Validity and reliability of an IMU-based method to detect APAs prior to gait initiation

Abstract

Anticipatory postural adjustments (APAs) prior to gait initiation have been largely studied in in traditional, laboratory settings using force plates under the feet to characterize the displacement of the center of pressure. However clinical trials and clinical practice would benefit from a portable, inexpensive method for characterizing APAs. Therefore, the main objectives of this study were: 1) to develop a novel, automatic IMU-based method to detect and characterize APAs during gait initiation and 2) to measure its test-retest reliability. Experiment I was carried out in the laboratory to determine the validity of the IMU-based method in ten subjects with PD (OFF medication) and 12 control subjects. Experiment II was carried out in the clinic, to determine test-retest reliability of the IMU-based method in a different set of 17 early-to-moderate, treated subjects with PD (tested ON medication) and 17 age-matched control subjects. Results showed that gait initiation characteristics (both APAs and 1st step) detected with our novel method were significantly correlated to the characteristics calculated with a force plate and motion analysis system. The size of APAs measured with either inertial sensors or force plate were significantly smaller in subjects with PD than in control subjects (p<0.05). Test-retest reliability for the gait initiation characteristics measured with inertial sensors was moderate-to-excellent (.56<ICC<.82) for both groups. Our findings support the feasibility of automatically characterizing postural preparation and gait initiation with body-worn inertial sensors that would be practical for unsupervised clinical and home settings.

Gait initiation is impaired in subjects with Parkinson’s disease in the OFF state: Evidence from the analysis of the anticipatory postural adjustments through wearable inertial sensors

“…Participants stood with feet externally rotated on separate, side-by-side force plates at heel-to-heel distance of 10 cm [9]. They performed 3 gait initiation trials starting with their most affected leg at comfortable pace.…”

“…Our method differs from those adopted in previous studies [9–11] because of the ability to characterize both the imbalance (from the APA onset to the heel-off of the stepping limb) and unloading (from the heel-off to the toe-off of the same limb) phases preceding the step execution. Unlike force plates and EMGs, a wireless, body-worn sensor approach to measuring APAs enables measurement of postural preparation for movement in clinical settings, even though optimal placements and outcomes have still to be identified [12,13].…”

Gait and Quiet-Stance Performance Among Adolescents After Concussion-Symptom Resolution

“…Gait and quiet-stance outcome variables were measured using an inertial sensor system (Opal Sensor; APDM Inc, Portland, OR) that has previously been identified as a valid and reliable system to characterize gait and postural control. 14 The sensors were attached at the lumbosacral junction level of the spine and on the dorsum of each foot with an elastic strap. Sensor data were obtained at a sampling frequency of 128 Hz, synchronized, and wirelessly transmitted to a laptop computer during each trial.…”

Mobility as the purpose of postural control

“…The range of CoM positions that can be maintained in quiet standing thus decreases with age and with the severity of Parkinson's disease. Moreover, the forwards acceleration of the CoM in gait initiation, as well as the subsequent walking speed, is reduced with age and with Parkinson's disease (Halliday et al, 1998;Mancini et al, 2016). Thus, although the elderly and Parkinsonian subjects are quite as capable as young adults of maintaining their CoM immobile during quiet standing, we suggest that their higher risk of falling is due to a limited capacity to move when this becomes necessary to prevent a fall.…”

“…The amplitude of the initial backwards shift of the CoP thus increases over the first several years of life as children learn to walk faster (Bril et al, 2015;Ledebt et al, 1998). It then decreases with age, and with certain neurological diseases such as Parkinson's disease (Halliday et al, 1998;Mancini et al, 2016).…”