Do GPS Capable Fitness Watches Accurately Measure Exercise Distances?

Abstract

Fitness watches have become popular for assessing activity habits. Manufacturers of GPS capable activity monitors claim their devices provide valid and reliable measures of distances traveled. PURPOSE: To determine if six popular physical activity watches provide accurate measures of GPS recorded distances. METHODS: An Apple Watch (AW), Fitbit Ionic (FI), Fitbit Versa (FV), Garmin Vivosport (GVS), Garmin Vivoactive 3 (GVA), and a Garmin Forerunner 35 (GF) were all tested on indoor and outdoor oval tracks, an outdoor walking trail and a zig-zag pattern course. Twenty trials were performed on each course by the same researcher. An industrial TR 88016 FX Series collapsible measuring wheel established actual distance (200 m). Two watches were worn at the same time on the left arm. Each watch was set to walking and their GPS signal was turned on and connected. Distance measured by the wheel and each watch was recorded. Means, standard deviations, and percent relative error were calculated for the GPS distance of each watch. RESULTS: For the outdoor trail condition, the results showed distances ranging from 180.0 to 204.4 m (FI: 180.2 m, 10.4%, FV: 186.6 m, 7.6%, GVA: 200.7 m, 4.0%, AW: 201.1 m, 4.2%, GVS: 204.4 m, 4.8%, GF: 204.4 m, 4.4%). For the zig-zag course condition, the range was from 184.2 to 204.4 m (GVS: 184.2 m, 4.1%, GF: 189.0 m, 6.0%, FI: 189.8 m, 5.6%, FV: 197.9 m, 4.0%, AW: 197.9 m, 4.0%, GVA: 204.4 m, 4.1%). For the outdoor track, the range was from 179.3 to 204.4 (FV: 179.3 m, 10.8%, AW: 189.8 m, 5.6%, FI: 195.5 m, 4.8%, GVS: 200.3 m, 4.0%, GVA: 202.8 m, 4.0%, GF: 204.4 m, 4.1%). For the indoor track, the range was from 164.2 to 169.0 (FI: 164.2 m, 18.3%, AW: 169.0 m, 16%). All Garmin devices failed to record an indoor measurement. CONCLUSIONS: The least and most accurate measurements for each condition were: trail (FI and GVA), zig-zag (GVS and FV), outdoor track (FV and GVS) and indoor track (FI and AW), respectively. The Garmins were the most accurate for the outdoor track with all exhibiting a 4.0% error. Indoor, all devices were less accurate. Only AW and FI had functioning GPS indoor and showed their most error in this setting. Caution must be used when relying on physical activity monitors if accuracy is desired in measuring distance via GPS.