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.     

The comparison of peak oxygen uptake between swim-bench exercise and arm stroke

To compare maximal cardio-respiratory stress between swim-bench exercise (SB) and arm stroke (AS), peak oxygen uptake (VO_{2 peak}) was measured in six trained swimmers. The SB was performed at stroke frequency of 50 · min^–1. Oxygen uptake (VO₂) was measured during exercise at 3-min constant exercise intensities in SB and at 4-min constant water flow rates in AS. We measured a steady-state VO₂ within 3 or 4 min after the beginning of each exercise. The exercise intensity or the water flow rate was increased by 14.7 W or by 0.05 m · s^–1, respectively, until a levelling-off of VO₂ was observed. The VO₂ was measured by the Douglas bag method. Heart rate (HR) and blood lactate concentration ([1a^–]_b) were determined at the exercise intensity and the water flow rate at which VO_{2 peak} was obtained. At submaximal levels, VO₂ increased in proportion to exercise intensity for SB and to the water flow rate for AS. A levelling-off of VO₂ was observed in all subjects for both kinds of exercise. The VO₂ during SB [2.13 (SD 0.25)1 · min^–1] was significantly lower than that during AS [2.72 (SD 0.39)1 · min^–1] and corresponded to 78.9 (SD 7.0)% of AS VO_{2 peak}. Maximal HR during SB was also significantly lower than that during AS. No significant differences between SB and AS were found for either pulmonary ventilation or [1a^–]_b. The peak exercise duration in SB [2.4 (SD 0.5) min] was significantly shorter than that in As [3.6 (SD 0.5) min]. These results would suggest that even though both kinds of exercise use the muscles of the upper body, active muscle groups involved during SB are different and/or smaller, and maximal stress on the cardio-respiratory system is lower when compared to AS.     

Relationship between cardiac output and oxygen uptake at the onset of exercise

Summary The purpose of the present study was to assess the relationship between the rapidity of increased gas exchange (i.e. oxygen uptake ) and increased cardiac output ( ) during the transient phase following the onset of exercise. Five healthy male subjects performed multiple rest-exercise or light exercise (25 W)-exercise transitions on an electrically braked ergometer at exercise intensities of 50, 75, or 100 W for 6 min, respectively. Each transition was performed at least eight times for each load in random order. The was obtained by a breath-by-breath method, and was measured by an impedance method during normal breathing, using an ensemble average. On transitions from rest to exercise, rapidly increased during phase I with time constants of 6.8–7.3 s. The also showed a similar rapid increment with time constants of 6.0–6.8 s with an apparent increase in stroke volume (SV). In this phase I, increased to about 29.7%–34.1% of the steady-state value and increased to about 58.3%–87.0%. Thereafter, some 20 s after the onset of exercise a mono-exponential increase to steady-state occurred both in and with time constants of 26.7–32.3 and 23.7–34.4 s, respectively. The insignificant difference between and time constants in phase I and the abrupt increase in both and SV at the onset of exercise from rest provided further evidence for a cardiodynamic contribution to following the onset of exercise from rest.     

Thermoregulation at rest and during exercise in prepubertal boys

Summary Thermal balance was studied in 11 boys, aged 10–12 years, with various values for maximal oxygen uptake ( ), during two standardized sweating tests performed in a climatic chamber in randomized order. One of the tests consisted in a 90-min passive heat exposure [dry bulb temperature (T _db) 45° C] at rest. The second test was represented by a 60-min ergocycle exercise at 60% of individual (T _db 20° C). At rest, rectal temperature increased during heat exposure similar to observations made in adults, but the combined heat transfer coefficient reached higher values, reflecting greater radiative and convective heat gains in the children. Children also exhibited a greater increase in mean skin temperature, and a greater heat dissipation through sweating. Conversely, during the exercise sweating-test, although the increase in rectal temperature did not differ from that of adults for similar levels of exercise, evaporative heat loss was much lower in children, suggesting a greater radiative and convective heat loss due to the relatively greater body surface area. Thermophysiological reactions were not related to in children, in contrast to adults.     

