Bio-energetic profile in 144 boys aged from 6 to 15 years with special reference to sexual maturation

Summary The effects of growth and pubertal development on bio-energetic characteristics were studied in boys aged 6–15 years (n = 144; transverse study). Maximal oxygen consumption (VO_2max, direct method), mechanical power at (VO_2max ( ), maximal anaerobic power (P_max; force-velocity test), mean power in 30-s sprint (P _30s; Wingate test) were evaluated and the ratios between P_max,P _30s and were calculated. Sexual maturation was determined using salivary testosterone as an objective indicator. Normalized for body massVO_2max remained constant from 6 to 15 years (49 ml· min^–1 · kg^–1, SD 6), whilst P_max andP _30s increased from 6–8 to 14–15 years, from 6.2 W · kg^–1, SD 1.1 to 10.8 W · kg^–1, SD 1.4 and from 4.7 W · kg^–1, SD 1.0 to 7.6 W · kg^–1, SD 1.0, respectively, (P < 0.001). The ratio P_max: was 1.7 SD 3.0 at 6–8 years and reached 2.8 SD 0.5 at 14–15 years and the ratioP _30s: changed similarly from 1.3 SD 0.3 to 1.9 SD 0.3. In contrast, the ratio P_max:P _30s remained unchanged (1.4 SD 0.2). Significant relationships (P < 0.001) were observed between P_max (W · kg^–1),P _30s (W · kg^–1), blood lactate concentrations after the Wingate test, and age, height, mass and salivary testosterone concentration. This indicates that growth and maturation have together an important role in the development of anaerobic metabolism.     

Heart rate threshold related to lactate turn point and steady-state exercise on a cycle ergometer

The aim of this study was to investigate heart rate threshold (HRT) related exercise intensities by means of two endurance cycle ergometer tests using blood lactate concentration. [La], pulmonary ventilation ( _E), oxygen uptake ( ), heart rate (HR) and electromyogram (EMG) activity of working muscle. Firstly, 16 healthy female students [age, 21.4 (SD 2.8) years; height, 167.1 (SD 5.1) cm; body mass 62.7 (SD 7.1) kg] performed an incremental exercise test (10 W each minute) on an electrically braked cycle ergometer until they felt exhausted. The HRT and lactate turn point (LTP) were assessed by means of computer-aided linear regression break point analysis from the relationship of HR or [La] to power output. No significant difference was found between HRT and LTP for all the variables measured. Secondly, two endurance tests (ET) of 20 min duration were performed by 7 subjects. The first (ET I) was performed at an exercise intensity which was about 10% lower than the power output at HRT [61.2 (SD 3.1) % maximal oxygen uptake ( _max)], the second (ET II) at an exercise intensity about 10% higher than the power output at HRT [79.2 (SD 3.4) % _max]. The parameters measured showed a clear steady state in ET I. All mean values were lower than values at HRT [power, 138.7 (SD 18.9) W; HR, 172.1 (SD 4.7) beats·min^–1; , 2.2 (SD 0.3) l·min^–1; _E, 54.0 (SD 9.1) l·min^–1; [La], 3.7 (SD 1.1) mmol·l^–1; EMG, 81.1 (SD 24.0) V] except HR which was the same. No parameters showed a steady state (except EMG activity) in ET II. No subject was able to maintain the exercise for the whole 20 min in ET II [mean time to cessation of the exercise was 10.4 (SD 3.7) min]. At the end of ET II all variables measured were significantly higher (P < 0.05) than in ET I (except EMG activity) [HR, 184.3 (SD 5.2) and 172.1 (SD 8.7) beats·min^–1; _E: 75.2 (SD 11.7) and 49.6 (SD 8.4) l·min^–1; , 2.9 (SD 0.7) and 2.1 (SD 0.5) l·min^–1; [La], 7.0 (SD 1.8) and 3.3 (SD 2.2) mmol·l^–1; EMG, 86.3 (SD 28.7) and 75.9 (SD 21.5) V]. Although no exercise, at HRT exactly was performed, we assume that maximal steady state lay in between ET I and ET II.     

