Estimation of<Emphasis Type="Italic"> V̇</Emphasis>O<Subscript>2max</Subscript> from the ratio between HR<Subscript>max </Subscript>and HR<Subscript>rest</Subscript> – the Heart Rate Ratio Method

The effects of ̇raining and/or ageing upon maximal oxygen uptake (O_2max) and heart rate values at rest (HR_rest) and maximal exercise (HR_max), respectively, suggest a relationship between O_2max and the HR_max-to-HR_rest ratio which may be of use for indirect testing of O_2max. Fick principle calculations supplemented by literature data on maximum-to-rest ratios for stroke volume and the arterio-venous O₂ difference suggest that the conversion factor between mass-specific O_2max (ml·min^–1·kg^–1) and HR_max·HR_rest ^–1 is ~15. In the study we experimentally examined this relationship and evaluated its potential for prediction of O_2max. O_2max was measured in 46 well-trained men (age 21–51 years) during a treadmill protocol. A subgroup (n=10) demonstrated that the proportionality factor between HR_max·HR_rest ^–1 and mass-specific O_2max was 15.3 (0.7) ml·min^–1·kg^–1. Using this value, O_2max in the remaining 36 individuals could be estimated with an SEE of 0.21 l·min^–1 or 2.7 ml·min^–1·kg^–1 (~4.5%). This compares favourably with other common indirect tests. When replacing measured HR_max with an age-predicted one, SEE was 0.37 l·min^–1 and 4.7 ml·min^–1·kg^–1 (~7.8%), which is still comparable with other indirect tests. We conclude that the HR_max-to-HR_rest ratio may provide a tool for estimation of O_2max in well-trained men. The applicability of the test principle in relation to other groups will have to await direct validation. O_2max can be estimated indirectly from the measured HR_max-to-HR_rest ratio with an accuracy that compares favourably with that of other common indirect tests. The results also suggest that the test may be of use for O_2max estimation based on resting measurements alone.An erratum to this article can be found at     

Lactate after exercise in man: III. Properties of the compartment model

Summary Lactate movements during recovery following muscular exercise in man were studied by means of a two-compartment model. Mathematical discussion of the literal expressions obtained allows one to represent parameters concerning lactate exchange, utilization, and production in the previously working muscles and in the remaining lactate distribution space. It also shows that bi-exponential time courses predicted for muscular and blood lactate concentrations as well as for rates of lactate uptake, release, and utilization can denote several morphologies. All of the time evolutions for muscular and blood lactate concentrations found in the literature are consistent with these theoretical possibilities in the model. A numerical application confirms this concordance. Thus, this simple model, for which the basic assumptions were previously justified, appears to be qualitatively able to describe lactate exchanges and disappearance after exercise. A practical algorithm is put forward to display its possibilities and to test further its quantitative validity.List of Abbreviations and Symbols ₁₂, ₂₁ Coefficients of efficiency in lactate transfer from (M) to (S) and (S) to (M), respectively (min^–1) - A ₁, A ₂ Amplitudes of the exponential terms of fits to L _a (t) (mmol·l^–1) - (AS1), (AS2), (AS3), (AS4) Assumptions on which the model is based - A-curves Graphs of monotonic time functions - B-curves Graphs of time functions showing an extremum and an inflexion point - C ₁, d ₁ Lactate production rates in (M) and (S), respectively (mmol·min^–1) - c ₂, d₂ Coefficients of efficiency in lactate utilization by (M) and (S), respectively (min^–1) - C ₁, C ₂ Amplitudes of the exponential terms of L _M (t) (mmol·l^–1) - D ₁, D ₂ Amplitudes of the exponential terms of L _S (t) (mmol·l^–1) - (D ₁), (D ₂), (D ₃) Separating lines for definitions (+) and (–) of the parameters (Fig. 4) - (F ₁), (F ₂) Areas of validity of the model - L _a (t) Lactate concentration in arterial blood at time t obtained by fits to experimental data (mmol·l^–1) - L _M (t), L _S (t) Lactate concentrations in (M) and (S), respectively, at time t (mmol·l^–1) - L _v (t) Lactate concentration in blood leaving (M) at time t (mmol·l^–1) - L ₁, L ₂, L ₃ Maximum allowable values for d ₂ (Fig. 4) (min^–1) - (M), (S) Worked muscle space and remaining lactate space - ₁, ₂ Invariant points of () - (P ₁), (P ₂), (P ₃) Properties of the function y(t) - q(t) Blood flow perfusing (M) at time t (l·min^–1) - t Time after the end of exercise (min) - t ₁, t ₂ Instants at which y _t (t) and y' _t (t) reduce to zero (min) - V _M , V _S Volumes of (M) and (S), respectively (l) - V _MS V _M to V _S ratio - V _SM V _S to V _M ratio - y _t General form of time functions generated by the model (mmol·l^–1 or mmol·min^–1) - ₁, ₂ Amplitudes of the transient terms of y(t) (mmol·l^–1 or mmol·min^–1) - () Conics describing the relation between c ₂ and d ₂ - ₁, ₂ Velocity constants of the exponential fits to L _a (t) (min^–1) - ₁, ₂ Theoretical velocity constants of the time functions (min^–1) - , Instants at which _MS (t) reduces to zero (min) - Net muscular release rate of lactate at t (mmol·min^–1) - ₁, ₁ Instants at which L _M (t) crosses L _S (t) (min) - _mM (t), _mS (t) Lactate utilization rates in (M) and (S), respectively (mmol·min^–1) - _MS (t) Net muscular release rate of lactate (mmol·min^–1)     

