Oxygen uptake kinetics during horizontal and uphill treadmill running in humans

The aim of this study was to examine the effect of increasing the ratio of concentric to eccentric muscle activation on oxygen uptake (V˙O₂) kinetics during treadmill running. Nine subjects [2 women; mean (SD) age 29 (7) years, height 1.77 (0.07) m, body mass 73.0 (7.5) kg] completed incremental treadmill tests to exhaustion at 0% and 10% gradients to establish the gradient-specific ventilatory threshold (VT) and maximal oxygen uptake (V˙O_2max). Subsequently, the subjects performed repeated moderate intensity (80% of gradient-specific VT) and heavy intensity (50% of the difference between the gradient specific VT and V˙O_2max) square-wave runs with the treadmill gradient set at 0% and 10%. For moderate intensity exercise, there were no significant differences between treadmill gradients for V˙O₂ kinetics. For heavy intensity exercise, the amplitude of the primary component of V˙O₂ was not significantly different between 0% and 10% treadmill gradients [mean (SEM) 2,940 (196) compared to 2,869 (156) ml·min^–1, respectively], but the amplitude of the V˙O₂ slow component was significantly greater at the 10% gradient [283 (43) compared to 397 (37) ml·min^–1; P<0.05]. These results indicate that the muscle contraction regimen (i.e. the relative contribution of concentric and eccentric muscle action) significantly influences the amplitude of the V˙O₂ slow component. Electronic Publication     

Scaling maximal oxygen uptake to predict cycling time-trial performance in the field: a non-linear approach

The purpose of the present article is to identify the most appropriate method of scaling for differences in body mass when assessing the energy cost of time-trial cycling. The data from three time-trial cycling studies were analysed (N=79) using a proportional power-function ANCOVA model. The maximum oxygen uptake-to-mass ratio found to predict cycling speed was precisely the same as that derived by Swain for sub-maximal cycling speeds (10, 15 and 20 mph). The analysis was also able to confirm a proportional curvilinear association between cycling speed and energy cost, given by The model predicts, for example, that for a male cyclist (72 kg) to increase his average speed from 30 km h^–1 to 35 km h^–1, he would require an increase in from 2.36 l min^–1 to 3.44 l min^–1, an increase of 1.08 l min^–1. In contrast, for the cyclist to increase his mean speed from 40 km h^–1 to 45 km h^–1, he would require a greater increase in from 4.77 l min^–1 to 6.36 l min^–1, i.e. an increase of 1.59 l min^–1. The model is also able to accommodate other determinants of time-trial cycling, e.g. the benefit of cycling with a side wind (5% faster) compared with facing a predominatly head/tail wind (P<0.05). Future research could explore whether the same scaling approach could be applied to, for example, alternative measures of recording power output to improve the prediction of time-trial cycling performance.     

The effect of salbutamol on performance in endurance cyclists

The effect of salbutamol (S) on cycling performance was examined in 15 highly trained non-asthmatic male cyclists. A double-blind, randomized cross-over design was used with S or placebo (P) administered using a metered-dose inhaler and a spacer device 20 min before each testing session. The S dose was 400 μg (four puffs), which is twice the normal therapeutic level. Subjects were habituated to all the laboratory procedures in the week prior to actual data collection. The subjects performed four tests under S and P conditions on separate days over 2 weeks. These included measurement of maximal O₂ uptake (cycle ergometry) with assessment of pulmonary function before and after, a submaximal (90% of ventilatory threshold) square-wave work transition from a base of unloaded cycling, a 60-s modified Wingate test, and a simulated 20 km time trial. No significant differences were observed in any of the dependent variables related to aerobic endurance or cycling performance between the S and P conditions. These results support other findings that an acute dose (400 μg) of S has no performance-enhancing properties.     

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.     

