The influence of antagonist muscle control strategies on the isometric frequency response of the cat's ankle joint

• Published in: IEEE transactions on biomedical engineering Vol. 44; no. 7; pp. 634 - 639
• Main Authors: Goodwin, A., Bing-He Zhou, Baratta, R.V., Solomonow, M., Keegan, A.P.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-07-1997; Institute of Electrical and Electronics Engineers
• Subjects: Analysis of Variance; Analytical models; Animals; Ankle Joint - physiology; Biological and medical sciences; Biomedical engineering; Cats; Electric Stimulation - methods; Electrical stimulation; Fast Fourier transforms; Fourier Analysis; Frequency response; Fundamental and applied biological sciences. Psychology; Isometric Contraction - physiology; Joints; Muscle, Skeletal - physiology; Muscles; Neuromuscular stimulation; Orthopedic surgery; Random Allocation; Stability; Striated muscle. Tendons; Vertebrates: osteoarticular system, musculoskeletal system; Fissipedia; Carnivora; Electrical stimulus; Lower limb; Isometric muscular contraction; Experimental study; Modeling; Osteoarticular system; Vertebrata; Ankle joint; Mammalia; Animal; Cat; Muscle; Frequency response; Agonist antagonist; Signal analysis
• ISSN: 0018-9294; 1558-2531
• DOI: 10.1109/10.594904

This study investigated the effect of various strategies to control the interaction between agonist and antagonist muscles on the frequency response of the isometric cat ankle joint actuated by the tibialis anterior (TA) and soleus (SOL) muscles. Some strategies were based on the physiologic need for increasing joint stability during forceful contractions; with these strategies, the proportional rate of physiologic antagonist activity was termed antagonist gain. Other strategies were based on the electrical stimulation literature, which advocates co-contraction at low force levels. The range of crossover of antagonist activity to the agonist's domain was termed overlap. Strategies consisting of 0%, 10%, and 20% antagonist gain were combined with 0%, 50%, and 100% overlap for a total of nine strategies. These were applied to the TA and SOL using sinusoidal input signals varying in frequency from 0.4 to 6 Hz. Gain and phase Bode plots were constructed through the use of the fast Fourier transforms (FFTs); and analysis of variance determined the significance of differences in gain and phase across frequencies. Best-fit models consisting of four poles and two zeroes were used to fit the experimental data and compared against an analytical model of muscles acting independently across the joint. Harmonic distortion was calculated to evaluate signal quality. It was found that changing the overlap and the antagonist gain produces significant changes in the dynamic response of the two-muscle joint system. The analytical approach to modeling such a system tends to consistently overestimate gain. It is suggested that signal quality is optimal when a moderate amount of antagonist gain (10%) is engaged, with overlap of 50% to smooth transitions between opposing movements. It is expected that this type of strategy will achieve optimum signal quality while preserving the long-term integrity of the joint.