Comments on Gait2392 Max Isometric Muscle Force

Samuel Hamner, September 12, 2008

There were some notes that were not transferred to the gait2392 model when it was converted from SIMM.

The comment states "Includes the 43 muscles specified in the Delp leg model and the 6 lumbar muscles included in Anderson's gait model. Peak isometric muscle forces of Delp scaled upward based on joint moment-angle data of healthy young males as done by Anderson (1999) and Carhart (2000, reported in Yamaguchi text)."

To further elaborate, the Delp model, which uses strengths based primarily on cadaver muscle cross-sections, is somewhat weak - and this was observed by both Anderson and Carhart. The the maximum contraction forces were scaled to better reflect Anderson and Pandy's model and the joint torque-angle relationships. This method of "strength scaling" is outlined in Anderson and Pandy (1999) and the Yamaguchi text. We tried to do this somewhat uniformly for all muscles at a joint, but bi-articular muscles are an exception as they span two joints. So in the end, it is not a strict uniform scaling, and in some cases Anderson and Pandy's muscle strength parameters were used when each model had the same muscle.

Here are two PDFs:

(1) includes the isometric muscle forces from Gait2392, Delp1990, and Carhart2000, along with the scale factors: MuscleIsometricForces.pdf
(2) a comparison of CMC results from the Gait2392 walking example was made between the "scaled" Gait2392 and isometric forces from Delp (1990): Gait2392ComparisonResultsCMC.pdf

Note, that the muscles activations predicted by CMC were not significantly different between the two sets of isometric muscle force. Therefore, I would not expect these increases would greatly affect the distribution of muscle force estimates, nor the interpretation of those results.

Here are the references mentioned:

Delp, "Surgery Simulation: A computer graphics system to analyze and design musculoskeletal reconstructions of the lower extremity," Ph.D. Dissertation, Stanford University, 1990.

Anderson FC and Pandy MG. A dynamic optimization solution for vertical jumping in three dimensions. Computer Methods in Biomechanics and Biomedical Engineering 2:201-231, 1999.

Yamaguchi, G. T. Dynamic Modeling of Musculoskeletal Motion: A Vectorized Approach for Biomechanical Analysis in Three Dimensions, Kluwer Academic Publishing, 2001.

Carhart, M. R. "Biomechanical Analysis of Compensatory Stepping: Implications for Paraplegics Standing Via FNS," Ph.D Dissertation, Arizona State University, 2000.

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