Cardiac output measured by acetylene rebreathing technique at rest and during exercise

Cardiac output ( ) was measured by a rebreathing technique, using acetylene and a mass-spectrometer for analyzing. In addition the rate of pulmonary uptake of O₂ ( ) during the rebreathing period and during a preceding steady-state period were determined. Measurements were made on 8 adult humans at rest and at different levels of exercise up to maximum at two occasions. The ratio ( ) during steady-state/ during rebreathing) was found to be significantly below 1 when the was below about 21·min^–1 and to be about 0.55 for subjects at rest. This indicates that , and hence is increased by the rebreathing procedure when this involves deeper and more frequent respirations than those of the preceding period. Accordingly, when was below about 21·min^–1, the value, calculated exclusively from acetylene concentrations recorded during rebreathing, was multiplied by the above-mentioned -ratio. It is shown that this correcting procedure gives more reasonable values than those obtained by acetylene data alone. It is pointed out in what respects this correcting procedure of calculation deviates from that originally used by Grollman, and it is shown that there are only moderate differences between the results obtained by the two procedures.List of Symbols Ac Acetylene - _Ac ^B Bunsen solubility coefficient for Ac in blood (0.700 ml·ml^–1·atm^–1, Chapman et al. 1950) - _PT ^Ac Solubility coefficient for Ac in pulmonary tissue (0.768 ml·ml^–1·atm^–1, Cander and Forster 1959) - Mixed end-capillary to mixed venous oxygen difference per ml blood - F _AC Fractional (dry) concentration of a gas (Ac) in the gas mixture during rebreathing (s) or in the initial mixture in the bag (b) - Alveolar oxygen tension (mm Hg) - pB Barometric pressure (mm Hg) - Pulmonary capillary blood flow (cardiac output), (ml·min^–1) - t Time (s) - V ^b Initial gas volume (ml STPD) in the rebreathing bag (b) - V ^L Initial gas volume in lungs and airways after a deep expiration - V ^PT Volume of pulmonary tissue and blood in the pulmonary capillaries - V _Ac ^s (t _O) Distribution compartment (system volume) of a gas (Ac) at timet _O - Oxygen uptake (ml·min^–1) during rebreathing (RB) or steady-state (SS)     

Cardiac output and oxygen release during very high-intensity exercise performed until exhaustion

Our objectives were firstly, to study the patterns of the cardiac output () and the arteriovenous oxygen difference [(a–)O₂] responses to oxygen uptake (O₂) during constant workload exercise (CWE) performed above the respiratory compensation point (RCP), and secondly, to establish the relationships between their kinetics and the time to exhaustion. Nine subjects performed two tests: a maximal incremental exercise test (IET) to determine the maximal O₂ ( V ̇O₂peak), and a CWE test to exhaustion, performed at p 50 (intermediate power between RCP and O₂peak). During CWE, V ̇O₂ was measured breath-by-breath, Q ̇ was measured beat-by-beat with an impedance device, and blood lactate (LA) was sampled each minute. To calculate ( a–v ̄)O₂, the values of V ̇O₂ and Q ̇ were synchronised over 10 s intervals. A fitting method was used to describe the V ̇O₂, Q ̇ and ( a–v ̄)O₂ kinetics. The ( a–v ̄)O₂ difference followed a rapid monoexponential function, whereas both V ̇O₂ and Q ̇ were best fitted by a single exponential plus linear increase: the time constant () V ̇O₂ [57 (20 s)] was similar to ( a–v ̄)O₂, whereas for Q ̇ was significantly higher [89 (34) s, P <0.05] (values expressed as the mean and standard error). LA started to increase after 2 min CWE then increased rapidly, reaching a similar maximal value as that seen during the IET. During CWE, the rapid component of O₂ uptake was determined by a rapid and maximal ( a–)O₂ extraction coupled with a two-fold longer Q ̇ increase. It is likely that lactic acidosis markedly increased oxygen availability, which when associated with the slow linear increase of Q ̇, may account for the V ̇O₂ slow component. Time to exhaustion was larger in individuals with shorter time delay for ( a–v ̄)O₂ and a greater for .     