Age predicts cardiovascular,but not thermoregulatory,responses to humid heat stress

Cross-section comparisons of the effect of age on physiological responses to heat stress have yielded conflicting results, in part because of the inability to separate chronological age from factors which change in concert with the biological aging process. The present study was designed to examine the relative influence of age on cardiovascular and thermoregulatory responses to low intensity cycle exercise (60 W for 1 h) in a warm humid environment (35°C, 80% relative humidity). Specifically, the relative importance of age compared to other individual characteristics [maximal oxygen uptake ( _max), physical activity level, anthropometry, and adiposity] was determined by multiple regression analysis in a heterogeneous sample of 56 subjects in which age (20–73 years) and _max (1.864–44 l · min^–1) were not interrelated. Dependent variables (with ranges) included final values of thermoregulatory responses [rectal temperature (T _re, 37.8–39.2°C), calculated heat storage (S, 3.4–8.1 J · g^–1), sweat loss (238–847 g · m^–2)] and cardiovascular responses [heart rate (HR, 94–176 beats min^–1), forearm blood flow (FBF, 5.3–31.3 ml · 100 ml^–1 · min^–1), mean arterial blood pressure (MAP, 68–122 mmHg), and forearm vascular conductance (FVC = FBF · MAP^–1, 0.06–0.44 ml · 100 ml^–1 · min^–1 · mmHg^–1). Age had no significant influence onT _re,S, or sweat loss, all of which were closely related to _max. On the other hand, HR, MAP, FBF, and FVC were related to both age and _max. Anthropometric variables and adiposity had secondary, but statistically significant, effects on MAP, FBF, FVC, and sweat loss. With respect to exercise in a warm humid environment, it was concluded that the effect of age on body temperature and sweating was negligible compared to effects related to _max, but that chronological age had an independent effect on cardiovascular effector responses.     

Energy expenditure and cardiorespiratory responses at the transition between walking and running

We investigated whether the spontaneous transition between walking and running during moving with increasing speed corresponds to the speed at which walking becomes less economical than running. Seven active male subjects [mean age, 23.7 (SEM 0.7) years, mean maximal oxygen uptake ( ), 57.5 (SEM 3.3) ml·kg ^–1·min ^–1, mean ventilatory threshold (VTh), 37.5 (SEM 3) ml·kg ^–1 ·min ^–1] participated in this study. Each subject performed four exercise tests separated by 1-week intervals: test 1, and VTh were determined; test 2, the speed at which the transition between walking and running spontaneously occurs (ST) during increasing speed (increases of 0.5 km·h ^–1 every 4 min from 5 km·h ^–1) was determined; test 3, the subjects were constrained to walk for 4 min at ST, at ST ± 0.5 km·h ^–1 and at ST ± 1 km·h ^–1; and test 4, the subjects were constrained to run for 4 min at ST, at ST±0.5 km·-h ^–1 and at ST±1 km·h ^–1. During exercise, oxygen uptake ( ), heart rate (HR), ventilation ( ), ventilatory equivalents for oxygen and carbon dioxide (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmOvayaaca% WaaSbaaSqaaiaabweaaeqaaOGaai4laiqadAfagaGaamaaBaaaleaa% caqGYaaabeaakiaacYcacaqGGaGaaeiiaiqadAfagaGaamaaBaaale% aacaqGfbaabeaakiaac+caceWGwbGbaiaacaqGdbGaae4tamaaBaaa% leaacaaIYaaabeaaaaa!4240!\[\dot V_{\text{E}} /\dot V_{\text{2}} ,{\text{ }}\dot V_{\text{E}} /\dot V{\text{CO}}_2 \]), respiratory exchange ratio (R), stride length (SL), and stride frequency (SF) were measured. The results showed that: ST occurred at 2.16 (SEM 0.04) m·s ^–1; , HR and speed at ST were significantly lower than the values measured at VTh (P< 0.001, P< 0.001 and P< 0.05, respectively); changed significantly with speed (P< 0.001) but was greater during running than walking below ST (ST minus 1 km·h ^–1, P< 0.001; ST minus 0.5 km·h ^–1, P< 0.05) with the converse above ST (ST.plus 1 km·h ^–1, P<0.05), whereas at ST the values of were very close [23.9 (SEM 1.1) vs 23.7 (SEM 0.8) ml·kg ^–1 · min ^–1 not significant, respectively, for walking and running]; SL was significantly greater during walking than running (P<0.001) and SF lower (P<0.001); and HR and were significantly greater during running than walking below ST (ST minus 1 km·h ^–1, P<0.01; ST minus 0.5 km·h ^–1, P{<0.05) with the converse above ST (ST plus 1 km·h ^–1, P·< 0.05), whereas no difference appeared for and R between the two types of locomotion. We concluded from this study that ST corresponded to the speed at which the energy expenditure of running became lower than the energy expenditure of walking but that the mechanism of the link needed further investigation.     

