Angers, France - Don't have a treadmill to measure the walking capacity of your patients with peripheral artery disease (PAD)? No worries. Just attach a pocket-sized global-positioning system (GPS) to their knapsack, open the office door, and send them on their merry way.

So suggest a group of French investigators who showed that the outdoor walking capacity measured by a low-cost GPS is highly correlated with the maximal walking distance (MWD) recorded on an exercise treadmill [1]. The findings, say investigators, led by Dr Alexis Le Faucheur (University of Angers, France), "open new perspectives in the study of walking capacity for vascular patients with claudication under free-living conditions or for physicians who do not have a treadmill."

In their paper, published online February 4, 2008 in Circulation, the authors write that while MWD is the current gold standard used to measure walking capacity in PAD patients, many physicians lack office treadmills. MWD is defined as the distance walked at a usual pace and on a flat surface until pain forces the patient to stop, and this distance provides an index for the classification of the severity of PAD and the available therapeutic options.

Various methods of assessing MWD without a treadmill have been proposed, including self-estimated MWD, standardized questionnaires, and the six-minute-walk test. However, with the development of commercially available, low-cost GPS devices—the device used in this study costs $450 US (Garmin GPS 60, Garmin Ltd)—the authors sought to determine how the GPS device, as well as other nontreadmill devices, compared with the gold-standard treadmill test.

The 24 patients were sent out into a designated public park with the GPS device, where they went on an unsupervised, unconstrained outdoor walk at their usual speed for 45 minutes, including eventual rest periods due to leg pain. On the treadmill, the patients were able to walk 184 m, but these same patients walked, on average, more than three times further in the park with the GPS, or approximately 600 m.

In a statistical analysis, the authors report that the correlation with the MWD measured on the treadmill was highest with walking capacity assessed with the GPS device. The fact that the distance walked with the GPS device was greater than the distance walked on the treadmill is consistent with previous studies, say investigators, suggesting "treadmill testing does not satisfactorily reflect unconstrained outdoor walking."

While treadmill tests are important—and much needed if physicians must record important hemodynamic parameters during walking in PAD patients—GPS recording of outdoor walking "appears to be an attractive approach for future studies in PAD patients or patients who have nonvascular walking limitations," write Le Faucheur and colleagues. The ability of the GPS to monitor speed, distance, altitude, and duration of walking/resting bouts should lead to other studies that investigate the effect of fatigue, the environment (including temperature, incline, and type of ground surface), or duration of resting intervals on walking capacity.