The effects of non-contingent feedback on the incidence of plateau at [??][O.sub.2max].

Author:Gordon, Dan
Position:Research article - Report
 
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Introduction

The traditionally accepted primary criterion for determination of [??][O.sub.2max] is the 'levelling out' in [??][O.sub.2] prior to the point of volitional exhaustion in spite of a continued increase in exercise intensity, the [??][O.sub.2]-plateau. The physiological rationale for the manifestation of the [??][O.sub.2]-plateau is that as exercise intensity increases an imbalance ensues between the delivery of oxygen to the muscle as expressed by the cardiac output ([??]) and the ability to extract oxygen at the muscle as represented by the arterio-venous oxygen difference (a-v[O.sub.2dif]) (Wagner, 2000). The role of HR in the manifestation of both [[??].sub.max] and [??][O.sub.2max] is well defined (Calbert et al., 2007) displaying a linear-like response as a function of exercise intensity, as a consequence of an ensuing imbalance between parasympathetic and sympathetic nervous activity (Persson, 1996), with the former exhibiting a down regulation and the latter being up-regulated.

Recent works (Gordon, 2011; Hawkins, 2007) have established that the expression of the [??][O.sub.2]-plateau is a function of the finite anaerobic capacity and the ability to regulate anaerobic substrate metabolism and the concomitant recruitment of less metabolically efficient type II muscle fibres. When the anaerobic capacity was expressed through the surrogate measure of the maximally accumulated oxygen deficit an inverse relationship was witnessed with [DELTA][??][O.sub.2] during the final 60 s of a [??][O.sub.2max] trial. These data were later confirmed through both the use of prior-priming in the heavy domain (Gordon 2012) and acute reductions in blood volume (~450 ml) (Gordon 2013) suggesting that when the availability of the finite anaerobic capacity was promoted there was an increased incidence of plateaus at [??][O.sub.2max]. Thus the significance and implications of identifying a plateau in [??][O.sub.2] is apparent, manifestation of such a response represents the primary criteria in establishing a [??][O.sub.2max] has been achieved.

During exercise which is classed as 'closed-loop' in design it is recognised that the individual will adopt a pacing strategy in order to optimise performance as a means of maximising substrate metabolism and compensating for the artefacts of fatigue (Stone et al 2012, Scruton et al., 2015). A proposed model (St Clair Gibson et al., 2006; Stone et al., 2012; Tucker, 2009) reflecting pace (exercise intensity) is implemented through efferent homeostatic-orientated responses is modulated through afferent feedback systems which are both physiological and psychological in nature. The modulation in pace is thus a product of a perceptually mediated algorithm which is continually compared to a sub-conscious template derived from exposure to previous exercise challenges. Thus the 'template' is based upon the associated sensations of pain, fatigue and the expectations for the duration of the exercise challenge. While, the modulations of pace that occur during exercise account for the need to preserve the finite anaerobic capacity and thereby prevent a catastrophic depletion in associated substrates and accumulation of associated metabolites (Foster et al., 2004). In contrast, open-looped exercise is defined by the lack of an anchor against which perception of effort is regulated, such as known duration or time (Jones et al., 2013). Thus under these conditions the perception of effort remains stable, based on the experience of the participant to judge an exercise intensity that can be tolerated (Tucker, 2009) [??][O.sub.2max] testing conducted using motorized treadmills or cycle ergometers pose a potential contradiction to the pacing schema. Firstly during such an exercise challenge aside from the participant altering stride rate and length when running or cadence when cycling there is little means of modulating pace, given that exercise intensity is a function of the imposed externally applied resistance. Secondly, unlike time-trial (TT) conditions a [??][O.sub.2max] test is defined as being open-looped in nature as the end time is not known and the test is only terminated when the participant reaches volitional exhaustion. However recent work (Gordon, 2015) has established that a pacing affect ensues across a series of four repeat [??][O.sub.2max] trials over a 2-week period. In a group of [??][O.sub.2max] testing naive participants it was suggested that a metabolically orientated pacing strategy was present as highlighted by significant increases in incidence of plateau at [??][O.sub.2max] from 20% in trial 1 to 70% in trial 4, together with an increase in RPE from 17.7 [+ or -] 1.3 in trial 1 to 19.0 [+ or -] 1.4 in trial 4 despite no change in exercise time to volitional exhaustion, [??][O.sub.2max] or onset of gas exchange threshold (GET) representing ventilatory threshold 2 (VT2). It was concluded that a closed loop condition was developed, firstly by informing the participants of the total number of trials to be completed and secondly by completing the initial trial and thereby establishing the perceptual pacing template for trials 2-4. Consequently it was postulated that plateau incidence was highest in the final trial as the anaerobic capacity, which represents the augmentation of anaerobic substrate metabolism had been preserved across trials 1-3 and the fact that there was to be no fifth trial meant that there was little need to preserve the limited anaerobic capacity.

The pacing paradigm has been challenged through the application of non-contingent feedback in the form of auditory, visual and extrinsic cues as a means of disturbing the pacing algorithm. It is argued that the provision of contingent visual feedback can foster an enhanced relationship between perceived and actual performance whilst under non-contingent (deception) conditions serves to magnify a discrepancy (Morton et al., 2009; Micklewright et al., 2010; Mauger et al., 2011, Ness and Patton, 1979). Indeed it has been show that during simulated TT's, performance was enhanced by the provision of noncontingent feedback (visual representation of past performance) through increased mean power output and heightened RPE which were associated with an increased energy yield from anaerobic energy sources. Alternatively during a series of repeat 4000m cycling time-trials recent work (Mauger et al., 2011) showed that performance was optimized when exposed to accurate feedback in the form of an animated avatar as opposed to the non-contingent feedback. However to date there is no data addressing the effects of non-contingent feedback on the outcome of a [??][O.sub.2max] test. Thus given the notion that pacing and effort regulation aim to prevent a catastrophic depletion of the finite anaerobic capacity and that the plateau at [??][O.sub.2max] has been attributed to the size of the finite anaerobic capacity the a-priori hypothesis was formed. We contend that in the presence of non-contingent feedback there would be an absence of V[??][O.sub.2]-plateau formation in order to prevent a depletion of the anaerobic capacity and the onset of premature volitional exhaustion. Therefore the purpose of this study was to assess if the application of non-contingent feedback in the form of a visual representation of exercise heart rate was associated with an altered response for the [??][O.sub.2max]-plateau at [??][O.sub.2max] and associated responses during a series of incremental tests to exhaustion.

Methods

Participants

Following local institutional ethical approval (Faculty Research and Ethics Panel, Anglia Ruskin University University) and having provided written informed consent, n = 10 physically active males (mean [+ or -] SD: age 24.8 [+ or -] 4.2 yrs; mass 81.4 [+ or -] 9.0 kg; stature 1.80 [+ or -] 0.11 m) volunteered and agreed...

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