Exploring actical accelerometers as an objective measure of physical activity in people with multiple sclerosis.

OBJECTIVE

To assess the feasibility, acceptability, and psychometric properties of Actical accelerometers in people with multiple sclerosis (MS).

DESIGN

Participants attended 2 testing sessions 7 days apart in which they completed 6 activities ranging in intensity while wearing an Actical accelerometer and Polar heart rate monitor. Perceived exertion was recorded after each activity.

SETTING

University research center.

PARTICIPANTS

People (N=31) with a definite diagnosis of MS were purposefully selected, aiming for diversity in level of reported disability, age, sex, and type of MS.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Actical accelerometer, Polar S810i and RS800sd heart rate monitors, Borg rating of perceived exertion, six-minute walk test (6MWT), 30-second chair stand test.

RESULTS

Accelerometers had good feasibility and acceptability in people with MS. Test-retest reliability was poor for sedentary and free-living activities, with low to moderate intraclass correlation coefficients (.00-.75), but was better for more vigorous or rhythmic activities (.85-.90). Bland-Altman 95% limits of agreement for average accelerometer counts were wide, ranging from +/-16 (newspaper reading) to +/-1330 (6MWT). Validity was not established with 95% prediction intervals showing high variability for all activities.

CONCLUSIONS

The psychometric problems highlighted here suggest Actical accelerometers should be used with caution in people with MS as a measure of physical activity, particularly when measuring comparatively sedentary or free-living activities.