Open-circuit respirometry: a historical review of portable gas analysis systems

Accuracy and repeatability of the COSMED® Q-NRG max mobile metabolic system

PURPOSE

To investigate the accuracy and repeatability of the Q-NRG Max® metabolic system against a VacuMed metabolic simulator using a wide range of metabolic rates.

METHODS

Sixteen metabolic rates (oxygen consumption 0.9-6 L/min), with different combinations of minute ventilation, oxygen consumption, and carbon dioxide production, were measured for 5 minutes, two times by a single Q-NRG Max® unit over the course of one week. Recordings were performed early in the morning, by the same trained technician, in a ventilated laboratory under the same atmospheric conditions. Accuracy was assessed by ordinary least products (OLP) regression analysis, Bland-Altman plots, intraclass correlation coefficients (ICC), mean percentage differences, technical errors (TE) and minimum detectable change (MDC) for all three variables. This analysis was performed using 10 metabolic rates (oxygen consumption 0.9-4 L/min) and 16 metabolic rates (oxygen consumption 0.9-6 L/min) to allow comparisons with previous research. Intra-device repeatability was performed by absolute percentage differences between measurements (MAPE), ICC, TE, and MDC for the same variables. Repeatability was investigated using 16 metabolic rates.

RESULTS

High agreement and excellent ICCs (>0.998) were observed for all variables when considering both 10 and 16 metabolic rates. The mean percentage difference, TE and MDC were 0.87%-1.01%, 0.67%-1.07%, 1.55%-2.49%, respectively for the first 10 metabolic rates, and -0.39%-0.65%, 0.58%-1.63%, 1.35%-3.81%, respectively for the 16 metabolic rates. The intra-device repeatability results showed an excellent ICCs (=1.000), MAPE < 0.5%, TE < 1%, and MDC ≤ 2%.

CONCLUSION

The Q-NRG Max® is a valid and reliable mobile metabolic system for the measurement of ventilation, oxygen consumption, and carbon dioxide production. Measurements were below the 5% TE and MDC, and 2% MAPE recommended thresholds across a wide range of metabolic rates up to 6 L/min oxygen consumption.

ENERGY expenditure of COmmuting to school (ENERGYCO): protocol for a cluster randomized controlled trial

Introduction

This article outlines the rationale and methodology of the ENERGY expenditure of COmmuting to school study (the ENERGYCO study), a cluster-randomized controlled trial. The ENERGYCO study is divided into two phases: Phase I will aim; to assess the physical activity energy expenditure (PAEE) of different modes of commuting to school (i.e., walking, cycling, and motorized-vehicle) using indirect calorimetry in Spanish adolescents; and Phase II will aim to assess the effect of a school-based cycling intervention on resting metabolic rate and PAEE, as well as on other physiological, physical, and psychosocial outcomes on Spanish adolescents.

Method

For Phase I, a convenience sample of ~50 adolescents will be recruited. These participants will have their PAEE assessed in three different modes of commuting. Regarding phase II, a total of 300 adolescents from different schools in three Spanish cities will participate in this cluster randomized controlled trial. As many schools as necessary to meet the target sample will be included. In addition, each school will be randomized as either an intervention or control group. Participants from intervention schools will be asked to complete a school-based cycling intervention, while participants from control schools will be asked to continue their same habits for 8 weeks. The school-based cycling intervention will last for 8 weeks and will include Bikeability sessions, along with encouragement strategies to increase adherence to cycling to and from school.

Conclusion

The ENERGYCO study will provide novel insights into the PAEE associated with different modes of commuting to school using indirect calorimetry, as well as a comprehensive overview of how an 8-week school-based cycling intervention impacts resting energy expenditure, daily energy expenditure, and the physical and psychosocial health of adolescents.

Validity and between-days reliability of two different metabolic systems for measuring gas exchange during walking

BACKGROUND

Portable metabolic systems for assessing gas exchange outside the laboratory and clinical settings are increasing their popularity. We aimed to determine the validity and the reliability of the K5 portable system (Cosmed, Rome, Italy) and the Omnical (Maastricht Instruments, Maastricht, The Netherlands) metabolic cart.

METHODS

Gas exchange was measured, using the K5 and the Omnical in a randomised and counterbalanced order, in 35 participants (19 women; age: 26 ± 3 yrs.) using a walking protocol on 2 non-consecutive (48 h apart) days. The protocol consisted of a 5 min walk and 2.5 min rest cycle starting at 3.5 km/h and increasing in 1 km/h to 6.5 km/h. The protocol was repeated twice after a 10-15 min resting. To determine validity and reliability, we conducted two-factor repeated measures analysis of variance (ANOVA), intraclass correlation coefficients (ICC), coefficients of variation (CV) and Bland-Altman analyses.

RESULTS

Repeated measures ANOVA showed that mean oxygen consumption, carbon dioxide production and energy expenditure were higher for the K5 compared to the Omnical on both visits (all P < 0.001). Respiratory exchange ratio (RER) was similar among systems at faster (≥4.5 km/h) walking speeds. ICC, CV and Bland-Altman showed a better reliability of the Omnical (ICCs ranged from 0.71 to 0.86, and CVs from 3.1 % to 7.1 %) compared to the K5 (ICCs ranged from 0.40 to 0.98, and CVs from 2.6 % to 6.3 %).

CONCLUSIONS

The K5 portable system provides similar RER values to the Omnical metabolic cart, although the Omnical reliability was better for most outcomes.

No sex differences in systemic metabolic responses to acute sprint interval training performed after an oral 75-g glucose load in adults with excess adiposity

BACKGROUND & AIMS

Research exploring sex-based variations in responses to acute sprint interval training (SIT) remains limited. This study aimed to examine the impact of biological sex on the systemic metabolic response to SIT. We hypothesized that acute metabolic responses to SIT would differ between males and females.

