Validity and Reliability of the Portable Metabolic Analyzer PNOE to assess cardiometabolic capacity during walking exercise

doi:10.21203/rs.3.rs-3036317/v1

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Validity and Reliability of the Portable Metabolic Analyzer PNOE to assess cardiometabolic capacity during walking exercise

https://doi.org/10.21203/rs.3.rs-3036317/v1

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Background

The accuracy of measurement of cardiometabolic functions of individuals is crucial. The objective of this study was to compare the validity and reliability of the PNOE in measuring cardiometabolic outcomes in the expired air of healthy individuals, during a treadmill walking protocol.

Methods

A total of 21 subjects (15 male, 6 females) aged 22.76 ± 3.85 years took part in this study. Oxygen consumption (VO₂), carbon dioxide production (VCO₂), respiratory exchange ratio (RER), metabolic equivalent (MET), ventilatory threshold (VT), energy expenditure (EE) was measured by PNOE and COSMED K5 portable systems during a four-stage incremental protocol on a treadmill. Test-retest reliability was tested on separate days with trail repetition. Validity was evaluated by Bland-Altman plots, intraclass correlation coefficients (ICC) and mean percentage difference.

Results

ICC found in VCO₂ is in the good range (0.75–0.90). ICC of RER from level 1–3 and VT of level 2–4 fall in good to excellent reliability. No specific pattern seen on VO₂, VCO₂ and EE on the changes of CV upon speeds variations. Pearson’s correlation coefficient was moderately high (r = 0.60–0.79) between metabolic variables measured by PNOE and K5 systems. All subjects, except few more cases in VT, lie within the upper and lower 95% confidence intervals acceptance range of the Bland Altman plots.

Conclusion

PNOE system is a valid and reliable measure for cardiometabolic outcomes and is as comparable to COSMED K5 system.

Cardiometabolic functions can be assessed and evaluated by metabolic carts (1). Metabolic analysis is a powerful test for early detection of predisposing factors for major chronic cardiometabolic diseases. According to the American Heart Association, it provides a powerful predictor of longevity, and for decades, it has been the gold standard for personalizing nutrition, training, and recovery programs(2). For instance, oxygen consumption (VO₂), carbon dioxide production (VCO₂), energy expenditure (EE), ventilatory threshold (VT), respiratory exchange ratio (RER) and metabolic equivalent (MET) are common measures used to assess cardiometabolic functions, determine fitness and are useful in clinical settings. In this way, these variables may become readily available to therapists and sports scientists to monitor cardiometabolic fitness, in the long-term and design exercise regimes for health and performance purposes(3).

The proposed cardiometabolic outcomes can be measured either by metabolic carts or portable devices. The accuracy of measurement ensured a true reflection of cardiometabolic functions of individuals. The advancement of technology has facilitated the transition from laboratory to on-field measurements by introducing a variety of portable systems which enable a measurement of metabolic costs (4). The measurement not only confined to the testing done in laboratory, since the process can be cumbersome, labour intensive and expensive (5). Potentially, these limitations prevent the widespread application of the assessment and highlight the necessity to design valid and reliable cardiometabolic measurement units which will be portable and practical to evaluate different sports performance in a cost-effective manner.

Until recently, several portable carts have been developed and made available in the market. For instance, COSMED (K5 version)(6), the CORTEX X1 and Meta Max (1) and Oxycon (7). Among these units, the latest portable metabolic system launched by COSMED (COSMED K5), culminating in significant hardware, firmware and software improvements from the previous model (COSMED K4b2). In the previous generation, the K4b² was a reliable and valid system for metabolic gas measurement (8). COSMED K5 is a single unit device (174×64×114 mm dimensions and of 900 g weight) combining breath-by-breath technology from the COSMED K4b² and the dynamic mixing chamber system used in the COSMED Fitmate series. Such new technology is supported by a series of significant hardware and software updates that aim to improve the reliability of its’ measures. The COSMED K5 unit has also been found to be reliable and valid when compared to a metabolic simulator (9) and Douglas bags (10) during cycling exercise, indicating that it performs comparably to the gold standard (Douglas bag). In spite of that, the accuracy was questionable since metabolic simulators exclude biological variation, where expired gas concentrations, temperature, and humidity may change throughout the test.

