A study of the accuracy of the Fitbit Zip in measuring steps both indoors and outdoors in a mixed rehabilitation population

Abstract

Objective: To assess (1) step count accuracy of the Fitbit Zip, compared to manual step count, in people receiving outpatient rehabilitation, in indoor and outdoor conditions, and (2) impact of slow walking speed on Fitbit accuracy. Design: Observational study. Setting: A metropolitan rehabilitation hospital. Subjects: Adults ( n = 88) attending a subacute rehabilitation outpatient clinic with walking speeds of between 0.4 and 1.0 m/s. Interventions: Two 2-minute walk tests, one indoors and one outdoors, completed in random order. Main measures: Step count recorded manually by observation and by a Fitbit Zip, attached to the shoe on the dominant or non-affected side. Subgroup analysis included assessment accuracy for those considered limited community walkers (slower than 0.8 m/s) and those considered community walkers (faster than 0.8 m/s). Results: The Fitbit significantly ( P < 0.05) undercounted steps compared to manual step count, indoors and outdoors, with percentage agreement slightly higher outdoors (mean 92.4%) than indoors (90.1%). Overall, there was excellent consistent agreement between the Fitbit and manual step count for both indoor (ICC 0.83) and outdoor (ICC 0.88) walks. The accuracy of the Fitbit was significantly ( P < 0.05) reduced in those who walked slower than 0.8 m/s outdoors (ICC 0.80) compared to those who walk faster than 0.8 m/s (ICC 0.90). Conclusions: The Fitbit Zip shows high step count accuracy with manual step count in a mixed subacute rehabilitation population. However, accuracy is affected by walking speed, with decreased accuracy in limited community walkers.

Measurement properties of device-based physical activity instruments in ambulatory adults with physical disabilities and/or chronic diseases: a scoping review

“…Most studies included people with stroke ( n = 27) [ 40 – 66 ], chronic obstructive pulmonary disease ( n = 11) [ 67 – 77 ] and multiple sclerosis ( n = 10) [ 78 – 87 ]. Six studies included a mixed population of people with different physical disabilities and/or chronic diseases [ 23 , 75 , 77 , 88 – 90 ]. Sample sizes ranged from 4 to 176, with a median of 28.…”

“…The majority of studies were performed in Northern America (USA, n = 28 [ 51 , 64 , 69 , 70 , 72 , 74 , 76 , 83 – 85 , 91 – 107 ]; Canada, n = 10 [ 40 , 47 , 50 , 52 , 53 , 89 , 108 – 111 ]) and Western Europe (UK, n = 11 [ 78 , 80 , 82 , 86 , 112 – 118 ]; France, n = 8 [ 42 – 45 , 55 , 119 ]; the Netherlands, n = 6 [ 48 , 75 , 77 , 120 – 122 ]; Germany, n = 4 [ 68 , 87 , 123 , 124 ]; Switzerland, n = 4 [ 66 , 81 , 125 , 126 ]; Denmark, n = 3 [ 127 – 129 ]; Belgium, n = 2 [ 67 , 88 ]; Italy, n = 2 [ 56 , 130 ]; Sweden, n = 2 [ 71 , 79 ]; Ireland, n = 1 [ 131 ]; Portugal, n = 1 [ 132 ]). Only 14 studies were performed in other countries (Brazil, n = 6 [ 46 , 49 , 57 , 62 , 63 , 133 ]; Japan, n = 4 [ 59 , 73 , 134 , 135 ]; Australia, n = 3 [ 60 , ...…”

“…Only 14 studies were performed in other countries (Brazil, n = 6 [ 46 , 49 , 57 , 62 , 63 , 133 ]; Japan, n = 4 [ 59 , 73 , 134 , 135 ]; Australia, n = 3 [ 60 , 90 , 136 ]; Czech Republic, n = 1 [ 65 ]). Of the 103 included studies, 65 were performed in a laboratory setting with protocolled activities [ 23 , 40 – 46 , 49 , 51 – 59 , 61 – 66 , 70 , 72 , 75 , 78 – 80 , 83 , 86 , 88 – 90 , 92 , 93 , 95 – 97 , 101 , 103 , 104 , 107 , 109 , 111 – 115 , 119 , 120 , 122 , 123 , 125 , 126 , 128 – 133 , 137 – 139 ], 28 during free-living (activities of own choice) [ 50 , 60 , 67 , 68 , 71 , 73 , 76 , 82 , 87 , 91 , 94 , 98 – 100 , 102 , 105 , 106 , ...…”

The Wearable Activity Tracker Checklist for Healthcare (WATCH): a 12-point guide for the implementation of wearable activity trackers in healthcare

“…Ideally, metrics should provide useful information to clinicians, be relevant to patients, and be sufficiently accurate in the populations they are being used with. For example, slow-walking older adult rehabilitation patients may be suited to step count metrics, as these would correspond to goals of reducing immobility and walking more, and have demonstrated sufficient validity and accuracy in these populations [ 33 ]. Whereas younger populations with greater physical capacity and goals of exercising at higher intensities may be well suited to moderate-vigorous physical activity minutes [ 34 ].…”

“…In such circumstances the wear site may vary for different patients (e.g. very slow walking patients, for whom the ankle may be a more suitable wear site for more accurate measures [ 33 , 41 ]). If the purpose for using activity trackers in this example is for individual activity promotion, then varied wear sites may not be an issue.…”