Standard Indirect Calorimetry Research Articles

Abstract 13181: Accurate, Non-Invasive Monitoring of VO2 Max Using Wearable ECG Technology

Introduction: Maximal aerobic capacity (VO2 max) corresponds to the maximum volume of oxygen the body can utilize during high-intensity exercise and is widely regarded as the criterion measurement for cardiorespiratory fitness (CRF). In addition to its use as a metric to evaluate aerobic endurance, VO2 max has been identified as a significant and independent risk factor for all-cause and disease-specific mortality. The integration of VO2 max functionality into wearable devices allows CRF to be unobtrusively monitored, providing an important insight into clinical health. Methods: ECG data acquired on the non-invasive HeartKey ® Chest Module throughout a multi-stage, high-intensity exercise protocol was used by the HeartKey VO2 Max algorithm to generate a VO2 max rate. The algorithm’s performance was evaluated against data simultaneously collected on gold standard CRF equipment using indirect calorimetry (Korr ® CardioCoach). Participants (N=45) of varying ages and physical fitness were recruited to ensure a wide range of CRF levels were represented. Results: A strong correlational relationship ( R= 0.9) was observed between the HeartKey VO2 max values and those generated on the criterion device. HeartKey VO2 Max algorithm demonstrated high accuracy, with a mean absolute percentage error of ~6% over the 45 subjects. The mean absolute error for the HeartKey algorithm was 3.1 ml/min/kg, with a root mean square error value of 3.9 ml/min/kg. Conclusions: HeartKey generated highly accurate and reliable VO2 max metrics from ECG data collected on a non-obstructive, non-invasive, dry electrode wearable device, with a performance comparable to that of a gold standard indirect calorimetry device. This study highlights the opportunity to make CRF monitoring accessible in everyday scenarios by using wearable ECG devices functionalized with accurate VO2 max capability, which is convenient, cost-effective, and highly scalable.

Coupling of energy intake and energy expenditure across a temperature spectrum: impact of diet-induced obesity in mice.

Obesity and its metabolic sequelae are implicated in dysfunction of the somatosensory, sympathetic, and hypothalamic systems. Because these systems contribute to integrative regulation of energy expenditure (EE) and energy intake (EI) in response to ambient temperature (Ta) changes, we hypothesized that diet-induced obesity (DIO) disrupts Ta-associated EE-EI coupling. C57BL/6N male mice were fed a high-fat diet (HFD; 45% kcal) or low-fat diet (LFD; 10% kcal) for ∼9.5 wk; HFD mice were then split into body weight (BWT) quartiles (n = 8 each) to study DIO-low gainers (Q1) versus -high gainers (Q4). EI and indirect calorimetry (IC) were measured over 3 days each at 10°C, 20°C, and 30°C. Responses did not differ between LFD, Q1, and Q4; EI and BWT-adjusted EE increased rapidly when transitioning toward 20°C and 10°C. In all groups, EI at 30°C was not reduced despite lower EE, resulting in positive energy balance and respiratory exchange ratios consistent with increased de novo lipogenesis, energy storage, and relative hyperphagia. We conclude that 1) systems controlling Ta-dependent acute EI/EE coupling remained intact in obese mice and 2) rapid coupling of EI/EE at cooler temperatures is an important adaptation to maintain energy stores and defend body temperature, but less critical at thermoneutrality. A post hoc analysis using digestible EI plus IC-calculated EE suggests that standard IC assumptions for EE calculation require further validation in the setting of DIO. The experimental paradigm provides a platform to query the hypothalamic, somatosensory, and sympathetic mechanisms that drive Ta-associated EI/EE coupling.