Of note, an extended review article conducted by Macfarlane et al. (2007) has highlighted the validity and reliability of current high-technology portable metabolic systems are not widely established and very few independent studies have been published(1). Essentially, portable metabolic carts like (COSMED K5) allows the measurement of the same variables as stationary metabolic carts, it has been suggested that the accuracy was low (11). In view of that, there were evidence that portable devices tend to be less accurate and there is still need for developing small, portable, albeit, valid and reliable metabolic analysers, to quantify cardiometabolic variables(12). PNO\(\stackrel{-}{\text{E}}\) is a newly developed portable metabolic device that was designed to measure cardiometabolic outcomes under laboratory and field conditions. The device features an electrochemical fuel cell sensor for oxygen measurement, a non-dispersive infrared sensor for carbon dioxide measurement, and a proprietary hot film anemometer sensor for flow sensor measurement. Together the PNO\(\stackrel{-}{\text{E}}\) device can be operated by a breath-by-breath mode which continuously measures volume and determines expired gas concentrations simultaneously. The advantage of this technology as it does not contain moving parts and is considered to be a stable construction to use PNOĒ. There has been one independent study conducted to measure the validity and reliability of the PNO\(\stackrel{-}{\text{E}}\) when compared to a previously validated stationary metabolic cart (COSMED QUARK-CPET). Breath by breath gaseous exchange was measured by both devices during a four-stage incremental protocol on a cycle ergometer. It was suggested that strong correlation and no significant differences found in cardiorespiratory outcomes (VO₂, VCO₂ or respiratory quotient) between the two devices. However, to the best of our knowledge, there has not been study evaluating the cardiometabolic outcomes (VO₂, VCO₂, VT, MET, EE, RER) of PNOĒ when compared to a portable metabolic cart (COSMED-K5).

Despite the previous mentioned study was the only independent study comparing PNOĒ with traditional analyser, it can be inconclusive making it difficult to consolidate the reliability and validity and failed to generalise to other metabolic outcomes. There was a niche to assess whether the PNOĒ and portable COSMED K5 device can be used interchangeably. An incremental treadmill walking protocol will be chosen to ensure the stability of both devices work with standardized speed and incremental loads. Thus, it was ensured that a constant load was applied at all times. It is believed that the workload performed on the treadmill is more natural and familiar to the subject. To address the niche, the objectives of this study is to address the validity and reliability of the PNOĒ (ENDO Medical, Palo Alto, CA), in measuring cardiometabolic outcomes (VO₂, VCO₂, RER, VT, MET, EE) in the expired air of healthy individuals, during a treadmill walking protocol. It is hypothesized that the accuracy and reliability of PNOĒ is comparable to the portable metabolic cart (COSMED-K5) in measuring cardiometabolic outcomes with a treadmill walking incremental protocol.

Participants

Twenty-one young healthy and active adults (15men, 6 women), were recruited to participate in this cross-sectional study. The inclusion criteria were adults who were clinically healthy, free of cardiorespiratory distress without using medication and between 20–35 years of age. The exclusion criteria included subjects who had cardiorespiratory, neurological pathology and/or had an orthopaedic fracture or any surgical intervention done to the lower extremities in the six months prior the study. All participants were informed of the study risks by an investigator, and signed an informed consent form prior data collection. The study was approved the Hong Kong Polytechnic University ethical committee for research involving human participants in accordance with the standards of the Helsinki Declaration (HSEARS20220318009).

Study design and procedures

Participants were required to perform an interview for screening and familiarization before signing off an informed consent to the study. Participants were then administered the International Physical Activity Questionnaire to assess their physical activity levels for descriptive purposes(13). All participants performed and completed a familiarization session a week before the study. The usage of mouthpiece and Hans Rudolph valve were practised. All participants receive feedback and instruction during the trials. Participants were required to attend two sessions, separated by 2–7 days, to the Gait and Motion Analysis laboratory at the Polytechnic University. Laboratory temperature and humidity were measured for each visit. In the first visit, the resting heart rate (HR), blood pressure (BP), body mass (kg) and height (cm) were measured. Participants were then asked to complete a 28-minutes walking protocol on a treadmill while wearing the portable cardiometabolic device. The protocol started with 5 minutes walking at 1.7 mph x 10% inclination after which 2 minutes of rest was given. Participants were asked to step on the treadmill during the walking phase while stepping out to rest during the rest phase. Such 5 minutes- 2 minutes rest cycle repeated as the walking speed reached 4.2 x 16%(14). Throughout the procedure, the breath-by-breath data were collected simultaneously. Participants were required to perform the walking protocol twice while wearing the two proposed devices in a randomized, counterbalanced order.