Energetics of locomotion in African pygmies

Summary The energy cost of walking (C _w). and running (C _r), and the maximal O₂ consumption (VO_2max) were determined in a field study on 17 Pygmies (age 24 years, SD 6; height 160 cm, SD 5; body mass 57.2 kg, SD 4.8) living in the region of Bipindi, Cameroon. TheC _w varied from 112 ml·kg^–1·km^–1, SD 25 [velocity (), 4 km·h^–1] to 143 ml·kg^–1·km^–1, SD 16 (, 7 km·h^–1). Optimal walking was 5 km·h^–1. TheC _r was 156 ml·kg^–1·km^–1, SD 14 (, 10 km·h^–1) and was constant in the 8–11 km·h^–1 speed range. TheVO_2max was 33.7 ml·kg^–1· min^–1, i.e. lower than in other African populations of the same age. TheC _r andC _w were lower than in taller Caucasian endurance runners. These findings, which challenge the theory of physical similarity as applied to animal locomotion, may depend either on the mechanics of locomotion which in Pygmies may be different from that observed in Caucasians, or on a greater mechanical efficiency in Pygmies than in Caucasians. The lowC _r values observed enable Pygmies to reach higher running speeds than would be expected on the basis of theirVO_2max.     

The metabolism of tramadol by human liver microsomes

Summary The metabolism of tramadol was investigated in vitro using microsomal fractions of human liver. The parent compound and its main metabolites were determined by a newly developed high performance liquid chromatography assay. O-demethylation of tramadol was found to be stereoselective. The V_max of the O-demethylation of (–)-tramadol was 210 pmol·mg^–·min^–1, whereas (+)-tramadol was O-demethylated with a V_max of 125 pmol·mg^–1·min^–1. The K_m for both enantiomers was determined to be 210 M. O-demethylation was inhibited competitively by quinidine (k_i=15 nM) and propafenone (k_i=34 nM). N-demethylation was also stereoselective, preferentially metabolizing the (+)-enantiomer. Whereas O-demethylation displayed monophasic Michaelis-Menten kinetics, N-demethylation was best described by a two-site model. Competitive inhibition of the O-demethylation both by quinidine and propafenone suggests that O-demethylation is carried out by P-450IID6.Abbreviations HPLC high performance liquid chromatography - k_i inhibitory constant - k_m apparent Michaelis-Menten constant - M1 O-demethylated metabolite of tramadol - M2 N-demethylated metabolite of tramadol - NADP nicotinamide-adenine dinucleotide phosphate - T tramadol - v_max maximum velocity of the reaction     

Identification of sodium-dependent and sodium-independent dicarboxylate transport systems in rat liver basolateral membrane vesicles

