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Muscle-Tendon Personalization

This tool is used to personalize the muscle-tendon properties of a model to the subject-specific data provided.

How It Works​

MTP uses EMG-driven modeling to personalize muscle-tendon properties. The following properties are optimized:

  • Electromechanical delay
  • Activation time constant
  • Activation nonlinearity constant
  • EMG scale factor
  • Optimal fiber length
  • Tendon slack length
  • Synergy Weights and Commands (if using SynX)

Cost Terms​

There are a series of cost terms that can be used to facilitate the personalization. They are listed here by the name of the cost term as it is passed in the <type> element of an <RCNLCostTerm> in an XML settings file.

  • inverse_dynamic_joint_moment - how closely the experimental joint moments should be tracked
  • activation_time_constant - how closely this term should match the <error_center>
  • activation_nonlinearity_constant - how closely this term should match the <error_center>
  • optimal_muscle_fiber_length - how closely the activation time constant should match the <error_center>
  • tendon_slack_length - how closely the activation time constant should match the <error_center>
  • emg_scale_factor - how closely the activation time constant should match the <error_center>
  • normalized_muscle_fiber_length - how much this term can deviate from the initial value
  • passive_muscle_force - how much passive muscle force is allowed for the motion
  • grouped_normalized_muscle_fiber_length - how much deviation from the mean value of the group is allowed
  • grouped_emg_scale_factor - how much deviation from the mean value of the group is allowed
  • grouped_electromechanical_delay - how much deviation from the mean value of the group is allowed
  • muscle_excitation_penalty - a penalty for muscle excitations above a certain level

Additional Notes​

Muscle-Tendon Length Initialization​

Muscle-Tendon Length Initialization is normally done before MTP to give realistic tendon slack length and optimal fiber lengths for MTP to use. This feature has its own page.

Synergy Extrapolation​

Information about Synergy Extrapolation can be found on its own page.

Group Muscles​

Grouped muscles are groups of muscles defined in the .osim file (under <ForceSet>) that are anatomically grouped by one of:

  • Normalized Fiber Length
  • EMG Scale Factor
  • Electromechanical Delay

Examples of this can be found in the examples of the NMSM Pipeline.