Instruments

The PNOĒ device operates on lithium batteries and weighs approximately 800 g. The device is composed of a single housing (120 × 110 × 45mm, height, width, length, respectively), fastened to a shoulder harness and carried by the participant throughout exercise. Participant wears a standard Hans Rudolph mask with mouthpiece and breathes through a flow sensor (Hans Rudolph Inc., Kansas City, MO, USA).

In contrast, the COSMED K5 (firmware version 1.1) is also a portable metabolic cart designed to be worn on an anatomical harness. The device features a Galvanic fuel cell O2 sensor and digital infrared CO2 sensor. The system transmits data via Bluetooth telemetry to the analysis software for visualization with provide real time measurement. Features that facilitate on field use of the K5 include GPS and an altimeter. It allows measures of gaseous exchange on VO₂, VCO2, RER, VT, MET and EE.

Validity assessment

The validation protocol was performed at an incremental rate in reference to the standardized Bruce protocol (15). Each stage lasted for five minutes, starting from 1.7km/h inclines at 10%, 2.5km/h inclines at 12%, 3.4km/h x 14% and completed once reached 4.2mph x 16% within walking speed as will be estimated by the are visual inspection of the heart rate response and the Borg Scale score. The intensity levels will be classified to reflect relatively light to moderate cardiometabolic demands, according to the American College of Sports Medicine(16). Cardiometabolic variables of VO₂, VCO₂, RER, VT, MET and EE were recorded using values from the final minute of each five-min stage. Measurements will be made in-line (sequential gas sampling) with the (COSMED – K5) and PNOĒ (ENDO Medical, Palo Alto, CA) while COSMED-K5 system acts as a reference standard.

Reliability assessment

The reliability of the PNOĒ device will be assessed by measuring cardiometabolic variables on the selected subjects with the same walking protocol, on separate days. The same experimental setup will be followed in both visits. The test will be performed at the same time of day and subjects are instructed to wear similar clothing and the same walking shoes for the two trials.

Statistical analysis

All results were normally distributed and are presented as mean values and standard deviation (mean ± SD). Statistical significance was accepted at the 5% level (P ≤ 0.05). Reliability was assessed by calculating the coefficient of variation (CV). Test-retest reliability of the PNOĒ system was assessed through a two-way random-effects (consistency) analysis of variance (ANOVA) model and reported as Intraclass coefficients to define agreement between the two metabolic carts. A 95% confidence interval (CI) was used to describe the variety in the ICC. An ICC of 0.50–0.75 indicated moderate reliability, good reliability was identified as an ICC = 0.75–0.90, with excellent reliability considered at an ICC > 0.90(17). Validity analysis of the PNOĒ system was assessed by comparing the data collected by the PNOĒ and COSMED K5. Student’s paired samples t tests were used to compare differences between the variables measured by PNOĒ and COSMED K5. To identify bias, an absolute mean difference was calculated. Pearson’s correlation coefficients (r) were used to evaluate the relationship between the devices. A moderate relationship was identified as r = 0.40–050, moderately high as r = 0.60–0.79, and high was considered r ≥ 0. 80(18). Bland Altman plots of the differences between PNOĒ and COSMED K5 were plotted against the average of the two measures(19). All analyses were performed using the Statistical Package for the Social Sciences (SPSS), Version 23.0, for Windows.

Fifteen men and six women successfully completed the reliability and validity tests. The descriptive statistics for the study sample are presented in Table 1. The mean age of the participants was 21.76 ± 3.85 yrs. Their average height was 169.38 ± 9.69 cm, average weight was 64.19 ± 11.92 kg and the average BMI was 22.20 ± 2.58. The average physical activity levels deduced from IPAQ was 28.6% of level 1, 19.0% of level 2 and 52.4% of level 3. Compared to women, men had a greater level of physical activity.