Cardiorespiratory effects of respiratory protective devices during exercise in well-trained men

Summary The effects of a filtering device, an air-line breathing apparatus and a self-contained breathing apparatus (SCBA) on pulmonary ventilation, oxygen consumption and heart rate were studied in 12 well-trained firemen aged 21–35 years. Their average maximal oxygen consumption ( max) was 64.9 ml·min^–1·kg^–1. Sequential tests without and with the respirator were performed on a treadmill. The continuous test contained five components, each of which lasted 5 min: sitting at rest, walking at 20%, 40%, and 60% of the individual max, and recovery sitting. During the higher submaximal work levels and recovery, ventilation, heart rate, and oxygen consumption in particular increased more with respirators than without them. At the highest work level the increments in oxygen consumption caused by the respirators were 13%, (8.7 ml·min^–1·kg^–1), 7% (4.4 ml·min^–1·kg^–1), and 20% (12.7 ml·min^–1·kg^–1) of max. All three respirators hampered respiration, resulting in hypoventilation. The additional effort of breathing and the weight of the apparatus (15 kg with the SCBA) increased the subjects' cardiorespiratory strain so clearly that the need for rest periods and the individual's work capacity when the respirators are worn must be carefully considered, particularly with the SCBA.     

A method for determining the maximal steady state of blood lactate concentration from two levels of submaximal exercise

The aim of this study was to estimate the characteristic exercise intensity _CL which produces the maximal steady state of blood lactate concentration (MLSS) from submaximal intensities of 20 min carried out on the same day and separated by 40 min. Ten fit male adults [maximal oxygen uptake _max 62 (SD 7) ml · min^–1 · kg^–1] exercisOed for two 30-min periods on a cycle ergometer at 67% (test 1.1) and 82% of _max (test 1.2) separated by 40 min. They exercised 4 days later for 30 min at 82% of _max without prior exercise (test 2). Blood lactate was collected for determination of lactic acid concentration every 5 min and heart rate and O₂ uptake were measured every 30 s. There were no significant differences at the 5th, 10th, 15th, 20th, 25th, or 30th min between , lactacidaemia, and heart rate during tests 1.2 and 2. Moreover, we compared the exercise intensities _CL which produced the MLSS obtained during tests 1.1 and 1.2 or during tests 1.1 and 2 calculated from differential values of lactic acid blood concentration ([1a^–]_b) between the 30th and the 5th min or between the 20th and the 5th min. There was no significant difference between the different values of _CL [68 (SD 9), 71 (SD 7), 73 (SD 6),71 (SD 11) % of _max (ANOVA test,P<0.05). Four subjects ran for 60 min at their _CL determined from periods performed on the same day (test 1.1 and 1.2) and the difference between the [la^–]_b at 5 min and at 20 min ( ([la^–]_b)) was computed. The [la^–]_b remained constant during exercise and ranged from 2.2 to 6.7 mmol · l^–1 [mean value equal to 3.9 (SD 1) mmol · l^–1]. These data suggest that the _CL protocol did not overestimate the exercise intensity corresponding to the maximal fractional utilization of _max at MLSS. For half of the subjects the _CL was very close to the higher stage (82% of _max where an accumulation of lactate in the blood with time was observed. It can be hypothesized that _CL was very close to the real MLSS considering the level of accuracy of [la^–]_b measurement. This study showed that exercise at only two intensities, performed at 65% and 80% of _max and separated by 40 min of complete rest, can be used to determine the intensity yielding a steady state of [la^–1]_b near the real MLSS workload value.     

Potassium activity in cells of isolated perfused cortical thick ascending limbs of rabbit kidney