METHODS

Sedentary adults (15 males; 14 females) with excess adiposity (defined as body fat >30 %) were matched for age (32.8 ± 7.5 vs. 29.5 ± 6.5 years) and body fat mass (33.0 ± 2.9 vs. 33.2 ± 2.8 %). Following a 75-g glucose load, participants were randomly allocated to either a control (resting) or SIT trial (8 × 30 s of "all-out" cycling at a resistance of 0.075 % W kg-1 of muscle mass, interspersed with 1 min of recovery). Parameters assessed included respiratory quotient (RQ), resting energy expenditure (REE), substrate utilization rates (fat and carbohydrate), total energy output, and blood lactate and glucose levels. These were collected during fasting and at 60, 120, and 240 min post-glucose load, with the area under the curve (AUC) calculated for both trials.

RESULTS

An interaction was observed in time (P = 0.012) and trial (P < 0.001) for RQ; however, there was no significant interaction between sex × trial (P = 0.818). Males exhibited higher mean REE values than females in both conditions. Nevertheless, AUC analysis showed no significant interaction between sex and trial (P = 0.562). A significant trial × time relationship was found for fat and carbohydrate percentage contributions (P < 0.001). Post-SIT, AUCs for fat contribution (g min-1 and mg kg-1 min-1) to energy expenditure increased in both sexes compared with resting (P < 0.05), with differences noted among trials over time (P < 0.001). Blood lactate levels also increased similarly post-SIT in both sexes (P < 0.05), without a significant sex × trial interaction (AUC, P = 0.798).

CONCLUSIONS

These data demonstrate that exercise differed between the sexes and did not support the premise that acute metabolic responses to SIT would vary between males and females.

Accuracy of respiratory gas variables, substrate, and energy use from 15 CPET systems during simulated and human exercise

PURPOSE

Various systems are available for cardiopulmonary exercise testing (CPET), but their accuracy remains largely unexplored. We evaluate the accuracy of 15 popular CPET systems to assess respiratory variables, substrate use, and energy expenditure during simulated exercise. Cross-comparisons were also performed during human cycling experiments (i.e., verification of simulation findings), and between-session reliability was assessed for a subset of systems.

METHODS

A metabolic simulator was used to simulate breath-by-breath gas exchange, and the values measured by each system (minute ventilation [V̇E], breathing frequency [BF], oxygen uptake [V̇O2 ], carbon dioxide production [V̇CO2 ], respiratory exchange ratio [RER], energy from carbs and fats, and total energy expenditure) were compared to the simulated values to assess the accuracy. The following manufacturers (system) were assessed: COSMED (Quark CPET, K5), Cortex (MetaLyzer 3B, MetaMax 3B), Vyaire (Vyntus CPX, Oxycon Pro), Maastricht Instruments (Omnical), MGC Diagnostics (Ergocard Clinical, Ergocard Pro, Ultima), Ganshorn/Schiller (PowerCube Ergo), Geratherm (Ergostik), VO2master (VO2masterPro), PNOĒ (PNOĒ), and Calibre Biometrics (Calibre).

RESULTS

Absolute percentage errors during the simulations ranged from 1.15%-44.3% for V̇E, 1.05-3.79% for BF, 1.10%-13.3% for V̇O2 , 1.07%-18.3% for V̇CO2 , 0.62%-14.8% for RER, 5.52%-99.0% for Kcal from carbs, 5.13%-133% for Kcal from fats, and 0.59%-12.1% for total energy expenditure. Between-session variation ranged from 0.86%-21.0% for V̇O2 and 1.14%-20.2% for V̇CO2 , respectively.

CONCLUSION

The error of respiratory gas variables, substrate, and energy use differed substantially between systems, with only a few systems demonstrating a consistent acceptable error. We extensively discuss the implications of our findings for clinicians, researchers and other CPET users.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 2: physiological measurements

In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions.

Maximal oxidative capacity during exercise is associated with muscle power output in patients with long coronavirus disease 2019 (COVID-19) syndrome. A moderation analysis

BACKGROUND & AIMS

Long COVID syndrome (LCS) involves persistent symptoms experienced by many patients after recovering from coronavirus disease 2019 (COVID-19). We aimed to assess skeletal muscle energy metabolism, which is closely related to substrate oxidation rates during exercise, in patients with LCS compared with healthy controls. We also examined whether muscle power output mediates the relationship between COVID-19 and skeletal muscle energy metabolism.

METHODS

In this cross-sectional study, we enrolled 71 patients with LCS and 63 healthy controls. We assessed clinical characteristics such as body composition, physical activity, and muscle strength. We used cardiopulmonary exercise testing to evaluate substrate oxidation rates during graded exercise. We performed statistical analyses to compare group characteristics and peak fat oxidation differences based on power output.

RESULTS

The two-way analysis of covariance (ANCOVA) results, adjusted for covariates, showed that the patients with LCS had lower absolute maximal fatty acid oxidation (MFO), relative MFO/fat free mass (FFM), absolute carbohydrates oxidation (CHox), relative CHox/FFM, and oxygen uptake (V˙˙O2) at maximum fat oxidation (g min-1) than the healthy controls (P < 0.05). Moderation analysis indicated that muscle power output significantly influenced the relationship between LCS and reduced peak fat oxidation (interaction β = -0.105 [95% confidence interval -0.174; -0.036]; P = 0.026). Therefore, when muscle power output was below 388 W, the effect of the LCS on MFO was significant (62% in our study sample P = 0.010). These findings suggest compromised mitochondrial bioenergetics and muscle function, represented by lower peak fat oxidation rates, in the patients with LCS compared with the healthy controls.

CONCLUSION

The patients with LCS had lower peak fat oxidation during exercise compared with the healthy controls, potentially indicating impairment in skeletal muscle function. The relationship between peak fat oxidation and LCS appears to be mediated predominantly by muscle power output. Additional research should continue investigating LCS pathogenesis and the functional role of mitochondria.

The efficacy of a home-use metabolic device (Lumen) in response to a short-term low and high carbohydrate diet in healthy volunteers

BACKGROUND

Based on stoichiometric assumptions, and real-time assessment of expired carbon dioxide (%CO2) and flow rate, the Lumen device provides potential for consumers/athletes to monitor metabolic responses to dietary programs outside of laboratory conditions. However, there is a paucity of research exploring device efficacy. This study aimed to evaluate Lumen device response to: i) a high-carbohydrate meal under laboratory conditions, and ii) a short-term low- or high-carbohydrate diet in healthy volunteers.

