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A new VO2max protocol allowing self-pacing in maximal incremental exercise
  1. Alexis R Mauger,
  2. Nick Sculthorpe
  1. Institute for Sport and Physical Activity Research, Department of Sport and Exercise Sciences, University of Bedfordshire, Bedford, UK
  1. Correspondence to Alexis R Mauger, Department of Sport and Exercise Sciences, University of Bedfordshire, Polhill Avenue, Bedford, BEDS, MK41 9EA, UK; Lex.Mauger{at}beds.ac.uk

Abstract

Introduction The traditional maximal oxygen uptake (VO2max) protocol has received criticism for being an unnatural form of exercise, lacking ecological validity and producing different VO2max responses depending on protocol duration and work rate increments.

Purpose The purpose of this investigation was to design and test a new VO2max protocol allowing subjects to self-pace their work rate while maintaining an incremental test structure.

Methods 16 untrained subjects completed a self-paced VO2max protocol (SPV) and a traditional VO2max test in a counter-balanced, crossover design. The SPV used incremental ‘clamps’ of ratings of perceived exertion (RPE) over 5 × 2-min stages (10-min duration) while allowing subjects to vary their power output (PO) according to the required RPE.

Results Subjects achieved significantly higher (p < 0.05) VO2max values (40 ± 10 ml/kg/min vs 37 ± 8 ml/kg/min) and peak POs (273 ± 58 W vs 238 ± 55 W) in the SPV. Higher VO2max values were observed in the SPV even when a plateau (VO2–time slope <0.05 l/min) occurred in the traditional test. No differences were found between any other measured physiological variable (minute ventilation, heart rate and respiratory exchange ratio).

Conclusions As SPV is a closed-loop test (10-min duration) that allows subjects to self-pace their work rate, it disregards the need for experimenters to estimate starting work rates, stage lengths and increments in order to bring about volitional exhaustion in 8–10 min. The observation that the SPV may also elicit higher VO2max values than a traditional test warrants further research in this area and its consideration as standard measure to elicit VO2max.

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Introduction

Maximal oxygen uptake (VO2max) can be defined as the maximal rate of oxygen consumption by active muscle during exercise to fatigue.1 Typically, this measure is obtained through a maximal incremental test to exhaustion (MIE), where the intensity (usually speed or power output (PO)) increases by a set amount, for a given time period, until volitional exhaustion. Despite being the most widely used test in exercise science, a number of concerns have been raised regarding the generic, prescriptive nature of the protocol.2 These concerns are threefold. First, the subject is unaware of the end point, which effectively creates an ‘open-loop’ form of exercise. The ability to accurately judge the end point is vital to the effective regulation of work rate over a bout of exercise,3 and without this information performance may be compromised. Second, the fixed, progressive intensity of the protocol produces a form of exercise that is not replicated in ‘natural’ exercise outside of laboratory conditions. This raises questions over the ecological validity of the test. Finally, the only ‘choice’ the subject has over the work rate is to stop exercising (volitional exhaustion). This adds a highly subjective and motivationary component to the test.

It has previously been shown that self-paced (variable PO) exercise at fixed ratings of perceived exertion (RPE) is less of a physiological challenge to homeostasis than forced-paced exercise (fixed PO) that corresponds to the mean PO at the same RPE.4 By allowing participants to self-pace, but keeping intensity the same by ‘clamping’ RPE,5 reduced blood lactate (B[La]), core temperature and integrated electromyography (iEMG) were observed. If afferent signallers (eg, B[La], core temperature) are used to anticipatorily regulate work rate,6 then fixing intensity through traditional methods (PO/speed) in an MIE may produce a different response than a test where work rate could be controlled by the subject. In a traditional MIE design, increasing afferent signalling produced by a fixed intensity can only be attenuated (by the subject) by volitional exhaustion. This response may lead to premature termination of the test and a failure to exhibit a VO2 plateau – the primary indication of attaining VO2max.7 In these instances, it is unclear as to whether peripheral discomfort or limits of the cardiorespiratory system have led to test termination.

