Automated VO2max calibrator for open-circuit indirect calorimetry systems

Characteristics of Pedaling Muscle Stiffness among Cyclists of Different Performance Levels

Background and Objectives: The aim of the present study was to compare the impact of an incremental exercise test on muscle stiffness in the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and gastrocnemius (GL) among road cyclists of three performance levels. Materials and Methods: The study group consisted of 35 cyclists grouped according to their performance level; elite (n = 10; professional license), sub-elite (n = 12; amateur license), and recreational (n = 13; cyclosportive license). Passive muscle stiffness was assessed using myometry before and after an incremental exercise test. Results: There was a significant correlation between time and category in the vastus lateralis with stiffness increases in the sub-elite (p = 0.001, Cohen's d = 0.88) and elite groups (p = 0.003, Cohen's d = 0.72), but not in the recreational group (p = 0.085). Stiffness increased over time in the knee extensors (RF, p < 0.001; VL, p < 0.001), but no changes were observed in the knee flexors (GL, p = 0.63, BF, p = 0.052). There were no baseline differences among the categories in any muscle. Conclusions: Although the performance level affected VL stiffness after an incremental exercise test, no differences in passive stiffness were observed among the main muscles implicated in pedaling in a resting state. Future research should assess whether this marker could be used to differentiate cyclists of varying fitness levels and its potential applicability for the monitoring of training load.

Comparison of Two Metabolic Simulators Used for Gas Exchange Verification in Cardiopulmonary Exercise Test Carts

Introduction

Metabolic simulators (MS) produce simulated human breaths for the purpose of verification of cardiopulmonary exercise test (CPET) equipment. MS should produce consistent identical breaths with known CO₂ and O₂ gas concentrations over a range of breath rates and tidal volumes. Reliability of a CPET metabolic cart depends on ongoing quality control and maintenance of the device, including intermittent verification with a MS. We compared two MS devices against two standard CPET systems.

Methods

The Vacumed 17056 (Vacumetrics, Ventura, CA) and Relitech (Relitech Systems BV, Nijkerk, The Netherlands) were used with two standard metabolic carts (Vyntus CPX and Vyntus ONE, both Vyaire Medical, Mettawa, IL, United States). Tidal volume (VT) was set at 2 and 3 L and breathing frequency ranged from 20 to 80 breaths per minute for each MS. At each set point, we measured three sets of 40 breaths. Primary outcome parameters collected were VT, oxygen consumption ( v . O₂), carbon dioxide production ( v . CO₂), and respiratory exchange ratio (RER).

Results

VT, RER, v . O₂, and v . CO₂ results as obtained from both MS were all within the limits of acceptability, at both tidal volume settings, and all ventilatory rates. No significant trends were identified for either MS device. The Relitech MS produced tidal volumes that were closer to the target VT for both CPET carts at both VT and all rates, but the results of both MS were within acceptable ranges.

Conclusion

Verification of CPET equipment using either the VM or RT metabolic simulator, producing highly accurate and predictable simulated breaths of known composition, enabling CPET laboratory managers to rely on subject test data obtained during cardiopulmonary exercise testing.

Inter- and intra-unit reliability of the COSMED K5: Implications for multicentric and longitudinal testing

Purpose

To evaluate the intra-unit (REL_INTRA) and inter-unit reliability (REL_INTER) of two structurally identical units of the metabolic analyser K5 (COSMED, Rome, Italy) that allows to utilize either breath-by-breath (BBB) or dynamic mixing chamber (DMC) technology.

Methods

Identical flow- and gas-signals were transmitted to both K5s that always operated simultaneously either in BBB- or DMC-mode. To assess REL_INTRA and REL_INTER, a metabolic simulator was applied to simulate four graded levels of respiration. REL_INTRA and REL_INTER were expressed as typical error (TE%) and Intraclass Correlation Coefficient (ICC). To assess also inter-unit differences via natural respiratory signals, 12 male athletes performed one incremental bike step test each in BBB- and DMC-mode. Inter-unit differences within biological testing were expressed as percentages.

Results

In BBB, TE% of REL_INTRA ranged 0.30–0.67 vs. REL_INTER 0.16–1.39 and ICC ranged 0.57–1.00 vs. 0.09–1.00. In DMC, TE% of REL_INTRA ranged 0.38–0.90 vs. REL_INTER 0.03–0.86 and ICC ranged 0.22–1.00 vs. 0.52–1.00. Mean inter-unit differences ranged -2.30–2.20% (Cohen’s ds (ds) 0.13–1.52) for BBB- and -0.55–0.61% (ds 0.00–0.65) for DMC-mode, respectively. Inter-unit differences for V˙O2 and RER were significant (p < 0.05) at each step.

Conclusion

Two structurally identical K5-units demonstrated accurate REL_INTRA with TE < 2.0% and similar REL_INTER during metabolic simulation. During biological testing, inter-unit differences for V˙O2 and RER in BBB-mode were higher than 2% with partially large ES in BBB. Hence, the K5 should be allocated personally wherever possible. Otherwise, e.g. in multicenter studies, a decrease in total reliability needs to be considered especially when the BBB-mode is applied.

The COSMED K5 in Breath-by-Breath and Mixing Chamber Mode at Low to High Intensities

PURPOSE

The portable metabolic analyzer COSMED K5 (Rome, Italy) allows for switching between breath-by-breath (BBB) and dynamic micro-mixing chamber (DMC) modes. This study aimed to evaluate the reliability and validity of the K5 in BBB and DMC at low, moderate, and high metabolic rates.

METHODS

Two K5 simultaneously operated in BBB or DMC, whereas (i) a metabolic simulator (MS) produced four different metabolic rates (repeated eight times), and (ii) 12 endurance-trained participants performed bike exercise at 30%, 40%, 50%, and 85% of their individual power output at V˙O2max (repeated three times). K5 data were compared with predicted simulated values and consecutive Douglas bag measurements.

RESULTS

Reliability did not differ significantly between BBB and DMC, whereas the typical error and intraclass correlation coefficients for oxygen uptake (V˙O2), carbon dioxide output (V˙CO2), and minute ventilation (V˙E) ranged from 0.27% to 6.18% and from 0.32 to 1.00 within four metabolic rates, respectively. Validity indicated by mean differences ranged between 0.61% and -2.05% for V˙O2, 2.99% to -11.04% for V˙CO2, and 0.93% to -6.76% for V˙E compared with MS and Douglas bag at low to moderate metabolic rates and was generally similar for MS and bike exercise. At high rates, mean differences for V˙O2 amounted to -4.63% to -7.27% in BBB and -0.38% to -3.81% in DMC, indicating a significantly larger difference of BBB at the highest metabolic rate.

CONCLUSION

The K5 demonstrated accurate to acceptable reliability in BBB and DMC at all metabolic rates. Validity was accurate at low and moderate metabolic rates. At high metabolic rates, BBB underestimated V˙O2, whereas DMC showed superior validity. To test endurance athletes at high workloads, the DMC mode is recommended.