Supra-maximal cycling efficiency assessed in humans by using a new protocol

This study proposed a non-invasive method to determine the gross (GE, no baseline correction), net (NE, resting metabolism as the baseline correction) and work (WE, unloaded cycling as the baseline correction) efficiencies during cycling at an intensity higher than the maximal aerobic power (MAP). Twelve male subjects performed two exercises consisting of 4 min at 50% MAP followed either by 8 min at 63% MAP or by 8 sequences of 60 s divided into 10 s at 130% MAP and 50 s at 50% MAP (i.e., 63% MAP on average). Oxygen uptake was continuously measured to calculate GE, NE and WE at 50%, 63% and 130% MAP, and the data presented as the means and standard deviations. The GE values were 18.2%, 19.1%, 22.7%, the NE values were 22.4%, 22.8%, 24.3% and the WE values were 34.2%, 31.4% and 27.2% at 50%, 63% and 130% MAP, respectively. The GE and NE increased (P<0.001) whereas the WE decreased (P<0.001) with each increment in power output. The GE was lower than the NE (P<0.001) at 50% and 63% MAP and than the WE (P<0.001) at all intensities. The NE was lower (P<0.001) than the WE at 50% and 63% MAP. These results showed that (1) efficiency index values obtained during supra-maximal exercise were consistent with previous proposals and (2) the efficiency-power output relationships were not limited to sub-maximal intensity levels but were confirmed at higher power output.     

The test-retest reliability of gas exchange kinetics in humans using a pseudo random binary sequence exercise test

The purpose of this study was to compare the test-retest reliability of oxygen uptake ( ) kinetics with carbon dioxide output( ) kinetics using a pseudo random binary sequence (PRBS) exercise test. A reliable test of gas exchange kinetics would have the potential of being applied as a sports fitness test. Ten healthy male subjects agreed to participate in the study and all subjects completed two identical PRBS exercise tests (test 1 and test 2), separated by a 30 min period of inactivity. Three consecutive 300 s PRBS cycles were completed in each test with 20 s exercise intensity changes between 25 and 85 W using an electrically braked cycle ergometer. Fourier analysis was computed for frequencies 3.3, 6.7 and 10 mHz. Statistical analysis by two-way ANOVA with repeated measures did not reveal significant differences between test 1 and test 2 for either kinetics or kinetics. Static gain of for test 1 [9.11 (SD 0.59) ml·min^–1·W^–1] and test 2 [9.23 (SD 0.64) ml·min^–1·W^–1] did not differ significantly between tests. The 95% limits of agreement for kinetics displayed increased variability in comparison to kinetics at each frequency of amplitude ratio and phase shift. Systematic bias ranged between 0% and 4%, except at frequency 10 mHz of kinetics phase shift which showed a 10% bias for slower kinetics in test 2. It is possible that the increased variability of kinetics compared to kinetics might be attributable to a lower signal to noise ratio in kinetics, variations in ventilation or the storage mechanisms of CO₂. The lower variability of kinetics compared with kinetics suggests that the PRBS test of kinetics has the greater potential for further development as an indicator of aerobic fitness. Electronic Publication     

Effect of exercise mode on blood glucose disposal during physiological hyperinsulinaemia in humans

The aim of this study was to compare whole-body glucose uptake in cycling and running performed during physiological hyperinsulinaemia. On three occasions, seven male subjects underwent a hyperinsulinaemic (30 mU m⁻² min⁻¹), euglycaemic (5 mmol l⁻¹) clamp for 120 min. On one occasion, subjects rested for the duration of the trial (CON). On the other two occasions, after an initial resting period of 30 min, subjects either cycled (CYC) or ran (RUN) for 90 min at 65% of maximal O₂ uptake (V˙O_2max). Insulin infusion resulted in physiological hyperinsulinaemia that was maintained for the duration of each trial [CON: 61 (3) mU l⁻¹; CYC: 77 (7) mU l⁻¹; RUN: 77 (5) mU l⁻¹]. The rate of glucose uptake was greater during RUN than during CYC [last 30 min of exercise: 140 (4) vs 109 (8) μmol kg⁻¹ min⁻¹, respectively; P <0.01]. A differential amount of active muscle mass and/or muscle fibre type recruitment might account for the observed differences in glucose disposal between cycling and running. Electronic Publication     