METHODS

Following institutional ethical approval, 12 healthy volunteers (age: 36 ± 4 yrs; body mass: 72.1 ± 3.6 kg; height: 1.71 ± 0.02 m) performed Lumen breath and Douglas bag expired air measures under fasted laboratory conditions and at 30 and 60 min after a high-carbohydrate (2 g·kg-1) meal, along with capilliarized blood glucose assessment. Data were analyzed using a one-way ANOVA, with ordinary least squares regression used to assess the model between Lumen expired carbon dioxide percentage (L%CO2) and respiratory exchange ratio (RER). In a separate phase, 27 recreationally active adults (age: 42 ± 2 yrs; body mass: 71.9 ± 1.9 kg; height: 1.72 ± 0.02 m) completed a 7-day low- (~20% of energy intake [EI]; LOW) or high-carbohydrate diet (~60% of EI; HIGH) in a randomized, cross-over design under free-living conditions. L%CO2 and derived Lumen Index (LI) were recorded daily across morning (fasted and post-breakfast) and evening (pre/post meal, pre-bed) periods. Repeated measures ANOVA were employed for main analyses, with Bonferroni post-hoc assessment applied (P ≤ 0.05).

RESULTS

Following the carbohydrate test-meal, L%CO2 increased from 4.49 ± 0.05% to 4.80 ± 0.06% by 30 min, remaining elevated at 4.76 ± 0.06% by 60 min post-feeding (P < 0.001, ηp2 = 0.74). Similarly, RER increased by 18.1% from 0.77 ± 0.03 to 0.91 ± 0.02 by 30 min post-meal (P = 0.002). When considering peak data, regression analysis demonstrated a significant model effect between RER and L%CO2 (F = 5.62, P = 0.03, R2 = 0.20). Following main dietary interventions, no significant interactions (diet × day) were found. However, main diet effects were evident across all time-points assessed, highlighting significant differences for both L%CO2 and LI between LOW and HIGH conditions (P < 0.003). For L%CO2, this was particularly noted under fasted (4.35 ± 0.07 vs. 4.46 ± 0.06%, P = 0.001), pre-evening meal (4.35 ± 0.07 vs. 4.50 ± 0.06%, P < 0.001), and pre-bed time-points (4.51 ± 0.08 vs. 4.61 ± 0.06%, P = 0.005).

CONCLUSION

Our findings demonstrated that a portable, home-use metabolic device (Lumen) detected significantly increased expired %CO2 in response to a high-carbohydrate meal, and may be useful in tracking mean weekly changes to acute dietary carbohydrate modifications. Additional research is warranted to further determine the practical and clinical efficacy of the Lumen device in applied compared to laboratory settings.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 1: Foundational principles and theories of regulation

This contribution is the first of a four-part, historical series encompassing foundational principles, mechanistic hypotheses and supported facts concerning human thermoregulation during athletic and occupational pursuits, as understood 100 years ago and now. Herein, the emphasis is upon the physical and physiological principles underlying thermoregulation, the goal of which is thermal homeostasis (homeothermy). As one of many homeostatic processes affected by exercise, thermoregulation shares, and competes for, physiological resources. The impact of that sharing is revealed through the physiological measurements that we take (Part 2), in the physiological responses to the thermal stresses to which we are exposed (Part 3) and in the adaptations that increase our tolerance to those stresses (Part 4). Exercising muscles impose our most-powerful heat stress, and the physiological avenues for redistributing heat, and for balancing heat exchange with the environment, must adhere to the laws of physics. The first principles of internal and external heat exchange were established before 1900, yet their full significance is not always recognised. Those physiological processes are governed by a thermoregulatory centre, which employs feedback and feedforward control, and which functions as far more than a thermostat with a set-point, as once was thought. The hypothalamus, today established firmly as the neural seat of thermoregulation, does not regulate deep-body temperature alone, but an integrated temperature to which thermoreceptors from all over the body contribute, including the skin and probably the muscles. No work factor needs to be invoked to explain how body temperature is stabilised during exercise.

Current definitions of the breathing cycle in alveolar breath-by-breath gas exchange analysis

Identification of the breathing cycle forms the basis of any breath-by-breath gas exchange analysis. Classically, the breathing cycle is defined as the time interval between the beginning of two consecutive inspiration phases. Based on this definition, several research groups have developed algorithms designed to estimate the volume and rate of gas transferred across the alveolar membrane ("alveolar gas exchange"); however, most algorithms require measurement of lung volume at the beginning of the ith breath (VLi-1; i.e., the end-expiratory lung volume of the preceding ith breath). The main limitation of these algorithms is that direct measurement of VLi-1 is challenging and often unavailable. Two solutions avoid the requirement to measure VLi-1 by redefining the breathing cycle. One method defines the breathing cycle as the time between two equal fractional concentrations of lung expired oxygen (Fo2) (or carbon dioxide; Fco2), typically in the alveolar phase, whereas the other uses the time between equal values of the Fo2/Fn2 (or Fco2/Fn2) ratios [i.e., the ratio of fractional concentrations of lung expired O2 (or CO2) and nitrogen (N2)]. Thus, these methods identify the breathing cycle by analyzing the gas fraction traces rather than the gas flow signal. In this review, we define the traditional approach and two alternative definitions of the human breathing cycle and present the rationale for redefining this term. We also explore the strengths and limitations of the available approaches and provide implications for future studies.

Limitations in evaluating COVID-19 protective face masks using open circuit spirometry systems: respiratory measurement mask introduces bias in breathing pressure and perceived respiratory effort

Objective.In response to the COVID-19 pandemic and the resulting widespread use of protective face masks, studies have been and are being conducted to investigate potential side effects of wearing masks on the performance and physiological parameters of wearers. The purpose of the present study is to determine whether and to what extent the use of a respiratory measurement (RM) mask-which is normally used during open-circuit spirometry-influences the results of these types of studies.Approach.34 subjects were involved in this intra-subject study with a cross-over design. Four different protective face masks, Community Mask, medical Mouth-Nose-Protection Mask, Filtering Face Piece Mask Class 2 (FFP2), and FFP2 with exhalation valve (FFP2ex), were tested at rest and during deep breathing by using or not using a RM mask (RM versus noRM). Breathing pressure inside the protective face masks was measured during inhalation and exhalation, and subjects rated breathing effort using an 11-stage Borg scale.Main results.The use of an additional RM mask-worn over the protective face masks-significantly increased inspiratory pressures under all mask conditions. The respiratory pressure rises to a level that substantially distorts the results. Expiratory pressure was also significantly increased except for the FFP2ex mask condition. The perceived respiratory effort was significantly increased by 1.0 to 2.8 steps on the Borgs scale for all mask conditions compared with noRM.Significance.We strongly recommend avoiding the use of RM masks for evaluating the effects of protective face masks on human physiology and subjective perception.