Rapid energy expenditure estimation for ankle assisted and inclined loaded walking

BackgroundEstimating energy expenditure with indirect calorimetry requires expensive equipment and several minutes of data collection for each condition of interest. While several methods estimate energy expenditure using correlation to data from wearable sensors, such as heart rate monitors or accelerometers, their accuracy has not been evaluated for activity conditions or subjects not included in the correlation process. The goal of our study was to develop data-driven models to estimate energy expenditure at intervals of approximately one second and demonstrate their ability to predict energetic cost for new conditions and subjects. Model inputs were muscle activity and vertical ground reaction forces, which are measurable by wearable electromyography electrodes and pressure sensing insoles.MethodsWe developed models that estimated energy expenditure while walking (1) with ankle exoskeleton assistance and (2) while carrying various loads and walking on inclines. Estimates were made each gait cycle or four second interval. We evaluated the performance of the models for three use cases. The first estimated energy expenditure (in Watts) during walking conditions for subjects with some subject specific training data available. The second estimated all conditions in the dataset for a new subject not included in the training data. The third estimated new conditions for a new subject.ResultsThe mean absolute percent errors in estimated energy expenditure during assisted walking conditions were 4.4%, 8.0%, and 8.1% for the three use cases, respectively. The average errors in energy expenditure estimation during inclined and loaded walking conditions were 6.1%, 9.7%, and 11.7% for the three use cases. For models not using subject-specific data, we evaluated the ability to order the magnitude of energy expenditure across conditions. The average percentage of correctly ordered conditions was 63% for assisted walking and 87% for incline and loaded walking.ConclusionsWe have determined the accuracy of estimating energy expenditure with data-driven models that rely on ground reaction forces and muscle activity for three use cases. For experimental use cases where the accuracy of a data-driven model is sufficient and similar training data is available, standard indirect calorimetry could be replaced. The models, code, and datasets are provided for reproduction and extension of our results.

Association of gene coding variation and resting metabolic rate in a multi-ethnic sample of children and adults

BackgroundResting metabolic rates (RMR) vary across individuals. Understanding the determinants of RMR could provide biological insight into obesity and its metabolic consequences such as type 2 diabetes and cardiovascular diseases.MethodsThe present study measured RMR using reference standard indirect calorimetry and evaluated genetic variations from an exome array in a sample of children and adults (N = 262) predominantly of African and European ancestry with a wide range of ages (10 – 67 years old) and body mass indices (BMI; 16.9 – 56.3 kg/m2 for adults, 15.1 – 40.6 kg/m2 for children).ResultsSingle variant analysis for RMR identified suggestive loci on chromosomes 15 (rs74010762, TRPM1, p-value = 2.7 × 10−6), 1 (rs2358728 and rs2358729, SH3D21, p-values < 5.8x10−5), 17 (AX-82990792, DHX33, 5.5 × 10−5) and 5 (rs115795863 and rs35433829, C5orf33 and RANBP3L, p-values < 8.2 × 10−5). To evaluate the effect of low frequency variations with RMR, we performed gene-based association tests. Our most significant locus was SH3D21 (p-value 2.01 × 10−4), which also contained suggestive results from single-variant analyses. A further investigation of all variants within the reported genes for all obesity-related loci from the GWAS catalog found nominal evidence for association of body mass index (BMI- kg/m2)-associated loci with RMR, with the most significant p-value at rs35433754 (TNKS, p-value = 0.0017).ConclusionsThese nominal associations were robust to adjustment for BMI. The most significant variants were also evaluated using phenome-wide association to evaluate pleiotropy, and genetically predicted gene expression using the summary statistics implicated loci related to in obesity and body composition. These results merit further examination in larger cohorts of children and adults.

Remote Quantification of Workout Energy Expenditure With a Cell Phone Camera

A method based on intelligent video processing is introduced here to objectively assess the intensity and energy expenditure of popular indoor workouts, including sit up, push up, jumping jack, and squat. The method is based a smart phone camera, which can count the repetition, assess the intensity level, and quantify the energy expenditure of the workouts. It uses an algorithm that analyzes body movement and body’s effort to overcome gravity in hierarchical layers, each with an increasing level of details. The energy expenditure values for different types of workouts at different intensities determined by the method are compared with a gold standard indirect calorimetry apparatus worn by the study subject.

Basal Metabolic Rate of Adolescent Modern Pentathlon Athletes: Agreement between Indirect Calorimetry and Predictive Equations and the Correlation with Body Parameters.

