Estimating energy expenditure during outdoor level walking using Global Positioning System or accelerometry in patients with peripheral artery disease

Introduction. Estimating energy expenditure (EE) related to outdoor walking capacity in peripheral artery disease (PAD) patients could allow a better standardization of the assessment of their limitations during free-living outdoor walking. However, there is no data regarding the accuracy of ambulatory methods to perform such estimations. Our aim was to study the accuracy of global positioning system (GPS) and accelerometry for estimating EE during outdoor walking in PAD patients. Methods. Thirteen PAD patients with walking limitations completed a 45-to-60-min outdoor walk (athletic track) while wearing a DG100 GPS receiver (shoulder; 1-Hz), a wGT3X+ accelerometer (hip; 30-Hz) and a K4b2 portable metabolic system. Patients had to walk until pain forces them to stop. Recovery time between walking bouts was free. For each walking bout, total EE (MET-min) was measured using the K4b2. METmin were estimated using appropriate MET or oxygen uptake equations that incorporated either i) GPS speed and grade or ii) accelerometer counts. The highest measured MET-min values (one value/patient) were compared with the corresponding GPS- or accelerometry-estimated MET-min values. Results. Estimated and measured MET-min were significantly correlated (r>0.98, p≤0.001 [all devices and equations]). Mean absolute percentage error ranged from 17 to 21% for GPS and from 18 to 25% for accelerometry according to the equation. One GPS-based equation (ACSM) significantly underestimated MET-min while one accelerometry-based equation (Leenders et al., 2003) significantly overestimated MET-min (p≤0.05). MET-min estimated using the other equations (GPS/accelerometry) were not significantly different from the measured MET-min. Discussion and conclusion. GPS and accelerometry provide acceptable accuracy for estimating EE related to outdoor walking capacity in most PAD patients although large errors are likely to occur in some patients (see figure: patient #2) (support: CHU Rennes-CORECT 2013).