Postural effect on cardiac output,oxygen uptake and lactate during cycle exercise of varying intensity

Owing to changes in cardiac output, blood volume distribution and the efficacy of the muscle pump, oxygen supply may differ during upright and supine cycle exercise. In the present study we measured, in parallel, circulatory (heart rate, stroke volume, blood pressure) and metabolic parameters (oxygen uptake, lactic acid concentration [1a]) during incremental-exercise tests and at constant power levels ranging from mild to severe exercise. In supine position, cardiac output exceeded the upright values by 1.0-1.5 1 · min^–1 during rest, light ([la] < 2 mmol · 1^–1) and moderate ([la] =2–4 mmol · 1^–1) exercise. At higher exercise intensities the cardiac output in an upright subject approached and eventually slightly exceeded the supine values. For both rest-exercise transitions and large-amplitude steps (W 140 W) the cardiac output kinetics was significantly faster in upright cycling. The metabolic parameters (VO₂ and [la]) showed no simple relationship to the circulatory data. In light to moderate exercise they were unaffected by body position. Only in severe exercise, when cardiac output differences became minimal, could significant influences be observed: with supine body posture, [la] started to rise earlier and maximal power (W=23 W) and exercise duration (64 s) were significantly reduced. However, the maximal [la] value after exercise was identical in both positions. The present findings generally show advantages of upright cycling only for severe exercise. With lower workloads the less effective muscle pump in the supine position appears to be compensated for by the improved central circulatory conditions and local vasodilatation.     

The validity of predicting maximal oxygen uptake from a perceptually-regulated graded exercise test

The purpose of this study was to assess the validity of predicting maximal oxygen uptake from sub-maximal values elicited during a perceptually-regulated exercise test. We hypothesised that the strong relationship between the ratings of perceived exertion (RPE) and would enable to be predicted and that this would improve with practice. Ten male volunteers performed a graded exercise test (GXT) to establish followed by three sub-maximal RPE production protocols on a cycle ergometer, each separated by a period of 48 h. The perceptually-regulated trials were conducted at intensities of 9, 11, 13, 15 and 17 on the RPE scale, in that order. and HR were measured continuously and recorded at the end of each 4 min stage. Individuals RPE values yielded correlations in the range 0.92–0.99 across the three production trials. There were no significant differences between measured (48.8 ml·kg^–1·min^–1) and predicted max values (47.3, 48.6 and 49.9 ml·kg^–1·min^–1, for trials 1, 2 and 3, respectively) when max was predicted from RPE values of 9–17. The same was observed when was predicted using RPE 9–15. Limits of agreement (LoA) analysis on actual and predicted values (from RPE 9–17) were (bias±1.96×SDdiff) 1.5±7.3, 0.2±4.9 and –1.2±5.8 ml·kg^–1·min^–1, for trials 1, 2 and 3, respectively. Corresponding LoA values for actual and predicted (from RPE 9–15) were 5.4±11.3, 4.4±8.7 and 2.3±8.4 ml·kg^–1·min^–1, respectively. The data suggest that a sub-maximal, perceptually-guided, graded exercise protocol can provide acceptable estimates of maximal aerobic power, which are further improved with practice in fit young males.     