The Na⁺2Cl^–K⁺ cotransporter in the apical membrane of the cortical thick ascending limb of the Henle's loop (cTAL) of rabbit nephron utilizes the electrochemical gradient for Na⁺ to transport K⁺ and Cl^– against an unfavorable electrochemical gradient from lumen to cell interior. In the present study attempts are made to measure intracellular K⁺ activity ( ) under control conditions and after inhibition of the cotransport system by furosemide (50·10^–6 mol·l^–1). 70 cTAL segments of 55 rabbits were perfused in vitro. Conventional Ling-Gerard and K⁺-selective microelectrodes were used to measure the PD across the basolateral membrane (PD_bl) as well as the PD sensed by the single barrelled K⁺-selective electrode ( ). PD_bl was –64±1 (n=65) mV and +15±1 (n=32) mV under control conditions. The positive value, significantly different from zero, indicates that is higher than predicted for passive distribution. The estimate for obtained from PD_bl and was 113±8 mmol·l^–1. Furosemide lead to the previously reported hyperpolarization of PD_bl by 17±4 (n=13) mV and to a reduction of from 15±1 to 5±1 (n=20) mV. The , obtained from this set of data, was 117±9 mmol·l^–1, and was not different from the control value. The present data indicate that is significantly above Nernst equilibrium under control conditions. The source for this above equilibrium accumulation of K⁺ stems from the carrier mediated uptake of Na⁺2Cl^– and K⁺. Consequently, the electrochemical gradient for K⁺ is rapidly reduced when the carrier is blocked by furosemide. The electrochemical gradient for K⁺, under control conditions, energizes the back leak of K⁺ from cell to lumen. This K⁺ flux is one component responsible for the lumen positive transepithelial PD.Parts of this study have been presented at the 58th Tagung Deutsche Physiologische und Deutsche Pharmakologische Gesellschaft, Mainz 1983; 67th Federation Meeting, Chicago 1983. This study was supported by Deutsche Forschungsgemeinschaft Gr. 480/5-7     

Use of oxygen uptake recovery curve to predict peak oxygen uptake in upper body exercise

A group of 18 well-trained white-water kayakers performed maximal upper body exercise in the laboratory and during.a field test. Laboratory direct peak oxygen uptake ( ) values were compared, firstly by a backward extrapolation estimation and secondly by an estimation calculated from measured during the first 20 s of exercise recovery. Direct peak correlated with backward extrapolation (r=0.89), but the results of this study showed that the backward extrapolation method tended to overestimate significantly peak by [0.57 (SD 0.31) 1·min^–1 in the laboratory, and 0.66 (SD 0.33) 1·min^–1 in the field,P<0.001]. The measured during the first 20 s of recovery, whether the exercise was performed in the laboratory or in the field, correlated well with the laboratory direct peak (r=0.92 andr=0.91, respectively). The use of the regression equation obtained from field data _2f20s, that is peak ₂=0.23+1.08 _2f20s, gave an estimated peak ₂, the mean difference of which compared with direct peak was 0.22 (SD 0.13) 1·min^–1. In conclusion, we propose the use of a regression equation to estimate peak from a single sample of the gas expired during the first 20 s of recovery after maximal exercise involving the upper part of the body.     

Effects of acute hypoxia and CO2 inhalation on systemic and peripheral oxygen uptake and circulatory responses during moderate exercise

Summary The effect of acute hypoxia and CO₂ inhalation on leg blood flow (LBF), on leg vascular resistance (LVR) and on oxygen supply to and oxygen consumption in the exercising leg was studied in nine healthy male subjects during moderate one-leg exercise. Each subject exercised for 20 min on a cycle ergometer in four different conditions: normoxia, normoxia +2% CO₂, hypoxia corresponding to an altitude of 4000 m above sea level, and hypoxia +1.2% CO₂. Gas exchange, heart rate (HR), arterial blood pressure, and LBF were measured, and arterial and venous blood samples were analysed for , , oxygen saturation, haematocrit and haemoglobin concentration. Systemic oxygen consumption was 1.83 l · min^–1 (1.48–2.59) and was not affected by hypoxia or CO₂ inhalation in hypoxia. HR was unaffected by CO₂, but increased from 136 beat · min^–1 (111–141) in normoxia to 155 (139–169) in hypoxia. LBF was 6.5 l · min^–1 (5.4–7.6) in normoxia and increased significantly in hypoxia to 8.4 (5.9–10.1). LVR decreased significantly from 2.23 kPa · l^–1 · min (1.89–2.99) in normoxia to 1.89 (1.53–2.52) in hypoxia. The increase in LBF from normoxia to hypoxia correlated significantly with the decrease in LVR. When CO₂ was added in hypoxia a significant correlation was also found between the decrease in LBF and the increase in LVR. In normoxia, the addition of CO₂ caused a significant increase in mean blood pressure. Oxygen consumption in the exercising leg (leg ) in normoxia was 0.97 l · min^–1 (0.72–1.10), and was unaffected by hypoxia and CO₂. It is concluded that the O₂ supply to the exercising leg and its are unaffected by hypoxia and CO₂. The increase in LBF in hypoxia is caused by a decrease in LVR. These changes can be counteracted by CO₂ inhalation. It is proposed that the regulatory mechanism behind these changes is that change in brain causes change in the central regulation of vascular tonus in the muscles.     

