The participants visited the university laboratory on five occasions (Fig. 1) to complete the study. The sessions were separated by 48–72 h between the first four visits and by 7–10 days between the fourth and the fifth visit. All tests were performed using a motored treadmill (Super https://www.globalcloudteam.com/ ATL, Inbrasport, Porto Alegre, RS, Brazil), a gas analyser (Metalyzer II, Cortex, Leipzig, Germany) that was calibrated before each test according to the manufacturer’s instructions, a heart rate monitor (Polar S810i, Kemple, Finland) and a Borg perception effort scale34.
In subjects tested on both exercise devices, anaerobic threshold and maximal oxygen uptake (VO2max) were higher for both protocols on the treadmill than on the cycle ergometer (P less than 0.001). However, when the 15-s and 1-min tests were compared using the same device (treadmill or cycle), there were no significant differences between protocols in anaerobic threshold or maximum exercise values of minute ventilation, respiratory rate, tidal volume, VO2max, oxygen pulse, and peak expiratory flow rate. Linear regression analyses indicated differences between the 15-s and 1-min protocols when cardiopulmonary measurements were related to power; however, the two protocols were comparable when cardiopulmonary data were related to oxygen uptake. Comparisons between protocols or between exercise devices were not systematically different in large vs small individuals, or in men vs women. Short-duration incremental exercise tests appear to be reliable, practical methods for assessing exercise performance in normal individuals.
Data availability
Furthermore, even if it did indicate submaximal effort at the limit of tolerance during both tests, it does not refute the use of the additional test because a high percentage of participants would have then achieved a submaximal ⩒o2 that was at least closer to their maximum value upon completion of the CWR bout. Use of the newly-proposed criteria for HR based on either APHRM210 or APHRM208 [14] resulted in acceptance of an additional seven tests, five of which were characterized by a lower ⩒o2peak compared to CWR. This means that compared to use of the traditional HR criterion, use of either of the less stringent newly-proposed ones resulted in acceptance of ⩒o2max for two additional RAMP-INC tests during which that might have been the case at the expense of acceptance of ⩒o2max for five additional tests during which it definitely was not. This forms the basis for the suggestion that a severe-intensity bout performed at a work rate that exceeds WRpeak achieved on RAMP-INC can be used to test for a “⩒o2 plateau” that verifies the value as ⩒o2max in lieu of an observed plateau during the final portion of RAMP-INC [7]. However, in our study, due to concerns regarding the ability of sedentary individuals to maintain supramaximal work for a long enough period of time for ⩒o2max to be reached, we had participants perform CWR at a work rate that was only equal to the WRpeak achieved during RAMP-INC (see below). Consequently, even when the “same” ⩒o2peak was observed for the two tests, we could not confirm a plateau (i.e., a similar ⩒o2 response for a greater rate of work) across tests.
As measurement technology improved and the need for time-efficient testing was recognized, single tests involving a progressive increase in work rate (incremental test; INC) either in steps [3] or continuously as a “smooth function of time” [4] (STEP-INC or RAMP-INC, respectively) became the standard methods of assessment. In theory, the continuous work-rate increase which characterizes RAMP-INC should be best suited for eliciting a ⩒o2 plateau because an extended stage does not have to be completed before a subsequent increase in work rate occurs. However, even when maximal effort appears present at exercise completion, a definitive plateau is often absent at limit of exercise tolerance (Tlim) during RAMP-INC tests [5].
Defining an exercise intensity that triggers the highest rates of fat oxidation can help devise training programs aiming to bring about specific adaptive changes in line with individual metabolic reactions (Cerezuela-Espejo et al., 2018). Different approaches to defining the maximal fat oxidation level have been suggested based on indirect calorimetry calculations. One of them consists of a single progressive test (IET) with 2 to 6-min stages (Achten et al., 2002; Marzouki et al., 2014; Nikolovski et al., 2020).
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We did so by comparing the ⩒o2peak during RAMP-INC performed to Tlim by sedentary men and women with and without overweight/obesity to the ⩒o2peak during CWR to Tlim at 100% of the peak work rate (WRpeak) achieved on RAMP-INC. Given the previous findings for athletes and recreationally-active individuals (see above), we hypothesized that the ⩒o2peak during CWR would not be significantly different compared to the ⩒o2peak during RAMP-INC. We also hypothesized that traditional criterion values for RER and HR would not be valid for identifying instances when the CWR bout confirmed that RAMP-INC was characterized by a submaximal ⩒o2peak. Finally, we hypothesized that newly-proposed age-dependent criterion values for RER and HR [14] would better identify such instances. The main finding from this study is that a CWR cycling bout to limit of tolerance at the WRpeak from a RAMP-INC performed 10 min prior resulted in a significantly higher ⩒o2peak compared to that which was achieved on RAMP-INC. This refuted our first hypothesis and indicates that RAMP-INC underestimates ⩒o2max in a heterogeneous population of sedentary individuals.