PurposeThe accurate estimative of energy needs is crucial for an optimal physical performance among athletes and the basal metabolic rate (BMR) equations often are not well adjusted for adolescent athletes requiring the use of specific methods, such as the golden standard indirect calorimetry (IC). Therefore, we had the aim to analyse the agreement between the BMR of adolescents pentathletes measured by IC and estimated by commonly used predictive equations.MethodsTwenty-eight athletes (17 males and 11 females) were evaluated for BMR, using IC and the predictive equations Harris and Benedict (HB), Cunningham (CUN), Henry and Rees (HR) and FAO/WHO/UNU (FAO). Body composition was obtained using DXA and sexual maturity data were retrieved through validated questionnaires. The correlations among anthropometric variables an IC were analysed by T-student test and ICC, while the agreement between IC and the predictive equations was analysed according to Bland and Altman and by survival-agreement plotting.ResultsThe whole sample average BMR measured by IC was significantly different from the estimated by FAO (p<0.05). Adjusting data by gender FAO and HR equations were statistically different from IC (p <0.05) among males, while female differed only for the HR equation (p <0.05).ConclusionThe FAO equation underestimated athletes’ BMR when compared with IC (T Test). When compared to the golden standard IC, using Bland and Altman, ICC and Survival-Agreement, the equations underestimated the energy needs of adolescent pentathlon athletes up to 300kcal/day. Therefore, they should be used with caution when estimating individual energy requirements in such populations.

Ventilator-derived carbon dioxide production to assess energy expenditure in critically ill patients: proof of concept.

IntroductionMeasurement of energy expenditure (EE) is recommended to guide nutrition in critically ill patients. Availability of a gold standard indirect calorimetry is limited, and continuous measurement is unfeasible. Equations used to predict EE are inaccurate. The purpose of this study was to provide proof of concept that EE can be accurately assessed on the basis of ventilator-derived carbon dioxide production (VCO2) and to determine whether this method is more accurate than frequently used predictive equations.MethodsIn 84 mechanically ventilated critically ill patients, we performed 24-h indirect calorimetry to obtain a gold standard EE. Simultaneously, we collected 24-h ventilator-derived VCO2, extracted the respiratory quotient of the administered nutrition, and calculated EE with a rewritten Weir formula. Bias, precision, and accuracy and inaccuracy rates were determined and compared with four predictive equations: the Harris–Benedict, Faisy, and Penn State University equations and the European Society for Clinical Nutrition and Metabolism (ESPEN) guideline equation of 25 kcal/kg/day.ResultsMean 24-h indirect calorimetry EE was 1823 ± 408 kcal. EE from ventilator-derived VCO2 was accurate (bias +141 ± 153 kcal/24 h; 7.7 % of gold standard) and more precise than the predictive equations (limits of agreement −166 to +447 kcal/24 h). The 10 % and 15 % accuracy rates were 61 % and 76 %, respectively, which were significantly higher than those of the Harris–Benedict, Faisy, and ESPEN guideline equations. Large errors of more than 30 % inaccuracy did not occur with EE derived from ventilator-derived VCO2. This 30 % inaccuracy rate was significantly lower than that of the predictive equations.ConclusionsIn critically ill mechanically ventilated patients, assessment of EE based on ventilator-derived VCO2 is accurate and more precise than frequently used predictive equations. It allows for continuous monitoring and is the best alternative to indirect calorimetry.

