Introduction
The most widely used instrument to measure perceived exertion or exercise intensity is the Borg’s Rating of Perceived Exertion (RPE) Scale (6–20).1 Objective measures of effort, such as heart rate (HR) and oxygen uptake, have be used in conjunction with RPE scores in clinical settings such as cardiac rehabilitation2–5 and with patients receiving β-blocker therapy.6 Using the Borg's RPE scale improves the safety of the challenge test when used in conjunction with objective measures.
According to its author, RPE scores correlate well with both physiological measures of stress and arousal (eg, HR, ventilatory threshold, blood lactate and creatinine concentration) as well as psychological measures of exhaustion.7
The subjective weighting of these physiological changes generates a response, which is measured by the RPE scale to provide a final score of subjective exertion.8 The putative similar perception of the exercise intensity (corresponding to anaerobic thresholds) among different individuals makes it possible to adequately prescribe exercise intensity.9
Of the many exercise challenge protocols available, Heck's10 test is the most widely used in sedentary subjects,11 12 due to its high reproducibility.10 13 This protocol determines the anaerobic threshold of the individual, which is the point at which the rate of lactate production exceeds that of removal.14
It is possible that patients with panic disorder do not perceive exertion in the same way as the general population. Spontaneous panic attacks (PAs) are bouts of inappropriately released fear. However, it is more likely that the underlying physiological mechanism is another brain defence reaction such as a mammalian suffocation alarm.15 Accordingly, a PA is usually associated with marked air hunger, which is not characteristic of external danger-induced fear. Another important difference is the lack of the emergency activation of the hypothalamic–pituitary–adrenal axis with lower levels of adrenocorticotropic hormone and cortisol observed in PAs.16
Further situational PAs and interpanic tonic anticipatory anxiety evolve due to several factors, one of which is fear conditioning.17 Over time, bodily sensations of arousal such as palpitations, breathlessness or dizziness can come to trigger PA due to increasing autonomic distress, sensitisation to panic and fear conditioning leading to catastrophic interpretation of those sensations as symptoms of an impending medical problem.18 Consequently, avoidance of physical exercise, which share with fear activation the same arousal bodily sensations, has been previously reported (eg, Muotri and Bernik), and was observed in this sample.19
Putatively, catastrophic interpretation of exercise-induced bodily sensations can alter the perception of current state of fatigue. Fatigue compromises exercise performance and is determined by central and peripheral mechanisms. Perceived exertion and fatigue are extremely important in the regulation of self-paced physical activity. These mechanisms have been proposed to interfere with the self-evaluation in the RPE Scale through an altered sensory tolerance limit.20
In the present study, we hypothesise that patients with panic disorder (PD) overestimate their exertion rendering the RPE Scale scores inappropriate for evaluating cardiovascular (CV) capacity in the patient with PD population.