Effects of moderate hyperoxia on oxygen consumption during submaximal and maximal exercise

The present study examined the effect of hyperoxia on oxygen uptake (V˙O₂) and on maximal oxygen uptake (V˙O_2max) during incremental exercise (IE) and constant work rate exercise (CWRE). Ten subjects performed IE on a bicycle ergometer under normoxic and hyperoxic conditions (30% oxygen). They also performed four 12-min bouts of CWRE at 40, 55, 70 and 85% of normoxic V˙O_2max (ex1, ex2, ex3 and ex4, respectively) in normoxia and in hyperoxia. V˙O_2max was significantly improved by 15.0 (15.2)% under hyperoxia, while performance (maximum workload, W _max) was improved by only +4.5 (3.0)%. During IE, the slope of the linear regression relating V˙O₂ to work rate was significantly steeper in hyperoxia than in normoxia [10.80 (0.88) vs 10.06 (0.66) ml·min^–1·W^–1]. During CWRE, we found a higher V˙O₂ at ex1, ex2, ex3 and ex4, and a higher V˙O₂ slow component at ex4 under hyperoxia. We have shown that breathing hyperoxic gas increases V˙O_2max, but to an extent that is difficult to explain by an increase in oxygen supply alone. Changes in metabolic response, fibre type recruitment and V˙O₂ of non-exercising tissue could explain the additional V˙O₂ for a given submaximal work rate under hyperoxia. Electronic Publication     

Effects of aerobic endurance training status and specificity on oxygen uptake kinetics during maximal exercise

The main purpose of this study was to analyze the effects of exercise mode, training status and specificity on the oxygen uptake (O₂) kinetics during maximal exercise performed in treadmill running and cycle ergometry. Seven runners (R), nine cyclists (C), nine triathletes (T) and eleven untrained subjects (U), performed the following tests on different days on a motorized treadmill and on a cycle ergometer: (1) incremental tests in order to determine the maximal oxygen uptake (O_2max) and the intensity associated with the achievement of O_2max (IO_2max); and (2) constant work-rate running and cycling exercises to exhaustion at IO_2max to determine the effective time constant of the O₂ response (O₂). Values for O_2max obtained on the treadmill and cycle ergometer [R=68.8 (6.3) and 62.0 (5.0); C=60.5 (8.0) and 67.6 (7.6); T=64.5 (4.8) and 61.0 (4.1); U=43.5 (7.0) and 36.7 (5.6); respectively] were higher for the group with specific training in the modality. The U group showed the lowest values for O_2max, regardless of exercise mode. Differences in O₂ (seconds) were found only for the U group in relation to the trained groups [R=31.6 (10.5) and 40.9 (13.6); C=28.5 (5.8) and 32.7 (5.7); T=32.5 (5.6) and 40.7 (7.5); U=52.7 (8.5) and 62.2 (15.3); for the treadmill and cycle ergometer, respectively]; no effects of exercise mode were found in any of the groups. It is concluded that O₂ during the exercise performed at IO_2max is dependent on the training status, but not dependent on the exercise mode and specificity of training. Moreover, the transfer of the training effects on O₂ between both exercise modes may be higher compared with O_2max.     

Influence of exercise intensity on time spent at high percentage of maximal oxygen uptake during an intermittent session in young endurance-trained athletes

The purpose of this study was to compare, during a 30s intermittent exercise (IE), the effects of exercise intensity on time spent above 90% and time spent above 95% in young endurance trained athletes. We hypothesized that during a 30sIE, an increase in exercise intensity would allow an increase in due to a decrease in time to achieve 90% or 95% of Nine endurance-trained male adolescents took part in three field tests. After determination of their and maximal aerobic velocity (MAV), they performed, until exhaustion, two intermittent exercise sessions alternating 30s at 100% of MAV (IE₁₀₀) or 110% of MAV (IE₁₁₀) and 30s at 50% of MAV. Mean time to exhaustion (t _lim) values obtained during IE₁₀₀ were significantly longer than during IE₁₁₀ (p < 0.01). Moreover, no significant difference was found in expressed in absolute or relative (%t _lim) values between IE₁₀₀ and IE₁₁₀. In conclusion, an increased of 10% of exercise intensity during a 30s intermittent exercise model (with active recovery), does not seem to be the most efficient exercise to solicit oxygen uptake to its highest level in young endurance-trained athletes.     

