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Expression of joint moment in the joint coordinate system
Guillaume Desroches1, Laurence Chèze, Raphaël Dumas
1Université de Lyon, Lyon, France. guillaume.desroches@gmail.com
Journal of Biomechanical Engineering
|November 2, 2010
Summary
This study clarifies expressing joint moments in nonorthogonal systems, proposing a method for net mechanical action assessment. Nonorthogonal projections are recommended for accurately representing joint resistance in joint coordinate systems.
Area of Science:
- Biomechanics
- Kinetics
- Orthogonal and Nonorthogonal Coordinate Systems
Background:
- Reporting joint moments using nonorthogonal joint coordinate systems (JCS) is debated.
- Existing methods for expressing joint moments in nonorthogonal systems lack clarity.
Purpose of the Study:
- To present a method for expressing any 3D vector in a nonorthogonal coordinate system.
- To clarify the interpretation of these expressions within the JCS.
- To provide examples for 3D joint moment vectors at the shoulder and knee.
Main Methods:
- A nonorthogonal projection method based on the mixed product was proposed.
- The method was applied to 3D joint moment vectors.
- Root mean squares (rmss) were used to compare nonorthogonal and orthogonal projections for shoulder and knee joint moments during specific activities.
Main Results:
- Nonorthogonal projections represent the net mechanical action on JCS axes, crucial for assessing joint resistance.
- Orthogonal projections on JCS axes were interpreted as 'motor torque,' dependent on the kinematic model.
- Significant differences in amplitudes were observed between nonorthogonal and orthogonal projections, particularly at the shoulder (6–22.3 Nm) compared to the knee (0.8–3.0 Nm).
Conclusions:
- Nonorthogonal projections should be used to represent the net mechanical action at a joint within a JCS.
- Orthogonal projections on proximal/distal coordinate systems represent net mechanical actions, unlike orthogonal projections on JCS axes.
- The proposed method clarifies the use of nonorthogonal systems for analyzing joint moments.
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