The question of ‘what limits VO2max?’ is a continual source of debate in exercise sciences. Arguments have been presented for the role of the heart,8 the brain2 and an integrated system.9 Although the role of the heart, lungs, circulatory system and muscle is well evidenced,8,,10 a clear role of the brain in the capacity of the system remains relatively equivocal. It may be that the VO2max test, in its current, traditional form, may negate the role of the brain in this form of exercise,2 at least in terms of anticipatory regulation, making this particular ‘brain-dependent’ paradigm difficult to test.

This article presents a novel design of VO2max test that allows subjects to self-pace their work rates according to a given end point, while maintaining an incremental format, thus addressing those concerns highlighted by Noakes.2 Although perceptually regulated, graded exercise has been used previously in the literature11,,15 to estimate VO2max through a submaximal protocol. These protocols have all used extrapolation equations to predict VO2max based on the submaximal RPE–VO2 relationship. Furthermore, these papers do not represent a fully self-paced protocol, as work rate was fixed for each stage when the correct RPE had been achieved. These continuous changes in PO during exercise have been shown to be important.16 As these tests do not directly exercise the subject to a maximum, a logical progression of this work would be to create an MIE version of the perceptually regulated exercise test outlined by previous authors.11,,15 The protocol highlighted in this article, therefore, represents a novel test design for establishing directly measured VO2max while allowing self-paced, maximal incremental exercise. We were interested in whether this novel design, that incorporates a role for the brain,2 would produce a different maximal oxygen uptake response when compared with a traditional VO2max test design.

Methods

Subjects

Sixteen (11 men, 5 women) untrained university students (age = 22 ± 7 years, weight = 78 ± 16 kg, height = 1.75 ± 0.1 m), familiar with VO2max testing, volunteered to participate in this study. The study was conducted with approval of the Institutional Ethics Committee, and participants read and signed a form of written informed consent.

Computrainer cycle ergometer

Both tests were conducted on a Computrainer cycle ergometry system (RacerMate Computrainer, Seattle, Washington, USA). These devices are now being widely used in research3 4 6 17 18 and are an accurate and reliable measure of PO. Before each test, the Computrainer was calibrated in accordance with the manufacturers' recommendations.

Self-paced VO2max test

The self-paced VO2max test (SPV) design consisted of 5 × 2-min stages (total test time of 10 min), where for each stage the subject could continually vary PO, but RPE (Borg's 6–20 scale) (3) was clamped.5 The 5 × 2-min stages that utilise RPE to establish PO has been used previously,11,,15 but not with a maximal protocol or with a variable PO within stages. In the current SPV, stage 1 (0–2 min) was clamped at an RPE of 11, stage 2 (2–4 min) was clamped at an RPE of 13, stage 3 (4–6 min) was clamped at an RPE of 15, stage 4 (6–8 min) was clamped at an RPE of 17 and stage 5 (8–10 min) was clamped at an RPE of 20. Particular RPE values (11, 13, 15, 17, 20) were selected to correspond with the verbal descriptors on the scale (eg, RPE 13 = somewhat hard) in order to facilitate subject understanding of the relative intensity required for the given stage. Throughout each stage, subjects were continually reminded of the RPE they should be cycling at and the RPE scale was continually on view to the subject. Using this design, subjects could vary their PO according to the RPE required at each stage, but the progressive RPE clamps allowed the test to retain an incremental format. The use of the Computrainer cycle ergometry system allowed subjects to vary their PO throughout each stage, so that PO could be self-regulated between and within stages, according to how the subject felt at any given moment. These non-monotonic fluctuations in PO are suggested to be important for exercise regulation.16 Before starting the SPV, subjects were given a full briefing of the design of the test and what would be required of them; the test did not begin until subject understanding had been confirmed. A laboratory assistant, blind to the purpose of the study, was present on each test occasion to provide verbal encouragement to the subject.