Relationship between muscle fatigue and oxygen uptake during cycle ergometer exercise with different ramp slope increments

Summary The surface electromyogram (EMG) from active muscle and oxygen uptake ( ) were studied simultaneously to examine changes of motor unit (MU) activity during exercise tests with different ramp increments. Six male subjects performed four exhausting cycle exercises with different ramp slopes of 10, 20, 30 and 40 W · min^–1 on different days. The EMG signals taken from the vastus lateralis muscle were stored on a digital data recorder and converted to obtain the integrated EMG (iEMG). The was measured, with 20-s intervals, by the mixing chamber method. A non-linear increase in iEMG against work load was observed for each exercise in all subjects. The break point of the linear relationship of iEMG was determined by the crossing point of the two regression lines (iEMG_bp). Significant differences were obtained in the exercise intensities corresponding to maximal oxygen uptake ( ) and the iEMG_bp between 10 and 30, and 10 and 40 W · min –1 ramp exercises (P < 0.05). However, no significant differences were obtained in and corresponding to the iEMG_bp during the four ramp exercises. With respect to the relationship between and exercise intensity during the ramp increments, the -exercise intensity slope showed significant differences only for the upper half (i.e. above iEMG_bp). These results demonstrated that the and at which a nonlinear increase in iEMG was observed were not varied by the change of ramp slopes but by the exercise intensity corresponding to and the iEMG_bp was varied by the change of ramp slopes. In addition, the significant differences in the exercise intensity slopes for the upper half of the tests would suggest that the recruitment patterns of MU and/or muscle metabolic state might be considerably altered depending upon the ramp slope increments.     

Effect of prior metabolic rate on the kinetics of oxygen uptake during moderate-intensity exercise

Pulmonary oxygen uptake ( ) dynamics during moderate-intensity exercise are often assumed to be dynamically linear (i.e. neither the gain nor the time constant (τ) of the response varies as a function of work rate). However, faster, slower and unchanged kinetics have been reported during work-to-work transitions compared to rest-to-work transitions, all within the moderate-intensity domain. In an attempt to resolve these discrepancies and to improve the confidence of the parameter estimation, we determined the response dynamics using the averaged response to repeated exercise bouts in seven healthy male volunteers. Each subject initially performed a ramp-incremental exercise test for the estimation of the lactate threshold ( ). They then performed an average of four repetitions of each of three constant-work-rate (WR) tests: (1) between 20 W and a work rate of 50% (WR50) between 20 W and 90% (step 1→2), (2) between WR50 and 90% (step 2→3), and (3) between 20 W and 90% (step 1→3); 6 min was spent at each work rate increment and decrement. Parameters of the kinetic response of phase II were established by non-linear least-squares fitting techniques. The kinetics of were significantly slower at the upper reaches of the moderate-intensity domain (step 2→3) compared to steps 1→2 and 1→3 [group mean (SD) phase II τ: step 1→2 25.3 (4.9) s, step 2→3 40.0 (7.4) s and step 1→3 32.2 (6.9) s]. The off-transient values of τ were not significantly different from each other: 36.8 (16.3) s, 38.9 (11.6) s and 30.8 (5.7) s for steps 1→2, 2→3 and 1→3, respectively. Surprisingly, the on-transient gain (G, ) was also found to vary among the three steps [G=10.56 (0.42) ml·min^–1·W^–1, 11.85 (0.64) ml·min^–1·W^–1 and 11.23 (0.52) ml·min^–1·W^–1 for steps 1→2, 2→3 and 1→3, respectively]; the off-transient G did not vary significantly and was close to that for the on-transient step 1→3 in all cases. Our results do not support a dynamically linear system model of during cycle ergometer exercise even in the moderate-intensity domain. The greater oxygen deficit per unit power increment in the higher reaches of the moderate-intensity domain necessitates a greater transient lactate contribution to the energy transfer, or a greater phosphocreatine breakdown, or possibly both. Electronic Publication     

Maximal oxygen uptake during field running does not exceed that measured during treadmill exercise

