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.     

Effects of prolonged cycle ergometer exercise on maximal muscle power and oxygen uptake in humans

Summary The mechanical power (W_tot, W·kg^–1) developed during ten revolutions of all-out periods of cycle ergometer exercise (4–9 s) was measured every 5–6 min in six subjects from rest or from a baseline of constant aerobic exercise [50%–80% of maximal oxygen uptake (VO_2max)] of 20–40 min duration. The oxygen uptake [VO₂ (W·kg^–1, 1 ml O₂ = 20.9 J)] and venous blood lactate concentration ([la]_b, mM) were also measured every 15 s and 2 min, respectively. During the first all-out period, W_tot decreased linearly with the intensity of the priming exercise (W_tot = 11.9–0.25·VO₂). After the first all-out period (i greater than 5–6 min), and if the exercise intensity was less than 60% VO_2max, W_tot, VO₂ and [la]_b remained constant until the end of the exercise. For exercise intensities greater than 60% VO_2max, VO₂ and [la]_b showed continuous upward drifts and W_tot continued decreasing. Under these conditions, the rate of decrease of W_tot was linearly related to the rate of increase of V [(d W_tot/dt) (W·kg^–1·s^–1) = 5.0·10^–5 –0.20·(d VO₂/dt) (W·kg^–1·s^–1)] and this was linearly related to the rate of increase of [la]_b [(d VO₂/dt) (W·kg^–1·s^–1) = 2.310^–4 + 5.910^–5·(d [la]_b/dt) (mM·s^–1)]. These findings would suggest that the decrease of W_tot during the first all-out period was due to the decay of phosphocreatine concentration in the exercising muscles occurring at the onset of exercise and the slow drifts of VO₂ (upwards) and of W_tot (downwards) during intense exercise at constant W_tot could be attributed to the continuous accumulation of lactate in the blood (and in the working muscles).     

Peak power output predicts maximal oxygen uptake and performance time in trained cyclists

Summary The purposes of this study were firstly to determine the relationship between the peak power output (W _peak) and maximal oxygen uptake (VO_2max) attained during a laboratory cycling test to exhaustion, and secondly to assess the relationship betweenW _peak and times in a 20-km cycling trial. One hundred trained cyclists (54 men, 46 women) participated in the first part of this investigation. Each cyclist performed a minimum of one maximal test during whichW _max andVO_2max were determined. For the second part of the study 19 cyclists completed a maximal test for the determination ofW _peak, and also a 20-km cycling time trial. Highly significant relationships were obtained betweenW _peak andVO_2max (r=0.97,P<0.0001) and betweenW _peak and 20-km cycle time (r= –0.91,P<0.001). Thus,W _peak explained 94% of the variance in measuredVO_2max and 82% of the variability in cycle time over 20 km. We concluded that for trained cyclists, theVO_2max can be accurately predicted fromW _peak, and thatW _peak is a valid predictor of 20-km cycle time.     

The influence of body position on maximal performance in cycling

Summary Six healthy male subjects performed a 3-min supramaximal test in four different cycling positions: two with different trunk angles and two with different saddle-tube angles. Maximal power output and maximal oxygen uptake (VO_2max) were measured. Maximal power output was significantly higher in a standard sitting (SS, 381 W, SD 49) upright position compared to all other positions: standard racing (SR, 364 W, SD 49), recumbent backwards (RB, 355 W, SD 44) and recumbent forwards (RF, 341 W, SD 54). Although VO_2max was also highest in SS (4.31 l · min^–1, SD 0.5) upright position, the differences in VO_2max were not significant (SR, 4.21 · min^–1, SD 0.53; RB, 4.17 l · min^–1, SD 0.58; RF, 4.11 l · min^–1, SD 0.66). It is concluded that (supra)maximal tests on a cycle ergometer should be performed in a sitting upright position and not in a racing position. In some cases when cycling on the road, higher speeds can be attained when sitting upright. This is especially true when cycling uphill when high power must be generated to overcome gravity but the road speed, and hence the power required to overcome air resistance, is relatively low.     

