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Biomechanics Research

Problem

Biomechanics research (e.g. gait analysis, sport or rehabilitation biomechanics, motor control studies) often involves measuring different signals such as kinematics, forces, and EMG. For inverse dynamic analysis (e.g. calculation of joint torques and joint reaction forces), kinematics and forces must be tightly synchronized in time AND space. A small spatial misalignment between the force plate coordinate system and the kinematic coordinate system can lead to large errors in the calculated joint torques.

Knee Joint Torques Figure

Figure 1: Knee torque during walking. Red lines represent a misalignment of the force plate by 1 cm.

Solution

Temporal Synchronization:

An elegant and simple way to achieve perfect temporal synchronization between kinematics and forces (or any other analog data source) is the Optotrak Data Acquisition Unit (ODAU). With the ODAU, you can sample up to 16 analog and/or 8 digital channels at a sample frequency of up to 100,000 Hz divided by the number of channels. As with kinematic Optotrak data, any analog data sampled through the ODAU can be monitored and recorded using First Principles.

First Principles Motion Capture Software Screen Shot

Figure 2: First Principles Software screen shot and photo of research application.

The recorded data can be exported in different formats for further analysis in MATLAB or any other custom made or commercially available analysis software*. Real-time feedback can be used to trigger external events, such as the operation of LCD glasses to control visual information input (i.e. Hansen et al. 2008) or the appearance of obstacles during gait (i.e. Pijnappels et al. 2005).

*Optotrak integrates with Visual 3D from C-Motion, and in real-time.

Spatial Synchronization:

Spatial synchronization can be achieved by digitizing the corners of the force plate (or force plates) in the Optotrak coordinate system. Since the entire capture volume is calibrated, the position and orientation of the force plate in the Optotrak coordinate system can be determined with high accuracy (even on the floor). Once the position of the force plate is known in the Optotrak coordinate system, data in the force plate coordinate system can be transformed into the Optotrak coordinate system. This can be done in First Principles, for force plates sampled through an ODAU, or in your analysis software.

Benefits

  • Perfect temporal and spatial synchronization of forces and kinematics.
  • Easy integration with analog signals from other research equipment (i.e. EMG, gas analyzer).

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