Comparison of different breath-by-breath gas exchange algorithms using a gas exchange simulation system

BACKGROUND

Mechanical Gas Exchange Simulation Systems (GESS) have never been used to compare different breath-by-breath oxygen uptake calculation algorithms.

METHODS

Oxygen uptakes were calculated for each GESS cycle by the "Expiration-only" algorithm (estimating inspiratory volume from the expiratory one), and by two "alveolar" algorithms (both processing inspiratory and expiratory flows and designed to account for the changes in lung gas stores). The volume of oxygen stored in the GESS from one cycle to the subsequent one was either maintained constant or increased/decreased by changing the pumped gas volumes.

RESULTS

Overlapping oxygen uptakes were obtained maintaining constant the volume of oxygen stored (grand average: 0.420 ± 0.019 L/min, p = ns). The "Expiration-only" algorithm overestimated the decreases of the stored oxygen by 34%, whereas the "alveolar" algorithms underestimated the increases by 25%; in the other conditions, the changes of the stored oxygen were appropriately accounted for.

CONCLUSIONS

The use of "alveolar" algorithms is recommended, particularly so when abrupt changes in the stored oxygen volume occur.

Validity, reliability and minimum detectable change of COSMED K5 portable gas exchange system in breath-by-breath mode

PURPOSE

This study aimed to examine the validity, reliability and minimum detectable change (MDC) of the Cosmed K5 in breath by breath (BxB) mode, against VacuMed metabolic simulator. Intra and inter-units reliability was also assessed.

METHODS

Fourteen metabolic rates (from 0.9 to 4 L.min-1) were reproduced by a VacuMed system and pulmonary ventilation (VE), oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured by two different K5 units. Validity was assessed by ordinary least products (OLP) regression analysis, Bland-Altman plots, intraclass correlation coefficients (ICC), mean percentage differences, technical errors (TE) and MDC for VE, VO2, and VCO2. Intra- and inter-K5 reliability was evaluated by absolute percentage differences between measurements (MAPE), ICCs, TE, and MDC.

RESULTS

Validity analysis from OLP regression data and Bland- Altman plots indicated high agreement between K5 and simulator. ICC values were excellent for all variables (>0.99). Mean percentage differences in VE (-0.50%, p = 0.11), VO2 (-0.04%, p = 0.80), and VCO2 (-1.03%, p = 0.09) showed no significant bias. The technical error (TE) ranged from 0.73% to 1.34% (VE and VCO2 respectively). MDC were lower than 4% (VE = 2.0%, VO2 = 3.8%, VCO2 = 3.7%). The intra and inter K5 reliability assessment reveled excellent ICCs (>0.99), MAPE <2% (no significant differences between trials), TE < or around 1%, MDC <or around 3%.

CONCLUSIONS

K5 in BxB mode is a valid and reliable system for metabolic measurements. This is the first study assessing the MDC accounting only for technical variability reporting intra- and inter-units MDCs <3.3%.

Open-circuit respirometry: real-time, laboratory-based systems

This review explores the conceptual and technological factors integral to the development of laboratory-based, automated real-time open-circuit mixing-chamber and breath-by-breath (B × B) gas-exchange systems, together with considerations of assumptions and limitations. Advances in sensor technology, signal analysis, and digital computation led to the emergence of these technologies in the mid-20th century, at a time when investigators were beginning to recognise the interpretational advantages of nonsteady-state physiological-system interrogation in understanding the aetiology of exercise (in)tolerance in health, sport, and disease. Key milestones include the 'Auchincloss' description of an off-line system to estimate alveolar O₂ uptake B × B during exercise. This was followed by the first descriptions of real-time automated O₂ uptake and CO₂ output B × B measurement by Beaver and colleagues and by Linnarsson and Lindborg, and mixing-chamber measurement by Wilmore and colleagues. Challenges to both approaches soon emerged: e.g., the influence of mixing-chamber washout kinetics on mixed-expired gas concentration determination, and B × B alignment of gas-concentration signals with respired flow. The challenging algorithmic and technical refinements required for gas-exchange estimation at the alveolar level have also been extensively explored. In conclusion, while the technology (both hardware and software) underpinning real-time automated gas-exchange measurement has progressively advanced, there are still concerns regarding accuracy especially under the challenging conditions of changing metabolic rate.

Accuracy and precision of CPET equipment: a comparison of breath-by-breath and mixing chamber systems

Cardiopulmonary exercise testing (CPET) has become an important diagnostic tool for patients with cardiorespiratory disease and can monitor athletic performance measuring maximal oxygen uptake [Formula: see text]Vo2(; max). The aim of this study is to compare the accuracy and precision of a breath-by-breath and a mixing chamber CPET system, using two methods. First, this study developed a (theoretical) error analysis based on general error propagation theory. Second, calibration measurements using a metabolic simulator were performed. Error analysis shows that the error in oxygen uptake ([Formula: see text]Vo2) and carbon dioxide production (Vco2[Formula: see text]) is smaller for mixing chamber than for breath-by-breath systems. In general, the error of the flow sensor [Formula: see text]δV, the error in temperature of expired air δT(B) and the delay time error δt(delay) are significant sources of error. Measurements using a metabolic simulator show that breath-by-breath systems are less stabile for different values of minute ventilation than mixing chamber systems.

Examination of the Moxus Modular Metabolic System by the Douglas-bag technique

The purpose of this study was to examine the performance of the Moxus Modular Metabolic System from AEI Technologies, Inc. using the Douglas-bag method as reference. To achieve this, eight moderately trained subjects cycled for 5 min at constant powers from 50 to 300 W in increments of 50 W. The O2 uptake was measured simultaneously by both systems during the last minute of each stage. The O2 uptake reported by the Moxus system was 83 ± 78 mL·min–1 higher (mean ± SD; ≈3%, +62 µmol·s–1, P < 0.001) than that reported by the Douglas-bag method; the bias varied by ≈2% between the subjects. The higher O2 uptake of the Moxus system was a consequence of 1.4% ± 3.0% higher reported ventilation and 2% ± 3% higher reported O2 extraction per volume of air breathed. The respiratory exchange ratio (R value) reported by the Moxus system rose proportionally to that of the Douglas-bag method and was 1% ± 2% higher for the range examined (0.75–1.10). Repeated tests of the maximal O2 uptake showed a variability (coefficient of variation) of 2.5%. The study concluded that measurements by the Moxus system showed some bias and residual variation and, in addition, some systematic differences between the subjects in the O2 uptake. The R value was reported quite accurately with moderate random error. Although there were some computer software and hardware instability problems that need to be solved, the Moxus system worked quite well and provided data more reliable than those of most commercial instruments.