Anaerobic and aerobic power of top athletes

Summary In this study the alactic anaerobic and aerobic power of top level sprinters, long-distance runners, and untrained students were compared. Maximal oxygen uptake was measured during a progressive test on a treadmill. The anaerobic power was estimated according to a newly developed bicycle ergometer technique. As reported elsewhere, the maximal oxygen uptake is very high in twelfe long-distance runners (77.6±2.7 ml/kg·min⁻¹) whereas the maximal oxygen uptake of six sprinters amounts to 60.1±5.9 ml/kg·min⁻¹. The average alactic anaerobic power of a control group of 32 students was 710 W or 10.1±1.2 W/kg. Significantly lower results were obtained by long-distance runners (551 W or 8.93 W/kg) whereas significantly higher results were obtained by sprinters (1,021 W or 14.16 W/kg). In top level athletes, but not in the control group, a negative relationship was found between aerobic power and anaerobic power.     

Muscle function during brief maximal exercise: accurate measurements on a friction-loaded cycle ergometer

A friction loaded cycle ergometer was instrumented with a strain gauge and an incremental encoder to obtain accurate measurement of human mechanical work output during the acceleration phase of a cycling sprint. This device was used to characterise muscle function in a group of 15 well-trained male subjects, asked to perform six short maximal sprints on the cycle against a constant friction load. Friction loads were successively set at 0.25, 0.35, 0.45, 0.55, 0.65 and 0.75 N·kg^–1 body mass. Since the sprints were performed from a standing start, and since the acceleration was not restricted, the greatest attention was paid to the measurement of the acceleration balancing load due to flywheel inertia. Instantaneous pedalling velocity (v) and power output (P) were calculated each 5 ms and then averaged over each downstroke period so that each pedal downstroke provided a combination of v, force and P. Since an 8-s acceleration phase was composed of about 21 to 34 pedal downstrokes, this many v-P combinations were obtained amounting to 137–180 v-P combinations for all six friction loads in one individual, over the widest functional range of pedalling velocities (17–214 rpm). Thus, the individual's muscle function was characterised by the v-P relationships obtained during the six acceleration phases of the six sprints. An important finding of the present study was a strong linear relationship between individual optimal velocity (v _opt) and individual maximal power output (P _max) (n = 15, r = 0.95, P < 0.001) which has never been observed before. Since v _opt has been demonstrated to be related to human fibre type composition both v _opt, P _max and their inter-relationship could represent a major feature in characterising muscle function in maximal unrestricted exercise. It is suggested that the present method is well suited to such analyses.     

Oxygen uptake kinetics and maximal aerobic power are unaffected by inspiratory muscle training in healthy subjects where time to exhaustion is extended

The aim of this study was to determine whether 4 weeks of inspiratory muscle training (IMT) would be accompanied by alteration in cardiopulmonary fitness as assessed through moderate intensity oxygen uptake (O₂) kinetics and maximal aerobic power (O_2max). Eighteen healthy males agreed to participate in the study [training group (Tra) n=10, control group (Con) n=8]. Measurements of spirometry and maximal static inspiratory mouth pressure (PI_max) were taken pre- and post-training in addition to: (1) an incremental test to volitional exhaustion, (2) three square-wave transitions from walking to running at a moderate intensity (80% ventilatory threshold) and (3) a maximal aerobic constant-load running test to volitional fatigue for the determination of time to exhaustion (T_lim). Training was performed using an inspiratory muscle trainer (Powerbreathe). There were no significant differences in spirometry either between the two groups or when comparing the post- to pre-training results within each group. Mean PI_max increased significantly in Tra (P<0.01) and showed a trend for improvement (P<0.08) in Con. Post-training T_lim was significantly extended in both Tra [232.4 (22.8) s and 242.8 (20.1) s] (P<0.01) and Con [224.5 (19.6) and 233.5 (12.7) s] (P<0.05). Post-training T_lim was significantly extended in Tra compared to Con (P<0.05). In conclusion, the most plausible explanation for the stability in O₂ kinetics and O_2max following IMT is that it is due to insufficient whole-body stress to elicit either central or peripheral cardiopulmonary adaptation. The extension of post-training T_lim suggests that IMT might be useful as a stratagem for producing greater volumes of endurance work at high ventilatory loads, which in turn could improve cardiopulmonary fitness.     