The mechanisms involved in the hepatocellular uptake of Krebs-cycle intermediates were investigated in isolated basolateral (sinusoidal and lateral) rat liver plasma membrane (blLPM) vesicles. An inwardly directed Na⁺ gradient markedly stimulated uptake of 2-oxoglutarate and succinate into voltage- and pH-clamped blLPM vesicles. This Na⁺-dependent portion of the dicarboxylate uptake was characterized by (a) saturability with increasing substrate concentrations (K _m= 6.4–10 mM; V _max0.2 nmol min^–1 mg protein^–1), (b) cisinhibition by lithium (10 mM), other Krebs-cycle dicarboxylates (1 mM) and DIDS (4,4-diisothiocyanostilbene-2,2-disulfonic acid; 1 mM) but not by sulphate, monocarboxylates, oxalate, acidic amino acids, bile salts and probenecid, (c) stimulation by an intravesicular negative K⁺-diffusion potential indicating electrogenic [(Na⁺) _n>2-succinate] cotransport, and (d) a pH optimum for transport between 7.0 and 7.5. In the absence of Na⁺, an inside alkaline pH gradient also markedly stimulated 2-oxoglutarate uptake. This pH-gradient-driven 2-oxoglutarate uptake was insensitive to lithium, but could also be inhibited by DIDS and succinate. Furthermore, saturation kinetics demonstrated K _m ( 34 mM) and V _max ( 0.8 nmol min^–1 mg protein^–1) values that were clearly different from those of the Na⁺-dependent uptake system. These results indicate the occurrence of two separate dicarboxylate transport systems along the sinusoidal border of hepatocytes, one being a Na⁺-dicarboxylate symporter and the other representing an anion-exchange system.     

Stroke volume response to progressive exercise in athletes engaged in different types of training

Summary Using the impedance cardiography method, heart rate ( _c) matched changes on indexed stroke volume (SI) and cardiac output (CI) were compared in subjects engaged in different types of training. The subjects consisted of untrained controls (C), volleyball players (VB) who spent about half of their training time (360 min · week^–1) doing anaerobic conditioning exercises and who had a maximal oxygen uptake ( ) 41% higher than the controls, and distance runners (D) who spent all their training time (366 min·week^–1) doing aerobic conditioning exercises and who had a 26% higher than VB. The subjects performed progressive submaximal cycle ergometer exercise (10 W·min^–1) up to _c of 150 beats·min^–1. In group C, SI had increased significantly (P<0.05) at _c of 90 beats·min^–1 ( + 32%) and maintained this difference up to 110 beats·min^–1, only to return to resting values on reaching 130 beats·min^–1 with no further changes. In group VB, SI peaked (+ 54%) at _c of 110 beats·min^–1, reaching a value significantly higher than that of group C, but decreased progressively to 22010 of the resting value on reaching 150 beats·min^–1. In group D, SI peaked at _c of 130 beats·min^–1 (+ 54%), reaching a value significantly higher than that of group VB, and showed no significant reduction with respect to this peak value on reaching 150 beats·min^–1. As a consequence, the mean CI increase per _c unit was progressively higher in VB than in C (+46%) and in D than in VB (+ 105%). It was concluded that thef _c value at which SI ceased to increase during incremental exercise was closely related to the endurance component in the training programme.     

Energy balance of human locomotion in water

In this paper a complete energy balance for water locomotion is attempted with the aim of comparing different modes of transport in the aquatic environment (swimming underwater with SCUBA diving equipment, swimming at the surface: leg kicking and front crawl, kayaking and rowing). On the basis of the values of metabolic power (Ė), of the power needed to overcome water resistance (_d) and of propelling efficiency (_P=_d/_tot, where _tot is the total mechanical power) as reported in the literature for each of these forms of locomotion, the energy cost per unit distance (C=Ė/v, where v is the velocity), the drag (performance) efficiency (_d=_d/Ė) and the overall efficiency (_o=_tot/Ė=_d/_P) were calculated. As previously found for human locomotion on land, for a given metabolic power (e.g. 0.5 kW=1.43 l·min^–1 O₂) the decrease in C (from 0.88 kJ·m^–1 in SCUBA diving to 0.22 kJ·m^–1 in rowing) is associated with an increase in the speed of locomotion (from 0.6 m·s^–1 in SCUBA diving to 2.4 m·s^–1 in rowing). At variance with locomotion on land, however, the decrease in C is associated with an increase, rather than a decrease, of the total mechanical work per unit distance (W_tot, kJ·m^–1). This is made possible by the increase of the overall efficiency of locomotion (_o=_tot/Ė=W_tot/C) from the slow speeds (and loads) of swimming to the high speeds (and loads) attainable with hulls and boats (from 0.10 in SCUBA diving to 0.29 in rowing).     