Inter-unit variability in two ParvoMedics TrueOne 2400 automated metabolic gas analysis systems

Knowing the inter-unit variability, especially the technological error, is important when using many physiological measurement systems, yet no such inter-unit analysis has been undertaken on duplicate automated gas analysis systems. This study investigated the inter-unit performance of two identical ParvoMedics TrueOne 2400 automated gas analysis systems during a range of submaximal steady-state exercises performed on an electromagnetic cycle ergometer. Fifteen adult males were tested on two separate days a rest, 30, 60, 90, and 120 Watts with the duplicate gas analysis units arranged (1) collaterally (2 min of steady-state expired gas was alternately passed through each system), and (2) simultaneously (identical steady-state expired gas was passed simultaneously through both systems). Total within-subject variation (biological + technological) was determined from the collateral tests, but the unique inter-unit variability (technological error between identical systems) was shown by the simultaneous tests. Absolute percentage errors (APE), coefficient of variations (CV), effect sizes and Bland-Altman analyses were undertaken on the metabolic data, including expired ventilation (V (E)), oxygen consumption (VO(2)) and carbon dioxide production (VCO(2)). The few statistically significant differences detected between the two duplicate systems were determined to have small or trivial effect sizes, and their magnitudes to be of little physiological importance. The total within-subject variations for VO(2), VCO(2) and V (E) each equated to a mean CV and mean APE value of ~4 and ~6 %, whilst the respective inter-unit technological errors equated to ~1.5 and ~2.1 %. The two ParvoMedics TrueOne 2400 systems demonstrated excellent inter-unit agreement.

Validation of a new mixing chamber system for breath-by-breath indirect calorimetry

Limited validation research exists for applications of breath-by-breath systems of expired gas analysis indirect calorimetry (EGAIC) during exercise. We developed improved hardware and software for breath-by-breath indirect calorimetry (NEW) and validated this system as well as a commercial system (COM) against 2 methods: (i) mechanical ventilation with known calibration gas, and (ii) human subjects testing for 5 min each at rest and cycle ergometer exercise at 100 and 175 W. Mechanical calibration consisted of medical grade and certified calibration gas ((4.95% CO(2), 12.01% O(2), balance N(2)), room air (20.95% O(2), 0.03% CO(2), balance N(2)), and 100% nitrogen), and an air flow turbine calibrated with a 3-L calibration syringe. Ventilation was mimicked manually using complete 3-L calibration syringe manouvers at a rate of 10·min(-1) from a Douglas bag reservoir of calibration gas. The testing of human subjects was completed in a counterbalanced sequence based on 5 repeated tests of all conditions for a single subject. Rest periods of 5 and 10 min followed the 100 and 175 W conditions, respectively. COM and NEW had similar accuracy when tested with known ventilation and gas fractions. However, during human subjects testing COM significantly under-measured carbon dioxide gas fractions, over-measured oxygen gas fractions and minute ventilation, and resulted in errors to each of oxygen uptake, carbon dioxide output, and respiratory exchange ratio. These discrepant findings reveal that controlled ventilation and gas fractions are insufficient to validate breath-by-breath, and perhaps even time-averaged, systems of EGAIC. The errors of the COM system reveal the need for concern over the validity of commercial systems of EGAIC.

Effects of short-term training with uncoupled cranks in trained cyclists

PURPOSE

Manufacturers of uncoupled cycling cranks claim that their use will increase economy of motion and gross efficiency. Purportedly, this occurs by altering the muscle-recruitment patterns contributing to the resistive forces occurring during the recovery phase of the pedal stroke. Uncoupled cranks use an independent-clutch design by which each leg cycles independently of the other (ie, the cranks are not fixed together). However, research examining the efficacy of training with uncoupled cranks is equivocal. The purpose of this study was to determine the effect of short-term training with uncoupled cranks on the performance-related variables economy of motion, gross efficiency, maximal oxygen uptake (VO2max), and muscle-activation patterns.

METHODS

Sixteen trained cyclists were matched-paired into either an uncoupled-crank or a normal-crank training group. Both groups performed 5 wk of training on their assigned cranks. Before and after training, participants completed a graded exercise test using normal cranks. Expired gases were collected to determine economy of motion, gross efficiency, and VO2max, while integrated electromyography (iEMG) was used to examine muscle-activation patterns of the vastus lateralis, biceps femoris, and gastrocnemius.

RESULTS

No significant changes between groups were observed for economy of motion, gross efficiency, VO2max, or iEMG in the uncoupled- or normal-crank group.

CONCLUSIONS

Five weeks of training with uncoupled cycling cranks had no effect on economy of motion, gross efficiency, muscle recruitment, or VO2max compared with training on normal cranks.

Validity, reliability and stability of the portable Cortex Metamax 3B gas analysis system

This study investigated the performance of the portable Cortex Metamax 3B (MM3B) automated gas analysis system during both simulated and human exercise using adolescents. Repeated measures using a Gas Exchange System Validator (GESV) across a range of simulated metabolic rates, showed the MM3B to be adequately reliable (both percentage errors, and percentage technical error of measurements <2%) for measuring expired ventilation (V_E), oxygen consumption (VO₂), and carbon dioxide production (VCO₂). Over a 3 h period, the MM3B was shown to be acceptably stable in measuring gas fractions, as well as V_E, VO₂, and VCO₂ generated by the GESV, especially at moderate and high metabolic rates (drifts <2% and of minor physiological significance). Using eight healthy adolescents during rest, moderate, and vigorous cycle ergometry, the validity of the MM3B was tested against the primary criterion Douglas bag method (DBM) and a secondary criterion machine known to be accurate, the Jaeger Oxycon Pro system. No significant errors in V_E were noted, yet the MM3B significantly overestimated both VO₂ and VCO₂ by approximately 10–17% at moderate and vigorous exercise as compared to the DBM and at all exercise levels compared to the Oxycon Pro. No significant differences were seen in any metabolic variable between the two criterion systems (DBM and Oxycon Pro). It is concluded the MM3B produces acceptably stable and reliable results, but is not adequately valid during moderate and vigorous exercise without some further correction of VO₂ and VCO₂.

Performance and physiological responses during a sprint interval training session: relationships with muscle oxygenation and pulmonary oxygen uptake kinetics

The purpose of this study was to examine the cardiorespiratory and muscle oxygenation responses to a sprint interval training (SIT) session, and to assess their relationships with maximal pulmonary O(2) uptake [Formula: see text], on- and off- [Formula: see text] kinetics and muscle reoxygenation rate (Reoxy rate). Ten male cyclists performed two 6-min moderate-intensity exercises (≈90-95% of lactate threshold power output, Mod), followed 10 min later by a SIT session consisting of 6 × 30-s all out cycling sprints interspersed with 2 min of passive recovery. [Formula: see text] kinetics at Mod onset ([Formula: see text]) and cessation ([Formula: see text]) were calculated. Cardiorespiratory variables, blood lactate ([La](b)) and muscle oxygenation level of the vastus lateralis (tissue oxygenation index, TOI) were recorded during SIT. Percentage of the decline in power output (%Dec), time spent above 90% of [Formula: see text] (t > 90% [Formula: see text]) and Reoxy rate after each sprint were also recorded. Despite a low mean [Formula: see text] (48.0 ± 4.1% of [Formula: see text]), SIT performance was associated with high peak [Formula: see text] (90.4 ± 2.8% of [Formula: see text]), muscle deoxygenation (sprint ΔTOI = -27%) and [La](b) (15.3 ± 0.7 mmol l(-1)) levels. Muscle deoxygenation and Reoxy rate increased throughout sprint repetitions (P < 0.001 for both). Except for t > 90% [Formula: see text] versus [Formula: see text] [r = 0.68 (90% CL, 0.20; 0.90); P = 0.03], there were no significant correlations between any index of aerobic function and either SIT performance or physiological responses [e.g., %Dec vs. [Formula: see text]: r = -0.41 (-0.78; 0.18); P = 0.24]. Present results show that SIT elicits a greater muscle O(2) extraction with successive sprint repetitions, despite the decrease in external power production (%Dec = 21%). Further, our findings obtained in a small and homogenous group indicate that performance and physiological responses to SIT are only slightly influenced by aerobic fitness level in this population.