Resting and exercise metabolic characteristics in obese children with insulin resistance

Purpose: This study aimed to explore the characteristics of resting energy expenditure (REE) and lipid metabolism during incremental load exercise in obese children and adolescents with insulin resistance (IR) to provide evidence for exercise intervention in obese children and adolescents with IR.

Method: From July 2019 to August 2021, 195 obese children and adolescents aged 13–17 were recruited through a summer camp. The participants were divided into IR (n = 67) and no-IR (without insulin resistance, n = 128) groups and underwent morphology, blood indicators, body composition, and resting energy consumption gas metabolism tests. Thirty participants each were randomly selected from the IR and no-IR groups to carry out the incremental treadmill test.

Results: Significant metabolic differences in resting and exercise duration were found between the IR and no-IR groups. In the resting state, the resting metabolic equivalents (4.33 ± 0.94 ml/min/kg vs. 3.91 ± 0.73 ml/min/kg, p = 0.001) and REE (2464.03 ± 462.29 kcal/d vs. 2143.88 ± 380.07 kcal/d, p &lt; 0.001) in the IR group were significantly higher than in the no-IR group. During exercise, the absolute maximal fat oxidation (0.33 ± 0.07 g/min vs. 0.36 ± 0.09 g/min, p = 0.002) in the IR group was significantly lower than in the no-IR group; maximal fat oxidation intensity (130.9 ± 8.9 bpm vs. 139.9 ± 7.4 bpm, p = 0.040) was significantly lower in the IR group.

Conclusion: Significant resting and exercise metabolic differences were found between obese IR and no-IR children and adolescents. Obese IR children and adolescents have higher REE and lower maximal fat oxidation intensity than obese no-IR children and adolescents.

Highlighting when animals expend excessive energy for travel using Dynamic Body Acceleration

Travel represents a major cost for many animals so there should be selection pressure for it to be efficient – at minimum cost. However, animals sometimes exceed minimum travel costs for reasons that must be correspondingly important. We use Dynamic Body Acceleration (DBA), an acceleration-based metric, as a proxy for movement-based power, in tandem with vertical velocity (rate of change in depth) in a shark (Rhincodon typus) to derive the minimum estimated power required to swim at defined vertical velocities. We show how subtraction of measured DBA from the estimated minimum power for any given vertical velocity provides a “proxy for power above minimum” metric (PPA_min), highlighting when these animals travel above minimum power. We suggest that the adoption of this metric across species has value in identifying where and when animals are subject to compelling conditions that lead them to deviate from ostensibly judicious energy expenditure.

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Plots of vertical speed vs DBA in sharks show swimming with minimum power

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DBA values above this minimum indicate higher speeds or increases in drag

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Linked to space use, this can identify regions and times of excess power use

Validity of Estimating the Maximal Oxygen Consumption by Consumer Wearables: A Systematic Review with Meta-analysis and Expert Statement of the INTERLIVE Network

Background

Technological advances have recently made possible the estimation of maximal oxygen consumption (VO_2max) by consumer wearables. However, the validity of such estimations has not been systematically summarized using meta-analytic methods and there are no standards guiding the validation protocols.

Objective

The aim was to (1) quantitatively summarize previous studies investigating the validity of the VO_2max estimated by consumer wearables and (2) provide best-practice recommendations for future validation studies.

Methods

First, we conducted a systematic review and meta-analysis of studies validating the estimation of VO_2max by wearables. Second, based on the state of knowledge (derived from the systematic review) combined with the expert discussion between the members of the Towards Intelligent Health and Well-Being Network of Physical Activity Assessment (INTERLIVE) consortium, we provided a set of best-practice recommendations for validation protocols.

Results

Fourteen validation studies were included in the systematic review and meta-analysis. Meta-analysis results revealed that wearables using resting condition information in their algorithms significantly overestimated VO_2max (bias 2.17 ml·kg⁻¹·min⁻¹; limits of agreement − 13.07 to 17.41 ml·kg⁻¹·min⁻¹), while devices using exercise-based information in their algorithms showed a lower systematic and random error (bias − 0.09 ml·kg⁻¹·min⁻¹; limits of agreement − 9.92 to 9.74 ml·kg⁻¹·min⁻¹). The INTERLIVE consortium proposed six key domains to be considered for validating wearable devices estimating VO_2max, concerning the following: the target population, reference standard, index measure, testing conditions, data processing, and statistical analysis.

Conclusions

Our meta-analysis suggests that the estimations of VO_2max by wearables that use exercise-based algorithms provide higher accuracy than those based on resting conditions. The exercise-based estimation seems to be optimal for measuring VO_2max at the population level, yet the estimation error at the individual level is large, and, therefore, for sport/clinical purposes these methods still need improvement. The INTERLIVE network hereby provides best-practice recommendations to be used in future protocols to move towards a more accurate, transparent and comparable validation of VO_2max derived from wearables.

PROSPERO ID

CRD42021246192.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40279-021-01639-y.

Telemonitoring Techniques for Lung Volume Measurement: Accuracy, Artifacts and Effort

Telemonitoring becomes more important in pulmonary research. It can be used to decrease the pressure on the health care system, to lower the costs of health care and to increase quality of life of patients. Previous studies show contradictory results regarding the effectiveness of telemonitoring. According to multiple researchers, inefficiency can be a result of poor study design, low data quality and usability issues. To counteract these issues, this review proves for an in-depth explanation of four (potential) telemonitoring systems in terms of work principle, accuracy, disturbing factors and usability. The evaluated systems are portable spirometry/breath-by-breath analyzers, respiratory inductance and magnetic plethysmography and electrical impedance tomography. These insights can be used to select the optimal technique for a specific purpose in future studies.

