Functional Electrical Stimulation Patterns Computed Using a Forward Dynamic Model
Forward dynamic modeling is the state-of-the-art biomechanics modeling method to study muscle
coordination in human movement. The model is generally comprised of segments representative of the
skeletal system and force actuators representative of the musculature. The model is designed to
represent the processes by which the body transforms neuromuscular excitations into muscle forces
that act on segments to produce movement. Simulations of movement are generated by using
optimization techniques to determine the set of muscle excitations that either replicate experimental
data (tracking simulation) or satisfy a stated goal, for example maximal height jumping.
The generation of movement in forward dynamic simulations parallels the generation of movement in
functional electrical stimulation (FES) activities. In both cases neuromuscular excitation inputs activate
muscles which generate forces that can lead to movement. Because of the similarities, forward dynamic
simulations are a good way to study and develop FES applications. Additionally, FES applications provide
a means to validate forward dynamic simulations.
FES pedaling provides a means by which individuals with spinal cord injury can obtain cardiorespiratory
exercise. However, the early onset of muscle fatigue is a limiting factor in the exercise benefit obtained
while pedaling a FES ergometer. In an effort to improve the benefit of FES pedaling exercise, I developed
a forward dynamic model to determine muscle excitation timing patterns that simulated increased
endurance in FES pedaling. The efficacy of the computed muscle excitation patterns to prolong the
duration of FES pedaling was evaluated in experiments with individuals with spinal cord injury. The
results indicated that the forward dynamic simulation muscle excitation timing patterns led to improved
FES pedaling outcomes.