title: Open-loop tracking performance of a limb joint controlled by random, periodic, and abrupt electrical stimulation inputs to the antagonist muscle pair.
abstract: The ability of the cat's ankle joint to track various input signals when controlled by electrically elicited motor unit recruitment, firing rate and antagonist muscle coactivation was examined. Pseudo-random, sinusoidal and staircase signals were used to control the soleus and tibialis anterior muscles isometrically and with a 250-g pendulum. Tracking was evaluated through cross correlation for pseudo-random and sinusoidal signals, and by rise time and steady-state error in step signals. Better tracking was obtained in isometric conditions than in load-moving conditions. Pseudo-random signals resulted in 250-ms delay between input and isometric torque output. For load-moving conditions, 340-ms and 400-ms delay in torque and angle were obtained. For sinusoids, delays decreased from 240 ms at 0.5 Hz, to 140 ms at 2 Hz in isometric conditions. Time delays for angle were between 300 and 400 ms, decreasing as frequency increased. Poor cross correlation was found for torque in load-moving conditions, because of pendulum nonlinear dynamics. Step size was not uniform in staircase trials, with steady-state errors between 9% and 39%, and rise times between 200 and 1000 ms. It is concluded that open-loop joint control results in poor tracking, presumably because it is devoid of feedback mechanisms.
authors.affiliation: Louisiana State University Medical Center, Department of Orthopaedic Surgery, New Orleans 70112, USA.
authors.forename: B H
authors.initials: BH
authors.lastname: Zhou
authors.forename: R V
authors.initials: RV
authors.lastname: Baratta
authors.forename: M
authors.initials: M
authors.lastname: Solomonow
authors.forename: N
authors.initials: N
authors.lastname: Matsushita
authors.forename: R D
authors.initials: RD
authors.lastname: D'Ambrosia
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000843:Ankle Joint / Q000502:physiology*; D002138:Calibration; D002415:Cats; D004558:Electric Stimulation; D005246:Feedback; D007537:Isometric Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D010507:Periodicity; D010543:Peroneal Nerve / Q000502:physiology; D011897:Random Allocation; D011999:Recruitment, Neurophysiological; D012584:Sciatic Nerve / Q000502:physiology