Effects of prosthetic feet on metabolic energy expenditure in people with transtibial amputation: a systematic review and meta-analysis

OBJECTIVE

To assess the effects of different prosthetic feet on energy costs associated with walking and running in people with transtibial amputation.

LITERATURE SURVEY

The Pubmed, CINAHL, and Web-of-Science bibliographic databases were searched for original research published through June 30, 2018. References from identified articles were also reviewed.

METHODOLOGY

Two reviewers screened titles, abstracts, and articles for pertinent studies. Details were extracted with a standardized template. Risk of bias was assessed using domain-based methods. Prosthetic feet were grouped into categories, and compared according to energy costs associated with walking or running over various terrain conditions. Meta-analyses were conducted when data quantity and homogeneity permitted. Evidence statements were formed when results were consistent or undisputed.

SYNTHESIS

15 studies were included. Participants (n = 144) were predominantly male (88.2%), had unilateral amputation (95.8%) from non-dysvascular causes (87.5%), and were classified as unlimited community ambulators or active adults (56.9%). Participants were often young, but varied in age (mean age 24.8-66.6 years). Available evidence indicates that feet with powered dorsiflexion reduce energy costs relative to dynamic response feet in unlimited community ambulators or active adults when walking on level or declined surfaces. Dynamic response feet do not significantly reduce energy costs compared to energy storing, flexible keel, or solid ankle feet when walking on level terrain. Running feet do not reduce energy costs relative to dynamic response in active adults when running. Select feet may reduce energy costs under specific conditions, but additional research is needed to confirm preliminary results.

CONCLUSIONS

The overall body of evidence is based on small samples, comprised mostly of participants who may not well represent the population of prosthesis users, and test conditions that may not well reflect how prostheses are used in daily life. However, evidence suggests energy costs are affected by prosthetic foot type, but only under select conditions. This article is protected by copyright. All rights reserved.

Is a verification phase useful for confirming maximal oxygen uptake in apparently healthy adults? A systematic review and meta-analysis

BACKGROUND

The 'verification phase' has emerged as a supplementary procedure to traditional maximal oxygen uptake (VO2max) criteria to confirm that the highest possible VO2 has been attained during a cardiopulmonary exercise test (CPET).

OBJECTIVE

To compare the highest VO2 responses observed in different verification phase procedures with their preceding CPET for confirmation that VO2max was likely attained.

METHODS

MEDLINE (accessed through PubMed), Web of Science, SPORTDiscus, and Cochrane (accessed through Wiley) were searched for relevant studies that involved apparently healthy adults, VO2max determination by indirect calorimetry, and a CPET on a cycle ergometer or treadmill that incorporated an appended verification phase. RevMan 5.3 software was used to analyze the pooled effect of the CPET and verification phase on the highest mean VO2. Meta-analysis effect size calculations incorporated random-effects assumptions due to the diversity of experimental protocols employed. I2 was calculated to determine the heterogeneity of VO2 responses, and a funnel plot was used to check the risk of bias, within the mean VO2 responses from the primary studies. Subgroup analyses were used to test the moderator effects of sex, cardiorespiratory fitness, exercise modality, CPET protocol, and verification phase protocol.

RESULTS

Eighty studies were included in the systematic review (total sample of 1,680 participants; 473 women; age 19-68 yr.; VO2max 3.3 ± 1.4 L/min or 46.9 ± 12.1 mL·kg-1·min-1). The highest mean VO2 values attained in the CPET and verification phase were similar in the 54 studies that were meta-analyzed (mean difference = 0.03 [95% CI = -0.01 to 0.06] L/min, P = 0.15). Furthermore, the difference between the CPET and verification phase was not affected by any of the potential moderators such as verification phase intensity (P = 0.11), type of recovery utilized (P = 0.36), VO2max verification criterion adoption (P = 0.29), same or alternate day verification procedure (P = 0.21), verification-phase duration (P = 0.35), or even according to sex, cardiorespiratory fitness level, exercise modality, and CPET protocol (P = 0.18 to P = 0.71). The funnel plot indicated that there was no significant publication bias.

CONCLUSIONS

The verification phase seems a robust procedure to confirm that the highest possible VO2 has been attained during a ramp or continuous step-incremented CPET. However, given the high concordance between the highest mean VO2 achieved in the CPET and verification phase, findings from the current study would question its necessity in all testing circumstances.

PROSPERO REGISTRATION ID

CRD42019123540.

Physiological interactions with personal-protective clothing, physically demanding work and global warming: An Asia-Pacific perspective

The Asia-Pacific contains over half of the world's population, 21 countries have a Gross Domestic Product <25% of the world's largest economy, many countries have tropical climates and all suffer the impact of global warming. That 'perfect storm' exacerbates the risk of occupational heat illness, yet first responders must perform physically demanding work wearing personal-protective clothing and equipment. Unfortunately, the Eurocentric emphasis of past research has sometimes reduced its applicability to other ethnic groups. To redress that imbalance, relevant contemporary research has been reviewed, to which has been added information applicable to people of Asian, Melanesian and Polynesian ancestry. An epidemiological triad is used to identify the causal agents and host factors of work intolerance within hot-humid climates, commencing with the size dependency of resting metabolism and heat production accompanying load carriage, followed by a progression from the impact of single-layered clothing through to encapsulating ensembles. A morphological hypothesis is presented to account for inter-individual differences in heat production and heat loss, which seems to explain apparent ethnic- and gender-related differences in thermoregulation, at least within thermally compensable states. The mechanisms underlying work intolerance, cardiovascular insufficiency and heat illness are reviewed, along with epidemiological data from the Asia-Pacific. Finally, evidence-based preventative and treatment strategies are presented and updated concerning moisture-management fabrics and barriers, dehydration, pre- and post-exercise cooling, and heat adaptation. An extensive reference list is provided, with >25 recommendations enabling physiologists, occupational health specialists, policy makers, purchasing officers and manufacturers to rapidly extract interpretative outcomes pertinent to the Asia-Pacific.