Traditional VO2max test

The traditional VO2max test (TMIE) followed a standard incremental design. The test commenced at a PO of 60 W and increased by 30 W every 2 min until the subject reached volitional exhaustion or cadence dropped below 60 RPM.

Experimental procedures

Subjects completed the SPV and TMIE in a counter-balanced, crossover design. Tests were separated by 5–7 days to allow the subject full recovery and were completed at the same time of day (±2 h). Before each test, subjects were asked to refrain from drinking alcohol (24 h abstinence) or caffeine (8 h abstinence) and instructed not to perform any exhaustive exercise in the 48 h preceding the TT. Subjects were asked to keep the same eating behaviours before each test. Before each test, subjects warmed up on the Computrainer for a period of 5 min at a self-selected intensity. During both tests oxygen consumption (Cortex Metalyzer 11R; Cortex, Lepzig, Germany) and heart rate (HR) (Polar Heart Rate Chest Strap T31, Polar Electro Inc, New York, New York, USA) were recorded for the duration of the test. A fan was positioned to the side of the participants throughout testing. In the TMIE, RPE was recorded 15 s before the end of each stage. In the SPV, PO was recorded continuously using the Computrainer software.

Statistical analysis

Descriptive data are presented as mean ± SD. As no previous literature has compared these protocol designs, dependent variables from a previous paper4 comparing fixed intensity and self-paced exercise were selected to provide power calculations.19 It was estimated that a sample size of ∼17 was required to achieve a statistical power of 80% at an α level of 0.05.19

Differences in peak PO (POpeak), VO2max, respiratory exchange ratio (RER), minute ventilation (VE), HR and test time were analysed using paired sample t tests. Statistical tests were conducted using SPSS version 16.0 (SPSS, Chicago, Illinois, USA) and significance was accepted when p < 0.05. A plateau in VO2 was considered to be achieved when VO2–time slope was <0.05 l/min at VO2max, according to the more conservative criteria outlined by Astorino et al.1 These criteria were used due to more traditional methods7 not being able to accommodate for the variable PO allowed by the SPV. Averaging of VO2 was performed over both 10- and 30-s time frames, due to different recommendations within the literature.20 21 As no differences in the measured variables were observed between these different averages, graphical data are presented in 30-s averages. The Computrainer collected PO data continuously, but measures were subsequently averaged every 30 s to parallel VO2 data.

Results

Physiological responses

A significant difference in VO2max between tests was found (p < 0.05), with participants achieving a significantly higher VO2max in the SPV (40 ± 10 ml/kg/min) than in the TMIE (37 ± 8 ml/kg/min), as shown in table 1. This represents an ∼8% higher VO2max score in the SPV compared with the TMIE. Figure 1 depicts the individual differences in VO2max between the protocols. A plateau was observed in the majority of tests, regardless of protocol, although on six occasions a higher VO2max was observed in the SPV despite a plateau being observed in both tests. Figure 2 shows this relationship in a representative subject. No significant differences in maximum HR, RER or VE were observed between the tests (p > 0.05), as shown in table 1. All subjects in the SPV and TMIE achieved VO2max as outlined by the ACSM.22

Figure 1

Individual subject data for differences in VO2max attained between the TMIE and SPV. Thicker black line represents mean subject data. Twelve of the 16 subjects achieved a higher VO2max in the SPV, only two subjects achieved a higher VO2max in the TMIE.

Figure 2

VO2 and power output data for the self-paced protocol and traditional protocol in a representative subject. A VO2 plateau is observed in both occasions, yet a higher VO2max is achieved in the self-paced test. A higher peak power output is also achieved in the self-paced test during the final stage (RPE 20). The plateau in both tests occurs in the presence of either a plateau or fall in power output, which in the SPV may be an anticipatory pacing response.