Single-leg cycle training is superior to double-leg cycling in improving the oxidative potential and metabolic profile of trained skeletal muscle

Single-leg cycling may enhance the peripheral adaptations of skeletal muscle to a greater extent than double-leg cycling. The purpose of the current study was to determine the influence of 3 wk of high-intensity single- and double-leg cycle training on markers of oxidative potential and muscle metabolism and exercise performance. In a crossover design, nine trained cyclists (78 ± 7 kg body wt, 59 ± 5 ml·kg(-1)·min(-1) maximal O(2) consumption) performed an incremental cycling test and a 16-km cycling time trial before and after 3 wk of double-leg and counterweighted single-leg cycle training (2 training sessions per week). Training involved three (double) or six (single) maximal 4-min intervals with 6 min of recovery. Mean power output during the single-leg intervals was more than half that during the double-leg intervals (198 ± 29 vs. 344 ± 38 W, P < 0.05). Skeletal muscle biopsy samples from the vastus lateralis revealed a training-induced increase in Thr(172)-phosphorylated 5'-AMP-activated protein kinase α-subunit for both groups (P < 0.05). However, the increase in cytochrome c oxidase subunits II and IV and GLUT-4 protein concentration was greater following single- than double-leg cycling (P < 0.05). Training-induced improvements in maximal O(2) consumption (3.9 ± 6.2% vs. 0.6 ± 3.6%) and time-trial performance (1.3 ± 0.5% vs. 2.3 ± 4.2%) were similar following both interventions. We conclude that short-term high-intensity single-leg cycle training can elicit greater enhancement in the metabolic and oxidative potential of skeletal muscle than traditional double-leg cycling. Single-leg cycling may therefore provide a valuable training stimulus for trained and clinical populations.

The physical and physiological demands of basketball training and competition

PURPOSE

To characterize the physical and physiological responses during different basketball practice drills and games.

METHODS

Male basketball players (n=11; 19.1+/-2.1 y, 1.91+/-0.09 m, 87.9+/-15.1 kg; mean+/-SD) completed offensive and defensive practice drills, half court 5on5 scrimmage play, and competitive games. Heart rate, VO2, and triaxial accelerometer data (physical demand) were normalized for individual participation time. Data were log-transformed and differences between drills and games standardized for interpretation of magnitudes and reported with the effect size (ES) statistic.

RESULTS

There was no substantial difference in the physical or physiological variables between offensive and defensive drills; physical load (9.5%; 90% confidence limits+/-45); mean heart rate (-2.4%; +/-4.2); peak heart rate (-0.9%; +/-3.4); and VO2 (-5.7%; +/-9.1). Physical load was moderately greater in game play compared with a 5on5 scrimmage (85.2%; +/-40.5); with a higher mean heart rate (12.4%; +/-5.4). The oxygen demand for live play was substantially larger than 5on5 (30.6%; +/-15.6).

CONCLUSIONS

Defensive and offensive drills during basketball practice have similar physiological responses and physical demand. Live play is substantially more demanding than a 5on5 scrimmage in both physical and physiological attributes. Accelerometers and predicted oxygen cost from heart rate monitoring systems are useful for differentiating the practice and competition demands of basketball.

Effects of starting strategy on 5-min cycling time-trial performance

The importance of pacing for middle-distance performance is well recognized, yet previous research has produced equivocal results. Twenty-six trained male cyclists (VO2 peak 62.8 +/- 5.9 ml x kg(-1) x min(-1); maximal aerobic power output 340 +/- 43 W; mean +/- s) performed three cycling time-trials where the total external work (102.7 +/- 13.7 kJ) for each trial was identical to the best of two 5-min habituation trials. Markers of aerobic and anaerobic metabolism were assessed in 12 participants. Power output during the first quarter of the time-trials was fixed to control external mechanical work done (25.7 +/- 3.4 kJ) and induce fast-, even-, and slow-starting strategies (60, 75, and 90 s, respectively). Finishing times for the fast-start time-trial (4:53 +/- 0:11 min:s) were shorter than for the even-start (5:04 +/- 0:11 min:s; 95% CI = 5 to 18 s, effect size = 0.65, P < 0.001) and slow-start time-trial (5:09 +/- 0:11 min:s; 95% CI = 7 to 24 s, effect size = 1.00, P < 0.001). Mean VO2 during the fast-start trials (4.31 +/- 0.51 litres x min(-1)) was 0.18 +/- 0.19 litres x min(-1) (95% CI = 0.07 to 0.30 litres x min(-1), effect size = 0.94, P = 0.003) higher than the even- and 0.18 +/- 0.20 litres x min(-1) (95% CI = 0.5 to 0.30 litres x min(-1), effect size = 0.86, P = 0.007) higher than the slow-start time-trial. Oxygen deficit was greatest during the first quarter of the fast-start trial but was lower than the even- and slow-start trials during the second quarter of the trial. Blood lactate and pH were similar between the three trials. In conclusion, performance during a 5-min cycling time-trial was improved with the adoption of a fast- rather than an even- or slow-starting strategy.

Validation of heart rate monitor-based predictions of oxygen uptake and energy expenditure

To validate VO2 and energy expenditure predictions by the Suunto heart rate (HR) system against a first principle gas analysis system, well-trained male (n = 10, age 29.8 +/- 4.3 years, VO2 65.9 +/- 9.7 ml x kg x min) and female (n = 7, 25.6 +/- 3.6 years, 57.0 +/- 4.2 ml x kg x min) runners completed a 2-stage incremental running test to establish submaximal and maximal oxygen uptake values. Metabolic cart values were used as the criterion measure of VO2 and energy expenditure (kJ) and compared with the predicted values from the Suunto software. The 3 levels of software analysis for the Suunto system were basic personal information (BI), BI + measured maximal HR (BIhr), and BIhr + measured VO2 (BIhr + v). Comparisons were analyzed using linear regression to determine the standard error of the estimate (SEE). Eight subjects repeated the trial within 7 days to determine reliability (typical error [TE]). The SEEs for oxygen consumption via BI, BIhr, and BIhr + v were 2.6, 2.8, and 2.6 ml.kg.min, respectively, with corresponding percent coefficient of variation (%CV) of 6.0, 6.5, and 6.0. The bias compared with the criterion VO2 decreased from -6.3 for BI, -2.5 for BIhr, to -0.9% for BIhr + v. The SEE of energy expenditure improved from BI (6.74 kJ) to BIhr (6.56) and BIhr + v (6.14) with corresponding %CV of 13.6, 12.2, and 12.7. The TE values for VO2 were approximately 0.60 ml x kg x min and approximately 2 kJ for energy expenditure. The %CV for VO2 and energy expenditure was approximately 1 to 4%. Although reliable, basic HR-based estimations of VO2 and energy expenditure from the Suunto system underestimated VO2 and energy expenditure by approximately 6 and 13%, respectively. However, estimation can be improved when maximal HR and VO2 values are added to the software analysis.