Validity of a velodrome test for competitive road cyclists

The aim of this study was to evaluate the validity of a velodrome field test consisting of repeated rides of 2,280 m, with an initial speed of 28 km·h^–1 and increments of 1.5 km·h^–1 interspersed with 1-min recovery periods until exhaustion. A group of 12 male competitive road cyclists performed maximal cycling tests under velodrome and laboratory conditions. Velodrome oxygen uptake ( O₂) and power output were estimated using equations previously published. Physiological responses to the two tests were compared. Relationships between performance in the velodrome and physiological parameters measured in the laboratory were studied. Maximal power output, heart rate and O₂ were similar in the velodrome and the laboratory [372 (SD 50) vs 365 (SD 36) W, 195 (SD 8) vs 196 (SD 9) beats·min^–1 and 4.49 (SD 0.56) vs 4.49 (SD 0.46) l·min^–1, respectively], while maximal velodrome blood lactate concentration was significantly higher [13.5 (SD 2.1) vs 11.8 (SD 3.1) mmol·l^–1]. Velodrome heart rate was higher at submaximal exercise intensities representing 40%, 50% and 60% of maximal aerobic power, and velodrome blood lactate concentration was also higher at 60%, 70% and 80% of maximal aerobic power. The laboratory parameter that showed the highest correlation with the maximal cycling speed in the velodrome was maximal oxygen uptake ( O_2max) expressed per unit of body mass (r = 0.93). In addition, the accuracy of different methods of estimation of the metabolic cost of cycling, rolling resistance, air resistance coefficients and O_2max were compared. Significant differences were found. In conclusion, the present results indicated the validity of a velodrome test used to estimate maximal aerobic parameters of competitive road cyclists, as long as the estimation is made using established equations. When road cyclists are tested in the laboratory, physiological values should be expressed per unit of body surface area or body mass, to predict more accurately the cyclist's performance level under specific field conditions.     

Upper body power as a determinant of classical cross-country ski performance

The purpose of this study was to evaluate the relationship between short (≤60 s) and long duration (4–12 min) measures of upper body power (UBP) and mass start classical cross-country ski performance. Several experienced skiers (eight men, five women) completed three separate tests of UBP on a double poling ergometer: two tests of highest average power output for 10 s (UBP₁₀) and 60 s (UBP₆₀), and an incremental test to exhaustion to measure peak oxygen uptake (VO_2PEAK) and peak power output (UBP_PEAK). Lastly, subjects competed in a 10-km classical cross-country ski race from which race speed (RS) was computed. RS correlated highly with UBP₁₀ (r = 0.93; P < 0.05), UBP₆₀ (r = 0.92; P < 0.05), and UBP_PEAK (r = 0.94; P < 0.05); the correlation was lower but still significant for VO_2PEAK (r = 0.88; P < 0.05). These findings suggest that both short and long duration measures of UBP are important determinants of mass start classical ski race performance.     

Effect of a pulsating anti-gravity suit on peak exercise performance in individual with spinal cord injuries

The aim of this study was to examine effects of a pulsating pressure anti-gravity suit on the peak values of oxygen uptake (V˙O₂) and power during maximal arm exercise in spinal-cord-injured (SCI) individuals. Five well-trained SCI men (with lesions at levels between T6 and L1) and seven well-trained able-bodied men (ABC) performed two incremental (10 W · min⁻¹) arm-cranking tests. During one test the pressure in the anti-G suit pulsated between 4.7 kPa (35 mmHg) and 9.3 kPa (70 mmHg) every 2 s (PPG+), during the other test (PPG−) all the subjects wore the anti-G suit in a deflated state. Tests were performed in a counter-balanced order. Peak V˙O₂ in SCI was 1 ml · kg⁻¹ · min⁻¹ lower during PPG+ compared to PPG− (P = 0.05). Peak power and peak heart rate were not significantly different during PPG+ compared to PPG−. These results would suggest that no increase in work capacity can be obtained with a pulsating pressure anti-gravity suit in either SCI or ABC. Accepted: 1 September 1998     

Maximal strength-training effects on force-velocity and force-power relationships explain increases in aerobic performance in humans

Maximal strength-training with an emphasis on maximal mobilization during cross-country skiing increases exercise economy when double-poling. The aim of this experiment was to investigate whether the mechanism of this increase is a change in the force-velocity relationship and the mechanical power output. A group of 19 cross-country skiers having an average peak oxygen uptake of 255 ml·kg^–0.67 body mass·min^–1 or 61 ml·kg^–1·min^–1 were randomly assigned to either a high resistance-training group (n=10) or a control group (n=9). Upper body endurance was tested on a ski ergometer. The high-resistance-training group trained for 15 min on three occasions a week for 9 weeks. Training consisted of three series of five repetitions using 85% of one repetition maximum (1RM), with emphasis on high velocity in the concentric part of the movement. Upper body exercise economy, 1RM and time to exhaustion increased significantly in the high resistance-training group, but was unchanged in the control group. Peak power and the velocities for a given load increased significantly, except for the two lowest loads. We conclude that the increased exercise economy after a period of upper body high resistance-training can be partly explained by a specific change in the force-velocity relationship and the mechanical power output. Electronic Publication     

