Summary
Force and electromyogram (EMG) responses of the medial gastrocnemius muscle were assessed during isometric contractions in 8 decerebrate cat preparations, before and after acute dorsal hemisection of the spinal cord at the T12 level. The measures derived included the relation between static force and mean rectified EMG, the EMG amplitude distribution, EMG power spectral density, and force power spectral density. Our findings were that the spinal lesion induced modifications in the shape of the EMG amplitude distribution, a substantial increase in mean rectified EMG per unit force, and increases in EMG spectral power and force spectral power over a broad band of frequencies. In 7/8 preparations, there was disproportionate enhancement of EMG spectral power below 40 Hz, with a commensurate reduction in the EMG mean power frequency (MPF) in 6 of these 7 cases. Recordings of motoneuron discharge from 9 decerebrate preparations taken before and after the spinal hemisection revealed that the lesion-induced changes in EMG and force power spectra were accompanied by lower mean discharge rates, and by a compression of the range of recruitment force. These changes in motoneuron rate and recruitment were probably responsible for the changes in EMG and force measures, especially for the relative increase in low-frequency EMG power. If these acute disturbances of motoneuron rate and recruitment persist in chronic human neurological disorders, they represent an important and largely unrecognized source of muscular weakness and increased fatigability.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Agarwal GC, Gottlieb GL (1975) An analysis of the electromyogram by Fourier, simulation, and experimental techniques. IEEE-BME 22: 225–229
Allum HJ, Dietz V, Freund H-J (1978) Neuronal mechanisms underlying physiological tremor. J Neurophysiol 41: 557–571
Bendat JS, Piersol AG (1971) Random data: analysis and measurement procedures. Wiley-Interscience, New York
Blaschak MJ, Rymer WZ, Marder-Meyer J (1984) Force-EMG relationships in spastic-paretic muscle. Soc Neurosci Abstr 10: 904
Blinowska K, Piotrkiewicz M (1978) A study of surface electromyograms by means of digital stimulation. II. Spectral analysis of simulated and experimental electromyograms. Electromyogr Clin Neurophysiol 18: 95–105
Burke D, Knowles L, Andrews C, Ashby P (1972) Spasticity, decerebrate rigidity and the clasp-knife phenomenon: an experimental study in the cat. Brain 95: 31–48
Burke RE (1968) Firing patterns of gastrocnemius motor units in the decerebrate cat. J Physiol 196: 631–654
Burke RE, Rudomin P, Zajac FE (1976) The effect of activation history on tension production by individual muscle units. Brain Res 109: 515–529
Cooper S, Eccles JC (1930) The isometric responses of mammalian muscles. J Physiol 69: 377–385
Cordo P, Rymer WZ (1982) Motor unit activation patterns in lengthening and isometric contractions of hindlimb extensor muscles in the decerebrate cat. J Neurophysiol 47: 782–796
Cox DR, Miller HD (1965) The theory of stochastic processes. Methuen, London
Grill S, Rymer WZ (1985) Reflex actions of muscle afferents on fusimotor innervation in decerebrated cats: an assessment of beta contributions. Exp Brain Res 59: 282–295
Jackson JH (1932) Selected writings of John Hughlings Jackson, Vol II, J Taylor (ed). Hodder and Stoughton, London
Kernell D, Eerbeek O, Verhey BA (1983) Relation between isometric force and stimulus rat in cat's hindlimb motor units of different twitch contraction time. Exp Brain Res 50: 230–237
Kwanty E, Thomas DH, Kwanty HG (1970) An application of signal processing techniques to the study of myoelectric signals. IEEE-BME 17: 303–312
LeFever RS, DeLuca CJ (1976) The contribution of individual motor units to the EMG power spectrum. Proceedings of the 29th ACEMB, Boston 56
Lindström L, Magnusson R (1977) Interpretations of myoelectric power spectra: a model and its applications. Proc IEEE 65: 653–662
Lindström L, Petersen I (1981) Power spectra of myoelectric signals: motor unit activity and muscle fatigue. In: Clinical neurophysiology. Butterworths, London, pp 66–87
Milner-Brown HS, Stein RN (1975) The relation between the surface electromyogram and muscular force. J Physiol 246: 549–569
Powers RK, Blaschak MJ, Rymer WZ (1985) EMG power spectrum and motor unit discharge in an animal model of spastic paretic weakness. Soc Neurosci Abstr 11: 408
Rabiner LR, Schafer RW, Dlugos D (1979) Periodogram method for power spectrum analysis. In: Digital signal processing committee, IEEE acoustics, speech, and signal processing society (ed) Programs for digital signal processing IEEE Press, pp 2.1-1–2.1-10
Rack PMH, Westbury DR (1969) The effects of length and stimulus rate on tension in the isometric cat muscle. J Physiol 204: 443–460
Rymer WZ, Houk JC, Crago PE (1979) Mechanisms of the claspknife reflex studied in an animal model. Exp Brain Res 37: 93–113
Tang A, Rymer W (1981) Abnormal force-emg relations in paretic limbs of hemiparetic human subjects. J Neurol Neurosurg Psychiat 44: 690–698
Van Boxtel A, Schomaker LRB (1983) Motor unit firing rate during static contraction indicated by the surface EMG power spectrum. IEEE-BME 30: 601–608
Welch PD (1967) The use of fast fourier transform for the estimation of power spectra: a method based on time averaging over short, modified periodograms. IEEE Trans Aud Electroacoust AU-15: 70–73
Weytjens JLF, van Steenberghe D (1984) The effects of motor unit synchronization in the power spectrum of the electromyogram. Biol Cybern 57: 71–77
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Blaschak, M.J., Powers, R.K. & Rymer, W.Z. Disturbances of motor output in a cat hindlimb muscle after acute dorsal spinal hemisection. Exp Brain Res 71, 377–387 (1988). https://doi.org/10.1007/BF00247497
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00247497