Magnitude and duration of excess of post-exercise oxygen consumption between high-intensity interval and moderate-intensity continuous exercise: A systematic review

The present systematic review examined the effect of exercise intensity (high-intensity interval exercise [HIIE] vs. moderate-intensity continuous exercise [MICE] vs. sprint interval exercise [SIE]) on excess post-exercise oxygen consumption (EPOC). Twenty-two studies were included in the final evaluation. The retrieved investigations were split into studies that analysed short-duration (until 3 h) and long-duration (more than 3 h) EPOC. Studies that subtracted the baseline energy expenditure (EE) were analysed separately from those that did not. Most short-duration evaluations that subtracted baseline EE reported higher EPOC for HIIE (average of ~136 kJ) compared with MICE (average of ~101 kJ) and higher values for SIE (average of ~241 kJ) compared with MICE (average of ~151 kJ). The long-duration evaluations resulted in greater EPOC for HIIE (average of ~289 kJ) compared with MICE (average of ~159 kJ), while no studies comparing SIE versus MICE provided appropriate values. EE from EPOC seems to be greater following HIIE and SIE compared with MICE, and long-duration evaluations seem to present higher values than short-duration evaluations. Additionally, more standardized methodologies are needed in order to determine the effective EPOC time following these protocols.

How Patients With Heart Failure Perform Daily Life Activities

Background:

Cardiopulmonary exercise test and 6-minute walking test are frequently used tools to evaluate physical performance in heart failure (HF), but they do neither represent activities of daily living (ADLs) nor fully reproduce patients’ symptoms. We assessed differences in task oxygen uptake, both as absolute value and as percentage of peak oxygen consumption (peakVO 2 ), ventilation efficiency (VE/VCO 2 ratio), and dyspnea intensity (Borg scale) in HF and healthy subjects during standard ADLs and other common physical actions.

Methods:

Healthy and HF subjects (ejection fraction <45%, stable conditions) underwent cardiopulmonary exercise test. All of them, carrying a wearable metabolic cart, performed a 6-minute walking test, two 4-minute treadmill exercises (at 2 and 3 km/h), and ADLs: ADL1 (getting dressed), ADL2 (folding 8 towels), ADL3 (putting away 6 bottles), ADL4 (making a bed), ADL5 (sweeping the floor for 4 minutes), ADL6 (climbing 1 flight of stairs carrying a load).

Results:

Sixty patients with HF (age 65.2±12.1 years; ejection fraction 30.4±6.7%, peakVO 2 14.2±4.0 mL/[min·kg]) and 40 healthy volunteers (58.9±8.2 years, peakVO 2 28.1±7.4 mL/[min·kg]) were enrolled. For each exercise, patients showed higher VE/VCO 2 ratio, percentage of peakVO 2 , and Borg scale value than controls, while absolute values of task oxygen uptake and exercise duration were lower and higher, respectively, in all activities, except for treadmill (fixed execution time and intensity). Differently from Borg Scale data, metabolic values and exercise time length changed in parallel with HF severity, except for ADL duration in very short (ADL3) and composite (ADL1) activities. Borg scale values correlated with percentage of peakVO 2 .

Conclusions:

During ADLs, patients self-regulated activities in parallel with HF severity by decreasing intensity (VO 2 ) and prolonging the effort.

Reliability and validity of the COSMED K5 portable metabolic system during walking

PURPOSE

Portable methods for assessing energy expenditure outside the laboratory and clinical environments are becoming more widely used. As such, it is important to understand the accuracy of such devices. Therefore, the purpose was to determine the reliability and validity of the COSMED K5 portable metabolic system.

METHODS

Reliability and validity were assessed in 27 adults (age: 27 ± 5 years; n = 15 women) using a walking protocol. The protocol consisted of a 5-min walk/2-min rest cycle starting at 1.5 mph and increasing in 0.5-mph increments to 4.0 mph. During visit one, participants wore the K5 to assess oxygen consumption ([Formula: see text]O₂), carbon dioxide production ([Formula: see text]CO₂), and other metabolic variables. Two to seven days later, the protocol was repeated twice with the COSMED K5 and K4b² systems in a randomized, counterbalanced order.

RESULTS

Intraclass correlation coefficients (ICC) revealed that the K5 reliably measured [Formula: see text]O₂ (ICC 0.64-0.85) and [Formula: see text]CO₂ across all walking speeds (ICC 0.50-0.80), with stronger reliability at faster walking speeds compared with slower speeds. Moderate-to-strong relationships were observed for measured gases between the K5 and K4b². Specifically, [Formula: see text]O₂ exhibited a moderately high-to-high relationship between devices (r = 0.72-0.82), and a similarly moderately high-to-high relationship was observed for [Formula: see text]CO₂ (r = 0.68-0.82). While there were no differences in [Formula: see text]O₂ measured between devices (p ≥ 0.10), the K5 provided lower [Formula: see text]CO₂ readings than the K4b² during the 3.0, 3.5, and 4.0 mph walking speeds (p ≤ 0.02).

CONCLUSIONS

The K5 provided reliable and valid measures of metabolic variables, with greater reliability and validity at faster walking speeds.

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.

Accuracy of the Cosmed K5 portable calorimeter

PURPOSE

The purpose of this study was to assess the accuracy of the Cosmed K5 portable metabolic system dynamic mixing chamber (MC) and breath-by-breath (BxB) modes against the criterion Douglas bag (DB) method.

METHODS

Fifteen participants (mean age±SD, 30.6±7.4 yrs) had their metabolic variables measured at rest and during cycling at 50, 100, 150, 200, and 250W. During each stage, participants were connected to the first respiratory gas collection method (randomized) for the first four minutes to reach steady state, followed by 3-min (or 5-min for DB) collection periods for the resting condition, and 2-min collection periods for all cycling intensities. Collection periods for the second and third methods were preceded by a washout of 1-3 min. Repeated measures ANOVAs were used to compare metabolic variables measured by each method, for seated rest and each cycling work rate.

RESULTS

For ventilation (VE) and oxygen uptake (VO2), the K5 MC and BxB modes were within 2.1 l/min (VE) and 0.08 l/min (VO2) of the DB (p≥0.05). Compared to DB values, carbon dioxide production (VCO2) was significantly underestimated by the K5 BxB mode at work rates ≥150W by 0.12-0.31 l/min (p<0.05). K5 MC and BxB respiratory exchange ratio values were significantly lower than DB at cycling work rates ≥100W by 0.03-0.08 (p<0.05).