The influence of work intensity on postexercise proteinuria

Summary Fifteen men were studied during 100 m, 400 m and 3,000 m runs at maximal speed to determine total urinary protein and albumin excretion rates in relation to different distances of running. Venous blood lactate rose to 7.5 mmol · l^–1 after the 100 m and 3,000 m events, while reaching 12 mmol · l^–1 after the 400 m dash. Total urinary protein excretion increased to 330, 1640 and 565 g · min^–1 after the 100 m, 400 m and 3,000 m runs respectively, as compared with basal values (70 g · min^–1). In the meantime, albumin excretion increased respectively by 5, 25 and 18 fold of the resting values. The renal clearance of albumin increased to 0.84, 5.62 and 3.35 l · min^–1 after the three runs, as compared with a mean value of 0.19 l · min^–1 at rest. Exponential relationships (r=0.85) were recorded between post-exercise venous lactate and albumin, and total protein excretion. The present work illustrates the major influence of the intensity of exercise (anaerobic glycolytic component), rather than its duration, on the excretion rate of urinary proteins.This work has been partially presented at the 1981 American College of Sports Medicine Annual Meeting (Miami Beach, USA)     

Thermogenesis due to noradrenaline in muscles under different rates of perfusion

Vascularly isolated hind legs of cold acclimated rats were perfused with arterial blood either without noradrenaline (NA) or with a constant concentration of NA (10 ng·ml^–1) at different perfusion rates ranging from 2 to 14l·g^–1·min^–1. The oxygen consumption of the leg during perfusion both with or without NA was linearly related to the perfusion rate. The linear increase of leg oxygen consumption with respect to the perfusion was steeper after NA, which indicates that the same arterial concentration of NA may produce a greater thermogenic effect at higher blood flow rates (the difference between resting metabolic rate and the thermogenesis stimulated by NA, was 8.20 l O₂·g^–1·h^–1 at a blood flow of 3l·g^–1·min^–1, compared with 45.02 l O₂·g^–1·h^–1 at a blood flow of 14 l·g^–1·min^–1). These data confirm the important role of the extravascular influx rate of NA in the control of thermogenesis due to NA in muscles.     

Anaerobic threshold and maximal steady-state blood lactate in prepubertal boys

Summary To elucidate further the special nature of anaerobic threshold in children, 11 boys, mean age 12.1 years (range 11.4–12.5 years), were investigated during treadmill running. Oxygen uptake, including maximal oxygen uptake (VO_2max), ventilation and the ventilatory anaerobic threshold were determined during incremental exercise, with determination of maximal blood lactate following exercise. Within 2 weeks following this test four runs of 16-min duration were performed at a constant speed, starting with a speed corresponding to about 75% ofVO_2max and increasing it during the next run by 0.5 or 1.0 km·h^–1 according to the blood lactate concentrations in the previous run, in order to determine maximal steady-state blood lactate concentration. Blood lactate was determined at the end of every 4-min period. Anaerobic threshold was calculated from the increase in concentration of blood lactate obtained at the end of the runs at constant speed. The mean maximal steady-state blood lactate concentration was 5.0 mmol · 1^–1 corresponding to 88% of the aerobic power, whereas the mean value of the conventional anaerobic threshold was only 2.6 mmol · 1^–1, which corresponded to 78% of theVO_2max. The correlations between the parameters of anaerobic threshold, ventilatory anaerobic threshold and maximal steady-state blood lactate were only poor. Our results demonstrated that, in the children tested, the point at which a steeper increase in lactate concentrations during progressive work occurred did not correspond to the true anaerobic threshold, i.e. the exercise intensity above which a continuous increase in lactate concentration occurs at a constant exercise intensity.     

