Optimization of MIMU Mounting Position on Shank in Posture Estimation Considering Muscle Protuberance

Area of Science:

• Biomechanics
• Human Motion Analysis
• Wearable Sensor Technology

Background:

• Accurate posture estimation is crucial for biomechanical analysis and clinical applications.
• The placement of magnetic-inertial measurement units (MIMUs) significantly impacts posture estimation accuracy.
• Optimal MIMU placement on the shank, particularly considering anatomical features, requires further investigation.

Purpose of the Study:

• To determine the optimal mounting position of a MIMU on the shank for accurate posture estimation.
• To compare the accuracy of shank posture estimation using MIMUs placed in commonly used (lateral, frontal) and a proposed (medial tibial) positions.
• To evaluate the influence of muscle contraction and anatomical structure on MIMU orientation and posture estimation.

Main Methods:

• Comparative experimental design involving three MIMU mounting positions on the shank: lateral, frontal, and medial tibial.
• Experiment 1: Ankle joint plantar-dorsiflexion and relaxation in a seated position to assess MIMU orientation changes due to muscle contraction.
• Experiment 2: Gait analysis comparing MIMU-based shank posture estimation with optical motion capture to evaluate accuracy across different mounting positions.

Main Results:

• The medial tibial position exhibited significantly smaller orientation changes (80% reduction vs. anterior tibia during dorsiflexion) due to muscle contraction.
• The medial tibial position achieved the highest posture estimation accuracy, with a 13% lower Root Mean Square Error (RMSE) compared to the anterior position during gait.
• MIMU placement on the medial tibia, free from underlying muscle, demonstrated reduced susceptibility to muscle protuberance effects.

Conclusions:

• The medial tibial position is identified as the optimal location for MIMU mounting on the shank for superior posture estimation accuracy.
• Mounting MIMUs on the medial tibia minimizes errors associated with muscle activity and anatomical variations.
• This finding has implications for improving the reliability of wearable sensor-based motion analysis in various applications.