Minimal correlation between physical exercise capacity and daily activity in patients with intermittent claudication

Background: Walking capacity measured by a treadmill test (TT) reflects the patient's maximal capacity in a controlled setting and is part of the physical exercise capacity (PEC). Daily physical activity (PA) is defined as the total of actively freely produced movements per day. A lower PA level has been increasingly recognized as a strong predictor of increased morbidity and mortality in patients with intermittent claudication (IC). Recent insights suggested that an increased PEC does not automatically lead to an increase in daily PA. However, the precise relation between PEC and PA in patients with IC is still unclear. Methods: A cross-sectional study was conducted to assess the association between several PEC outcomes and PA in a general IC population. PEC was determined by well-established tests (Gardner-Skinner TT, a physical performance battery, a timed up-and-go test, and a 6-minute walk test distance). PA was obtained during 7 consecutive days using a triaxial accelerometer (Dynaport MoveMonitor; McRoberts BV, The Hague, The Netherlands). Five PA components (lying, sitting, standing, shuffling, and locomotion) and four parameters (total duration, number of periods, mean duration per period, and mean movement intensity per period) were analysed. Correlation coefficients between PEC and PA components were calculated. Results: Data of 46 patients were available for analysis. Patients were sedentary (sitting and lying) during 81% of the day and were physically active (standing, shuffling, and locomotion) for the remaining 19% of the time. Correlations between PEC outcomes and PA ranged from very weak (0.025) to moderate (0.663). Moderate correlations (as therefore assumed to be relevant) were only found for outcomes of both the TT and 6-minute walk test and the locomotion components of PA. For instance, functional claudication distance (measured by TT) and number of steps per day correlated reasonably well (Spearman correlation rho = 0.663; P < .01). Conclusions: Exercise capacity and PA correlate minimally in patients with IC. PA may be preferred as a novel outcome measure and future treatment target in patients with IC.