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.     

Criteria for maximum oxygen uptake in progressive bicycle tests

Summary Different criteria for O₂ max in a progressive bicycle exercise were studied in 115 healthy subjects. In the repeated progressive tests performed on 16 men, aged 25–35 years, three types of O₂ response against work load were noticed: a linear increase, an unexpectedly high increase, and a plateau; the last two only appearing when O₂ max was achieved. The last three O₂ values at least were required to define the plateau. Most commonly, subjective exhaustion was achieved, respiratory quotient (R) was over 1.15 and maximal heart rate (HR) at the estimated level for age, though O₂ max was not achieved. No significant differences were found between peak O₂ in the first progressive test (mean=2.95 l/min), the second progressive test (mean=3.14 l/min), or the constant-load test (mean=3.05 l/min). In the progressive test performed once on 55 men and 44 women, aged 35–62 years, subjective exhaustion was achieved by most of the subjects, but the plateau in O₂ was shown only in 17 subjects, and the peak O₂ values were somewhat lower than expected. Moreover, R max did not correlate with peak O₂, and was over 1.15 only in 9 subjects, and HR max was often below the estimated level. Thus, the progressive test appeared to be convenient in testing the physical work capacity of the subjects, but the establishment of the physiological maximum was more difficult: the relatively uncommon plateau in O₂ was the only useful criterion for O₂ max, the value of other criteria being unacceptable.     

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     

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.     

Critical analysis of the “anaerobic threshold” during exercise at constant workloads

Summary The method described by Wasserman for anaerobic threshold (AT) determination, based on the recording of ventilatory parameters, was supported by the simultaneous appearance of hyperlactacidemia and hyperventilation during a standardized incremental work test. Our study aimed at testing the AT in another profile of exercise, viz., during exercises at constant workloads.A homogenous population of 66 healthy subjects performed on a treadmill a total of 100 exercises of 20 min duration at constant workloads (43, 48, 52, 57, 63, and 71% O₂max). The O₂, , and venous plasma lactic acid (LA) were determined every minute.LA showed an initial transient increase at 43% O₂ max and a steady-state elevated level above 48% O₂ max. In contrast, the hyperventilation threshold (HVT) was only observed above 57% O₂ max, simultaneously with a delayed steady-state O₂ and with a sustained increase of lactate until the end of exercise.The meaning of the simultaneity of these three events must still be studied. However, the dissociation between both early and steady-state lactate thresholds and HVT is not in keeping with the concept of AT. In these conditions, there is no evidence that HVT necessarily represents an AT, viz., a critical intensity of exercise inducing an insufficient oxygen delivery to the muscles. This conclusion does not imply that the measurement of HVT should be rejected as an empirical test of physical fitness.     

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.     

Noninvasive measurement of human forearm oxygen consumption by near infrared spectroscopy

Summary This study reported on the application of near infrared spectroscopy (NIRS) to noninvasive measurements of forearm brachio-radial muscle oxygen consumption ( O₂) and recovery time (t _r) in untrained volunteers. Seven healthy subjects were submitted to four consecutive protocols involving measurements made at rest, the induction of an ischaemia, and during a maximal increase of metabolic demand achieved with and without vascular occlusion. Two isometric maximal voluntary contractions (MVC) of 30-s duration were executed with and without vascular occlusion and a 50% MVC lasting 125 s was also performed. The protocols were repeated on 2 different days. The results showed that, during vascular occlusion at rest, the time to 95% of the final haemoglobin (Hb) + myoglobin (Mb) desaturation value was independent of O₂. The MVC, performed during vascular occlusion, caused complete Hb + Mb desaturation in 15–20 s, which was not followed by any further desaturation when the second contraction was performed. No difference was found between O₂during MVC with and without vascular occlusion. A consistent difference was seen between O₂measured during occlusion at rest and O₂measured during MVC with and without occlusion. During prolonged exercise (125 s) Hb + Mb desaturation was maintained for the whole contraction period. The results of this study show that O₂can be measured noninvasively by NIRS. The O₂during MVC was very similar both in the presence and absence of blood flow limitation in most of the subjects tested. This would suggest that muscle O₂might be accurately evaluated dynamically without cuff occlusion.     

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.     

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.     

Maximal aerobic capacity for repetitive lifting: comparison with three standard exercise testing modes

Summary A multi-stage, repetitive lifting maximal oxygen uptake ( ) test was developed to be used as an occupational research tool which would parallel standard ergometric testing procedures. The repetitive lifting test was administered to 18 men using an automatic repetitive lifting device. An intraclass reliability coefficient of 0.91 was obtained with data from repeated tests on seven subjects. Repetitive lifting test responses were compared to those for treadmill, cycle ergometer and arm crank ergometer. The mean±SD repetitive lifting of 3.20±0.42 l · min^–1 was significantly (p<0.01) less than treadmill ( = 0.92 l · min^–1) and cycle ergometer ( = 0.43 l· min^–1) and significantly greater than arm crank ergometer ( = 0.63 l · min^–1). The correlation between repetitive lifting oxygen uptake and power output wasr = 0.65. correlated highly among exercise modes, but maximum power output did not. The efficiency of repetitive lifting exercise was significantly greater than that for arm cranking and less than that for leg cycling. The repetitive lifting test has an important advantage over treadmill or cycle ergometer tests in the determination of relative repetitive lifting intensities. The individual curves of vs. power output established during the multi-stage lifting test can be used to accurately select work loads required to elicit given percentages of maximal oxygen uptake.     