CONCLUSION

Compared to the DB method, the K5 MC and BxB modes are acceptable for measuring VE and VO2 across a wide range of cycling intensities. Both K5 modes provided comparable values to each other.

The heart rate method for estimating oxygen uptake: analyses of reproducibility using a range of heart rates from commuter walking

Background

The heart rate method, based on the linear relation between heart rate and oxygen uptake, is potentially valuable to monitor intensity levels of physical activities. However, this depends not least on its reproducibility under standard conditions. This study aims, therefore, to evaluate the reproducibility of the heart rate method in the laboratory using a range of heart rates associated with walking commuting.

Methods

On two different days, heart rate and oxygen uptake measurements were made during three submaximal (model 1) and a maximal exercise intensity (model 2) on a cycle ergometer in the laboratory. 14 habitual walking commuters participated. The reproducibility, based on the regression equations from test and retest and using three levels of heart rate from the walking commuting, was analyzed. Differences between the two models were also analyzed.

Results

For both models, there were no significant differences between test and retest in the constituents of the regression equations (y intercept, slope and r value). Neither were there any systematic differences in estimated absolute levels of VO₂ between test and retest for either model. However, some rather large individual differences were seen in both models. Furthermore, no significant differences were seen between the two models in slopes, intercepts and r values of the regression equations or in the estimated VO₂.

Conclusion

The heart rate method shows good reproducibility on the group level in estimating oxygen consumption from heart rate–oxygen uptake relations in the laboratory, and based on three levels of heart rate which are representative for walking commuting.

The heart rate method for estimating oxygen uptake: Analyses of reproducibility using a range of heart rates from cycle commuting

Monitoring aerobic exercise intensities of free-living physical activities is valuable for purposes such as education and research. The heart rate (HR) method, based on the linear relation between HR and oxygen uptake (VO₂), is potentially valuable for this purpose. Three prerequisites are that the method is reproducible, and valid for the specific form of physical activity executed as well as under field conditions. The aim of this study is to evaluate reproducibility of the heart rate method in the laboratory. VO₂ and HR measurements were made on two different occasions during three submaximal (model 1) plus a maximal exercise intensity (model 2) on a cycle ergometer in the laboratory. 19 habitual commuter cyclists (9 males and 10 females), aged 44 ± 3 years, were measured. The reproducibility of the estimated VO₂, based on three levels of HR from commuting cycling and the regression equations from test and retest were analyzed. Differences between the two models were also studied. For both models, there were no significant differences between test and retest in the constituents of the regression equations (y-intercept, slope and r-value). Neither were there any systematic differences in estimated absolute levels of VO₂ between test and retest. The relative differences between test and retest, based on estimations from three different levels of HR, were 0.99 ± 11.0 (n.s.), 2.67 ± 6.48 (n.s.) and 3.57 ± 6.24% (p<0.05) for model 1, and 1.09 ± 10.6, 1.75 ± 6.43 and 2.12 ± 5.92% (all n.s.) for model 2. However, some large individual differences were seen in both models. There were no significant differences between the two models in the slopes, intercepts or r-values of the regression equations or in the estimated levels of VO₂. The heart rate method shows good reproducibility on the group level in estimating oxygen consumption from HR-VO₂ relations in the laboratory, and based on three levels of HR which are representative for cycle commuting. However, on the individual level, some large variations were seen.

Optimizing Maximal Fat Oxidation Assessment by a Treadmill-Based Graded Exercise Protocol: When Should the Test End?

Maximal fat oxidation during exercise (MFO) and the exercise intensity eliciting MFO (Fatmax) are considered important factors related to metabolic health and performance. Numerous MFO and Fatmax data collection and analysis approaches have been applied, which may have influenced their estimation during an incremental graded exercise protocol. Despite the heterogeneity of protocols used, all studies consistently stopped the MFO and Fatmax test when the respiratory exchange ratio (RER) was 1.0. It remains unknown however whether reaching a RER of 1.0 is required to have an accurate, reliable, and valid measure of MFO and Fatmax. We aimed to investigate the RER at which MFO and Fatmax occurred in sedentary and trained healthy adults. A total of 166 sedentary adults aged between 18 and 65 years participated in the study. MFO and Fatmax were calculated by an incremental graded exercise protocol before and after two exercise-based interventions. Our findings suggest that a graded exercise protocol aiming to determine MFO and Fatmax could end when a RER = 0.93 is reached in sedentary healthy adults, and when a RER = 0.90 is reached in trained adults independently of sex, age, body weight status, or the Fatmax data analysis approach. In conclusion, we suggest reducing the RER from 1.0 to 0.95 to be sure that MFO is reached in outliers. This methodological consideration has important clinical implications, since it would allow to apply smaller workload increments and/or to extend the stage duration to attain the steady state, without increasing the test duration.

Box-Jenkins Transfer Function Modelling for Reliable Determination of VO2 Kinetics in Patients with COPD

Oxygen uptake (VO2) kinetics provide information about the ability to respond to the increased physical load during a constant work rate test (CWRT). Box-Jenkins transfer function (BJ-TF) models can extract kinetic features from the phase II VO2 response during a CWRT, without being affected by unwanted noise contributions (e.g., phase I contribution or measurement noise). CWRT data of 18 COPD patients were used to compare model fits and kinetic feature values between BJ-TF models and three typically applied exponential modelling methods. Autocorrelation tests and normalised root-mean-squared error values (BJ-TF: 2.8 ± 1.3%; exponential methods A, B and C: 10.5 ± 5.8%, 11.3 ± 5.2% and 12.1 ± 7.0%; p < 0.05) showed that BJ-TF models, in contrast to exponential models, could account for the most important noise contributions. This led to more reliable kinetic feature values compared to methods A and B (e.g., mean response time (MRT), BJ-TF: 74 ± 20 s; methods A-B: 100 ± 56 s–88 ± 52 s; p < 0.05). Only exponential modelling method C provided kinetic feature values comparable to BJ-TF features values (e.g., MRT: 75 ± 20 s). Based on theoretical considerations, we recommend using BJ-TF models, rather than exponential models, for reliable determinations of VO2 kinetics.