Table 1

Mean peak values for physiological variables recorded during both protocols

Power output

A significant difference in POpeak between the tests was observed (p < 0.05), with participants achieving a significantly higher POpeak in the SPV (273 ± 58 W) than in the TMIE (238 ± 55 W). Participants' PO increased in a linear fashion (a mean of 30-W increments each stage) throughout the SPV, until the final stage where a sudden increase (a mean of 70 W) in PO was observed, followed by a subsequent drop (see figure 3). Therefore, the SPV followed similar incremental intensities to the TMIE, up until the 8th min, where participants produced significantly higher POpeak. Mean PO sustained by each participant in the final stage was not significantly different (p > 0.05) between tests (TMIE = 238 ± 55 W vs SPV = 241 ± 56 W).

Figure 3

Subject mean VO2 and power output profiles for the self-paced protocol. VO2 and power output show a linear increase from 0 to 8 min, until the final stage where a sudden increase in VO2 and power output are shown, followed by levelling off.

Discussion

The purpose of this study was to design and test a novel VO2max test protocol that would allow subjects to regulate their work rate in an anticipatory, self-paced fashion, while maintaining the incremental nature of a standard MIE. Our principal and novel finding was that in an untrained population, the self-paced VO2max design (SPV) produced a significantly higher VO2max value than in a traditional test. This is a significant and important methodological advance, which answers recommendations in the literature concerning the design of VO2max protocols.1 2 21

The SPV design has several features that make it preferable to traditional MIE designs. First, the test has a set duration (10 min) that complies with the 8–10-min duration recommended in previous literature.23 This is beneficial as it disregards the need for the experimenter to estimate a starting PO and intensity increments in order to bring about volitional exhaustion in 8–10 min. Furthermore, the closed-loop format allows subjects to pace themselves according to exercise end point, which is suggested to be important in allowing a role for the brain in exercise regulation.2 Second, the test allows subjects to vary their work rate for a given RPE. Self-paced exercise has been shown to be less physiologically challenging than exercise that is of matched intensity but of an enforced pace,4 evidenced by reductions in core temperature, B[La] and iEMG. Therefore, the SPV design may reduce pain and discomfort by allowing a varying work rate, and this may in turn reduce the effect these factors have on attaining a plateau in VO2. Indeed, the PO and level of increment between the two tests for the first 8 min was not significantly different, despite some variation in PO during stages in the SPV. However, the final stage of the SPV produced a significant end-sprint in PO, typical of medium duration self-paced exercise,3 6 17 which suggests a willingness of subjects to endure significantly higher levels of discomfort when they know that exercise end point is proximal.

The reasons for the observed higher VO2max values in the SPV are unclear. Indeed, the complexity of the integrated factors that limit VO2max8,,10 and the relative simplicity of the design of the current study mean that this article cannot satisfactorily answer this question. Further research using the SPV with more complex methodologies may shed light on this issue. However, the current authors suggest and speculate that several mechanisms may be at play and should be investigated. The nature of the self-paced design may allow a more efficient use of muscle mass, namely a reduced recruitment of type 2 fibres, therefore increasing relative recruitment of more oxygen-dependent type 1 fibres. This may in turn reduce oxygen demand heterogeneity and effectively decrease the anaerobic component of the test, or at least confine it to the latter stages. However, the presence of a VO2 plateau in the TMIE, but a higher recorded VO2max in the SPV is curious.

The observation of the VO2 plateau in the SPV may occur due to the drop in PO (see figure 3) in the final stage that is allowed by the self-paced nature of the test. The initial peak in PO during the final stage is clearly not maintainable for the whole 2 min, and therefore an anticipatory drop in PO is observed that allows the subject to complete the test. It may be that the higher motor unit recruitment (evidenced by the higher PO in the final stage) in the SPV increased oxygen demand and utilisation. However, this would mean that in the traditional test, subjects terminated the test with a motor unit reserve and this does not explain differences in VO2max values despite plateaus in both protocols. Finally, it may be that the self-paced nature of the SPV allowed a higher PO for the same level of perceived exertion or discomfort,4 which in turn allowed a higher VO2max to be achieved before volitional exhaustion. The non-significant differences in VE between protocols suggest that the observed differences in VO2max values are not to do with differences in oxygen cost of ventilation.