Severe hypoxia decreases oxygen uptake relative to intensity during submaximal graded exercise

Summary The effect of severe acute hypoxia (fractional concentration of inspired oxygen equalled 0.104) was studied in nine male subjects performing an incremental exercise test. For power outputs over 125 W, all the subjects in a state of hypoxia showed a decrease in oxygen consumption ( O₂) relative to exercise intensity compared with normoxia (P < 0.05). This would suggest an increased anaerobic metabolism as an energy source during hypoxic exercise. During submaximal exercise, for a given O₂, higher blood lactate concentrations were found in hypoxia than in normoxia (P < 0.05). In consequence, the onset of blood lactate accumulation (OBLA) was shifted to a lower O₂ ( O₂ 1.77 l·min^–1 in hypoxia vs 3.10 l·min^–1 in normoxia). Lactate concentration increases relative to minute ventilation ( _E) responses were significantly higher during hypoxia than in normoxia (P < 0.05). At OBLA, _E during hypoxia was 25% lower than in the normoxic test. This study would suggest that in hypoxia subjects are able to use an increased anaerobic metabolism to maintain exercise performance.     

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.     

Lipid metabolism during exercise I: Physiological and biochemical characterization of normal healthy male subjects in relation to their physical fitness

Summary On the basis of maximal oxygen uptake ( O₂ max) 18 normal, healthy men were divided into two groups of equal size: moderately trained subjects (MTR) each having O₂ max below 65.0 ml·min^–1·kg^–1 body weight (54.0±8.3) and well trained subjects (WTR), whose O₂ max exceeded 65.0 ml·min^–1·kg^–1 body weight (69.2±4.1). The WTR group had slightly (non significant, n.s.) higher percentage of slow twitch, oxidative (SO) fibers in M. vastus lateralis and higher (n.s.) activities of cytochrome c oxidase (CytOx), succinate dehydrogenase (SDH), 3-hydroxyacyl-CoA-dehydrogenase (HADH), and citrate synthase (CS), while lactate dehydrogenase (LDH) activity was lower (n.s.). In the MTR group only, the SO-%, and the activities of CytOx, SDH and HADH correlated positively with O₂ max, and LDH negatively with O₂ max. These correlations were not significant in the WTR group possibly because of the adaptations produced by training in this group. Multiple regression analysis was used to elucidate the best combination of variables to explain the variance in O₂ max. The best model consisted of the sum of relative activities of oxidative muscle enzymes (CytOx, SDH, HADH, CS), muscle LDH activity, body fat content (% F) and lean body mass. This model explained 69% of the variance in O₂ max; and of the individual variables % F was of utmost importance.     

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.     

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 influence of inspired oxygen on the oxygen uptake response to ramp exercise

The relation between and work rate (WR) was examined in seven male subjects who performed ramp (1 W·3 s^–1) two-legged cycle ergometry to exhaustion while inspiring either hypoxic (12% O₂), normoxic (21% O₂), or hyperoxic (40% O₂) air. The anaerobic threshold was estimated from respiratory gas exchange data and is thus referred to as the respiratory gas exchange threshold (RGET). Prior to the RGET, the was greater under normoxic [mean (SD); 10. 19(1.04) ml O₂·min^–1·W^–1] and hyperoxic [10.44 (0.72)] conditions compared with hypoxia [9.34 (0.89)]. Above the RGET, the for hypoxia [8.91 (0.63)], normoxia [10.40 (0.77)], and hyperoxia [11.08 (0.48)] were all significantly different from each other. These data indicated that for two-legged, cycle, ramp ergometry in normoxia below the RGET, both the and response time was constant. Above the RGET, the normoxic response was the net result of a declining and a longer response time to the unsteady state character of a ramp exercise protocol.     

Effect of previous supramaximal work on lacticaemia during supra-anaerobic threshold exercise

Summary Twelve male and female subjects (eight trained, four untrained) exercised for 30 min on a treadmill at an intensity of maximal O₂ consumption (% O_2max) 90.0%, SD 4.7 greater than the anaerobic threshold of 4 mmol ·1^–1 (Th_an =83.6% O_2max, SD 8.9). Time-dependent changes in blood lactate concentration ([la_b]) during exercise occurred in two phases: the oxygen uptake ( O₂) transient phase (from 0 to 4 min) and the O₂ steady-state phase (4–30 min). During the transient phase, [la_b] increased markedly (l.30 mmol · l ^–1 · min ^–1, SD 0.13). During the steady-state phase, [la_b] increased slightly (0.02 mmol · 1^–1 · min^–1, SD 0.06) and when individual values were considered, it was seen that there were no time-dependent increases in [la_b] in half of the subjects. Following hyperlacticaemia (8.8 mmol -l^–1, SD 2.0) induced by a previous 2 min of supramaximal exercise (120% O_2max), [la_b] decreased during the O₂ transient (–0.118 mmol · 1^–1 · min^–1, SD 0.209) and steady-state (–0.088 mmol · 1^–1 · min ^–1, SD 0.103) phases of 30 min exercise (91.4% O_2max, SD 4.8). In conclusion, it was not possible from the Th_an to determine the maximal [la_b] steady state for each subject. In addition, lactate accumulated during previous supramaximal exercise was eliminated during the O₂ transient phase of exercise performed at an intensity above the Th_an. This effect is probably largely explained by the reduction in oxygen deficit during the transient phase. Under these conditions, the time-course of changes in [la_b] during the O₂ steady state was also affected.     

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     

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.