Our second hypothesis was partially supported as the traditional criterion value for RER was not valid for identifying instances when the CWR bout confirmed that RAMP-INC was characterized by a submaximal ⩒o2peak. However, despite the fact that it was surpassed on average at ~93% of the bout’s ⩒o2peak, the fact that the criterion value for HR identified 20 of the 23 individuals who did not achieve their ⩒o2max on RAMP-INC suggests that at least for some individuals, it might have been valid for this purpose. Finally, contrary to our third hypothesis, use of newly-proposed age-dependent values for RER and HR [14] did not improve the ability to identify instances when CWR confirmed that RAMP-INC was characterized by a submaximal ⩒o2peak. Specifically, use of more stringent RER values yielded the same conclusion (acceptance of ⩒o2max for 33 of 35 RAMP-INC tests including 23 during which it was confirmed to have not been reached) while use of less stringent HR values resulted in seven additional confirmations of ⩒o2max on RAMP-INC that included five tests during which the CWR bout refuted that conclusion.
All tests were performed on a motor-driven treadmill with a constant inclination of 5% (to ensure that participants do not exceed the capacity of the treadmill). All trial sessions were completed in 15–20 days by each participant. All tests were preceded by a 5-min warm-up at 10 km h−1 with no treadmill inclination and participants were verbally encouraged throughout each test.
Consequently, exercise performance (and the ability to achieve a “true ⩒o2max”) might have been compromised by the lack of pre-test feeding during both tests. Interestingly, previous research indicates that overnight fasting does not impair the peak ⩒o2 response for competitive cyclists [29]; however, the degree to which this is also the case for sedentary individuals like the ones that we assessed requires further investigation. Finally, it is important to note that our methodology did not provide an opportunity to familiarize participants with the performance of exhaustive cycle-ergometer exercise prior to testing. Consequently, individuals like these who are unaccustomed to exercise in general might have reached a higher ⩒o2peak during the second of two such bouts regardless of the type of exhaustive exercise that was performed. After initial telephone screening, prospective participants visited the laboratory for a comprehensive medical examination that included blood work, an ECG and an oral glucose tolerance test.
Stage duration and increase of work load in incremental testing on a cycle ergometer
However, these researchers used supramaximal work rates for CWR bouts performed long enough after RAMP-INC to allow ⩒o2 to return to its resting level; specifically, 105% of WRpeak after 24 hrs (study 1) and 115% of WRpeak after 60–90 min (study 2) [27]. These differences might explain the contrasting findings compared to our study. Sedentary individuals would likely possess slower ⩒o2 kinetics which would result in a higher proportion of “non-sustainable” work rates (i.e., work rates situated above the “critical power”) that they would not be able to maintain long enough to reach ⩒o2max (i.e., work rates situated within the extreme-intensity domain). Given the importance placed on ⩒o2max and the array of individuals that are critically assessed using its measurement, it is intuitive to suggest that the ⩒o2peak achieved on a given INC should be verified as ⩒o2max in some other way when a ⩒o2 plateau is absent.
Further research into MFO, FATmax and FATmin should comprise a dietary analysis and pre-measurement standardization of diet composition. Solely youth male cyclists were tested, and the results are consequently only valid for that group. As in the present work we compared two different loading protocols on a cycle-ergometer, further research could include long-lasting continuous exercise at a steady-state ±10% intensity, in accordance with works available in the literature. Representative-subject data for ⩒o2 (Panel A), RER (Panel B) and HR (Panel C) for the two tests. Vertical dashed lines represent the onset of exercise for RAMP-INC (left side) and CWR (right side). Horizontal dashed lines indicate the higher ⩒o2peak observed across the two tests (Panel A) and traditional criterion values for RER (1.10; Panel B) and HR (95% of the age-predicted maximum; Panel C) that are often used to verify attainment of ⩒o2max.
Similarly, measures of V˙O2max have been used to determine the efficacy of different exercise training interventions aimed at improving physiological function both from performance as well as health perspectives (Pogliaghi et al., 2006; Murias et al., 2010a; Bruseghini et al., 2015). Considering the importance of V˙O2max for assessment of performance and health, adequate protocols capable of establishing a true maximal value are needed to provide confidence for evaluation and longitudinal follow-up. Despite the interesting findings, some limitations of the study should be mentioned.
The maximum rate of oxygen uptake (⩒o2max) is universally recognized as the criterion measure of cardiorespiratory fitness. Assessment of ⩒o2max, therefore, comprises a standard component of health/fitness testing in an array of settings spanning from elite-athletic to clinical. Early studies that established the concept required completion of a series of exhaustive exercise bouts at increasing constant work rates performed on separate days [1] or the same day [2]. The objective was to identify a range of work rates characterized by a similar peak ⩒o2 (⩒o2peak) response (a “⩒o2 plateau”) indicating an upper limit that could not be exceeded.
The work performed at The University of Western Ontario was supported by Natural Sciences and Engineering Research Council of Canada. The authors would like to acknowledge the participants for the time and effort they contributed to this investigation. N.M.F.S., G.M.S., P.L.R.A.P. and D.M.R. contributed to the data collection and analysis. N.M.F.S. and D.R.B. wrote the manuscript and prepared the figures and tables. G.M.S., P.L.R.A.P. and D.M.R. contributed edits, feedback, and suggestions for the manuscript.
- The purpose was to determine the participant’s resting metabolic rate.
- (B) Individual absolute differences (Δ V˙O2) between measures of the highest V˙O2 during the RI test and the verification phase are plotted as a function of the average of the two measures.
- The main conclusion reached is the absence of MFO variance between the tests as well as the relative exercise intensities at FATmax and FATmin.
- The latter approach may, however, be excessively time-consuming and therefore inconvenient in sports training.
The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Muscular exercise, lactic acid and the supply and utilization of oxygen. HL invented the modeling principles, carried out the calculations, made the figures and wrote the first draft manuscript.