Validation of an accelerometer system for activity monitoring in children with functional disabilities

This study aimed to assess the validity of the SENS motion® system (SENS) for measuring postures and movements in school-aged children with functional disabilities, using direct video observation as the criterion method. In this cross-sectional study, 29 children (51.7% male; mean age 10.8 ± 2.9 years) from two special schools in Denmark participated. Each child wore a SENS device on the thigh while completing a standardised protocol comprising six activity categories: lying/sitting, standing, walking, running, cycling, and step count. All activities were video recorded. Video data were coded in 5-second epochs and synchronised with the SENS output. Agreement was evaluated by comparing observed time spent in each activity with the corresponding time estimated by SENS, expressed as mean values, standard deviations, mean differences, and percentage agreement. SENS demonstrated excellent agreement for walking (93.2%) and lying/sitting (96.2%), good agreement for running (89.2%), and moderate agreement for standing (74.1%). Cycling was poorly detected, with only 6.4% agreement, as it was frequently misclassified as walking (50.8%) or lying/sitting (42.7%). Step counts were slightly overestimated by SENS (mean difference: 7.2 steps). Overall, SENS tended to underestimate activity duration compared with direct observation.

Conclusion: SENS demonstrated excellent to good validity for detecting lying/sitting and walking, and acceptable validity for running in children with functional disabilities. Validity was moderate for standing and limited for cycling. These findings suggest that SENS may be useful for monitoring several common postures and activities in this population. However, further refinement of the algorithms and broader validation are warranted, particularly for cycling and postural transitions.