Table 1

Descriptive characteristics of participants: (mean± SD)
	Total (n = 21)	Women (n = 6)	Men (n = 15)
Age (years)	22.76 ± 3.85	21 ± 3	23.47 ± 3.93
Height (cm)	169.38 ± 9.69	157.67 ± 3.77	174.07 ± 6.99
Weight (kg) BMI (kg/m²)	64.19 ± 11.92 22.20 ± 2.58	50.17 ± 2.61 21.86 ± 1.44	69.8 ± 9.28 22.33 ± 2.90
IPAQ level 1 (High)	28.6%	0%	40%
IPAQ level 2 (Moderate)	19.0%	33.3%	13.3%
IPAQ level 3 (Low)	52.4%	66.7%	46.7%
IPAQ: international physical activity questionnaire; BMI: Body mass index

Reliability

Overall, the coefficient of variation (CV) was low for HR, VT and RER at the faster walking speed and high at the slower walking speeds despite RER showed a high CV at the fastest walking speed. However, no specific pattern seen on VO₂, VCO₂ and EE on the changes of CV upon speeds variations. The CV ranged from 3.4–20.8% for all variable across all speeds (Table 2). The ICC was found to be moderate in (0.50–0.75) across HR level 1–2, level 4 of RER and level 1 of VT respectively. For the rest of the variables at all speeds, generally, ICC remain at good level 0.75–0.9. In particular, ICC found in level 3 & 4 of VT falls larger than 0.9 which regarded as indicating excellent reliability. Most of the ICC found in VCO₂ is in the good range (0.75–0.90). ICC of RER from level 1–3 and VT of level 2–4 fall in good to excellent reliability.

Table 2

Test-retest reliability of metabolic variables with PNOĒ (n = 21)
Bruce protocol	Level 1 1.7mph x 10%	Level 2 2.5 x 12%	Level 3 3.4 x 14%	Level 4 4.2 x 16%
HR (bpm) visit 1 Visit 2 ICC (95% CI) CV (%)	111.47 ± 14.70 113.06 ± 12.16 0.51 (0.12–0.77) * 12.4	123.28 ± 17.46 123.43 ± 12.50 0.65 (0.32–0.84) * 10.5	141.44 ± 19.48 142.35 ± 15.38 0.84 (0.64–0.93) * 7.4	163.97 ± 21.20 165.21 ± 16.61 0.90 (0.77–0.96) * 5.5
VO₂ (mL/min) Visit 1 Visit 2 ICC CV (%)	1157.49 ± 286.96 1132.85 ± 316.37 0.80 (0.57–0.91) * 18.9	1565.77 ± 338.51 1454.54 ± 356.70 0.82 (0.61–0.92) * 15.9	2023.15 ± 422.31 1979.34 ± 472.97 0.86 (0.68–0.94) * 16.2	2520.68 ± 520.62 2426.50 ± 599.67 0.81 (0.58–0.92) * 19.0
VCO₂ (ml/min) Visit 1 Visit 2 ICC CV (%)	877.34 ± 233.36 885.70 ± 268.38 0.81 (0.59–0.91) * 18.4	1240.43 ± 285.58 1173.67 ± 305.18 0.87 (0.70–0.94) * 15.1	1719.0 ± 379.21 1718.55 ± 423.44 0.86 (0.69–0.94) * 15.1	2363.1 ± 502.38 2320.65 ± 568.20 0.82 (0.61–0.92) * 17.9
RER Visit 1 Visit 2 ICC CV (%)	0.76 ± 1.07 0.79 ± 0.13 0.79 (0.55–0.91) * 10.3	0.80 ± 1.03 0.82 ± 0.13 0.85 (0.67–0.94) * 8.0	0.85 ± 1.09 0.88 ± 0.14 0.85 (0.66–0.94) * 7.8	0.97 ± 0.18 0.97 ± 0.15 0.51 (0.11–0.77) * 17.5
VT (L/min) Visit 1 Visit 2 ICC CV (%)	1.24 ± 0.38 1.35 ± 0.34 0.72 (0.43–0.88) * 20.8	1.56 ± 0.34 1.56 ± 0.41 0.88 (0.73–0.95) * 11.4	1.98 ± 0.52 2.01 ± 0.53 0.93 (0.84–0.97) * 8.1	2.35 ± 0.60 2.35 ± 0.60 0.99 (0.98-1.0) * 3.4
EE (kcal/min) Visit 1 Visit 2 ICC CV (%)	5.45 ± 1.34 5.45 ± 1.40 0.81 (0.59–0.92) * 15.8	7.47 ± 1.60 7.01 ± 1.54 0.83 (0.62–0.93) * 13.9	9.82 ± 1.97 9.72 ± 2.05 0.88 (0.72–0.95) * 12.5	12.43 ± 2.50 12.20 ± 2.56 0.81(0.58–0.92) * 16.0