Testing a Novel Method for Measuring Sleeping Metabolic Rate in Neonates

Sleeping metabolic rate (SMR) is used as a proxy for basal metabolic rate in infants, when measurement while awake is not practical. Measuring SMR via indirect calorimetry (IC) can be useful for assessing feeding adequacy especially in compromised neonates. Standard IC equipment, including a hood placed over the head, is not designed for the smallest of patients. Our aim was to determine whether a nonstandard smaller hood measures SMR in neonates similarly compared with a standard large hood. SMR was measured in healthy neonates (controls) and those born with single-ventricle congenital heart disease (cases). Two measurements were performed: SMR using a standard large hood and SMR using a smaller hood. Time-to-steady state, minute ventilation (V̇E), and fraction of exhaled carbon dioxide (FĒCO2 ; an indicator of data quality) were also measured. Primary outcome was SMR using both hoods. Results are stated as median (interquartile range). Spearman's correlations measured association between the small and large hoods. We studied 9 controls and 7 cases. SMR in controls was not different between the small and large hoods (35.7 [15.14] vs 37.8 [7.41] kcal/kg/d, respectively). In cases, SMR with the small hood was significantly greater than that with the large hood (45.5 [4.63] vs 34.2 [8] kcal/kg/d, P < .02). FĒCO2 was significantly higher with the small hood versus the large hood in both groups, and V̇E was significantly lower with the small hood versus the large hood in controls only. The SMRs with the small and large hoods were significantly correlated in the control group (r = 0.80, P < .01). Time-to-steady state was similar in both groups regardless of hood size. SMR measured with a small hood yields results similar to those measured with a large hood in healthy neonates without affecting testing time or other aspects of the IC procedure. Furthermore, results in compromised infants suggest that a smaller hood may facilitate SMR testing in this population.

An Evaluation of a Handheld Indirect Calorimeter Against a Standard Calorimeter in Obese and Nonobese Adults

Handheld indirect calorimetry has the potential to allow simple and inexpensive measurement of resting metabolic rate in spontaneously breathing people. However, validation work on these devices is contradictory. The purpose of the current study was to determine the bias and level of agreement of oxygen consumption and resting metabolic rate as measured by a handheld indirect calorimeter against a standard open-circuit indirect calorimetry cart. One hundred community-living, spontaneously breathing, ambulatory nonobese and obese adults were studied in single sessions by a single investigator. Sequential measurements were undertaken using the handheld indirect calorimeter and the standard metabolic cart. Measurement sequence was varied randomly. The mean value for oxygen consumption and metabolic rate of the 2 devices was not significantly different. However, agreement between the 2 devices was only 43% in nonobese and obese participants, and there was proportional and fixed bias, with the handheld calorimeter tending to produce a higher value for oxygen consumption and resting metabolic rate. Limits of agreement for resting metabolic rate between the 2 calorimeters were -240 to +300 kcal/d. Measurements of resting metabolic rate by the handheld indirect calorimeter tested in this study are not equivalent to measurements by standard indirect calorimetry.

Body Composition and Resting Energy Expenditure in Short Stature Adults: A Field Study

Results: 12 males and 30 females participated (6 and 23 achondroplasia). BIA failed in 4 (9.5%):foot malformation , weight/height below Tanita algorithm (31kg, 120 cm), inability to stand. Mean female BF% (29.1%; 5.6-45.7%) was greater than males (27.8%; 19-40.7%) with 42% of females in the obese category and 64% of males. In females, Tanita BMR (1307 89) and the ReeVue REE (1314 97) were comparable, and neither was different than gold standard indirect calorimetry (1266 102; p 0.38, p 0.32) in 9 comparable achondroplasia females. Similarly, Tanita BMR (1138 109) was similar to the ReeVue REE (1408 185) in 6 achondroplasia males and no different than gold standard indirect calorimetry (1256 172; n 11 males).

Testing a Novel Method for Measuring Sleeping Metabolic Rate in Neonates

BACKGROUND: Sleeping metabolic rate (SMR) is used as a proxy for basal metabolic rate in infants, when measurement while awake is not practical. Measuring SMR via indirect calorimetry (IC) can be useful for assessing feeding adequacy especially in compromised neonates. Standard IC equipment, including a hood placed over the head, is not designed for the smallest of patients. Our aim was to determine whether a nonstandard smaller hood measures SMR in neonates similarly compared with a standard large hood. METHODS: SMR was measured in healthy neonates (controls) and those born with single-ventricle congenital heart disease (cases). Two measurements were performed: SMR using a standard large hood and SMR using a smaller hood. Time-to-steady state, minute ventilation (VE), and fraction of exhaled carbon dioxide (FĒCO2; an indicator of data quality) were also measured. Primary outcome was SMR using both hoods. Results are stated as median (interquartile range). Spearman's correlations measured association between the small and large hoods. RESULTS: We studied 9 controls and 7 cases. SMR in controls was not different between the small and large hoods (35.7 [15.14] vs 37.8 [7.41] kcal/kg/d, respectively). In cases, SMR with the small hood was significantly greater than that with the large hood (45.5 [4.63] vs 34.2 [8] kcal/kg/d, P < .02). FĒCO2 was significantly higher with the small hood versus the large hood in both groups, and VE was significantly lower with the small hood versus the large hood in controls only. The SMRs with the small and large hoods were significantly correlated in the control group (r = 0.80, P < .01). Time-to-steady state was similar in both groups regardless of hood size. CONCLUSIONS: SMR measured with a small hood yields results similar to those measured with a large hood in healthy neonates without affecting testing time or other aspects of the IC procedure. Furthermore, results in compromised infants suggest that a smaller hood may facilitate SMR testing in this population.