Modern ergometric equipment enables the simulation of laboratory maximal oxygen uptake (V˙O_2max) testing in the field. Therefore, it was investigated whether the improved event specificity on the track might lead to higher V˙O_2max measurements in running. Identical protocols were used on the treadmill and on the track (speed was indicated by a computer-driven flashing light system). Ambulatory measurements of gas exchange were carried out throughout both tests, which were executed in randomized order. There were no significant differences (P=0.71) in V˙O_2max between treadmill [4.65 (0.51) ml·min^–1] and field tests [4.63 (0.55) ml·min^–1]. However, the test duration differed significantly (P<0.001) by approximately 5%: treadmill 691 (39) s; field test 727 (42) s. With the exception of maximum heart rate (HR_max; significantly higher in the field with P=0.02) all criteria for the degree of effort were similar between the two tests. However, the difference in HR_max at less than 2 beats·min^–1, was practically negligible. Submaximal measurements of oxygen uptake and minute ventilation were significantly higher on the treadmill (P<0.001 for both parameters). In summary, field tests with incremental running protocols do not result in higher V˙O_2max measurements compared to laboratory treadmill exercise. A better running economy on the track results in higher maximal velocities and longer exercise durations being sustained. The determination of V˙O_2max is not a reasonable application for ambulatory gas exchange measurements because laboratory values are not surpassed. Electronic Publication     

Growth hormone regulation in two types of aerobic exercise of equal oxygen uptake

Summary Five normal men, aged 23 to 35 years, participated in two bouts of continuous aerobic cycling separated by five days. The first type of exercise (EI) was cycling at a pedalling frequency of 50 rev · min⁻¹ with a load which produced a steady state O₂ uptake of approximately 40% of the subjects' . The second type of exercise (EII) was cycling at a pedalling frequency of 90 rev · min⁻¹ with a load such that an equal steady state was reached and maintained. Both EI and EII lasted 40 min. GH levels increased in EI and EII, reaching their maximum at 8 min of recovery (245 and 300% of resting values, respectively). No significant differences were observed between EI and EII in GH, lactate, glucagon, insulin, cortisol and glucose levels between the two exercises. While it has been reported earlier that GH levels were frequently related to lactate levels and/or decreased O₂ availability (Sutton 1977; Raynaud et al. 1981; Kozlowski et al. 1983; VanHelder et al. 1984a, b), this study suggests that the opposite is also valid, that is, different types of exercise of equal , duration and lactate production do not produce significantly different GH responses.     

Criteria for maximum oxygen uptake in progressive bicycle tests

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

Oxygen uptake kinetics during high-intensity arm and leg exercise

The purpose of the present study was to examine the oxygen uptake kinetics during heavy arm exercise using appropriate modelling techniques, and to compare the responses to those observed during heavy leg exercise at the same relative intensity. We hypothesised that any differences in the response might be related to differences in muscle fibre composition that are known to exist between the upper and lower body musculature. To test this, ten subjects completed several bouts of constant-load cycling and arm cranking exercise at 90% of the mode specific V(O(2)) peak. There was no difference in plasma [lactate] at the end of arm and leg exercise. The time constant of the fast component response was significantly longer in arm exercise compared to leg exercise (mean+/-S.D., 48+/-12 vs. 21+/-5 sec; P < 0.01), while the fast component gain was significantly greater in arm exercise (12.1+/-1.0 vs. 9.2+/-0.5 ml min(-1) W(-1); P < 0.01). The V(O(2)) slow component emerged later in arm exercise (126+/-27 vs. 95+/-20 sec; P < 0.01) and, in relative terms, increased more per unit time (5.5 vs. 4.4% min(-1); P < 0.01). These differences between arm crank and leg cycle exercise are consistent with a greater and/or earlier recruitment of type II muscle fibres during arm crank exercise.     

