Shun Kanega, Master's degree, Yoshihiro Muraoka, PhD
Jpn J Compr Rehabil Sci 16: 19-29, 2025
Objective: A low-computational-load posture estimation
method was employed, assuming integration into a
functional electrical stimulation (FES) device, to estimate
thigh and shank inclination angles as well as the knee
joint angle during gait. The accuracy and processing time
of the method were evaluated to assess its practical
feasibility.
Methods: Two inertial measurement units (IMUs)
were mounted on the lateral thigh and shank. Two
healthy adults performed level-ground gait, including
normal gait and gait reproducing the characteristics of
circumduction gait, which is typically observed in
individuals with post-stroke hemiparesis. A custom
gait pacemaker was developed to replicate the
spatiotemporal asymmetry of hemiparetic gait.
Posture estimation in the sagittal and frontal planes
was performed on a microcontroller using a lowcomputational-
load Madgwick filter, and the
processing time was recorded. The estimation accuracy
was assessed by comparing the results with optical
motion capture data using root mean square error
(RMSE) and cross-correlation analysis.
Results: The average total processing time, including
sampling, posture estimation, and stimulation control,
was 6.8 ms. The RMSE of sagittal plane posture angles
was less than 4ﾂｰ in all cases, suggesting estimation
accuracy comparable to previous studies. For the frontal
plane posture angles, the estimation accuracy was
relatively high during the reproduced circumduction
gait, indicating that the system effectively captured the
circumduction motion. Conversely, the accuracy tended
to be lower during normal gait.
Conclusion: Compared with previous studies, the
posture estimation method used in this study, which
employed the Madgwick filter, was able to estimate
posture without compromising accuracy. The entire
process, including sampling, posture estimation, and
stimulation control, was completed within 10 ms,
reflecting the feasibility of real-time processing at 100
Hz.
Key words: 6-axis IMU, circumduction gait, thigh inclination angle, shank inclination angle, knee joint angle