Predicting Maximal Oxygen Uptake in Nordic Skiers

Maximal oxygen uptake (VO2MAX) is a common lab-based measure of cardiovascular fitness and strong correlate of endurance performance in young Nordic skiers. The measurement of VO2MAX, however, requires expensive metabolic testing equipment that is not available to all testing facilities. PURPOSE: This study sought to derive a VO2MAX prediction equation specific to young Nordic skiers that could be used in place of metabolic testing equipment. METHODS: 13 female (Mean±SD [Range]: 19±4 [16-26] yrs; 168±5 [161-176] cm height; 59.3±5 [46.8-66.0] kg body mass) and 16 male (20±4 [16-29] yrs; 178±7 [169-190] cm height; 71.0±8 [61.8-86.4] kg body mass) competitive Nordic skiers performed a treadmill test to volitional exhaustion to measure VO2MAX. The test protocol started at 99.2 m/min and 6% grade and increased by 8 m/min and 2% grade each stage thereafter with subjects using rubber-tipped ski poles and a ski striding technique that simulates diagonal stride. Measures of VO2 were recorded using standard indirect calorimetry procedures and a 20-sec sampling interval. Using standard stepwise multiple linear regression procedures, relative VO2MAX (ml/kg/ min) for the validation (V) group was predicted using a pool of potential dependent variables: Test completion time (T, mins), age (A, yrs), body mass (M, kg), gender (G; 0 = females, 1 = males), and final treadmill speed and grade at test completion. Data for a separate group of 4 female and 4 male Nordic skiers (20±2 yrs, 172±9 cm, 69.5±8.8 kg), all of whom completed the same testing as the V group, were used to cross-validate (CV) the final equation using a paired t-test. RESULTS: Females averaged 61.1±4.1 [55.4-68.8) ml/kg/min and 6.9±0.8 [5.7-8.1] mins for VO2MAX and T, respectively, while males averaged 70.5±4.3 [61.9-78.3] ml/kg/min and 7.9±0.9 [6.3-9.3] mins. The best predicted equation was as follows: VO2MAX (ml/kg/min) = 33.98 + 3.95xT + 5.34xG (R2= 0.84, SEE = ±2.6 ml/kg/min). Predicted and measured VO2MAX for both V (Mean±SE: 66.3±1.1 vs 66.3±1.1 ml/kg/min) and CV groups (65.5±3.1 vs 66.6±3.2 ml/kg/min) did not differ significantly (P=0.98 and 0.14, respectively). CONCLUSIONS: Accurate prediction of relative VO2MAX in young Nordic skiers is possible with gender and time to exhaustion as predictor variables from a ski striding treadmill protocol.