Metabolic testing in the office

The three most commonly used metabolic tests are the Resting Metabolic Rate, Anaerobic Threshold Testing, and V.O2max. For several decades, these metabolic tests have been confined to the setting of university-based physiology laboratories and cardiopulmonary environments, i.e., metabolic carts in the intensive care units. The information gathered is used as a research and clinical tool in evaluating metabolic activity in a variety of physiological states from a body at rest, to exercise (aerobic and anaerobic), in certain medical states like illness, fed/starvation, and medicinal or supplementation affective states. Over the last decade, as technology has improved, so have the metabolic testing carts. They have become widely available for mainstream use by a variety of health care professionals. The purpose of this article is to review these three tests and how they may be useful in a medical practice.

Effect of carbohydrate ingestion and ambient temperature on muscle fatigue development in endurance-trained male cyclists

The aim of the present study was to determine the effect of carbohydrate (CHO; sucrose) ingestion and environmental heat on the development of fatigue and the distribution of power output during a 16.1-km cycling time trial. Ten male cyclists (V̇o2max = 61.7 ± 5.0 ml·kg−1·min−1, mean ± SD) performed four 90-min constant-pace cycling trials at 80% of second ventilatory threshold (220 ± 12 W). Trials were conducted in temperate (18.1 ± 0.4°C) or hot (32.2 ± 0.7°C) conditions during which subjects ingested either CHO (0.96 g·kg−1·h−1) or placebo (PLA) gels. All trials were followed by a 16.1-km time trial. Before and immediately after exercise, percent muscle activation was determined using superimposed electrical stimulation. Power output, integrated electromyography (iEMG) of vastus lateralis, rectal temperature, and skin temperature were recorded throughout the trial. Percent muscle activation significantly declined during the CHO and PLA trials in hot (6.0 and 6.9%, respectively) but not temperate conditions (1.9 and 2.2%, respectively). The decline in power output during the first 6 km was significantly greater during exercise in the heat. iEMG correlated significantly with power output during the CHO trials in hot and temperate conditions ( r = 0.93 and 0.73; P < 0.05) but not during either PLA trial. In conclusion, cyclists tended to self-select an aggressive pacing strategy (initial high intensity) in the heat.

Validity and reliability of selected commercially available metabolic analyzer systems

Automated metabolic gas analysis systems have advanced considerably over the past decade. They provide an abundance of information, which is not possible by using the traditional Douglas bag method and have become an essential tool in both physiological monitoring and in the diagnosis of cardiopulmonary disease. The validity and reliability of the different online metabolic analyzer systems are not well known, with relatively few independent studies being published. The purpose of this review was to examine and evaluate current literature regarding the validity and reliability of commercially available metabolic analyzer systems. This review reveals significant differences between the available systems in the way that they capture and process basic respiratory measurements. Online metabolic analyzer systems were found to vary significantly when compared with Douglas bag methods. These variations have the potential to introduce error into the accuracy with which the health of cardiovascular system can be assessed or training loads can be assigned. Compounding this is the fact that many automated systems are a "black box", which makes it easy to generate data without the user having much understanding of how the data were generated. In conclusion automated metabolic analyser systems are a scientifically robust method for the evaluation of cardiopulmonary function. Individual researchers and clinicians must, however, be able to make their own decisions about the level of error that is tolerable for their individual needs. This presents a significant practical challenge in light of the speed with which technical developments in the field occur and we make some suggestions for the formulation of intersystem comparison studies.

Repeated measurement of the gas exchange threshold: relative size of measurement and biological variabilities

If an individual's gas exchange threshold (GET) is measured on several separate occasions, without a change in aerobic fitness, a random variability will be observed. However, it is not known how much of this variability is biologically determined and how much results from variability in the calibration and measurement processes. The statistical re-sampling technique of Bootstrapping was used to estimate the variability of the GET on a single occasion. This analysis provides the first estimate of the combined contribution of breath-by-breath measurement and calibration processes (6%), to the total between-occasion random variability, leaving biological variability to account for the remainder of the imprecision in the measurement of the GET.

Reliability and variability of running economy in elite distance runners

PURPOSE

To establish the typical error (TE) associated with equipment, testing, and biological variation of a running economy (RE) test in 11 elite male distance runners (VO2max 70.3 +/- 7.3 mL x min(-1) x kg(-1)), and measure the between-athlete variation of 70 highly trained runners (VO2max 69.7 +/- 6.0 mL x min(-1) x kg(-1)) to determine the magnitude of the smallest worthwhile change (SWC) required for RE.

METHODS

Runners performed three 4-min bouts of submaximal treadmill running at speeds of 14, 16, and 18 km x h(-1) (0% grade), on two separate occasions within a 7-d period to determine reliability and once over a 3-yr period to measure the SWC. During all RE tests O2 consumption (VO2), ventilation (VE), respiratory exchange ratio (RER), heart rate (HR), stride rate (SR), and concentration of blood lactate (Lac) were determined.

RESULTS

The TE for the pooled data of three running speeds (14, 16, and 18 km x h(-1)) was 2.4% for VO2, 7.3% for VE, 27% for Lac, and ranged between 1 and 4% for RER, HR, and SR.

CONCLUSIONS

The results demonstrate that although the magnitude of the TE for a submaximal treadmill running protocol of three 4-min work efforts is small (2.4-7.3%) for measures associated with cardiorespiratory parameters, it is three- to fourfold higher for Lac. Given the small TE associated with RE, and a SWC of similar magnitude for this cohort of distance runners, the RE test is useful in detecting changes attributable to training interventions. Changes in RE greater than approximately 2.4% in this cohort of elite distance runners are likely to be "real" and "worthwhile," and not simply related to testing error and typical variation.

CPX/D underestimates VO(2) in athletes compared with an automated Douglas bag system

PURPOSE

Based on persistent reports of low oxygen consumption VO(2) from Medical Graphics CPX/D metabolic carts, we compared the CPX/D against an automated Douglas bag system.