Effect of posture on high-intensity constant-load cycling performance in men and women

The time sustained during a graded cycle exercise is ~10% longer in an upright compared with a supine posture. However, during constant-load cycling this effect is unknown. Therefore, we tested the postural effect on the performance of high-intensity constant-load cycling. Twenty-two active subjects (11 men, 11 women) performed two graded tests (one upright, one supine), and of those 22, 10 subjects (5 men, 5 women) performed three high-intensity constant-load tests (one upright, two supine). To test the postural effect on performance at the same absolute intensity, during the upright and one of the supine constant-load tests subjects cycled at 80% of the peak power output achieved during the upright graded test. To test the postural effect on performance at the same relative intensities, during the second supine test subjects cycled at 80% of the peak power output achieved during the supine graded test. Exercise time on the graded and absolute intensity constant-load tests for all subjects was greater (P<0.05) in the upright compared with supine posture (17.9±3.5 vs. 16.1±3.1 min for graded; 13.2±8.7 vs. 5.2±1.9 min for constant-load). This postural effect at the same absolute intensity was larger in men (19.4±8.5 upright vs. 6.6±1.6 supine, P<0.001) than women (7.1±2 upright vs. 3.9±1.4 supine, P>0.05) and it was correlated (P<0.05) with both the difference in between positions during the first minute of exercise (r=0.67) and the height of the subjects (r=0.72). In conclusion, there is a very large postural effect on performance during constant-load cycling exercise and this effect is significantly larger in men than women.     

Reproducibility of the parameters of the on-transient cardiopulmonary responses during moderate exercise in patients with chronic obstructive pulmonary disease

To be clinically useful as indices reflective of altered physiological function consequent to interventions in patients with chronic obstructive pulmonary disease (COPD), the time constant (τ) and steady-state amplitude of the kinetic responses for oxygen uptake ( ) carbon dioxide output ( ) ventilation ( ) and heart rate (HR) have to be appropriately differentiable and reproducible. We therefore assessed the reproducibility of τ and steady state amplitude values in 41 patients with severe COPD [mean (SD)] [forced expiratory volume in 1 s=41 (7)% predicted], aged 64 (5) years. Of the total, 6 of the patients (15%) did not produce breath-by-breath data of sufficient quality to warrant kinetic analysis. The remaining 35 patients completed two moderate-intensity 10 min square-wave exercise tests separated by 2 h, both before and after an endurance training programme. Tests were conducted on an electromagnetically-braked cycle ergometer at an exercise intensity corresponding to 80% of the estimated lactate threshold (θ_La) or 50% of peak oxygen uptake if θ_La was insufficiently differentiable. Breath-by-breath measurements of , , and HR were averaged into 10 s bins and the on-transient response kinetics were estimated using a mono-exponential model. Analysing the pre-training and the post-training test 1 and test 2 comparisons together, the test 1 –test 2 differences were not significantly different from 0 for either τ or A. The standard deviation of the test 1 –test 2 differences allowed us to define the magnitude of change that would reach statistical significance. For τ, this averaged some 8, 10, 11 and 8 s, for , , and HR, respectively, for a one-tailed paired-comparisons test (i.e. appropriate for assessing hypothesised improvements resulting from an intervention); for a two-tailed comparison, the differences were approximately 2 s greater. The corresponding one-tailed values for A were 100 ml·min^–1, 95 ml·min^–1, 2.5 1·min^–1 and 4 beats·min^–1, respectively; the two-tailed values were 10%–15% greater. We therefore conclude that both τ and A for moderate-intensity exercise can be reproducibly estimated in patients with COPD when the data set provides a sufficiently large amplitude of response and sufficiently low sample variability to allow appropriate parameter estimation. Electronic Publication     