Effect of hyperoxia on maximal O2 uptake in exercise-induced arterial hypoxaemic subjects

This study focuses on the effect of hyperoxia on maximal oxygen uptake and maximal power (Pmax) in subjects exhibiting exercise-induced arterial hypoxemia (EIH) at sea level. Sixteen competing male cyclists >60 ml·min^–1·kg^–1) performed exhaustive ramp exercise (cycle-ergometer) under normoxia and moderate hyperoxia (FIO₂=30%). After the normoxic trial, the subjects were divided into those demonstrating EIH during exercise [arterial O₂ desaturation ( SaO₂) >5%; n=9] and those who did not (n=7). Under hyperoxia, SaO₂ raised and the increase was greater for the EIH than for the non-EIH group (P<0.001). improved for both groups and to a greater extent for EIH (12.8±5.7% vs. 4.2±4.6%, P<0.01; mean±SD) and the increase was correlated to the gain in SaO₂ for all subjects (r=0.71, P<0.01). Pmax improved by 3.3±3.3% (P<0.01) regardless of the group. These data suggest that pulmonary gas exchange contributes to a limitation in and power for especially EIH subjects.     

Optimal velocity for maximal power production in non-isokinetic cycling is related to muscle fibre type composition

To determine whether power-velocity relationships obtained on a nonisokinetic cycle ergometer could be related to muscle fibre type composition, ten healthy specifically trained subjects (eight men and two women) performed brief periods of maximal cycling on a friction loaded cycle ergometer. Frictional force and flywheel velocity were recorded at a sampling frequency of 200 Hz. Power output was computed as the product of velocity and inertial plus frictional forces. Force, velocity and power were averaged over each down stroke. Muscle fibre content was determined by biopsy of the vastus lateralis muscle. Maximal down stroke power [14.36 (SD 2.37)W·kg^–1] and velocity at maximal power [120 (SD 8) rpm] were in accordance with previous results obtained on an isokinetic cycle ergometer. The proportion of fast twitch fibres expressed in terms of cross sectional area was related to optimal velocity (r = 0.88, P < 0.001), to squat jump performance (r = 0.78, P < 0.01) and tended to be related to maximal power expressed per kilogram of body mass (r = 0.60, P = 0.06). Squat jump performance was also related to cycling maximal power expressed per kilogram of body mass (r = 0.87, P < 0.01) and to optimal velocity (r = 0.86, P < 0.01). All these data suggest that the nonisokinetic cycle ergometer is a good tool with which to evaluate the relative contribution of type II fibres to maximal power output. Furthermore, the strong correlation obtained demonstrated that optimal velocity, when related to training status, would appear to be the most accurate parameter to explore the fibre composition of the knee extensor muscle.     

Determination of the maximal fat oxidation point in obese children and adolescents: validity of methods to assess maximal aerobic power

We aimed to examine the interchangeability of techniques used to assess maximal oxygen consumption () and maximal aerobic power (MAP) employed to express the maximal fat oxidation point in obese children and adolescents. Rate of fat oxidation were measured in 24 obese subjects (13.0 ± 2.4 years; Body Mass Index 30.2 ± 6.3 kg m⁻²) who performed a five 4-min stages submaximal incremental cycling exercise. A second cycling exercise was performed to measure . Results are those of the 20 children who achieved the criterion of RER (>1.02) to assess the attainment of . Although correlations between results obtained by different methods were strong, Bland–Altman plots showed little agreement between the maximal fat oxidation point expressed as a percentage of measured and as % estimated according to ACSM guidelines (underestimation : −5.9%) or using the predictive equations of Wasserman (−13.9%). Despite a mean underestimation of 1.4% several values were out of the limits of agreement when comparing measured MAP and Theoretical MAP. Estimations of lead to underestimations of the maximal fat oxidation point.     

Comparison between maximal power in the power-endurance relationship and maximal instantaneous power

The purpose of this study was to analyze the relevance of introducing the maximal power ( P _m) into a critical-power model. The aims were to compare the P _m with the instantaneous maximal power ( P _max) and to determine how the P _m affected other model parameters: the critical power ( P _c) and a constant amount of work performed over P _c ( W ). Twelve subjects [22.9 (1.6) years, 179 (7) cm, 74.1 (8.9) kg, 49.4 (3.6) ml/min/kg] completed one 15 W/min ramp test to assess their ventilatory threshold (VT), five or six constant-power to exhaustion tests with one to measure the maximal accumulated oxygen deficit (MAOD), and six 5-s all-out friction-loaded tests to measure P _max at 75 rpm, which was the pedaling frequency during tests. The power and time to exhaustion values were fitted to a 2-parameter hyperbolic model (NLin-2), a 3-parameter hyperbolic model (NLin-3) and a 3-parameter exponential model (EXP). The P _m values from NLin-3 [760 (702) W] and EXP [431 (106) W] were not significantly correlated with the P _max at 75 rpm [876 (82) W]. The P _c value estimated from NLin-3 [186 (47) W] was not significantly correlated with the power at VT [225 (32) W], contrary to other models ( P <0.001). The W from NLin-2 [25.7 (5.7) kJ] was greater than the MAOD [14.3 (2.7) kJ, P <0.001] with a significant correlation between them ( R =0.76, P <0.01). For NLin-3, computation of W _{P >P c}, the amount of work done over P _C, yielded results similar to the W value from NLin-2: 27.8 (7.4) kJ, which correlated significantly with the MAOD ( R =0.72, P <0.01). In conclusion, the P _m was not related to the maximal instantaneous power and did not improve the correlations between other model parameters and physiological variables.     