Effects of power training on mechanical efficiency in jumping

The present study investigates the effects of power training on mechanical efficiency (ME) in jumping. Twenty-three subjects, including ten controls, volunteered for the study. The experimental group trained twice a week for 15 weeks performing various jumping exercises such as drop jumps, hurdle jumps, hopping and bouncing. In the maximal jumping test, the take-off velocity increased from 2.56 (0.24) m·s^–1 to 2.77 (0.18) m·s^–1 (P<0.05). In the submaximal jumping of 50% of the maximum, energy expenditure decreased from 660 (110) to 502 (68) J·kg^–1·min^–1 (P<0.001) while, simultaneously, ME increased from 37.2 (8.4)% to 47.4 (8.2)% (P<0.001). Some muscle enzyme activities of the gastrocnemius muscle increased during the training period: citrate synthase from 35 (8) to 39 (7) mol·g^–1 dry mass·min^–1 (P<0.05) and -hydroxyacyl CoA dehydrogenase from 21 (4) to 23 (5) mol·g^–1 dry mass·min^–1 (P<0.05), whereas no significant changes were observed in phosphofructokinase and lactate dehydrogenase. In the control group, no changes in ME or in enzyme activities were observed. In conclusion, the enhanced performance capability of 8% in maximal jumping as a result of power training was characterized by decreased energy expenditure of 24%. Thus, the increased neuromuscular performance, joint control strategy, and intermuscular coordination (primary factors), together with improved aerobic capacity (secondary factor), may result in reduced oxygen demands and increased ME.     

Endurance training slows down the kinetics of heart rate increase in the transition from moderate to heavier submaximal exercise intensities

Summary To find out whether endurance training influences the kinetics of the increases in heart rate (f _c) during exercise driven by the sympathetic nervous system, the changes in the rate off _c adjustment to step increments in exercise intensities from 100 to 150 W were followed in seven healthy, previously sedentary men, subjected to 10-week training. The training programme consisted of 30-min cycle exercise at 50%–70% of maximal oxygen uptake ( O_2max) three times a week. Every week during the first 5 weeks of training, and then after the 10th week the subjects underwent the submaximal three-stage exercise test (50, 100 and 150 W) with continuousf _c recording. At the completion of the training programme, the subjects' O_2max had increased significantly(39.2 ml·min^–1·kg^–1, SD 4.7 vs 46 ml·min^–1·kg^–1, SD 5.6) and the steady-statef _c at rest and at all submaximal intensities were significantly reduced. The greatest decrease in steady-statef _c was found at 150 W (146 beats·min^–1, SD 10 vs 169 beats·min^–1, SD 9) but the difference between the steady-statef _c at 150 W and that at 100 W (f _c) did not decrease significantly (26 beats·min^–1, SD 7 vs 32 beats·min^–1, SD 6). The time constant () of thef _c increase from the steady-state at 100 W to steady-state at 150 W increased during training from 99.4 s, SD 6.6 to 123.7 s, SD 22.7 (P<0.01) and the acceleration index (A=0.63·f _c·^–1) decreased from 0.20 beats·min^–1·s^–1, SD 0.05 to 0.14 beats·min^–1·s^–1, SD 0.04 (P<0.02). The major part of the changes in and A occurred during the first 4 weeks of training. It was concluded that heart acceleration following incremental exercise intensities slowed down in the early phase of endurance training, most probably due to diminished sympathetic activation.     

Ventilatory threshold during treadmill exercise in kindergarten children

Summary The cardiorespiratory response to graded treadmill exercise was studied in a group of kindergarten children, aged 5 to 6 years. From the non-linear change of pulmonary ventilation with increasing exercise intensity a ventilatory threshold was determined which averaged 28.1±4.9 (SD) ml O₂·min^–1·kg^–1. A significant correlation was established between this ventilatory threshold (ml O₂·min^–1) and the physical working capacity at a heart rate of 170 beats per min (PWC₁₇₀, ml O₂·min^–1):r=0.93,p<0.001. These data show that a ventilatory threshold can be obtained in young children which is an objective index of cardiorespiratory performance capacity.     