The effects in humans of rapid loss of body mass on a boxing-related task

The physiological effects of strategies for a rapid loss of body mass immediately before weighing-in for competition in weight-governed sports are unclear. This study examined the effects of a 3%–4% loss in body mass on a boxing-related task. Seven novice amateur boxers completed three 3 min rounds of simulated boxing on a prototype boxing ergometer in an euhydrated state (E-trial) and after exercise-induced thermal dehydration (D-trial). All subjects lost body mass following dehydration–mean body mass fell 3.8 (SD ± 0.3)% [77.3 (SD ± 11.3) to 74.4 (SD ± 10.7) kg, P < 0.001] – but changes in plasma volume (PV) were inconsistent. Four subjects suffered reductions in PV between 15% and 30%, one subject maintained his E-trial value and two recorded an increase. The D-trial mean PV value was 8.0 (SD ± 17.2)% lower but this fall was not statistically significant (P > 0.05). Analysis of D-trial boxing performance showed one subject maintained his performance over the two trials and a second improved 17.8%. A two-way ANOVA (condition × time) with repeated measures on both factors showed no significant main effect differences for condition (F _1,6=3.93 P > 0.05), time (F _1.83,48=1.12, P > 0.05) or interaction between them (F _1.93,48, P > 0.05). Furthermore, neither heart rate nor blood lactate responses in the boxing task differed between trials. These data were affected by the small sample. Power and effect size analysis using η² procedure and removing the outlier data produced a mean fall in boxing performance of 26.8%. However, some subjects appeared able to resist the deleterious effects of a rapid loss of body mass prior to competition and further research is needed to explain the mechanisms under-pinning this ability. Accepted: 12 May 2000     

Influence of pedalling rate on the energy cost of cycling in humans

To determine the optimal pedalling rate that minimises both the oxygen consumption (f _V˙O2,min) and the energy cost of cycling (f _Cr,min), 22 male subjects were asked to cycle on an ergometer on five occasions of 4 min each at a constant power output of 150 W and at pedalling rates of 40, 60, 80, 100 and 120 rpm. The oxygen consumption (V˙O₂ in millilitres per minute per kilogram) and the energy cost (Cr in joules per kilogram per metre) were determined during each period. The individual V˙O₂-pedalling rate and Cr-pedalling rate relationships were fitted by parabolic regressions which allowed the determination for each individual of f _V˙O2,min [mean (SD) 57.0 (4.9) rpm] and f _Cr,min [101.1 (3.2) rpm], respectively. Contrary to the values obtained for f _V˙O2,min, those for f _Cr,min were in agreement with the pedalling rates (90–110 rpm) usually selected in road cycling. It is therefore suggested that the minimisation of Cr is the main factor that determines the pedalling rate in field conditions. The lack of a significant correlation between f _V˙O2,min and f _Cr,min further indicated that, although f _V˙O2,min is often used for determining the metabolic capacities of subjects, f _Cr,min is a better index of optimal mechanical parameters of cycling in field conditions. Electronic Publication     

The effect of training on cardiovascular responses to arm exercise in individuals with tetraplegia

The aim of this study was to investigate the physiological responses to maximal and submaximal arm-cranking exercise in 21 individuals with tetraplegia (TP) and to evaluate the effect of a 3 and 6-month training period (mean frequency of 1.5 h · week^–1, mean intensity at 35% of the training time above 60% of the heart rate reserve) on these physiological responses. The TP were divided into 8 trained subjects (T), 7 untrained subjects (U) who started their training at the beginning of the study, and 6 sedentary subjects (S). All the subjects were tested at the beginning of training and after 6 months, whereas T and U were also tested in between, at 3 months. During maximal exercise, peak power output and peak oxygen uptake per kilogram bodymass were significantly higher in T (49.9 W and 14.2 ml·min^–1 · kg^–1 respectively) compared to U (20.7 W and 8.8 ml · min^–1 · kg^–1 respectively) and S (15.9 W and 7.4 ml · min^–1 · kg^–1 respectively), whereas all other peak responses showed tendencies to be higher in T. This is most likely to have been the result of participation in sport and the effect of it on performance capacity in T, although differences in completeness of the lesion may have influenced the results. No significant differences were found for submaximal and maximal responses after 3 or 6 months of training in either T and U or in S. This may have been due on the one hand to the vulnerability of the subjects to diseases and injuries and on the other hand to the low frequency of training. On an individual basis, however, remark able improvement was observed during the training period, especially for individuals in the U group. These results would suggest that a 3 or 6-month training period has no measurable positive effect on the fitness level of TP.     

