Overview and Authors
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The experimental data included with the model files in the OpenSim distribution was collected as part of the study cited below. Please note that the data distributed with OpenSim is from a different subject than the one described in the paper. Data collection protocols were the same for both subjects.
Chand T. John, Frank C. Anderson, Jill S. Higginson & Scott L. Delp (2012): Stabilisation of walking by intrinsic muscle properties revealed in a three-dimensional muscle-driven simulation, Computer Methods in Biomechanics and Biomedical Engineering, DOI:10.1080/10255842.2011.627560. Download here
Accessing the Models
The musculoskeletal file (.osim), the setting files (.xml), and associated result files (.mot, .sto) for this model are provided free of charge with the OpenSim software for researchers interest in reproducing the result of the simulation. These files can be accessed via the Models/Gait2392_Simbody or Models/Gait2354_Simbody folder in the OpenSim 3.0 installation directory, and the example/Gait2392_Simbody or Models/Gait2392_Simbody folder in the OpenSim 2.4.0 installation directory.
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Pelvic Tilt and Hip Flexion Angle (Gait2354 vs. Clinical Measurements)
The pelvic frame is located midway between the two ASIS. In the neutral position, the model has zero pelvic tilt with respect to ground (or lab). In other words, the pelvic frame and ground frame are aligned at neutral (pelvic tilt = 0 degrees). In many clinical papers, neutral corresponds to 12-13 degrees of pelvic tilt. This will lead to an offset when comparing pelvic tilt and hip flexion angles from the gait2354 model to some data from clinical papers or gait analysis lab data.
To compare angles from the gait2354 model to clinical data, you can subtract the angle formed between the horizontal plane and a line between the ASIS and PSIS markers from the clinical pelvic tilt measurements. You should also add this value to the clinical hip flexion measurement. If angle formed between the horizontal plane and a line between the ASIS and PSIS markers is not known, a value of 12-13 degrees is typical.
Hip Joint
The hip is characterized as a ball-and-socket joint. The transformation between the pelvic and femoral reference frame is thus determined by successive rotations of the femoral frame about three orthogonal axes fixed in the femoral head.
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Actuators and Other Force-Generating Elements
Peak isometric force
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The gait2392 model Includes the 43 muscles specified in the Delp leg model and the 6 lumbar muscles included in Anderson's gait model.
Peak isometric force
In the original lower limb model developed by Delp et al. (1990), values for the muscle-tendon parameters are determined with a procedure similar to that used by Hoy et al. (1990). Values for muscle physiological cross-sectional area (PCSA), which determine the peak isometric force, are taken from Friederich et al. (1990) and Wickiewicz (1983). Because the measurements reported by Friederich et al. (1990) [25 N-m2] are obtained from experiments on young cadavers, and those reported by Wickiewicz et al. (1983) [61 N-m2 ] are obtained from experiments on elderly cadavers, a factor that is larger than the “specific tension” reported by Spector at al. (1980) [23 N-m2] is used to scale the PCSA values from the elderly cadavers.
While constructing the Gait 2392 Model from the original Delp model, Anderson noticed that the muscle strengths in the Delp model were still weak compared to the experimental results from Anderson and Pandy (1999) and Carhart (2000) on healthy, living subjects. To better match the strength of the Delp model to the joint torque-angle relationships measured in living subjects, additional strength scaling was employed. Despite efforts to keep the scaling factor consistent across all muscles, a different scaling factor is needed for bi-articular muscles because they span two joints. In many cases, the muscle strength parameters from Anderson and Pandy are used instead, as they are more physiologically accurate.
For details, refer to the following PDF of the maximum isometric muscle forces from Gait2392/Gait2354, Delp1990, and Carhart2000, along with the scale factors: MuscleMaxIsometricForces.pdf We also conducted 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,we do not expect these increases would greatly affect the distribution of muscle force estimates, nor the interpretation of those results.
Optimal fiber length and pennation angle
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