METHODS

Twelve male athletes completed three, randomized 25-min bouts (5 min at 100, 150, 200, 250, and 300 W) on a cycle ergometer with intervening 30-min rests. One bout was measured on each of the CPX/D, the CPX/D with altered software (CPX/DDelta), and an automated Douglas bag system at Flinders University (FU). The CPX/DDelta software alteration was an apparent lag time correction factor of 60 ms.

RESULTS

For the CPX/D, both VO(2) and VCO(2) were significantly lower than the FU system at 100-300 W, and the relative differences ranged -10.7 to -12.0% and -7.7 to -8.2%, respectively. Altering the software approximately halved the VO(2) discrepancy between the CPX/DDelta and FU systems. When data from all five workloads were pooled, V(E) of the CPX/D (67.2 +/- 26.4 L x min-1) and CPX/DDelta (67.5 +/- 26.9 L x min-1) were significantly lower than for the FU system (70.5 +/- 27.1 L x min-1); and at 300 W, the relative differences were -4.0% and -3.4% for the CPX/D and CPX/DDelta, respectively. Altering the software changed the pooled %O(2) from 16.24 +/- 0.40% for the CPX/D to 16.04 +/- 0.39% for the CPX/DDelta, and these were significantly different than pooled data for the FU system (16.15 +/- 0.39%).

CONCLUSIONS

During submaximal exercise, the CPX/D yields VO(2) values that are approximately 11% lower than the criterion system, and the source of the discrepancy does not appear to be primarily related to volume measurement. A disturbing observation is that factory defaults for the lag time use different correction factors, which vary by 60 ms and this significantly alters VO(2) and VCO(2).

A methodology to assess the accuracy of a portable metabolic system (VmaxST)

PURPOSE

Validity of a portable metabolic system (VmaxST) was investigated during gas exchanges simulations by a mechanical system (GESS) and during human exercise.

METHODS

Three tests were conducted while gas exchanges were measured continuously by VmaxST. Test 1 was composed of six simulations of gas exchanges during steady-state exercise (20 min at V̇E = 80 L.min-1). Test 2 was composed of seven simulations of gas exchanges during incremental exercise (V̇O(2) from 300 to 5600 mL.min-1). In the human trial, 11 subjects performed an incremental running exercise on a treadmill while gas exchanges were measured at the end of each stage with the Douglas bag method (DBM).

RESULTS

Test 1 showed that the VmaxST measurements were stable, despite inaccurate measurements of gas concentrations at the start of the test. During test 2, the mean error (difference between measured and predicted value) and the upper and lower limits of agreement were -8.0%, -12.6%, and -3.4% for V̇O(2); -4.6%, -12.0%, and +2.8% for V̇CO(2); and -0.7%, -4.7%, and +3.3% for V̇E. During the human trial, no significant difference was shown between V̇O(2) measured by VmaxST and by DBM at any stage of exercise. The mean difference and the upper and lower limits of agreement between the VmaxST and the DBM measurements were -0.5%, -14.3%, and +13.3% for V̇O(2); -6.3%, -20.9%, and +8.3% for V̇CO(2); and -9.9%, -25.5%, and +5.7% for V̇E.

CONCLUSIONS

The use of GESS showed that measurements of V̇O(2) by VmaxST could be biased in a standardized condition. In more realistic condition of use, this bias was lower but the accuracy of measurements was impaired.

Metabolic and mitogenic signal transduction in human skeletal muscle after intense cycling exercise

We determined whether mitogen-activated protein kinase (MAPK) and 5'-AMP-activated protein kinase (AMPK) signalling cascades are activated in response to intense exercise in skeletal muscle from six highly trained cyclists (peak O(2) uptake (.V(O2,peak)) 5.14 +/- 0.1 l min(-1)) and four control subjects (Vdot;(O(2))(,peak) 3.8 +/- 0.1 l min(-1)) matched for age and body mass. Trained subjects completed eight 5 min bouts of cycling at approximately 85% of .V(O2,peak) with 60 s recovery between work bouts. Control subjects performed four 5 min work bouts commencing at the same relative, but a lower absolute intensity, with a comparable rest interval. Vastus lateralis muscle biopsies were taken at rest and immediately after exercise. Extracellular regulated kinase (ERK1/2), p38 MAPK, histone H3, AMPK and acetyl CoA-carboxylase (ACC) phosphorylation was determined by immunoblot analysis using phosphospecific antibodies. Activity of mitogen and stress-activated kinase 1 (MSK1; a substrate of ERK1/2 and p38 MAPK) and alpha(1) and alpha(2) subunits of AMPK were determined by immune complex assay. ERK1/2 and p38 MAPK phosphorylation and MSK1 activity increased (P < 0.05) after exercise 2.6-, 2.1- and 2.0-fold, respectively, in control subjects and 1.5-, 1.6- and 1.4-fold, respectively, in trained subjects. Phosphorylation of histone H3, a substrate of MSK1, increased (P < 0.05) approximately 1.8-fold in both control and trained subject. AMPKalpha(2) activity increased (P < 0.05) after exercise 4.2- and 2.3-fold in control and trained subjects, respectively, whereas AMPKalpha(1) activity was not altered. Exercise increased ACC phosphorylation (P < 0.05) 1.9- and 2.8-fold in control and trained subjects. In conclusion, intense cycling exercise in subjects with a prolonged history of endurance training increases MAPK signalling to the downstream targets MSK1 and histone H3 and isoform-specific AMPK signalling to ACC. Importantly, exercise-induced signalling responses were greater in untrained men, even at the same relative exercise intensity, suggesting muscle from previously well-trained individuals requires a greater stimulus to activate signal transduction via these pathways.

Interval training program optimization in highly trained endurance cyclists

PURPOSE

The purpose of this study was to examine the influence of three different high-intensity interval training (HIT) regimens on endurance performance in highly trained endurance athletes.

METHODS

Before, and after 2 and 4 wk of training, 38 cyclists and triathletes (mean +/- SD; age = 25 +/- 6 yr; mass = 75 +/- 7 kg; VO(2peak) = 64.5 +/- 5.2 mL x kg(-1) min(-1)) performed: 1) a progressive cycle test to measure peak oxygen consumption (VO(2peak)) and peak aerobic power output (PPO), 2) a time to exhaustion test (T(max)) at their VO(2peak) power output (P(max)), as well as 3) a 40-km time-trial (TT(40)). Subjects were matched and assigned to one of four training groups (G(2), N = 8, 8 x 60% T(max) at P(max), 1:2 work:recovery ratio; G(2), N = 9, 8 x 60% T(max) at P(max), recovery at 65% HR(max); G(3), N = 10, 12 x 30 s at 175% PPO, 4.5-min recovery; G(CON), N = 11). In addition to G(1), G(2), and G(3) performing HIT twice per week, all athletes maintained their regular low-intensity training throughout the experimental period.

RESULTS

All HIT groups improved TT(40) performance (+4.4 to +5.8%) and PPO (+3.0 to +6.2%) significantly more than G(CON) (-0.9 to +1.1%; P < 0.05). Furthermore, G(1) (+5.4%) and G(2) (+8.1%) improved their VO(2peak) significantly more than G(CON) (+1.0%; P < 0.05).