Ergometry for estimation of mechanical power output in sprinting in humans using a newly developed self-driven treadmill

An evaluation of mechanical power during walking and running in humans was undertaken after developing a specially designed running ergometer (RE) in which the subjects gripped the handlebar in front of them keeping both arms straight and in a horizontal position. Ten subjects participated in comparisons of the mean horizontal pushing force (MF _am) on the handlebar with the mean horizontal ground reaction force (MF _fp) recorded by force platform under the RE during five different constant speeds of walking or running and sprint running with maximal effort. Mechanical power developed during sprint running on the RE was compared with a 50 m sprint. Mean linear velocity (Mv) of the RE belt was recorded by the rotary encoder attached to the axis of the belt. Mean mechanical power calculated from the handlebar setting (MP _am=MF _am × Mv) was compared to that calculated from force platform recordings (MP _fp=MF _fp × Mv). A high test-retest reproducibility was observed for both MF _fp (r=0.889) and MF _am (r=0.783). Larger values for the coefficient of variation for MF _am (11.3%–15.8%) were observed than for MF _fp (3.3%–8.2%). The MP _am, which were obtained from five different constant speeds of walking, running and sprint running were closely correlated to those of MP _fp (y=0.98x − 19.10,r=0.982, P < 0.001). In sprint running, MP _am was 521.7 W (7.67 W · kg⁻¹) and was correlated to the 50 m sprint time (r=−0.683, P < 0.01). It is concluded that the newly developed RE was useful in the estimation of mechanical power output during human locomotion such as when walking, jogging and sprinting. Accepted: 10 October 2000     

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.     

Coordination-related changes in the rhythms of breathing and walking in humans

Coordination of the respiratory rhythm with the rhythm of limb movements has often been observed during rhythmical exercise (e.g. in locomotion). It is usually associated with changes in the respiratory time course, but not in the locomotor rhythm. Therefore, we hypothesised that in walking, the extent of coordination-related changes (CRC) in respiratory parameters would increase with closer coordination. With respect to the controversially discussed question of a possible energetic advantage due to coordination, we devoted particular interest to the CRC in oxygen uptake (V˙O₂). In addition, we investigated the incidence and the extent of CRC in the stepping rhythm. We examined 18 volunteers walking on a treadmill at three different workload levels, which were adjusted by altering either the velocity or slope of the treadmill. Each walking test was carried out twice, once with spontaneous breathing and once with breathing paced by a step-related acoustic signal to enhance the coordination between breathing and walking. No correlation was found between the CRC in the analysed parameters and the degree of coordination. However, the extent of CRC of ventilation and V˙O₂ decreased with increasing workload. With the transition to coordination, increases and decreases of V˙O₂ occurred about equally often. From this we conclude that energetic economisation in walking, as reflected by a reduction in V˙O₂, is rather a side-effect of coordination, and is probably due to a more precise regulation of the breathing pattern. The economisation was more pronounced at higher work loads than at lower work loads. Our results revealed that coordination is also associated with changes in the stepping rate, which occurred more frequently when the variability of breathing was restricted by acoustic pacing of the breathing rhythm. This finding suggests that the choice of walking rhythm is not completely free, but can be influenced by the breathing rhythm. CRC in the walking rhythm might contribute to the avoidance of excessive CRC in the respiratory time course, which would entail an inefficient breathing pattern and thus, an energetic disadvantage. Accepted: 29 March 2000     

Respiratory gas exchange and physiological demands during a fire fighter evaluation circuit in men and women

We examined the oxygen uptake (VO2) and carbon dioxide output (VCO2) during completion of a circuit developed for testing fire fighters and related performance time to laboratory measures of fitness. Twenty-two healthy university students (ten women) were trained in the tasks then performed the circuit as quickly as possible. Breath-by-breath gas exchange and heart rate were continuously measured with a portable system. Median circuit time was 6:13 (min:s, 25-75% = 5:46-6:42) for men and 7:25 (25-75% = 6:49-10:21) for 8 women finishers (P = 0.023), and VO2 averaged 68 and 64% VO2max for the men and women during the circuit. Both men and women had high respiratory exchange ratios (>1.0) suggesting marked anaerobic energy contribution. Physiological variables associated with circuit time were assessed by backward stepwise regression yielding a significant model that included only peak work rate during arm cranking exercise as a function of circuit completion time across men and women combined (P < 0.001). For men, but especially for women, the time required for the simulated victim drag (68.2 kg mannequin) was positively correlated with total time to complete the other circuit elements (r = 0.51, r = 0.96 respectively). The simple correlation between circuit time and VO2max (mL/kg/min) revealed poor relationships for men (r = -0.37, P > 0.05) and women (r = 0.20, P > 0.05). These data demonstrated that upper body fitness as reflected by peak work rate during arm cranking correlated with total circuit time for the men and women in our population sample.