when the increase was reduced. Ventilatory flow ( _E), oxygen uptake ( O₂), carbon dioxide output ( CO₂), and ventilatory equivalents of O₂ and CO₂ were determined during the last 30 s of every minute. Venous blood samples were drawn at the end of each stage of effort and analysed enzymatically for lactate concentration. After each test, LT₂ and VT₂ were determined visually by two investigators from the graphic results using a double-blind procedure. The results [mean (SEM)] indicate no significant difference between LT₂ and VT₂ expressed as O₂ [43.98 (1.70) vs 44.93 (2.39) ml - min^– - kg^–], lactataemia [4.01 (0.28) vs 4.44 (0.37) mM - 1^–], or heart rate [171 (3.36) vs 173 (3.11) min^–]. In addition, strong correlations were noted between the two methods for O₂ (r=0.90,P<0.001), lactataemia (r=0.75,P<0.01), and heart rate (r=0.96,P<0.001). It is concluded that VT₂ coincides with LT₂ determination and that the ventilatory gas exchange method can thus satisfactorily evaluate the lactate accumulation threshold in young athletes.     

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.     

Cardiac output during exercise in paraplegic subjects

Summary The purpose of this study was to measure the cardiac output using the CO₂ rebreathing method during submaximal and maximal arm cranking exercise in six male paraplegic subjects with a high level of spinal cord injury (HP). They were compared with eight able bodied subjects (AB) who were not trained in arm exercise. Maximal O₂ consumption ( O_2max) was lower in HP (1.1 1·min^–1, SD 0.1; 17.5 ml·min^–·kg, SD 4) than in AB (2.5 1·min^–1, SD 0.6; 36.7 ml·min^–1·kg, SD 10.7). Maximal cardiac output was similar in the groups (HP, 141·min^–1 SD 2.6; AB, 16.81·min^–1 SD 4). The same result was obtained for maximal heart rate (f _c,max (HP, 175 beats·min^–1, SD 18; AB, 187 beats·min^–, SD 16) and the maximal stroke volume (HP, 82 ml, SD 13; AB, 91 ml, SD 27). The slopes of the relationshipf _c/ O₂ were higher in HP than AB (P<0.025) but when expressed as a % O_2max there were no differences. The results suggests a major alteration of oxygen transport capacity to active muscle mass in paraplegics due to changes in vasomotor regulation below the level of the lesion.     

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.