The Inter- and Intra-Unit Variability of a Low-Cost GPS Data Logger/Receiver to Study Human Outdoor Walking in View of Health and Clinical Studies

Pierre Abraham,Thomas Sauvaget,Guillaume Mahé,Georges Leftheriotis,Marie Gernigon,Bénédicte Noury-Desvaux,Alexis Le Faucheur,Conrad P Earnest

doi:10.1371/journal.pone.0031338

Abstract

PurposeThe present study evaluates the intra- and inter-unit variability of the GlobalSat® DG100 GPS data logger/receiver (DG100) when estimating outdoor walking distances and speeds.MethodsTwo experiments were performed using healthy subjects walking on a 400 m outdoor synthetic track. The two experiments consisted of two different outdoor prescribed walking protocols with distances ranging from 50 to 400 m. Experiment 1 examined the intra-unit variability of the DG100 (test-retest reproducibility) when estimating walking distances. Experiment 2 examined the inter-unit variability of four DG100 devices (unit to unit variability) when estimating walking distances and speeds.ResultsThe coefficient of variation [95% confidence interval], for the reliability of estimating walking distances, was 2.8 [2.5–3.2] %. The inter-unit variability among the four DG100 units tested ranged from 2.8 [2.5–3.2] % to 3.9 [3.5–4.4] % when estimating distances and from 2.7 [2.4–3.0] % to 3.8 [3.4–4.2] % when estimating speeds.ConclusionThe present study indicates that the DG100, an economical and convenient GPS data logger/receiver, can be reliably used to study human outdoor walking activities in unobstructed conditions. This device let facilitate the use of GPS in studies of health and disease.

Highlights

The use of the Global Positioning System (GPS) is an emerging approach in the study of physical activity [1]
Stated hypotheses The first hypothesis we tested was that the DG100 has a high level of reliability in the measured walking distances resulting from identical prescribed walking protocols (PWPs) performed on two different days
The second hypothesis we tested was that various DG100 units used simultaneously during PWPs show low inter-unit variability when estimating walking distances and speeds

Summary

Introduction

The use of the Global Positioning System (GPS) is an emerging approach in the study of physical activity [1]. GPS has been recently used to study functional limitations in patients with chronic diseases such as multiple sclerosis [2], peripheral artery disease [3,4] and spine surgery [5,6]. Low-cost, lightweight GPS receivers are commercially available Such devices can accurately detect walking and resting bouts [7] as well as accurately estimate walking speed and walking distances [7,8,9,10]. In order to use GPS technology for clinical cohort studies, the technique must be accurate and reliable This applies to studies that compare two tests of the same patient. The capability of investigators to observe significant intra-group changes or inter-group differences with GPS-derived parameters may be compromised

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Discussion

Conclusion