CONCLUSION

The present study has shown that when HIT incorporates P(max) as the interval intensity and 60% of T(max) as the interval duration, already highly trained cyclists can significantly improve their 40-km time trial performance. Moreover, the present data confirm prior research, in that repeated supramaximal HIT can significantly improve 40-km time trial performance.

Effect of different protocols of caffeine intake on metabolism and endurance performance

Competitive athletes completed two studies of 2-h steady-state (SS) cycling at 70% peak O(2) uptake followed by 7 kJ/kg time trial (TT) with carbohydrate (CHO) intake before (2 g/kg) and during (6% CHO drink) exercise. In Study A, 12 subjects received either 6 mg/kg caffeine 1 h preexercise (Precaf), 6 x 1 mg/kg caffeine every 20 min throughout SS (Durcaf), 2 x 5 ml/kg Coca-Cola between 100 and 120 min SS and during TT (Coke), or placebo. Improvements in TT were as follows: Precaf, 3.4% (0.2-6.5%, 95% confidence interval); Durcaf, 3.1% (-0.1-6.5%); and Coke, 3.1% (-0.2-6.2%). In Study B, eight subjects received 3 x 5 ml/kg of different cola drinks during the last 40 min of SS and TT: decaffeinated, 6% CHO (control); caffeinated, 6% CHO; decaffeinated, 11% CHO; and caffeinated, 11% CHO (Coke). Coke enhanced TT by 3.3% (0.8-5.9%), with all trials showing 2.2% TT enhancement (0.5-3.8%; P < 0.05) due to caffeine. Overall, 1) 6 mg/kg caffeine enhanced TT performance independent of timing of intake and 2) replacing sports drink with Coca-Cola during the latter stages of exercise was equally effective in enhancing endurance performance, primarily due to low intake of caffeine (approximately 1.5 mg/kg).

Automated metabolic gas analysis systems: a review

The use of automated metabolic gas analysis systems or metabolic measurement carts (MMC) in exercise studies is common throughout the industrialised world. They have become essential tools for diagnosing many hospital patients, especially those with cardiorespiratory disease. Moreover, the measurement of maximal oxygen uptake (VO2max) is routine for many athletes in fitness laboratories and has become a defacto standard in spite of its limitations. The development of metabolic carts has also facilitated the noninvasive determination of the lactate threshold and cardiac output, respiratory gas exchange kinetics, as well as studies of outdoor activities via small portable systems that often use telemetry. Although the fundamental principles behind the measurement of oxygen uptake (VO2) and carbon dioxide production (VCO2) have not changed, the techniques used have, and indeed, some have almost turned through a full circle. Early scientists often employed a manual Douglas bag method together with separate chemical analyses, but the need for faster and more efficient techniques fuelled the development of semi- and full-automated systems by private and commercial institutions. Yet, recently some scientists are returning back to the traditional Douglas bag or Tissot-spirometer methods, or are using less complex automated systems to not only save capital costs, but also to have greater control over the measurement process. Over the last 40 years, a considerable number of automated systems have been developed, with over a dozen commercial manufacturers producing in excess of 20 different automated systems. The validity and reliability of all these different systems is not well known, with relatively few independent studies having been published in this area. For comparative studies to be possible and to facilitate greater consistency of measurements in test-retest or longitudinal studies of individuals, further knowledge about the performance characteristics of these systems is needed. Such information, along with the costs and the common features associated with these systems, may aid physicians and scientists to select a system that is best suited to their requirements and may also improve the quality of these frequently-reported physiological measures.

Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability

PURPOSE

Five days of a high-fat diet produce metabolic adaptations that increase the rate of fat oxidation during prolonged exercise. We investigated whether enhanced rates of fat oxidation during submaximal exercise after 5 d of a high-fat diet would persist in the face of increased carbohydrate (CHO) availability before and during exercise.

METHODS

Eight well-trained subjects consumed either a high-CHO (9.3 g x kg(-1) x d(-1) CHO, 1.1 g x kg(-1) x d(-1) fat; HCHO) or an isoenergetic high-fat diet (2.5 g x kg(-1) x d(-1) CHO, 4.3 g x kg(-1) x d(-1) fat; FAT-adapt) for 5 d followed by a high-CHO diet and rest on day 6. On day 7, performance testing (2 h steady-state (SS) cycling at 70% peak O(2) uptake [VO(2peak)] + time trial [TT]) of 7 kJ x kg(-1)) was undertaken after a CHO breakfast (CHO 2 g x kg(-1)) and intake of CHO during cycling (0.8 g x kg(-1) x h(-1)).

RESULTS

FAT-adapt reduced respiratory exchange ratio (RER) values before and during cycling at 70% VO(2peak); RER was restored by 1 d CHO and CHO intake during cycling (0.90 +/- 0.01, 0.80 +/- 0.01, 0.91 +/- 0.01, for days 1, 6, and 7, respectively). RER values were higher with HCHO (0.90 +/- 0.01, 0.88 +/- 0.01 (HCHO > FAT-adapt, P < 0.05), 0.95 +/- 0.01 (HCHO > FAT-adapt, P < 0.05)). On day 7, fat oxidation remained elevated (73 +/- 4 g vs 45 +/- 3 g, P < 0.05), whereas CHO oxidation was reduced (354 +/- 11 g vs 419 +/- 13 g, P < 0.05) throughout SS in FAT-adapt versus HCHO. TT performance was similar for both trials (25.53 +/- 0.67 min vs 25.45 +/- 0.96 min, NS).

CONCLUSION

Adaptations to a short-term high-fat diet persisted in the face of high CHO availability before and during exercise, but failed to confer a performance advantage during a TT lasting approximately 25 min undertaken after 2 h of submaximal cycling.

The energy cost of running on grass compared to soft dry beach sand

This study compared the energy cost (EC) (J x kg(-1) x m(-1)) of running on grass and soft dry beach sand. Seven male and 5 female recreational runners performed steady state running trials on grass in shoes at 8, 11 and 14 km x h(-1). Steady state sand runs, both barefoot and in shoes, were also attempted at 8 km x h(-1) and approximately 11 km x h(-1). One additional female attempted the grass and sand runs at 8 km x h(-1) only. Net total EC was determined from net aerobic EC (steady state VO2, VCO2 and RER) and net anaerobic EC (net lactate accumulation). When comparing the surface effects (grass, sand bare foot and sand in shoes) of running at 8 km x h(-1) (133.3 m x min(-1)) in 9 subjects who most accurately maintained that speed (133.3 +/- 2.2 m x min(-1)), no differences (P>0.05) existed between the net aerobic, anaerobic and total EC of sand running barefoot or in shoes, but these measures were all significantly greater (P<0.05) than the corresponding values when running on grass. Similarly, when all running speed trials (n = 87) performed by all subjects (n = 13) for each surface condition were combined for analysis, the sand bare foot and sand in shoes values for net aerobic EC, net anaerobic EC and net total EC were significantly greater (P<0.001) than the grass running measures, but not significantly different (P>0.05) from each other. Expressed as ratios of sand to grass running EC coefficients, the sand running barefoot and sand in shoes running trials at 8 km x h(-1) revealed values of 1.6 and 1.5 for net aerobic EC, 3.7 and 2.7 for net anaerobic EC and 1.6 and 1.5 for net total EC respectively. For all running speeds combined, these coefficients were 1.5 and 1.4 for net aerobic EC, 2.5 and 2.3 for net anaerobic EC and 1.5 and 1.5 for net total EC for sand running barefoot and in shoes respectively. Sand running may provide a low impact, but high EC training stimulus.