Validity

The paired t test showed there were no significant differences between the mean values for HR, VO₂, VCO₂, RER, VT level 3 and EE level 1–3 obtained by the PNOĒ and K5 device. However, there were significant mean difference in 3 walking speeds in VT and one walking speed in EE (Fig. 1). The mean VT was significantly higher (P < 0.05) at speeds of in level 1, 2 and 4 when measured by the PNOĒ compared with the K5. Similarly, the mean EE was significantly higher (P < 0.05) at the highest speed of level 4 when compared PNOĒ with K5.

Pearson’s correlation coefficient was in the moderately high (r = 0.60–0.79) between metabolic variables measured by PNOĒ and K5 systems. RER was exception with values out of the moderate range. Pearson’s correlation coefficient was in high range (r ≥ 0.80) between metabolic variables of level 3–4 HR and level 4 VT measured by the PNOĒ and K5 systems (Table 3).

The absolute mean percentage difference revealed that PNOĒ tend to have a bias towards higher values for all metabolic variables compared with the K5 system. Scores for the absolute mean percentage difference ranged between 0.01–25.53%. The greatest absolute mean percentage difference was occurred at all speeds of VT, in particular fastest speed at 4.2 mph treadmill walking of Level 4. RER exhibited the low mean absolute mean percentage difference scores (ranged 0.01 to 0.05) of all metabolic variables.

Table 3

Validity of the PNOĒ for select metabolic variables compared with K5 (n = 21)
Bruce protocol	Level 1 1.7mph x 10%	Level 2 2.5 mph x 12%	Level 3 3.4 mph x 14%	Level 4 4.2 mph x 16%
HR (bpm) Pearson’s r Absolute Mean % Difference	0.57* 0.55	0.74* 1.50	0.89* 0.37	0.95* 0.18
VO₂ (mL/min) Pearson’s r Absolute Mean % Difference	0.67* 6.54	0.65* 6.07	0.53* 12.90	0.58* 14.00
VCO₂ (mL/min) Pearson’s r Absolute Mean % Difference	0.66* 1.40	0.67* 0.66	0.55* 5.50	0.62* 5.49
RER Pearson’s r Absolute Mean % Difference	0.12 0.01	-0.07 0.03	-0.30 0.04	-0.27 0.05
VT (L/min) Pearson’s r Absolute Mean % Difference	0.62* 17.16	0.74* 16.67	0.62* 21.39	0.86* 25.53
EE (kcal/ min) Pearson’s r Absolute Mean % Difference	0.69* 6.97	0.69* 5.97	0.58* 13.07	0.63* 14.40

Bland- Altman plots for the relationships between the two metabolic carts are shown in Figs. 2. The Bland-Altman plots look for evidence of proportional bias. It is a simple way to evaluate a bias between the mean differences, and to estimate an agreement interval, within which 95% of the differences of the two metabolic carts of PNOĒ and COSMED K5. Cases outside the upper and lower confidence intervals should also be noted. All participants, except few more cases in VT, lie within the upper and lower 95% confidence intervals acceptance range of the Bland Altman plots. Clusters of outcomes with the means are low and differences are negative. A potential bias and a regression have been done. Regression non-significant results shown in HR, VCO2 and VT. Therefore, there were no proportional bias.

Reliable and valid measurements are imperative when measuring cardiometabolic outcomes using portable metabolic devices. To the best of the authors knowledge, this is the first study sought to investigate the validity and reliability of the PNOĒ device when compared against COSMED K5 across four levels of treadmill walking speed on cardiometabolic outcomes. The PNOĒ device has been previously assessed for reliability and validity against COSMED – Quark CPET, a stationary metabolic cart(20). The study indicated that the PNOĒ portable metabolic cart is as accurate as stationary metabolic cart, capable of measuring respiratory variables with precision in a wide range of exercise intensities, under laboratory conditions in performing respiratory gas analysis in healthy adults(21).