A study of lactate metabolism without tracer during passive and active postexercise recovery in humans

Tracers have been used extensively to study lactate metabolism in humans during rest and exercise. Nevertheless, quantification of in vivo lactate kinetics as measured by lactate tracers remains controversial and new data are necessary to clarify the issue. The present study has developed a simple kinetic model which does not require labelled molecules and which yields proportional and quantitative information on lactate metabolism in humans during postexercise recovery performed at different levels of intensity. Five subjects took part in six experiments each of which began with the same strenuous exercise (StrEx; 1 min, 385 W, 110 rpm). The StrEx of each session was followed by a different intensity of recovery: passive recovery (PR) and active recoveries (AR) with power outputs of 60, 90, 120, 150 and 180 W, respectively. Blood lactate concentration was measured prior to and immediately after StrEX and regularly during the 1st h of recovery. Oxygen uptake ( ) was measured every 30 s during the whole session. The results showed that the disappearance rate constant (k_e) increases abruptly from PR [0.080 (SEM 0.004) min^–1] to moderate AR [60W: 0.189 (SEM 0.039) min^–1] and decreases slowly during more intense AR [180 W: 0.125 (SEM 0.027) min^–1]. The lactate apparent clearance (Cl·F^–1) was calculated from the area under the lactate concentration-time curve. The Cls·F^–1 increased 1.81 (SEM 0.17) fold from PR to moderate AR (60 W) and only 1.31 (SEM 0.14) from PR to the most intense AR (180 W). Using the model, the apparent lactate production (FK₀) was also calculated. The FK₀ increased regularly following a slightly curvilinear function of and was 2.61 (SEM 0.53) fold greater during the most intense AR (180 W) than during PR. Because of the lack of data concerning the size of apparent lactate distribution volume (V _d), the apparent turnover rate (R_bl) has been presented here related toV _d. The R_bl·V _d ^–1 increased also following a slightly curvilinear function of . The R_bl·V _d ^–1 was 85.90 (SEM 14.42) mol·min^–1·l^–1 during PR and reached 314.09 (SEM 153.95) mol·min^–1·l^–1 during the most intense AR (180 W). In conclusion the model presented here does not require labelled molecules and firstly makes it possible to follow the proportional change of apparent lactate clearance and apparent lactate production during active postexercise recovery in comparison with passive recovery conditions and secondly to estimate the blood lactate turnover.     

Maximal working capacity of two professional groups in North Sumatra (Indonesia)

Summary Two groups of male students from the medical school and sports academy and two groups of tricycle drivers performed maximally on two occassions on a brake type ergometer against a load sustainable between 2–6 min according to Tornvall. In the students the difference in work performance between the medical and sports academy students, maybe due to difference in their training condition, shown by the increment and decrement of pulse rate respectively on starting and stopping the test, since all their anthropometric measurements are the same. A comparison of the maximum working capacity between the tricycle drivers to study the effect of a potion called jamu showed no difference (N₁=11, X₁=1523 m·kp·min^–1, N₂=10, X₂=1,664 m·kp·min^–1, p>0.05). The maximum working capacity of the tricycle drivers was found to be the same as the students from the sports academy (N₁=21, X₁=1,587 m·kp·min^–1, N₂=9, X₂=1,524 m·kp·min^–1, p>0.05). Maximal heart rate between the medical students and the sports academy students differ significantly (N₁=22, X₁=186 min^–1, N₂=9, X₂=175 min^–1, p<0.01), but not significantly different between the sports academy students and the beca drivers (N₁=9, X₁=175 min^–1, N₂=21, X₂=180 min^–1, p>0.05).     