The relationship between changing body height and growth related changes in maximal aerobic power

Summary In order to analyse the relationship between maximal aerobic power and height, body mass and lean body mass a multi-longitudinal survey was conducted on three different age groups of randomly selected children from a small Czech community. Beginning at the initial ages of 8, 12 and 16 years subjects were subsequently retested three times at 2-year intervals. At overlapping ages there were no differences in the various age groups between height and . By utilizing mean values for the various parameters at specific calendar ages a growth curve was constructed for each sex for the age range 8–20 years. The values were compared with longitudinal studies in various countries and no substantial differences were found. When was then compared to height, body mass and lean body mass it was apparent that the almost linear relationship with height was the most precise. In addition the children remained, generally speaking, in their same rank order for for the three different age groupings.     

Anaerobic and aerobic components during arm-crank exercise in sprint and middle-distance swimmers

Summary The purpose of this investigation was to compare anaerobic and aerobic components measured during arm exercise in sprint and middle-distance swimmers and to investigate whether the peak anaerobic power :peak aerobic power ratio (W _{an, peak} :W aer, peak) was related to specialization for the event and to performance. TheW _{an, peak} force at zero velocity (F ₀), and velocity at zero-force (₀),W _{aer, peak}, peak oxygen uptake ( O_2peak), and ventilatory threshold (Th _v ) were compared during arm exercise tests in sprint (group I,n = 8) and middle-distance (group II,n = 9) competitive male swimmers. Anaerobic indices were estimated by the force-velocity test, an anaerobic test using incremental braking forces; aerobic indices were measured during an incremental aerobic exercise test (30 W · min^–1). TheW _{an, peak} andW aer, peak were greater in group I [828 (SEM 70) W; 236 (SEM 12) W] than in group II [678 (SEM 28) W; 230 (SEM 5) W], but the differences were not significant. There were also no significant differences observed between the mean values ofF ₀, ₀, O_2peak, and Th _v . TheW _{an, peak}:W _{aer, peak}, however, was significantly higher in sprint swimmers (t = 3.08,P < 0.01). In seven of the swimmers, who had recently performed both the 100-m and 400-m front crawl, a relationship existed between their swim time and theW _{an, peak}:Waer,peak (100m:r = –0.80,P<0.05 and 400m:r=+0.75,P<0.05). In conclusion, during arm-crank exercise, we did not observe significant differences in anaerobic and aerobic components between sprint and middle-distance swimmers. However, the results of the present study demonstrated the usefulness of theW _{an, peak} :W _{aer, peak} in the physiological evaluation of swimmers as it reflects the proportion of anaerobic to aerobic systems involved in the supply of energy.     

Neuromuscular characteristics and fatigue in endurance and sprint athletes during a new anaerobic power test

