title: Predicting muscle forces of individuals with hemiparesis following stroke.
abstract: BACKGROUND
  Functional electrical stimulation (FES) has been used to improve function in individuals with hemiparesis following stroke. An ideal functional electrical stimulation (FES) system needs an accurate mathematical model capable of designing subject and task-specific stimulation patterns. Such a model was previously developed in our laboratory and shown to predict the isometric forces produced by the quadriceps femoris muscles of able-bodied individuals and individuals with spinal cord injury in response to a wide range of clinically relevant stimulation frequencies and patterns. The aim of this study was to test our isometric muscle force model on the quadriceps femoris, ankle dorsiflexor, and ankle plantar-flexor muscles of individuals with post-stroke hemiparesis.
  
  
  METHODS
  Subjects were seated on a force dynamometer and isometric forces were measured in response to a range of stimulation frequencies (10 to 80-Hz) and 3 different patterns. Subject-specific model parameter values were obtained by fitting the measured force responses from 2 stimulation trains. The model parameters thus obtained were then used to obtain predicted forces for a range of frequencies and patterns. Predicted and measured forces were compared using intra-class correlation coefficients, r2 values, and model error relative to the physiological error (variability of measured forces).
  
  
  RESULTS
  Results showed excellent agreement between measured and predicted force-time responses (r2 >0.80), peak forces (ICCs>0.84), and force-time integrals (ICCs>0.82) for the quadriceps, dorsiflexor, and plantar-fexor muscles. The model error was within or below the +95% confidence interval of the physiological error for >88% comparisons between measured and predicted forces.
  
  
  CONCLUSIONS
  Our results show that the model has potential to be incorporated as a feed-forward controller for predicting subject-specific stimulation patterns during FES.
authors.affiliation: 301 McKinly Laboratory, Department of Physical Therapy, University of Delaware, Newark, DE 19716, USA. kesar@udel.edu
authors.forename: Trisha M
authors.initials: TM
authors.lastname: Kesar
authors.forename: Jun
authors.initials: J
authors.lastname: Ding
authors.forename: Anthony S
authors.initials: AS
authors.lastname: Wexler
authors.forename: Ramu
authors.initials: R
authors.lastname: Perumal
authors.forename: Ryan
authors.initials: R
authors.lastname: Maladen
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Binder-Macleod
mesh_terms: D000368:Aged; D003198:Computer Simulation; D004558:Electric Stimulation / Q000379:methods*; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010291:Paresis / Q000150:complications* / Q000503:physiopathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D020521:Stroke / Q000150:complications / Q000503:physiopathology*