The variation in PO allowed by the SPV renders many traditional classifications of a VO2 plateau, that state that a plateau occurs when no further increase in VO2 is observed despite an increase in PO,7 inadequate. By clamping RPE, but allowing PO to vary, the final stage of the SPV causes a situation where a subject can produce a PO peak at the beginning of the stage that may consequently drop. However, it is following this initial peak in PO that the highest VO2 values are observed (see figures 2 and 3), and thus directly contradict traditional markers of a plateau (ie, VO2 should be highest when work rate is highest).7 Without the utility of traditional VO2 plateau criteria,7 and the higher RPE values in the SPV (subjects were ‘clamped’ to RPE 20 in the SPV) (see table 1), it may be suggested that the subjects did not reach a true maximum during the TMIE. However, as HR, VE and RER were not significantly different between protocols, a VO2 plateau was still observed in the majority of the TMIE tests and secondary criteria for achieving a VO2max were attained on all test occasions; the authors suggest this is not the case. Rather, as the SPV will always take a subject to maximal effort (RPE = 20) while allowing work rate to vary around this subjective intensity (thus allowing maximal effort to be maintained for a complete stage), it is suggested that the SPV design will help untrained individuals produce a greater effort and thus VO2max.

Previous literature has used similar perceptually regulated incremental exercise to make estimations of VO2max, although the thrust of these papers was focused on the accuracy of these methods to predict maximal oxygen uptake rather than to assess whether traditional measures of VO2max are valid.11,,15 In general, these studies have shown that these perceptually regulated, submaximal designs do produce accurate estimations. However, Faulkner et al13 showed that one extrapolation produced significantly higher VO2max estimations than those that were tested using a graded exercise test. Indeed, extrapolations to RPE 19 tend to produce more accurate VO2max predictions when compared with a TMIE,13 as subjects rarely reach an RPE 20 in TMIEs.24 As the SPV always takes a subject to RPE 20, it is perhaps not surprising that a higher VO2max was observed in the current study. In light of this, we suggest that extrapolation predictions to RPE 20 may actually be the correct estimation of VO2max and comparison of these techniques11,,15 to the VO2max produced in an SPV would be interesting.

One factor the authors cannot ignore is difference between the mean test time of the SPV (10 min) and the traditional protocol (13 min). It has previously been shown that longer test designs can elicit lower VO2max values in men23 and resultantly, current recommendations are for VO2max protocols to last between 8 and 10 min.23 However, the differences in test duration do not appear to affect women,23 and in the current study, we still observed five cases where the SPV produced a higher VO2max value, despite a plateau in the traditional test, and the traditional test lasting <11 min. Although the increased test duration may have had some effect on the differences in VO2max between the protocols, we believe that it does not explain the observed differences in all cases.

In conclusion, this study presents a novel test design for directly measuring maximal oxygen uptake by allowing self-paced, anticipatory regulation of work rate. The novel finding that the test may produce higher VO2max values in an untrained population warrants further study. This novel protocol has several advantages over traditional VO2max designs and may be especially applicable to populations (eg, children) where exercise associated peripheral discomfort, motivation or low aerobic fitness may affect the attainment of a VO2 plateau. This work builds on original research using RPE to regulate exercise intensity11,,15 25 and links it to current criticisms of the validity of traditional VO2max test design.2 Further research should seek to assess the efficacy of this novel design in different populations and to identify the mechanisms by which this design allows the achievement of higher VO2max values.

References

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Footnotes

  • Competing interests None.

  • Ethics approval Ethics approval was provided by the University of Bedfordshire ISPAR Ethics Committee.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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