Wearable Sensor for Measuring Unsupported Sitting Balance in Humans with Cervical Spinal Cord Injury

STUDY DESIGN: Cross-sectional study. OBJECTIVES: To investigate unsupported sitting balance using a wearable inertial measurement unit (IMU)-based sensor in persons with cervical spinal cord injury (cSCI). SETTING: A research lab in the United States of America. METHODS: cSCI participants and healthy controls maintained postural stability during unsupported sitting with eyes open or closed. Cumulative sway motion was calculated using the accelerometer data recorded by the head-mounted IMU sensor. Postural regulatory strategy following cSCI was investigated by analyzing the normalized power spectral density (PSD) in four frequency bands: 0-0.1 Hz (arising from visual regulation), 0.1-0.5 Hz (vestibular regulation), 0.5-1 Hz (cortical structures), and 1> Hz (proprioception and muscle control). RESULTS: We found significant increases in postural sway in cSCI participants compared with healthy participants during unsupported sitting. Normalized PSD was significantly increased in the low-frequency bands (0-0.1 Hz and 0.1-0.5 Hz) but decreased in the high-frequency band (1> Hz) for cSCI participants compared with healthy participants. CONCLUSIONS: cSCI participants relied less on proprioception and muscle control to maintain sitting balance than healthy controls. In contrast, the contributions of visual and vestibular systems to sitting balance were augmented following cSCI. These findings indicated that the change in postural regulatory strategy was ineffective in maintaining postural stability during unsupported sitting, highlighting the importance of proprioception and muscle control in seated postural stability in persons with cSCI.