Summary
When using electromyographic techniques in the evaluation of muscular load it is necessary to determine the mathematical relationship between the torque and the amplitude of the electromyographic signal. Isometric gradually increasing contractions up to 100% MVC can then be used. Often more than linear increases for the amplitude (RMS) — force regression have been reported. The present study was designed to test whether changes in power spectral density function take place during a gradually increasing isometric contraction (duration 10 s). Twenty-two clinically healthy females performed an increasing isometric shoulder forward flexion for 10 s using an isokinetic dynamometer. Electromyographic activity was measured in trapezius, deltoid, infraspinatus and biceps brachii using surface electrodes. Mean torque values were determined together with mean power frequency (MPF) and root mean square values (RMS) from the EMG signals for each 256 ms period. The RMS-torque regressions showed higher regression coefficients during the 6th to 9th sec than during the first 5 s. No significant correlation existed between MPF for the four muscles and the torque. A gradual decrease in MPF was generally found from the 6th s. It is concluded that this decrease in power spectral density function might have contributed to the significantly higher regression coefficient for the RMS torque regression at the high output part of the gradually increasing isometric contraction.
Similar content being viewed by others
References
Basmajian JV, DeLuca CJ (1985) Muscles alive — their function revealed by electromyography. 5th edition. Williams & Wilkins, Baltimore, USA, pp 212
Bigland-Ritchie BR, Johansson R, Lippold OCJ, Woods JJ (1982) Changes of single motor units firing rates during sustained maximal voultary contractions. J Physiol 328:27–28P
Bigland-Ritchie BR, Dawson NJ, Johansson RS, Lippold OCJ (1986) Reflex origin for the slowing of motoneurone firing rates in fatigue of human voluntary contractions. J Physiol 379:451–459
Broman H, Bilotto G, DeLuca CJ (1985) Myoelectric signal conduction velocity and spectral parameters: influence of force and time. J Appl Physiol 58:1428–1437
Chaffin DB, Lee M, Freivalds A (1980) Muscle strength assessment from EMG analysis. Med Sci Sports Exerc 12:205–211
DeLuca CJ (1985) Myoelectrical manifestations of localized muscular fatigue in humans. CRC Crit Rev Biomed Enginer 11:251–279
Hagberg M, Ericsson BE (1982) Myoelectric power spectrum dependence on muscular contraction level of elbow flexors. Eur J Appl Physiol 48:147–156
Hagberg C, Agerberg G, Hagberg M (1985) Regression analysis of electromyographic activity of masticatory muscles versus bite force. Scand J Dent Res 93:396–402
Jones NB, Lago PJA (1982) Spectral analysis and the interference EMG. IEEE Proc 129:673–678
Kaiser E, Petersen I (1963) Frequency analysis of muscle action potentials during tetanic contraction. Electromyography 3:5–17
Lago L, Jones NB (1977) Effect of motor unit firing time statistics on EMG spectra. Med Biol Eng Comput 15:648–655
Lawrence JH, DeLuca CJ (1983) Myoelectric signal versus force relationship in different human muscles. J Appl Physiol 54:1653–1659
Lindström L, Magnusson R, Petersen I (1970) Muscular fatigue and action potential conduction velocity changes studied with frequency analysis of EMG signals. Electromyography 10:341–355
Maton B (1981) Human motor unit activity during the onset of muscle fatigue in submaximal isometric isotonic contraction. Eur J Appl Physiol 46:271–281
Merletti R, Sabbahi MA, DeLuca CJ (1984) Medium frequency of the myoelectrical signal — effects of muscle ischemia and cooling. Eur J Appl Physiol 52:258–265
Moritani T, Nagata A, Muro M (1982) Electromyographic manifestations of muscular fatigue. Med Sci Sport Exerc 14:198–202
Naeije M, Zorn H (1982) Relation between EMG power spectrum shifts and muscle fibre action potential conduction velocity changes during local muscular fatigue in man. Eur J Appl Physiol 50:23–33
Siegel S (1956) Non-parametric statistics for the behavioural sciences. Mc Graw-Hill, Tokyo, pp 75–83
Walton JN (1952) The electromyogram in myopathy: analysis with the audio-frequency spectrometer. J Neurol Neurosurg Psychiat 15:219–226
Winter DA, Rau G, Kadefors R (1979) Units, terms and standards in the reporting of electromyographic research. Proc of the 4th Congr of ISEK, Boston
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Gerdle, B., Eriksson, N.E. & Hagberg, C. Changes in the surface electromyogram during increasing isometric shoulder forward flexions. Europ. J. Appl. Physiol. 57, 404–408 (1988). https://doi.org/10.1007/BF00417984
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00417984