Physical work capacity in dynamic exercise with differing muscle masses in healthy young and older men

Ten young (aged 23–30 years) and nine older (aged 54–59 years) healthy men with similar estimated limb muscle volumes performed, in random order, three different types of ergometer exercise tests (one-arm cranking, two-arm cranking, and two-leg cycling) up to the maximal level. Values for work load (WL), peak oxygen consumption , peak heart rate (HR), peak ventilation , respiratory gas exchange ratio (R), recovery blood lactate concentration [La^–], and rating of perceived exertion (RPE) were compared between the age-groups in the given exercise modes. No significant age-related differences in WL, peak , peak HR, R, [La^–], or RPE were found in one-arm or two-arm cranking. During one-arm cranking the mean peak was 1.65 (SD 0.26)1 · min^–1 among the young men and 1.63 (SD 0.10)1 · min^–1 among the older men. Corresponding mean peak during two-arm cranking was 2.19 (SD 0.32)1 · min-1 and 2.09 (SD 0.18)1 · min^–1, respectively. During one-arm cranking peak was higher (P < 0.05) among the older men compared to the young men. During two-leg cycling the young men showed higher values in WL (P < 0.001), peak (P < 0.001), and peak HR (P < 0.001). The mean peak was 3.54 (SD 0.24)1 · min^–1 among the young men and 3.02 (SD 0.20)1 · min^–1 among the older men. Corresponding mean peak HR was 182 (SD 5) beats · min^–1 and 170 (SD 8) beats · min^–1, respectively. During two-leg cycling, peak , R, [La^–], and RPE did not differ between the two age-groups. In summary, the older men with similar sizes of estimated arm and leg muscle volumes as the young men had a reduced physical work capacity in two-leg cycling. In one-arm or two-arm cranking, no significant difference in work capacity was found between the age-groups. These results indicate, that in healthy men, age, at least up to the 6th decade of life, is not necessarily associated with a decline in physical work capacity in exercises using relatively small muscle groups, in which the limiting factors are more peripheral than central.     

Prediction of individual oxygen uptake on-step transients from frequency responses

Power-oxygen uptake ( ) frequency responses can be used to predict responses to arbitrary exercise intensity patterns. It is still an open question for which range of exercise intensities such computed response patterns yield valid predictions. In the present study, we determined the power- frequency response of nine sports students by means of pseudo-randomised switching between 20 W and 80 W during upright and supine cycle exercise. Starting from a baseline of 20 W each subject also performed sustained step increases to 40 W, 80 W, 120 W, and 160 W in both positions. The individual step responses were then compared with the expected time-courses predicted on the basis of the individual frequency responses. The comparison showed a close agreement for the 20 W–40 W and 20 W–80 W steps in both positions. With larger step amplitudes the kinetics became increasingly slower than the predicted time course in both positions. During additional ramp tests (10 W · 30 s^–1) whole blood lactic acid concentration [1a^–]_b tended to be higher in the supine position at exercise intensities higher than 160 W. The mean power at 4 mmol · 1^–1 [la^–]_b amounted to 234 (SD 32) W and 253 (SD 44) W (P<5%) in the supine and the upright position, respectively. The maximal oxygen uptake relative to body mass was not found to be significantly different [upright, mean 57 (SD 10) ml · (min · kg)^–1;supine, mean 54 (SD 10) ml · (min · kg)]. These findings would suggest that for a range of mild exercise intensities kinetics are not appreciably influenced by the step amplitude or by cardiovascular changes associated with the upright and the supine position.     

Oxygen uptake as related to work rate increment during cycle ergometer exercise

Summary We postulated that the commonly observed constant linear relationship between and work rate during cycle ergometry to exhaustion is fortuitous and not due to an unchanging cost of external work. Therefore we measured continuously in 10 healthy men during such exercise while varying the rate of work incrementation and analyzed by linear regression techniques the relationship between and work rate ( / wr). After excluding the first and last portions of each test we found the mean ±SD of the / wr in ml · min^–1· W^–1 to be 11.2±0.15, 10.2±0.16, and 8.8±0.15 for the 15, 30, and 60 W·min^–1 tests, respectively, expressed as ml·J^–1 the values were 0.187±0.0025, 0.170±0.0027 and 0.147±0.0025. The slopes of the lower halves of the 15 and 30 W·min^–1 tests were 9.9±0.2 ml·min^–1·W^–1 similar to the values for aerobic work reported by others. However the upper halves of the 15, 30, and 60 W·min^–1 tests demonstrated significant differences: 12.4±0.36 vs 10.5±0.31 vs 8.7±0.23 ml·min^–1·W^–1 respectively. We postulate that these systematic differences are due to two opposing influences: 1) the fraction of energy from anaerobic sources is larger in the brief 60 W·min^–1 tests and 2) the increased energy requirement per W of heavy work is evident especially in the long 15 W·min^–1 tests.     

