Accuracy and precision of consumer-level activity monitors for stroke detection during wheelchair propulsion and arm ergometry

Abstract

The purpose of this study was to evaluate whether consumer-level activity trackers can estimate wheelchair strokes and arm ergometer revolutions. Thirty able-bodied participants wore three consumer-level activity trackers (Garmin VivoFit, FitBit Flex, and Jawbone UP24) on the wrist. Participants propelled a wheelchair at fixed frequencies (30, 45 and 60 strokes per minute (spm)) three minutes each and at pre-determined varied frequencies, (30-80 spm) for two minutes. Participants also freely wheeled through an obstacle course. 10 other participants performed arm-ergometry at 40, 60 and 80 revolutions per minute (rpm), for three minutes each. Mean percentage error (MPE(SD)) for 30 spm were ≥46(26)% for all monitors, and declined to 3-6(2-7)% at 60 spm. For the obstacle course, MPE ranged from 12-17(7-13)% for all trackers. For arm-ergometry, MPE was at 1-96(0-37)% with the best measurement for the Fitbit at 60 and 80 rpm, and the Garmin at 80rpm, with MPE = 1(0-1)%. The consumer-level wrist-worn activity trackers we tested have higher accuracy/precision at higher movement frequencies but perform poorly at lower frequencies.

Fig 1. Wheelchair rollers setup.

An illustration of the participant propelling the wheelchair on suspended rollers.

Fig 2. Mixed frequencies trial.

A graphic representation of the frequencies and number of strokes performed for the Mixed condition during the rollers task.

Fig 3. Obstacle course depiction.

The obstacle course negotiated by participants in a manual wheelchair. The course covered ~9m x7.5m area.

Fig 4. Wheelchair rollers task statistics.

Means and 95%CI for (a) counts, (b) mean percentage error, and (c) standard error of measurement. Significant difference (p≤.05) *from Predetermined, ^afrom 30 spm, ^bfrom 45 spm, ¹from Garmin, ²from Fitbit.

Fig 5. Obstacle course task statistics.

Means and 95%CI for (a) counts, (b) mean percentage error, and (c) standard error of measurement. *significant difference from true (p≤.05).

Fig 6. Statistic and 95%CI for obstacle course task.

*Significant difference from 0 (p≤.05).

Fig 7. Modified Bland-Altman plots for obstacle course task.

Observed values on x-axis. LoA were centered on 0. MCID = 25% of observed values. LoA, Limit of Agreement; MCID, minimal clinically important difference.

Fig 8. Ergometer task statistics.

Means and 95%CI for (a) counts, (b) mean percentage error, and (c) standard error of measurement. Significant difference (p≤.05) *from true values, ^afrom 40 rpm, ^bfrom 60 rpm, ¹from Garmin, ²from Fitbit.