Similarly, there were evidence determine the accuracy of COSMED K5 by comparison with a metabolic cart during submaximal cycling exercise. COSMED K5 measured VO₂, VCO₂, RER, and EE with an accuracy similar to metabolic cart while underestimated by 6–7% VO₂ and VCO₂ due to underestimation or bias (22). When COSMED K5 compared to K4b², K5 displayed a moderately high relationship when measuring VO₂, VCO₂, and EE across a range of walking speed. A strong correlation was found in measuring VO₂ and VCO₂ between PNOĒ and COSMED-CPET metabolic cart with a satisfactory repeatability of PNOĒ device(20).

In this study, the reliability test in terms of CV percentages for all metabolic variables was fairly small. Particularly among higher speeds of RER and VT, the lower values for the CV were considered better because that means less variability over the mean(23). With the exception of VT which had moderate reliability at slower speed, the PNOĒ device measured VO₂, VCO₂, RER, METs and EE with good to excellent reliability across higher speeds. Such results might have suggested that PNOĒ is less reliable at slower speed across the speed spectrum or as a consequence of the calculation of CV. It was suggested that slower speed would might attribute to greater variations in step length and increased the metabolic costs(24). Hence, it could potentially result in lower reliability at slower speed for the PNOĒ device.

In light of the cardiometabolic variability in test-retest reliability of PNOĒ. The PNOĒ appears to be a reliable portable metabolic device. Level 4 of RER was found to be less reliable with moderate reliability at highest speed based on ICC values, this may be related to statistical artifact of estimating reliability of ICC while ICC compared the stability of rank across days(25). From the data obtained suggested that the PNOĒ is reliable across the levels of spectrum as evidenced by moderate to high ICC scores and lesser CVs. Given that the participants completed the test-retest assessments on the second visit, potential variability can be resulted. However, no such pattern resulted for the PNOĒ in cardiometabolic outcomes measurement.

The incremental Bruce protocol adopted involved four walking speeds with a wide range of exercise intensities ranging from light to high (approximately 50–85% max HR), according to ACSM position statement (26). Walking rather than running was chosen to avoid potential artifacts due to mask displacement and to reduce thermal strain, hence the participants were not required to remove mask during assessment. At such range of exercise intensities, The PNOĒ device was capable to provide a valid outcome on VO₂, VCO₂, RER, MET, VT and EE for all participants across various speed spectrum.

Regarding validity, we used the Bland-Altman plot analysis to assess the interchangeability of both metabolic portable analysers PNOĒ and COSMED K5. Our results showed a good agreement with an acceptable bias value between PNOĒ and COSMED K5 in the measurement of VO₂, VCO₂, RER, MET and EE measured at fours levels of incremental protocol. The level of similarity lies within the range acceptance as observed in Bland Altman plots. It is clear that the difference between the two devices agrees across the exercise intensity spectrum. However, VT failed to demonstrate a similarity fell between upper and lower 95% confidence interval between the two portable metabolic devices. The VT measured might be a variable itself, it is an absolute measure that tend to eliminate individual variability and expected spread of values for such variable is therefore restricted. Leprete et al. (2012), previously concluded a strong relationship between respiratory variables collected simultaneously using two commercially portable metabolic systems(27). There were no significant differences between measures of VO₂, VT, however a substantial difference in RER and VCO₂ at the maximal exercise intensity. It could be attributed to the participants’ characteristics and mask property (dead space, resistance to air flow). Another possible reason explaining these differences could involve methodological issues in tested protocol (treadmill VS cycling).

Clearly, the validity findings suggest the PNOĒ metabolic system is comparable and acceptable for VO₂, VCO₂, RER, MET and EE over the four levels of incremental exercise intensities. Despite VT measurement were significantly different between two devices, the magnitude of the difference was small. The disparate results could be due to the sensitivity of the PNOE device to ambient CO₂ levels, highlighting the influence of environmental factors on the ability of the PNOĒ to reliably and accurately assess metabolic data (28). These results support the use of PNOĒ portable metabolic system for measuring cardiometabolic outcomes over a four stages of incremental exercise intensities. The strength of relationship increased with walking speed indicating that the accuracy of the PNOĒ improved with faster speeds.