Longitudinal study of the effect of high intensity weight training on aerobic capacity

To investigate the effect of a long-term weight lifting programme characterized by high intensity, low repetition and long rest period between sets on maximal oxygen consumption ( _max) and to determine the advantage of this programme combined with jogging, 26 male untrained students were involved in weight training for a period of 3 years. The _max and body composition of the subjects were examined at beginning, 1 year, 2 years (T₂), and 3 years after (T₃) training. Of the group, 19 subjects performed the weight lifting programme 5 days each week for 3 years (W-group), 4 subjects performed the same weight lifting programme for 3 years with an additional running programme consisting of 2 miles of jogging once a week during the 3rd year (R1-group), and 3 subjects performed the weight lifting programme during the 1st year and the same combined jogging and weight lifting programme as the R1-group during the 2nd and 3rd years (R2-group). The average _max relative to their body mass of the W-group decreased significantly during the 1st year, followed by an insignificant decrease in the 2nd year and a levelling off in the 3rd year. The average _max Of the W-group at T₂ and T₃ was 44.2 and 44.1 ml · kg^–1 · min^–1, respectively. The tendency of _max changes in the R1- and R2-groups was similar to the W-group until they started the jogging programme, after which they recovered significantly to the initial level within a year of including that programme, and they then levelled off during the next year. Lean body mass estimated from skinfold thicknesses had increased by about 8% after 3 years of weight lifting. The maximal muscle strength, defined by total olympic lifts (snatch, and clean and jerk), of these three groups increased significantly and there was no significant difference among the amounts of the increase in the three groups. These results suggested that high intensity weight training combined with jogging could be recommended for weight-trained athletes for developing optimal muscle strength without a concomitant reduction in _max.     

Some simple multiple linear regression equations for estimation of maximal aerobic power in healthy indian males

Summary An attempt has been made to evolve some simple multiple linear regression equations for the prediction of max from body weight, time for 3.2 km run and exercise dyspnoeic index (DI_std Ex%). The predictor variables have been selected by examining the product moment correlations of body weight, relative body weight indices, time for 3.2 km run, chest expansion, height, and DI_std Ex% with max, based on data collected on 320 healthy Indian males (17–22 years). It has been observed that body weight, time for 3.2 km run and DI_std Ex% attained maximum correlations with max. Thus, two regression equations with two and three predictor variables have been established in this paper to predict max. The first regression equation yielded a multiple correlation of 0.608 (P<0.001) with a standard error of 0.214 l·min^–1. In this equation, body weight and time for 3.2 km run were considered as significant predictors. To increase the precision of this equation, another multiple linear regression equation based on body weight, time for 3.2 km run and DI_std Ex% as predictors has been developed. This equation yielded a multiple correlation of 0.658 (P<0.001) with a standard error of 0.204 l·min^–1. Applications of these regression equations will be of practical importance to biomedical scientists engaged in the development of a simple procedure for indirect assessment of max, and may serve well as preliminary screening procedures for personnel selection.     

Ventilatory response during incremental exercise tests in weight lifters and endurance cyclists

Summary The effect of a progressively increasing work rate (15 W·min^–1) up to exhaustion on the time course of O₂ uptake ( ), ventilation ( ) and heart rate (HR) has been studied in weight lifters (WL) in comparison to endurance cyclists (Cycl) and sedentary controls (Sed). and were measured as average value of 30-s intervals by a semiautomatic open circuit method. was 2.55±0.33; 4.29±0.53 and 2.86±0.19·min^–1 in WL, Cycl and Sed respectively. With time and work rate, while and HR increased linearly, changed its slope at two levels. The 1st change occured at a work load corresponding to a mean (± SD) of 1.50±0.26; 1.93±0.34; and 1.23±0.14 l·min^–1 in WL, Cycl, and Sed respectively. values corresponding to the second change of slope were 2.18±0.32 in WL; 3.48±0.53 in Cycl and 2.17±0.28 l·min^–1 in Sed. The first change of slope might be the consequence of the different readjustment of on-response and hence of early lactate in the different subjects. The second change seems to be comparable to the conventional anaerobic threshold and is achieved in all subjects when vs time slope is 7–10 l·min^–1/min of exercise.This work has been supported in part by a grant from the Italian National Research Council (CNR)     