Effect of altering substrate availability on metabolism and performance during intense exercise

The purpose of this study was to determine the effect of altering substrate availability on metabolism and performance during intense cycling. Seven highly trained men ingested a random order of three isoenergetic meals 90 min before cycling at 80% maximal oxygen uptake (VO2max) for 20 min (about 310 W), followed by a 600 kJ time trial lasting about 30 min. Meals consisted of either 1.2 g saturated fat/kg body mass (BM) with 3500 U heparin intravenously (HIFAT) to elevate circulating plasma free fatty acid (FA) concentration, 2.5 g carbohydrate/kg BM (CHO) to elevate plasma glucose and insulin concentrations or 2.5 g carbohydrate +20 mg nicotinic acid/kg BM (NA) to suppress lipolysis and reduce free FA concentration. HIFAT elevated free FA concentration (HIFAT 1.3 (sem 0.2), CHO 0.2 (sem 0.1), NA 0.1 (sem 0.1) mm; P < 0.001) lowered the RER (HIFAT 0.94 (sem 0.01), CHO 0.97 (sem 0.01), NA 0.98 (sem 0.01); P < 0.01) and increased the rate of fat oxidation (HIFAT 24 (sem 3), CHO 12 (sem 2), NA 8 (sem 3) micromol/kg per min; P < 0.01) during the 20 min ride. Marked differences in fat availability and fuel utilisation, however, had little effect on performance in the subsequent time trial (HIFAT 320 (sem 16), CHO 324 (sem 15), NA 315 (sem 13) W). We conclude: (1) increased fat availability during intense cycling increases the rate of fat oxidation; but (2) the reduction in the rate of carbohydrate oxidation in the presence of high circulating plasma free FA is unlikely to enhance intense exercise performance lasting about 1 h; (3) substrate selection during intense (about 80% VO2max) exercise is dominated by carbohydrate oxidation.

Effect of fat adaptation and carbohydrate restoration on metabolism and performance during prolonged cycling

For 5 days, eight well-trained cyclists consumed a random order of a high-carbohydrate (CHO) diet (9.6 g. kg(-1). day(-1) CHO, 0.7 g. kg(-1). day(-1) fat; HCHO) or an isoenergetic high-fat diet (2.4 g. kg(-1). day(-1) CHO, 4 g. kg(-1). day(-1) fat; Fat-adapt) while undertaking supervised training. On day 6, subjects ingested high CHO and rested before performance testing on day 7 [2 h cycling at 70% maximal O(2) consumption (SS) + 7 kJ/kg time trial (TT)]. With Fat-adapt, 5 days of high-fat diet reduced respiratory exchange ratio (RER) during cycling at 70% maximal O(2) consumption; this was partially restored by 1 day of high CHO [0.90 +/- 0.01 vs. 0.82 +/- 0.01 (P < 0.05) vs. 0.87 +/- 0.01 (P < 0.05), for day 1, day 6, and day 7, respectively]. Corresponding RER values on HCHO trial were [0. 91 +/- 0.01 vs. 0.88 +/- 0.01 (P < 0.05) vs. 0.93 +/- 0.01 (P < 0.05)]. During SS, estimated fat oxidation increased [94 +/- 6 vs. 61 +/- 5 g (P < 0.05)], whereas CHO oxidation decreased [271 +/- 16 vs. 342 +/- 14 g (P < 0.05)] for Fat-adapt compared with HCHO. Tracer-derived estimates of plasma glucose uptake revealed no differences between treatments, suggesting muscle glycogen sparing accounted for reduced CHO oxidation. Direct assessment of muscle glycogen utilization showed a similar order of sparing (260 +/- 26 vs. 360 +/- 43 mmol/kg dry wt; P = 0.06). TT performance was 30.73 +/- 1.12 vs. 34.17 +/- 2.48 min for Fat-adapt and HCHO (P = 0.21). These data show significant metabolic adaptations with a brief period of high-fat intake, which persist even after restoration of CHO availability. However, there was no evidence of a clear benefit of fat adaptation to cycling performance.

Arterial hypoxaemia in endurance athletes is greater during running than cycling

The effect of both training discipline and exercise modality on exercise-induced hypoxaemia (EIH) was examined in seven runners and six cyclists during 5 min high intensity treadmill and cycle exercise. There were no significant interactions between training discipline, exercise modality and arterial P(O(2)) (Pa(O(2))) when subject groups were considered separately but when pooled there were significant differences between exercise modalities. After min 2 of exercise arterial hydrogen ion concentration, minute ventilation, alveolar P(O(2)) (PA(O(2))) and Pa(O(2)) were all lower with treadmill running with the largest differential for the latter occurring at min 5 (treadmill, 80.8+/-1.8; cycle, 90.2+/-2.5, mmHg, N=13, P< or = 0.05). At every min of exercise, the differences in Pa(O(2)) between the ergometers were strongly associated with similar differences in PA(O(2)) and alveolar to arterial P(O(2)) (PA(O(2))-Pa(O(2))). It is concluded that the greater EIH with treadmill running is a consequence of the combined effect of a reduced lactic acidosis-induced hyperventilation and greater ventilation-perfusion inequality with this exercise mode.

Effects of heat stress on physiological responses and exercise performance in elite cyclists

This study examined the effect of heat stress on physiological responses and exercise performance in elite road cyclists. Eleven members of the Australian National Road Cycling Squad completed two 30 min cycling time-trials in an environmental chamber set at either 32 degrees C, (HT) or 23 degrees C (NT) with a relative humidity of 60% in each circumstance. The trials were separated by two days, with six subjects performing HT first. Power output was 6.5% lower (P<0.05) during HT compared with NT. Mean skin temperature and sweat rate were higher (P<0.05) in HT compared with NT. In contrast, rectal temperature was remarkably similar throughout each trial. During the first 10 min of exercise in HT when power output was not different between trials, blood lactate was higher (P<0.05), and blood pH lower (P<0.05). In contrast, during the last 10 min of exercise when power output was reduced (P<0.05), blood lactate was lower (P<0.05), and pH higher (P<0.05), in HT. These data indicate that heat stress is associated with a reduced power output during self-paced exercise in highly trained men. This decrease in performance appears to be associated with factors associated with body temperature rather than metabolic capacity.