The incremental intensity provided a valid measure of VO₂, VCO₂, RER, MET and EE in healthy young adults. The R-values observed in VO₂, VCO₂, VT and EE yielded a moderately valid measure (r = 0.60–0.79). These results are slightly comparable with previous investigations related to VO₂ measured between PNOĒ and metabolic cart (20). However, the correlation between the PNOĒ and COSMED K5 were not significant and strong as evident by the Pearson’s r correlation coefficient. RER had a low absolute percent difference indicating that it is an absolute measure tend to eliminate individual variability and the expected spread of values was restricted. The significant correlations between VO₂, VCO₂, VT and EE support validity measurement in cardiometabolic outcomes between PNOĒ and COSMED K5.

The present results were similar to other studies that substantiated the importance of aerobic contributions to energy demands of an incremental walking protocol(28). Examining the aerobic contribution to a graded walking protocol is of value since potential artifacts due to mask displacement and thermal strain could be avoided. This is insightful and may inform exercise specialists or coaches regarding important considerations concerning the role of aerobic measurement with different portable metabolic devices. The moderate high correlation between two devices were consistent with the experimental design of PNOĒ and COSMED -Quark CPET examining the cardiometabolic outcomes. It should be mentioned that in the current study, with a strong relation in high range (r = 0.86) between metabolic variables at higher speed for VT measured by the PNOĒ and K5 systems observed.

This reliability and validity study is a novel approach to assessing cardiometabolic outcomes with PNOĒ and COSMED K5 system. Assessment of aerobic power and metabolic outcomes are vital to exercise specialists because it serves as both a fundamental baseline measure as well as both a monitoring and motivational tool for the evaluation of exercise progression. By understanding the results of reliability and validity of PNOĒ and COSMED K5 were comparable to each other would assist with objective measurement consideration for both portable metabolic devices. The practicality of this evaluation process will facilitate sports scientists in providing individualized exercise prescription (29). Hence, the development of a reliable and accurate test of metabolic outcomes using two portable metabolic devices PNOĒ and COSMED K5 is an essential step toward for metabolic assessment of individuals seeking to increase cardiometabolic fitness or improve aerobic power for sports performance.

Despite carefully conducted, this study is not free of limitations. Food intake was not strictly measured to ensure compliance prior the assessments. Not all participants performed at the same time of the day which might have influenced the measured metabolic variables between the participants. The partcipants are healthy and physically active adults, therefore, the ability to generalise the true performance validity using these data was limited due to possible temporal changes related to physical training or physical health status. Only treadmill walking was investigated in this study and other modes and intensities of exercise should be examined. Further testing is needed to assess the accuracy of the system using different mode of exercise at various intensity under different environments.

PNOĒ, a portable metabolic device was found to exhibit good to excellent test- retest reliability. It is as comparable as COSMED K5 in measuring cardiometabolic variables with precision, across levels of exercise intensity. PNOĒ was moderately reliable at higher speed for RER only and was found to be valid when compared to COSMED K5 in all variables except for RER.

BP- Blood Pressure

CI- Confidence Interval

CV- Coefficient Of Variation

EE- Energy Expenditure

HR- Resting Heart Rate

ICC- Intraclass Correlation Coefficients

MET- Metabolic Equivalent

r- Pearson’s Correlation Coefficients

RER- Respiratory Exchange Ratio

VCO₂- Carbon Dioxide Production

VO₂- Oxygen Consumption

VT- Ventilatory Threshold

Acknowledgement

The authors would like to thank all participants for donating their time and energy for completing this study.

Authors’ contributions

All authors participated in the study design. MK collected all data and computed the statistical analyses. MK wrote the manuscript, BS and SN provided feedback on drafts and all authors approved the final draft.

Funding

This research received no external funding.

Availability of Data and Materials

The datasets used and/or analyzed in the current study are available from the corresponding author on reasonable request.

Ethics Approval and Consent to Participate

The study was approved by the Hong Kong Polytechnic University ethical committee for research involving human participants in accordance with the standards of the Helsinki Declaration (HSEARS20220318009). All participants were informed of the study risks by an investigator, and signed an informed consent form prior data collection.

Consent for Publication

Not applicable

Competing Interests

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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No competing interests reported.

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Validity and Reliability of the Portable Metabolic Analyzer PNOE to assess cardiometabolic capacity during walking exercise

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Abstract

Background

Methods

Results

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Background

Methods

Participants

Study design and procedures

Instruments

Validity assessment

Reliability assessment

Statistical analysis

Results

Reliability

Validity

Discussion

Conclusion

List of Abbreviations

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References

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