Effect of high intensity interval training on 2,3-diphosphoglycerate at rest and after maximal exercise

Summary The purpose of this study was to examine the effect of intense interval training on erythrocyte 2,3-diphosphoglycerate (2,3-DPG) levels at rest and after maximal exercise. Eight normal men, mean ± SE=24.2±4.3 years, trained 4 days·week^–1 for a period of 8 weeks. Each training session consisted of eight maximal 30-s rides on a cycle ergometer, with 4 min active rest between rides. Prior to and after training the subjects performed a maximal 45-s ride on an isokinetic cycle ergometer at 90 rev·min^–1 and a graded leg exercise test (GLET) to exhaustion on a cycle ergometer. Blood samples were obtained from an antecubital vein before, during and after the GLET only. Training elicited significant increases in the amount of work done during the 45-s ride (P<0.05), and also in maximal oxygen uptake ( max: Pre=4.01±0.13; Post=4.29±0.07 l·min^–1;P<0.05) during exercise and total recovery (Pre=19.14±0.09; Post=21.45±0.10 l·30 min^–1;P<0.05) after the GLET. After training blood lactate was higher, base excess lower and pH lower during and following the GLET (P<0.05 for all variables). Training caused no significant differences in erythrocyte 2,3-DPG levels at rest (Pre=11.8±0.7; Post=12.1±0.7 mol·g^–1 hemoglobin (Hb);P>0.05), at exhaustion (Pre=12.0±0.8; Post=11.2±0.8 mol·g^–1 Hb;P>0.05) or during 30 min of recovery from the GLET. Additionally, acute exercise (pre-training GLET) did not effect any change in 2,3-DPG at exhaustion or during recovery from exercise compared to resting values. The higher max and total recovery values observed after training appear to be unrelated to 2,3-DPG levels. Under the present conditions, the role, if any, of 2,3-DPG in enhancing tissue oxygenation during increased metabolic demand remains obscure.Supported by grants from Miles Laboratories, Elkhart, Indiana, and the Ball State Graduate Student Research Fund     

Cardiorespiratory and metabolic adaptations to hyperoxic training

This study examined the effects of hyperoxic training on specific cardiorespiratory and metabolic responses. A group of 19 male subjects trained for 5 weeks on a cycle ergometer at 70% of hyperoxic or normoxic maximal heart rate, the hyperoxic group (HG) breathing 70% O₂, the normoxic group (NG) breathing 21% O₂. The subjects were tested pre- and post-training under both hyperoxia and normoxia. Measurements included cardiac output , stroke volume (SV), heart rate (HR), pulmonary ventilation , oxygen consumption , partial pressure of oxygen (PO₂), partial pressure of inspired carbon dioxide (PCO₂), blood lactate concentration [L], and fiber type composition. The was significantly lower at submaximal work rates (P < 0.05) and maximal increased after training in both groups for both test conditions; hyperoxic was lower than normoxic (P < 0.05). The maximal increased significantly (P < 0.05) in both groups for both tests and was 11%–12% higher during hyperoxia. Post-training maximal heart rate (HR_max) was significantly decreased (P < 0.05) at the same absolute work rate regardless of the training group or test type. The SV was increased at each work rate and was unchanged. The maximal increased significantly (P < 0.05) for both groups and types of test: for normoxia: NG 27.3–30.4 l · min^–1 and HG 30.3–32.31 · min^–1 and for hyperoxia: NG 24.7–25.6 and HG 27.9–31.2 l · min^–1. Although working at the same intensity relative to HR_max, HG showed significantly lower [L] following a single training session, yet maximal values were unchanged after training. Both groups showed a significant increase in the percentage of type IIA fibers post-training but HG retained a larger percentage of HB fibers. Mitochondrial enzymes; citrate kinase, 3-hydroxyacyl CoA dehydrogenase, and cytochrome c-oxidase were increased in the normoxic trained subjects (P < 0.05). In summary, training induced adaptive responses in maximal aerobic power, HR, SV, , [L], and muscle fiber type composition, independent of inspired PO₂. Intramuscular data suggested there may be some differences between hyperoxic and normoxic training and these were substantiated by mitochondrial enzyme and lactate findings. Our data would suggest that transport mechanisms may limit the ability to increase aerobic power.     

