Intermittent claudication (IC) is closely associated with cardiovascular and cerebrovascular disease.1-3 Compared to healthy adults, IC patients are burdened with a low health-related quality of life and functional impairment during daily activities.4, 5 A reduced exercise capacity and lower daily free-living physical activity (PA) level are both strong predictors of long-term mortality. In contrast, higher PA levels are associated with less functional decline.6-9
The ACSM/AHA have issued recommendations on types and amounts of PA needed for (older) adults to improve and maintain health.10 Specific recommendations are provided that apply to adults >65 years of age or to adults aged 50-64 years with chronic conditions or physical functional limitations.11 All adults are advised to engage in moderate-intensity aerobic exercise for a minimum of 30 minutes during five days a week, or vigorous-intensity aerobic PA for a minimum of 20 minutes at three days a week. Activities should be performed in bouts of at least 10 minutes. Combinations of moderate- and vigorous-intensity aerobic PA can also be performed to meet these recommendations.
Metabolic equivalents (METs) are used by the ACSM/AHA as a means to express the energy expenditure or energy costs of physical activities. The total amount of PA is a function of its intensity, duration and frequency. Accordingly, vigorous intensity activities (>6.0 METs) performed for a particular duration and frequency generate greater energy expenditure than moderate-intensity activities (3.0-6.0 METs) of the same duration and frequency. When combining the recommendations on moderate- and vigorous-intensity physical activity, the daily minimum goal of PA should be in the range of 64-107 METs?min.10, 11
In literature, PA is defined and determined in different ways. Frequently used definitions of PA are 'time spent in different activities (sedentary/ambulatory), number of steps, duration of walking events or the score on a specific exercise test or questionnaire'.8, 12-15 PA objectively measured by energy expenditure is seldomly performed in patients with IC.15-17 Regularly described methods for PA measurement are PA questionnaires, pedometers or activity monitors. However, only the latter method is found capable of adequately assessing energy expenditure.18, 19
The newest generation of activity monitors are based on tri-axial accelerometer techniques measuring accelerations in three dimensions that can be converted to intensities and METs. In contrast to unilateral accelerometers (or vertical accelerometers), tri-axial accelerometers also measure activities that do not include vertical movement. As such, PA is determined more precisely as demonstrated with high correlations between indirect calorimetry and generated MET output at different walking speeds. 18, 20, 21 To our knowledge, no studies are available on the use of a tri-axial accelerometer in patients with IC compared to healthy adults.
The purpose of this prospective observational study was to objectively determine the PA using a tri-axial accelerometer in patients with IC and healthy adults. Furthermore, number and percentage of participants meeting the lower limit of the ACSM/AHA recommendations for PA and public health are determined. It was hypothesized that healthy adults had a higher PA level and complied more frequently to these minimum recommendations compared to IC patients.