The purpose of this study was to investigate neuromuscular and energy performance characteristics of anaerobic power and capacity and the development of fatigue. Ten endurance and ten sprint athletes performed a new maximal anaerobic running power test (MARP), which consisted ofn x 20-s runs on a treadmill with 100-s recovery between the runs. Blood lactate concentration [la^–]_b was measured after each run to determine submaximal and maximal indices of anaerobic power (P _3mmol·1 ^–1,P_5mmol·1 ^–1,P_10mmol·1 ^–1andP _max) which was expressed as the oxygen demand of the runs according to the American College of Sports Medicine equation: the oxygen uptake (ml·kg^–1·min^–1)=0.2·velocity (m·min^–1) +0.9·slope of treadmill (frac)·velocity (m·min^–1)+3.5. The height of rise of the centre of gravity of the counter movement jumps before (CMJ_rest) and during (CMJ) the MARP test, as well as the time of force production (t _F) and electromyographic (EMG) activity of the leg muscles of CMJ performed after each run were used to describe the neuromuscular performance characteristics. The maximal oxygen uptake ( _max), anaerobic and aerobic thresholds were determined in the _max test, which consisted ofn x 3-min runs on the treadmill. In the MARP-testP _max did not differ significantly between the endurance [116 (SD 6) ml·kg^–1·min^–1] and sprint [120 (SD 4) ml·kg^–1·min^–1] groups, even though CMJ_rest and peak [la^–]_b were significantly higher and _max was significantly lower in the sprint group than in the endurance group and CMJ_rest height correlated withP _max (r=0.50,P<0.05). The endurance athletes had significantly higher mean values ofP _3mmol·1 ^–1andP _5mmol·1 ^–1[89 (SD 7) vs 76 (SD 8) ml·kg^–1·min^–,P<0.001 and 101 (SD 5) vs 90 (SD 8) ml·kg^–1·min^–1,P<0.01. Significant positive correlations were observed between theP _3mmol·l ^–1and _max, anaerobic and aerobic thresholds. In the sprint group CMJ and the averaged integrated iEMG decreased andt _F increased significantly during the MARP test, while no significant changes occurred in the endurance group. The present findings would suggest thatP _max reflected in the main the lactacid power and capacity and to a smaller extent alactacid power and capacity. The duration of the MARP test and the large number of CMJ may have induced considerable energy and neuromuscular fatigue in the sprint athletes preventing them from producing their highest alactacidP _max at the end of the MARP test. Due to lower submaximal [la^–]_b (anaerobic sprinting economy) the endurance athletes were able to reach almost the sameP _max as the sprint athletes.     

A systems model approach to the ventilatory anaerobic threshold

Summary An analogue systems model of whole-body human bioenergetics predicts a change in kinetics of time series values as a result of exercise levels above an anaerobic threshold. Plotted results from exercising subjects appear to confirm this change. The purpose of this study is to describe the background to the systems model analogue of the anaerobic threshold and a test procedure devised to estimate this threshold. The estimate so obtained has the dual advantages of being based on model theory and of not being subject to the sort of ambient variations inherent in a single-test determination. A non-homogeneous group of eight subjects comprising a full replicate of a 2³ factorial experimental design, with factors age, sex and training status, took part in the study. On one hand the results indicate acceptance of the systems model theory. On the other, the analogue threshold measure possesses corresponding properties to the conventional anaerobic threshold. It is higher for trained (155–214 W) than for untrained subjects (108–158 W), higher for males (149–214 W) than for females (108–170 W), and displays no evident interaction effects. Results for the time constant and for the work efficiency, display similar effects except for an interaction in the latter between age and training status. These experimental findings are regarded as confirmatory of the nature of the analogue threshold measure.     

The validity of indirect estimations of maximal oxygen uptake in children 11–12 years of age

Summary The predictability of maximal oxygen uptake was tested on 123 normal, healthy children (80 boys and 43 girls) aged 11–12 years. Submaximal and maximal heart rate and maximal oxygen uptake were measured. VO₂ max was calculated using the åstrand and Ryhming nomogram. The calculated values for VO₂ max (without correction for differences in maximal heart rate) were lower than when measured directly, the average differences being 26% in boys and 23% in girls. Accuracy of the calculated maximal oxygen uptake can be increased by using the proposed regression equations: Girls ¯Y=1.299+0.502 predicted VO₂ max (r=0.82) l/min, Boys ¯Y=1.444+0.522 predicted VO₂ max (r=0.52) l/min.     

Contribution of oxygen extraction fraction to maximal oxygen uptake in healthy young men

We analysed the importance of systemic and peripheral arteriovenous O₂ difference ( difference and a‐v_fO₂ difference, respectively) and O₂ extraction fraction for maximal oxygen uptake ( ). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with . Articles (n = 17) publishing individual data (n = 154) on , maximal cardiac output ( ; indicator‐dilution or the Fick method), difference (catheters or the Fick equation) and systemic O₂ extraction fraction were identified. For the peripheral responses, group‐mean data (articles: n = 27; subjects: n = 234) on leg blood flow (LBF; thermodilution), a‐v_fO₂ difference and O₂ extraction fraction (arterial and femoral venous catheters) were obtained. and two‐LBF increased linearly by 4.9‐6.0 L · min^–1 per 1 L · min^–1 increase in (R² = .73 and R² = .67, respectively; both P < .001). The difference increased from 118‐168 mL · L^–1 from a of 2‐4.5 L · min^–1 followed by a reduction (second‐order polynomial: R² = .27). After accounting for a hypoxemia‐induced decrease in arterial O₂ content with increasing (R² = .17; P < .001), systemic O₂ extraction fraction increased up to ~90% ( : 4.5 L · min^–1) with no further change (exponential decay model: R² = .42). Likewise, leg O₂ extraction fraction increased with to approach a maximal value of ~90‐95% (R² = .83). Muscle O₂ diffusing capacity and the equilibration index Y increased linearly with (R² = .77 and R² = .31, respectively; both P < .01), reflecting decreasing O₂ diffusional limitations and accentuating O₂ delivery limitations. In conclusion, although O₂ delivery is the main limiting factor to , enhanced O₂ extraction fraction (≥90%) contributes to the remarkably high in endurance‐trained individuals.     