Ventilatory and lactate threshold determinations in healthy normals and cardiac patients: methodological problems

In healthy normal individuals (n = 69), coronary patients with myocardial ischaemia (n = 27) and patients with chronic heart failure (CHF, n = 33), four widely applied methods to determine ventilatory threshold (VT) were analysed: V-slope, ventilatory equivalent for O₂ (EqO₂), gas exchange ratio (R) and end-tidal partial pressure of oxygen. Lactate threshold [LAT, log lactate vs log oxygen uptake ( )] was also determined. Analysis focused on rate of success of threshold determination, comparability of threshold methods, reproducibility and interobserver variability. Cycle ergometry protocols with ramp-like mode and graded steady-state mode used in exercise testing were considered separately. In healthy normal individuals and coronary patients with myocardial ischaemia, at least three VT could be determined during ramp-like mode and two VT during graded steady-state mode, 82% of the time. For CHF patients, the rate of successful determination of VT was lower. Compared to LAT, at VT was significantly higher using R and EqO₂ methods of VT determination in healthy normal subjects (P < 0.01), and significantly higher when using all four methods in coronary patients (P < 0.01 or P < 0.05, respectively). No difference was observed between at VT and LAT in CHF patients. In healthy normal individuals, day-to-day reproducibility of VT and LAT was high (error of a single determination from duplicate determinations was between 3.9% and 6.2% corresponding to a of 52.2 and 89.2 ml·min ^–1). Interobserver variability was low (error between 0.3% and 5% corresponding to a of 9.8 and 68 ml·min^–). In CHF patients, interobserver variability was moderately greater (error between 4.6% and 8.2%, corresponding to a of 35.1 and 62.4 ml·min^–1). To optimize threshold determination, standardized procedures are suggested.     

Times to exhaustion at 100% of velocity at\dot V{\text{O}}_{\text{2}} max and modelling of the time-limit / velocity relationship in elite long-distance runners

The aim of this study was to measure running times to exhaustion (Tlim) on a treadmill at 100% of the minimum velocity which elicits _{max max} in 38 elite male long - distance runners _max = 71.4 ± 5.5 ml.kg^–1.min^–1 and _max = 21.8 ± 1.2 km.h^–1). The lactate threshold (LT) was defined as a starting point of accelerated lactate accumulation around 4 mM and was expressed in _max. Tlim value was negatively correlated with _max (r = -0.362, p< 0.05) and _max (r = –0.347, p< 0.05) but positively with LT (%v _max) (r = 0.378, p < 0.05). These data demonstrate that running time to exhaustion at _max in a homogeneous group of elite male long-distance runners was inversely related to _max and experimentally illustrates the model of Monod and Scherrer regarding the time limit-velocity relationship adapted from local exercise for running by Hughson et al. (1984) .     

Physiological correlates of middle-distance running performance

Summary To compare the relative contributions of their functional capacities to performance in relation to sex, two groups of middle-distance runners (24 men and 14 women) were selected on the basis of performances over 1500-m and 3000-m running races. To be selected for the study, the average running velocity ( ) in relation to performances had to be superior to a percentage (90% for men and 88% for women) of the best French achieved during the season by an athlete of the same sex. Maximal O₂ consumption ( _max) and energy cost of running (C_R) were measured in the 2 months preceding the track season. This allowed us to calculate the maximal that could be sustained under aerobic conditions, _a,max. A : _{a, max} ratio derived from 1500-m to 3000-m races was used to calculate the maximal duration of a competitive race for which = _a,max (t a,max) In both groups _a,max was correlated to . The relationships calculated for each distance were similar in both sexes. The C_R [0.179 (SD 0.010) ml · kg^–1 · m^–1 in the women versus 0.177 (SD 0.010) in the men] andt _a,max [7.0 (SD 2.0) min versus 8.4 (SD 2.1)] also showed no difference. The relationships between _max and body mass (m _b) calculated in the men and the women were different. At the samem _b the women had a 10% lower C_R than the men; their lowerm _b thus resulted in an identical C_R. In both groups C_R and _max were strongly correlated (r=0.74 and 0.75 respectively,P<0.01), suggesting that a high level of _max could hardly be associated with a low C_R. These relationships were different in the two groups (P<0.05). At the same _max the men had a higher _a,inax than the women. Thus, the disparity in track performances between the two sexes could be attributed to _max and to the _max/C_R relationships.