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Estimating Movement Smoothness From Inertial Measurement Units.

Alejandro Melendez-Calderon1,2,3, Camila Shirota4,5,6, Sivakumar Balasubramanian7

  • 1Cereneo Advanced Rehabilitation Institute (CARINg), Vitznau, Switzerland.

Frontiers in Bioengineering and Biotechnology
|February 1, 2021
PubMed
Summary

Inertial measurement units (IMUs) can estimate movement smoothness, but direct application of spectral arc length (SPARC) and log dimensionless jerk (LDLJ-V) to reconstructed velocity is error-prone. A modified LDLJ-A measure is proposed for acceleration data.

Keywords:
SPARCassessmentinertial measurement unitsjerkmovement kinematicsmovement smoothness

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Area of Science:

  • Biomechanics
  • Robotics
  • Human-Computer Interaction

Background:

  • Inertial measurement units (IMUs) are widely used for quantifying human movement.
  • Movement smoothness is a key indicator of motor behavior, often assessed using metrics like spectral arc length (SPARC) and log dimensionless jerk (LDLJ-V).
  • Current research often assumes IMU kinematic data can be directly applied to these smoothness measures without validation.

Purpose of the Study:

  • To systematically evaluate the validity of using SPARC and LDLJ-V with IMU-derived kinematics for movement smoothness analysis.
  • To investigate the impact of IMU data processing, particularly integration drift and orientation errors, on smoothness measures.
  • To propose and evaluate a modified jerk-based measure (LDLJ-A) for translational movements using acceleration data.

Main Methods:

  • Systematic evaluation of SPARC and LDLJ-V applied to translational and rotational velocities derived from IMU data.
  • Analysis of simulated and experimental data to assess measure performance.
  • Development and validation of a modified log dimensionless jerk measure for acceleration data (LDLJ-A).

Main Results:

  • SPARC and LDLJ-V are valid only when applied to velocity data.
  • Applying SPARC and LDLJ-V to IMU-reconstructed translational velocity is highly error-prone due to integration drift.
  • SPARC is suitable for gyroscope-measured rotational velocity, while LDLJ-V may be error-prone.
  • The proposed LDLJ-A measure's accuracy depends on IMU orientation reconstruction errors.

Conclusions:

  • Direct application of standard smoothness measures to IMU-derived translational velocity is not recommended.
  • SPARC can be reliably used with gyroscope rotational velocity, but LDLJ-V requires careful consideration.
  • The LDLJ-A measure offers a viable alternative for assessing smoothness in discrete translational movements from acceleration data.
  • Recommendations are provided for appropriate application of smoothness measures with IMU data across various scenarios.