Assessment of maximal fat oxidation during exercise: A systematic review

Maximal fat oxidation during exercise (MFO) and the exercise intensity eliciting MFO (Fat_max ) are considered biological markers of metabolic health and performance. A wide range of studies have been performed to increase our knowledge about their regulation by exercise and/or nutritional intervention. However, numerous data collection and analysis approaches have been applied, which may have affected the MFO and Fat_max estimation. We aimed to systematically review the available studies describing and/or comparing different data collection and analysis approach factors that could affect MFO and Fat_max estimation in healthy individuals and patients. Two independent researchers performed the search. We included all original studies in which MFO and/or Fat_max were estimated by indirect calorimetry through an incremental graded exercise protocol published from 2002 to 2019. This systematic review provides key information about the factors that could affect MFO and Fat_max estimation: ergometer type, metabolic cart used, warm-up duration and intensity, stage duration and intensities imposed in the graded exercise protocol, time interval selected for data analysis, stoichiometric equation selected to estimate fat oxidation, data analysis approach, time of the day when the test was performed, fasting time/previous meal before the test, and testing days for MFO/Fat_max and maximal oxygen uptake assessment. We suggest that researchers measuring MFO and Fat_max should take into account these key methodological issues that can considerably affect the accuracy, validity, and reliability of the measurement. Likewise, when comparing different studies, it is important to check whether the above-mentioned key methodological issues are similar in such studies to avoid ambiguous and unacceptable comparisons.

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%.

Evaluation of a graded exercise test to determine peak fat oxidation in individuals with low cardiorespiratory fitness

The maximal capacity to utilise fat (peak fat oxidation, PFO) may have implications for health and ultra-endurance performance and is commonly determined by incremental exercise tests employing 3-min stages. However, 3-min stages may be insufficient to attain steady-state gas kinetics, compromising test validity. We assessed whether 4-min stages produce steady-state gas exchange and reliable PFO estimates in adults with peak oxygen consumption < 40 mL·kg−1·min−1. Fifteen participants (9 females) completed a graded test to determine PFO and the intensity at which this occurred (FATMAX). Three short continuous exercise sessions (SCE) were then completed in a randomised order, involving completion of the graded test to the stage (i) preceding, (ii) equal to (SCEequal), or (iii) after the stage at which PFO was previously attained, whereupon participants then continued to cycle for 10 min at that respective intensity. Expired gases were sampled at minutes 3–4, 5–6, 7–8, and 9–10. Individual data showed steady-state gas exchange was achieved within 4 min during SCEequal. Mean fat oxidation rates were not different across time within SCEequal nor compared with the graded test at FATMAX (both p > 0.05). However, the graded test displayed poor surrogate validity (SCEequal, minutes 3–4 vs. 5–6, 7–8, and 9–10) and day-to-day reliability (minutes 3–4, SCEequal vs. graded test) to determine PFO, as evident by correlations (range: 0.47–0.83) and typical errors and 95% limits of agreement (ranges: 0.03–0.05 and ±0.09–0.15 g·min−1, respectively). In conclusion, intraindividual variation in PFO is substantial despite 4-min stages establishing steady-state gas exchange in individuals with low fitness. Individual assessment of PFO may require multiple assessments.

Effects of β-alanine and sodium bicarbonate supplementation on the estimated energy system contribution during high-intensity intermittent exercise

The effects of β-alanine (BA) and sodium bicarbonate (SB) on energy metabolism during work-matched high-intensity exercise and cycling time-trial performance were examined in 71 male cyclists. They were randomised to receive BA + placebo (BA, n = 18), placebo + SB (SB, n = 17), BA + SB (BASB, n = 19), or placebo + placebo (PLA, n = 18). BA was supplemented for 28 days (6.4 g day^-1) and SB (0.3 g kg^-1) ingested 60 min before exercise on the post-supplementation trial. Dextrose and calcium carbonate were placebos for BA and SB, respectively. Before (PRE) and after (POST) supplementation, participants performed a high-intensity intermittent cycling test (HICT-110%) consisting of four 60-s bouts at 110% of their maximal power output (60-s rest between bouts). The estimated contribution of the energy systems was calculated for each bout in 39 of the participants (BA: n = 9; SB: n = 10; BASB: n = 10, PLA: n = 10). Ten minutes after HICT-110%, cycling performance was determined in a 30-kJ time-trial test in all participants. Both groups receiving SB increased estimated glycolytic contribution in the overall HICT-110%, which approached significance (SB: + 23%, p = 0.068 vs. PRE; BASB: + 18%, p = 0.059 vs. PRE). No effects of supplementation were observed for the estimated oxidative and ATP-PCr systems. Time to complete 30 kJ was not significantly changed by any of the treatments, although a trend toward significance was shown in the BASB group (p = 0.06). We conclude that SB, but not BA, increases the estimated glycolytic contribution to high-intensity intermittent exercise when total work done is controlled and that BA and SB, either alone or in combination, do not improve short-duration cycling time-trial performance.

Innovations in energy expenditure assessment

PURPOSE OF REVIEW

Optimal nutritional therapy has been associated with better clinical outcomes and requires providing energy as closed as possible to measured energy expenditure. We reviewed the current innovations in energy expenditure assessment in humans, focusing on indirect calorimetry and other new alternative methods.

RECENT FINDINGS

Although considered the reference method to measure energy expenditure, the use of indirect calorimetry is currently limited by the lack of an adequate device. However, recent technical developments may allow a broader use of indirect calorimetry for in-patients and out-patients. An ongoing international academic initiative to develop a new indirect calorimeter aimed to provide innovative and affordable technical solutions for many of the current limitations of indirect calorimetry. New alternative methods to indirect calorimetry, including CO2 measurements in mechanically ventilated patients, isotopic approaches and accelerometry-based fitness equipments, show promises but have been either poorly studied and/or are not accurate compared to indirect calorimetry. Therefore, to date, energy expenditure measured by indirect calorimetry remains the gold standard to guide nutritional therapy.

SUMMARY

Some new innovative methods are demonstrating promises in energy expenditure assessment, but still need to be validated. There is an ongoing need for easy-to-use, accurate and affordable indirect calorimeter for daily use in in-patients and out-patients.

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.