Changes in maximal aerobic power,aerobic capacity,and muscle enzyme activities at two stages of the annual training cycle in ski-runners

Summary Changes of cardiorespiratory capacity, of the activity of seven enzymes involved in energy metabolism and of laboratory endurance were investigated in a group of nine male ski-runners before and after exhausting training and a competing period during the winter.Despite the decrease in laboratory endurance and total work oxygen consumption between the investigations, O₂ max, O₂-pulse max and O₂ debt did not change; and O₂-pulse per kg b.w. showed a significant increase.In biopsy samples of the vastus lateralis muscle, the activity of enzymes of carbohydrate metabolism, both anaerobic and total (triose phosphate dehydrogenase — TPDH, lactate dehydrogenase — LDH, hexokinase — HK), and of total aerobic metabolism (citrate synthetase — CS, malate dehydrogenase — MDH), was decreased during this period by 27 to 59% (mean values for different enzymes). The mean activity of cytoplasmic glycerol phosphate dehydrogenase (GPDH) and of hydroxyacyl — CoA dehydrogenase (HOADH) did not change, although the activity of the latter enzyme was decreased in the muscle of those ski-runners who were trained predominantly for speed, and it was increased in those trained mainly for endurance.The changes in activity of the muscle enzymes associated with glycolysis (TPDH and LDH) and of MDH, connected with metabolism and hydrogen transport between cytoplasmic and aerobic mitochondrial compartments, correlate inversely with those of aerobic capacity (total work O₂ consumption).     

Changes in aerobic fitness and body fat during army recruit training

Summary Aerobic fitness and related indices were evaluated in 254 soldiers at the beginning and near the end of initial army recruit training. Aerobic fitness in terms of maximal aerobic power was predicted from the Astrand-Ryhming submaximal heart rate bicycle test. Estimated vO₂ max increased by 8%, 42.0–45.3 ml/kg·min. Accompanying this increase in aerobic capacity was a decline in body fat content without a change in body weight. It is concluded that army recruit training at the time of this study was effective in terms of increasing aerobic work capacity and reducing excess body fat.HQ UNFICYP BFPO 567     

Critical velocity during continuous and intermittent exercises in children

The purpose of this study was to apply the “critical velocity” concept to short intermittent high-intensity running exercises in prepubescent girls and boys and to compare the running performances obtained either by intermittent or continuous exercise runs. Eleven 8 to 11-year-old children underwent a maximal graded field test to determine peak oxygen uptake (peakVO₂) and maximal aerobic velocity (MAV). During the six following sessions, they randomly performed three continuous runs (90, 100, and 110% of MAV) and three intermittent runs (120, 130, and 140% of MAV) until exhaustion. Intermittent exercises consisted of repeated 15 s runs each one separated by a 15 s passive recovery interval. For continuous as well as intermittent exercises, distance versus time to exhaustion (TTE) relationships were calculated to determine continuous (CVc) and intermittent (CVi) critical velocities. Values for peakVO₂ and MAV were 45.8 ± 5.3 ml·kg⁻¹·min⁻¹ and 10.5 ± 1.0 km h⁻¹, respectively. For the whole population, a significant relationship was found between the distance to exhaustion (DTE) and TTE for continuous (r ² = 0.99, P < 0.05) and intermittent exercises (r ² = 0.99, P < 0.05). Significant relationships were found between peakVO₂ and both CVc (r ² = 0.60, P < 0.01) and CVi (r ² = 0.47, P < 0.05). In conclusion, as for continuous exercises, a linear relationship was found between DTE and TTE for short high-intensity intermittent exercises. CVc was significantly related to peakVO₂, while a significant lower relationship was found between peakVO₂ and CVi.