In daily life, patients with symptomatic peripheral arterial disease (PAD) may be severely limited due to symptoms of intermittent claudication (IC). Disease severity and effect of treatment modalities are often assessed by outcome measures such as maximum and pain-free walking distance. However, a large discrepancy and variability has been reported between walking ability and claudication walking distances as measured on a treadmill, suggesting that treadmill assessments may not be representative of daily life walking ability (1-3). Assessment of IC using patient reported outcome is subjective, insensitive and a poorly reproducible tool for determining severity of symptoms (4-6). Objective clinical measurements such as Doppler ultrasonography and angiography provide only information on vessel patency and lesion severity. These imaging techniques are registered under standardized conditions and do not take the patients' coherent daily ambulatory limitations into account.
A clear call was made for alternative tests to determine walking capacity over a prolonged period of time (1, 2). Moreover, despite the fact that IC patients have an increased risk for cardiovascular or cerebrovascular events (7), current PAD treatment is mainly focussed on the limitation in walking distance. However an increased walking capacity does not automatically imply a change in a patients' exercise behaviour. From a therapeutic as well as research standpoint, it may be more relevant to determine physical activity (PA) as outcome measure for treatment modalities of IC. Improved levels of PA might be indicative of an increased exercise behaviour resulting in cardiovascular event risk reduction and improvement of Quality of Life (QoL) on the long term (8, 9). Formerly, habitual PA was frequently ascertained using questionnaires or diaries, but patients are known to report inaccurately and results tend to be biased due to socially desirable answers (4-6). Therefore, it seems necessary to obtain an objective measure of the patient's PA over a prolonged period of time.
Nowadays PA levels can be measured with activity monitors. Tri-axial accelerometers measure accelerations in three dimensions that can be converted to intensities and metabolic equivalents (METs) enabling a quantification of overall PA. The Dynaport MoveMonitor (DP) is such an activity monitor and is easily applicable in a daily life setting and is optimized for clinical research assessments. The DP was previously validated in an elderly population (10), in Parkinsons disease (11, 12) and COPD patients (13-15). To our knowledge, studies validating the DP in detecting daily activities in a PAD population were not previously reported. However, IC symptoms may significantly influence the DP outcomes due to altered walking patterns which may have impact on the detection of gait and postures (16-18). Furthermore, all previous studies were performed in a laboratory setting with patients walking a specific trajectory (10-13). Moreover, the number of observation hours was rather limited and obtained from small groups (10, 11, 13, 15). One study excluded patients with walking impairments (13) and two other studies used out-dated accelerometer technology (14, 15). Overall, most studies suffered from substantial methodological shortcomings when using the DP
for assessing daily life ambulatory activities in patients with walking impairments due to IC.
The aim of the present study is to validate the Dynaport MoveMonitor in symptomatic IC patients in a near real-life setting. If valid, the accelerometer can be used for the assessment of PA as a potential outcome measure in these populations.