Effects of reduced muscle temperature on the oxygen uptake kinetics at the start of exercise

SHIOJIRI, T., SHIBASAKI, M., AOKI, K., KONDO, N. & KOGA, S. 1997. Effects of reduced muscle temperature on the oxygen uptake kinetics at the start of exercise. Acta Physiol Scand 159 , 327–333. Received 25 September 1995, accepted 5 November 1996. ISSN 0001–6772. Laboratory of Exercise and Sports Science, Yokohama City University; Division of Intelligence Science, Graduate School and Technology, Division of Education, Graduate School, Faculty of Human Development, Kobe University; and Applied Physiology Laboratory, Kobe Design University, Japan. The purpose of this study was to examine the effects of reduced muscle temperature (T_m ) on gas exchange kinetics and haemodynamics at the start of exercise. Six male subjects performed moderate cycle exercise under reduced (C) and normal (N) T_m conditions. T_m and rectal temperature were significantly reduced by immersion in cold water (by 6.6 °C and 1.8 °C, respectively). The increases in oxygen uptake (V˙o ₂) and oxygen pulse (V˙o ₂/HR) during phase 1 (abrupt increase after the start of exercise) were significantly lower under C than under N. The time constant for O₂ under C (36.0 ± 7.7 (SD) s) was significantly greater than under N (27.5 ± 4.4 s); however, the time constants of cardiac output under C (38.3 ± 16.6 s) and N (33.7 ± 18.5 s) were similar. These results suggest that the slower V˙o ₂ on-response under reduced T_m conditions is caused by decreased O₂ extraction in working muscle and/or by impairment of oxidative reactions by reduced muscle temperature.     

Influence of body position and pre-exercise activity on cardiac output and oxygen uptake following step changes in exercise intensity

Summary Parallel measurements of breath-by-breath oxygen uptake, cardiac output (Doppler technique), blood pressure (Finapres technique) and heart rate were performed in nine subjects during cycle ergometer exercise in the upright and supine positions. Transients were monitored during power steps starting from and leading to either rest or lower levels of exercise intensity. Oxygen uptake ( ) and cardiac output kinetics were markedly faster than in all other conditions when exercise was started from rest. In contrast to exercise-exercise on steps, the computed arteriovenous difference in O₂ content increased almost immediately in this situation, indicating that not only the additional energy expenditure due to the acceleration of the flywheel but also an increased venous admixture from non-exercising parts of the body contributed to the early kinetics. The off kinetics generally showed a more uniform pattern and did not simply mirror the on transients. The present findings indicate that transitions from rest should be avoided when muscle kinetics are to be assessed on the basis of ₂ measurements at the mouth.     

Influence of recovery mode (passive vs. active) on time spent at maximal oxygen uptake during an intermittent session in young and endurance-trained athletes

The aim of this study was to analyze the effects of recovery mode (active/passive) on time spent at high percentage of maximal oxygen uptake i.e. above 90% of and above 95% of during a single short intermittent session. Eight endurance-trained male adolescents (15.9 ± 1.4 years) performed three field tests until exhaustion: a graded test to determine their (57.4 ± 6.1 ml min⁻¹ kg⁻¹), and maximal aerobic velocity (MAV; 17.9 ± 0.4 km h⁻¹), and in a random order, two intermittent exercises consisting of repeated 30 s runs at 105% of MAV alternated with 30 s passive (IE_P) or active recovery (IE_A, 50% of MAV). Time to exhaustion (t _lim) was significantly longer for IE_P than for IE_A (2145 ± 829 vs. 1072 ± 388 s, P < 0.01). No difference was found in and between IE_P (548 ± 499–316 ± 360 s) and IE_A (746 ± 417–459 ± 332 s). However, when expressed as a percentage of t _lim, and were significantly longer (P < 0.001 and P < 0.05, respectively) during IE_A (67.7 ± 19%–42.1 ± 27%) than during IE_P (24.2 ± 19%–13.8 ± 15%). Our results demonstrated no influence of recovery mode on absolute or mean values despite significantly longer t _lim values for IE_P than for IE_A. In conclusion, passive recovery allows a longer running time (t _lim) for a similar time spent at a high percentage of