Cardiovascular and metabolic responses to noradrenaline in men acclimatized to cold baths

Summary The purpose of this study was to see whether artificial acclimatization to cold would reduce the pressor response to noradrenaline (NA) as natural acclimatization has been shown to do, and whether it would induce nonshivering thermogenesis. Three white men were infused with NA at four dosage levels between 0.038 and 0.300 g·kg^–1·min^–1 (2–23 g·min^–1), before and after artificial acclimatization to cold and again 4 months later when acclimatization had decayed. Acclimatization was induced by ten daily cold (15°Q baths of 30–60 min followed by rapid rewarming in hot (38–42°C) water, and was confirmed by tests of the subjects responses to whole-body cooling in air. Three control subjects also underwent the first and third tests. Acclimatization substantially reduced the pressor response to NA at 0.150 and 0.300 g·kg^–1·min^–1, confirming earlier findings by the same technique in naturally acclimatized men, and its decay increased this response to beyond its initial levels (P<0.05 for both changes). Acclimatization did not change the response to NA of heart rate, subjective impressions, skin temperature of finger and toe, pulmonary ventilation, or plasma free fatty acids and ketone bodies. At no time did NA increase oxygen consumption, or increase skin temperature or heat flow over reported sites of brown fat. These findings would seem to show that acclimatization to cold reduces sensitivity to the pressor effect of NA but does not induce nonshivering thermogenesis, and that the reduced sensitivity is replaced by a hypersensitivity to NA when acclimatization decays.     

Scaling or normalising maximum oxygen uptake to predict 1-mile run time in boys

There is still considerable debate and some confusion as to the most appropriate method of scaling or normalizing maximum oxygen uptake (O_2max) for differences in body mass (m) in both adults and children. Previous studies on adult populations have demonstrated that although the traditional ratio standard O_2max (ml kg^–1 min^–1) fails to render O_2max independent of body mass, the ratio standard is still the best predictor of running performance. However, no such evidence exists in children. Hence, the purpose of the present study was to investigate whether the ratio standard is still the most appropriate method of normalising O_2max to predict 1-mile run speed in a group of 12-year-old children (n=36). Using a power function model and log-linear regression, the best predictor of 1-mile run speed was given by: speed (m s^–1)=55.1O_2max^0.986m^–0.96. With both the O_2max and body mass exponents being close to unity but with opposite signs, the model suggest the best predictor of 1-mile run speed is almost exactly the traditional ratio standard recorded in the units (ml kg^–1 min^–1). Clearly, reporting the traditional ratio standard O_2max, recorded in the units (ml kg^–1 min^–1), still has an important place in publishing the results of studies investigating cardiovascular fitness of both children and adults.     

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.     

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.     

Lactate kinetics during passive and partially active recovery in endurance and sprint athletes

We investigated the effects of passive and partially active recovery on lactate removal after exhausting cycle ergometer exercise in endurance and sprint athletes. A group of 14 men, 7 endurance-trained (ET) and 7 sprint-trained (ST), performed two maximal incremental exercise tests followed by either passive recovery (20 min seated on cycle ergometer followed by 40 min more of seated rest) or partially active recovery [20 min of pedalling at 40% maximal oxygen uptake ( O_2max) followed by 40 min of seated rest]. Venous blood samples were drawn at 5 min and 1 min prior to exercise, at the end of exercise, and during recovery at 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 30, 40, 50, 60 min post-exercise. The time course of changes in lactate concentration during the recovery phases were fitted by a bi-exponential time function to assess the velocity constant of the slowly decreasing component (₂) expressing the rate of blood lactate removal. The results showed that at the end of maximal exercise and during the 1st min of recovery, ET showed higher blood lactate concentrations than ST. Furthermore, ET reached significantly higher maximal exercise intensities [5.1 (SEM 0.5) W · kg^–1 vs 4.0 (SEM 0.3) W · kg^–1,P < 0.05] and O_2max [68.4 (SEM 1.1) ml · kg^–1 · min^–1 vs 55.5 (SEM 5.1) ml · kg^–1 · min^–1,P < 0.01]. There was no significant difference between the two groups during passive recovery for ₂ During partially active recovery, ₂ was higher than during passive recovery for both groups (P < 0.001), but ET recovered faster and sooner than ST (P < 0.05). Compared to passive recovery, the ₂ measured during partially active recovery was increased threefold in ET and only 1.5-fold in ST. We concluded that partially active recovery potentiates the enhanced ability to remove blood lactate induced by endurance training.