In Vivo Validation of the M-COVX® Metabolic Monitor in Patients under Anaesthesia

A practical method of breath-by-breath monitoring of metabolic gas exchange has been developed by GE Healthcare/Datex Ohmeda and incorporated into existing anaesthetic and critical care monitoring systems (M-COVXO). This device relates flow measurements made at the mouth by pneumotachograph to measurements of inspired and expired gas composition by matching the two waveforms thereby allowing continuous, breath-by-breath monitoring of an intubated patient's oxygen uptake and carbon dioxide production. Given that there is a paucity of data comparing this new device against methods more widely used clinically, we tested the device on 11 patients undergoing cardiopulmonary bypass surgery. Using a standard anaesthetic machine (Datex Ohmeda Excel 210 SE) with a semi-closed circle absorber system, oxygen uptake was measured at the mouth continuously throughout the operation at approximately six-second intervals. The data were compared against the reverse Fick method and against standard indirect calorimetry using the Haldane transformation. When compared to the calculated reverse Fick oxygen uptake, a mean difference of +16.5% was found pre-bypass and +9.9% post-bypass, consistent with uptake of oxygen by lung tissue, which is not taken into account by the reverse Fick method. Measurements made comparing the M-COVX metabolic monitor against standard Haldane showed a mean difference of +5.1% pre-bypass and -2.1% post-bypass. Given the ease with which this device can be incorporated into existing anaesthetic monitoring systems and its accuracy in measuring oxygen uptake, the M-COTVX module is an attractive addition to existing perioperative monitoring.

The agreement between the MedGem® indirect calorimeter and a standard indirect calorimeter in anorexia nervosa

Measurement of the basal metabolic rate (BMR) can be used to estimate the calories required for weight gain during refeeding in anorexia nervosa (AN). The reference method for measuring the BMR is indirect calorimetry. MedGem has developed a new indirect calorimeter that calculates the metabolic rate much more quickly than standard indirect calorimeters. This study compared the BMR measured by the MedGem and standard indirect calorimetry in an AN population. We measured the BMR using the Deltatrac metabolic cart followed immediately by the MedGem indirect calorimeter in 27 subjects (12 patients and 15 controls). Bland-Altman plots show that there is poor agreement between the BMR reported by the MedGem compared to the Deltatrac. Until better agreement with standard indirect calorimetry can be shown the MedGem should not be used for calorimetry in AN. Possible factors that may limit the MedGem's reliability include patient discomfort with the mouthpiece, use of a fixed RQ, and the short sampling period.

Whole‐body fat oxidation determined by graded exercise and indirect calorimetry: a role for muscle oxidative capacity?

During whole-body exercise, peak fat oxidation occurs at a moderate intensity. This study investigated whole-body peak fat oxidation in untrained and trained subjects, and the presence of a relation between skeletal muscle oxidative enzyme activity and whole-body peak fat oxidation. Healthy male subjects were recruited and categorized into an untrained (N=8, VO(2max) 3.5+/-0.1 L/min) and a trained (N=8, VO(2max) 4.6+/-0.2 L/min) group. Subjects performed a graded exercise test commencing at 60 W for 8 min followed by 35 W increments every 3 min. On a separate day, muscle biopsies were obtained from vastus lateralis and a 3 h bicycle exercise test was performed at 58% of VO(2max). Whole-body fat oxidation was calculated during prolonged and graded exercise from the respiratory exchange ratio using standard indirect calorimetry equations. Based on the graded exercise test, whole-body peak fat oxidation was determined. The body composition was determined by DEXA. Whole-body peak fat oxidation (250+/-25 and 462+/-33 mg/min) was higher (P<0.05) and occurred at a higher (P<0.05) relative workload (43.5+/-1.8% and 49.9+/-1.2% VO(2max)) in trained compared with untrained subjects, respectively. Muscle citrate synthase activity and beta-hydroxy-acyl-CoA-dehydrogenase activity were higher (49% and 35%, respectively, P<0.05) in trained compared with untrained subjects. Both lean body mass and maximal oxygen uptake were significantly correlated to whole-body peak fat oxidation (r(2)=0.57, P<0.001), but leg muscle oxidative capacity was not correlated to whole-body peak fat oxidation. In conclusion, whole-body peak fat oxidation occurred at a higher relative exercise load in trained compared with untrained subjects. Whole-body peak fat oxidation was not significantly related to leg muscle oxidative capacity, but was related to lean body mass and maximal oxygen uptake. This may suggest that leg muscle oxidative activity is not the main determinant of whole-body peak fat oxidation.

