PURPOSE:Measuring step count using activity monitors is an increasingly popular method of quantifying physical activity, however it is unknown whether gait irregularities or the use of gait aids affect the accuracy of these devices. This study evaluates the validity of the ActivPAL3, Fitbit Flex, and Jawbone UP Move activity monitors for measuring step count in hospital inpatients after lumbar fusion. METHODS:The ActivPAL3 was tested on the thigh, the Fitbit, and the Jawbone were tested on the wrist and thigh, each monitor was tested 20 times. Validity was examined by calculating the percentage of steps detected by each monitor compared to the criterion measure of observed step count, the Standard Error of Measurement, and the Intraclass Correlation Coefficient. RESULTS:The ActivPAL3 detected 85% (SD 27%) of observed steps. On the wrist, the Fitbit detected 24% (SD 34%) and the Jawbone detected 17% (SD 40%) of observed steps. On the thigh, the Fitbit detected 66% (SD 42%) and the Jawbone detected 22% (SD 35%) of observed steps. CONCLUSION:The ActivPAL3 activity monitor is a sufficiently valid tool to detect step count immediately after lumbar fusion. Wrist worn monitors are not recommended in this population, particularly with patients using gait aids. Implications for Rehabilitation Walking may be quantified using activity monitoring, as both an assessment tool and as an adjunct to treatment The ActivPAL3 is sufficiently valid for use after lumbar fusion surgery The Fitbit Flex and Jawbone UP Move had low accuracy, particularly when a gait aid was used.