title: Predicting the effect of muscle length on fatigue during electrical stimulation.
abstract: Mathematical models have been developed to predict fatigue during functional electrical stimulation, but the predictive accuracy at different muscle lengths is unknown. The objectives of our study were to: (1) experimentally determine the relationship between knee extension angle (20 degrees, 40 degrees, 65 degrees, and 90 degrees) and fatigue of the quadriceps muscles, and (2) predict that relationship using a mathematical model. A computer-controlled stimulator sent trains of pulses to surface electrodes on the thighs of five subjects while forces were measured at the ankle. A two-component mathematical model was developed. One component accounted for force, and the other accounted for fatigue. The model was fit to the data, and parameters were identified at 90 degrees . The fitted subject-averaged r(2) value was 0.89. The model was used to predict fatigue at the remaining angles, and the subject-averaged r(2) values were >0.75. Therefore, at least 75% of the variability in the measurements was explained by the model. The force model is explicitly dependent on angle, and the fatigue model is explicitly dependent on force; therefore, the dependence of fatigue on knee angle was implicit.
authors.affiliation: Biomedical Engineering Program, Bainer Hall, Mechanical Engineering, One Shields Avenue, University of California, Davis, California 95616, USA. msmarion@ucdavis.edu
authors.forename: M Susan
authors.initials: MS
authors.lastname: Marion
authors.forename: Anthony S
authors.initials: AS
authors.lastname: Wexler
authors.forename: Maury L
authors.initials: ML
authors.lastname: Hull
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Binder-Macleod
mesh_terms: D000328:Adult; D000465:Algorithms; D001696:Biomechanical Phenomena; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D007717:Knee / Q000033:anatomy & histology / Q000502:physiology; D007866:Leg / Q000502:physiology; D008297:Male; D015233:Models, Statistical; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*; D011237:Predictive Value of Tests; D055815:Young Adult