VALIDITY OF A STATIONARY CYCLING PROTOCOL FOR TRACKING CHANGES IN UPHILL CYCLING TIME-TRIAL PERFORMANCE

PURPOSE: The ability to accurately quantify and predict changes in endurance performance is imperative when assessing the effect of training interventions, dietary regimes, equipment modifications, and/or alterations in athlete position or technique. The purpose of the present study was to determine the ability of a previously validated (Heil et al., MSSE 85:374–382, 2001) scaling-derived cycle ergometer protocol (SDP) to track changes in uphill time-trial (TT) cycling performance. METHODS: Local competitive cyclists participated in either two (n = 5 males, 1 female) or three (n = 6 males, 1 female) testing periods (T1,T2,T3) separated by a minimum of ten weeks (May, July, September 2001). Each testing period consisted of an outdoor uphill TT (5-km, 8% grade) followed within ten days by a laboratory-based SDP. Changes in average TT speed (m/s) (T2-T1 & T3-T2) between successive trials were correlated with changes in SDP time-to-exhaustion (TTE, min), SDP relative peak power output (WMAX, Watts/kg), and maximal oxygen uptake (VO2MAX, ml/kg/min). VO2MAX was determined with the SDP for each trial via standard indirect calorimetry procedures. RESULTS: Changes in average TT speed correlated highly with changes in relative WMAX (r = 0.70–0.94), correlated moderately with changes in VO2MAX (r = 0.47–0.72), and more variably correlated with changes in TTE (r = 0.26–0.87). In addition, intraclass reliability across a separate administration of three SDP tests (n = 21) ranged from R = 0.933–0.992 for WMAX, TTE, and VO2MAX. CONCLUSIONS: These results suggest that changes in relative SDP WMAX can validly and practically track changes in uphill TT performance. These results should be of benefit to cyclists, coaches, and sport scientists as they design cycling programs for training and youth talent identification.

Prediction of uphill time-trial bicycling performance in humans with a scaling-derived protocol.

The present study sought to create a scaling-derived cycle ergometer protocol (SDP) that was derived theoretically and would correlate highly with actual uphill time-trial (TT) cycling performance. Local competitive cyclists each completed the SDP (an incremental test to exhaustion) using their own bicycle mounted on a stationary trainer, together with either a short (6.2 km, 2.9% grade; n = 8 men and 5 women) or long-course (12.5 km, 2.7% grade; n = 8 men) uphill TT. Maximal power output (Wmax) and power at the ventilatory threshold (WVT) were determined from the SDP results, as well as maximal oxygen uptake (VO2max), using standard indirect calorimetry procedures. Actual TT speed correlated very highly with both SDP completion time (r = 0.97-0.98) and relative Wmax (watts per kilogram; r = 0.92-0.97) for both uphill TT races. Correlations between TT speed and more demanding measurements (VO2max, WVT) (VO2max, WVT) were generally lower and more variable (r = 0.54-0.97). These results would indicate that two non-laboratory dependent measurements (SDP completion time and relative Wmax) derived from the SDP are valid markers for predicting actual uphill TT performance. This protocol may be useful to cycling coaches and athletes in identifying talented cyclists or for tracking changes in cycling performance outside of the sports science laboratory environment.

Closed-circuit metabolic system with multiple applications.

A closed-circuit metabolic system has been designed and tested for multiple applications. Air pressure within a closed chamber is regulated electronically while allowing for respiratory gas exchange. Compared with a previously reported standard indirect calorimetry system, the new device had by virtue of longer duration of measurement improved precision (coefficient of variation 3% vs. 14%) during studies of O2 consumption both at room temperature and at 5 degrees C. In addition, a more physiological atmospheric environment is maintained. This system has also been utilized for simultaneously labeling groups of up to 20 weanling rats with 18O2 over a 2-day period and for exposure of rats to a hyperoxic (84% O2), normobaric environment for 4-day periods. Potential applications include maintenance of pressure (hypobaric through hyperbaric) and O2 (hypoxic through hyperoxic) controlled environments, exposure to toxic gases, study of diurnal variations in metabolic rate, measurement of metabolic expenditure with activity, and adaptation to other species including humans.