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Booth and Adams' report on the use of the shuttle walking test (SWT) in breathless patients with advanced cancer1addresses the important role of assessing exercise limitation in disease. Although they were primarily investigating breathlessness, it was surprising that only one of the 32 patients (completing at least one SWT) complained of leg pain at the end of the test. In patients with cardiorespiratory disease peripheral muscle strength correlates with maximal exercise capacity,2 and in one large series up to one third of patients referred for exercise testing because of breathlessness stopped because of discomfort in the exercising muscle.3 Given that peripheral muscle deconditioning would be an expected finding in patients with advanced cancer and breathlessness, a greater proportion than that reported would be expected to stop because of subjective muscle fatigue. Often patients stop exercising because of subjective leg fatigue and breathlessness but they may not volunteer this information unless specifically asked.
Their data support the use of the SWT for assessing exercise capacity in this patient group, but it is important to realise that not all breathless patients stop exercising because of breathlessness. Assessment of peripheral muscle symptoms during exercise is simple to perform and should be included in standard tests of exercise capacity.
authors' reply We completely agree with Drs Doffman and Hawkins that the comprehensive studies of Hamiltonet al clearly demonstrate that perceived leg discomfort is an important factor limiting exercise in patients with cardiorespiratory disease. Furthermore, we would guess that, had we asked our volunteers with cancer to rate their leg discomfort, we would have found a similar outcome for the reasons that Doffman and Hawkins give. However, we did not do this because we were not convinced that our subjects could reliably scale two exercise related sensations independently within a single test. We cannot therefore quantify the extent to which leg discomfort was a factor in determining exercise tolerance in this group. We tried to ensure that all subjects included in the analysis were limited at least in part by their breathlessness. In patients with advanced cancer it is this symptom, and not leg fatigue, which causes intense distress and towards which more effective therapeutic strategies need to be developed. In this respect, the shuttle walk test would seem to be a reliable objective means of assessing the function impact of this symptom.
Doffman and Hawkins have incorrectly equated our one report of leg pain as the only instance where leg discomfort was reported in this study. This patient experienced overt pain secondary to a musculoskeletal problem and this was the reason for stopping. The leg discomfort reported by Hamilton et al relates to a sense of tiredness or fatigue in the legs which is a common exercise related phenomenon. Therapeutic strategies aimed at improving peripheral muscle function may well impact favourably on perceived breathlessness as well as on leg fatigue. Further investigation of the interaction between these perceptions are warranted in cancer and other conditions where exertional breathlessness is a primary morbid symptom. The shuttle walk test would seem to be a useful tool in studies of this nature.
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