Summary
Studies of motor unit recruitment thresholds have demonstrated the existence of task-specific motor units within the muscles controlling the elbow. Two degree-of-freedom (df) task specificity was investigated at higher levels of elbow torque using the amplitude and frequency characteristics of surface electromyography (EMG). Flexion and supination torque data were collected together with EMG from electrode pairs on the brachioradialis (BRAD), biceps brachii short head, and medial and lateral aspects of biceps brachii long head, while subjects (n=14) performed the following four combinations of isometric tasks: (1) maximum voluntary contraction (MVC) flexion (F) and (2) MVC supination (S), each with a targeted torque of zero in the second d f; (3) MVC flexion with targeted MVC supination (FS); and (4) MVC supination with targeted MVC flexion (SF). Median power frequency (MEDF) and root mean square (RMS) amplitude under steady-state torque conditions were calculated and analyzed using ANCOVA models with planned contrasts (α=0.05). A significant main effect for task was found in RMS, but not in MEDF. Contrasts showed a significant increase in RMS response in the dual MVC tasks (FS and SF) over the single MVC tasks of F and S. The lack of frequency changes with alterations in RMS data indicates that the underlying recruitment/rate coding scheme in use for dual-d f tasks may be different than in single-d f tasks, and provides possible support for the notion of motor unit task groups. Task-by-site interactions were found for both MEDF and RMS, and illustrated that the three biceps sites differed from BRAD in their responses to the F versus S tasks. These results provide further support that the synergy between biceps and BRAD is not fixed, and that the concept of flexor equivalence at the elbow does not hold under all torque task conditions
Similar content being viewed by others
References
Bilodeau M, Arsenault AB, Gravel D, Bourbonnais D (1990) The influence of an increase in the level of force on the EMG power spectrum of elbow extensors. Eur J Appl Physiol 61:461–466
Bouisset S (1973) EMG and muscle force in normal motor activities. In: Desmedt JE (ed) New developments in electromyography and clinical neurophysiology. Karger, Basel, Switzerland, pp 547–583
Buchanan TS, Almdale DP, Lewis JL, Rymer WZ (1986) Characteristics of synergic relations during isometric contractions of human elbow muscles. J Neurophysiol 56:1225–1241
Buchanan TS, Rovai GP, Rymer WZ (1989) Strategies for muscle activation during isometric torque generation at the human elbow. J Neurophysiol 62:1201–1212
Caldwell GE, Leemputte M van (1991) Elbow torques and EMG patterns of flexor muscles during different isometric tasks. Electromyogr Clin Neurophysiol 31:433–445
Fuglevand AJ, Winter DA, Patla AE, Stashuk D (1992) Detection of motor unit action potentials with surface electrodes: influence of electrode size and spacing. Biol Cybern 67:143–153
Haar Romeny BM ter, Denier van der Gon JJ, Gielen CCAM (1982) Changes in recruitment order of motor units in the human biceps muscle. Exp Neurol 78:360–368
Haar Romeny BM ter, Denier van der Gon JJ, Gielen CCAM (1984) Relation between location of a motor unit in the human biceps brachii and its critical firing level for different tasks. Exp Neurol 85:631–650
Henneman E, Clamann HP, Gillies VD, Skinner RD (1974) Rank order of motoneurons within a pool: law of combination. J Neurophysiol 37:1338–1349
Hoffer JA, Loeb GE, Sugano N, Marks WB, O'Donovan MJ, Pratt CA (1987) Cat hindlimb motoneurons during locomotion. III. Functional segregation in sartorius. J Neurophysiol 57:554–562
Johnson MA, Polgar J, Weightman D, Appleton D (1973) Data on the distribution of fibre types in thirty-six human muscles. An autopsy study. J Neurol Sci 18:111–129
Knaflitz M, Merletti R (1988) Suppression of stimulation artifacts from myoelectric-evoked potential recordings. IEEE Trans Biomed Eng 35:758–763
Komi PV, Tesch P (1979) EMG frequency spectrum, muscle structure, and fatigue during dynamic contractions in man. Eur J Appl Physiol 42:41–50
Kukulka C, Clamann P (1981) Comparison of the recruitment and discharge properties of motor units in human brachial biceps and adductor pollicus during isometric contraction. Brain Res 219:45–55
Leemputte M van, Willems EJ (1987) EMG quantification and its application to the analysis of human movements. In: Van Ghelume B, Atha J (eds) Medicine in sport science, vol 25. Karger, Basel, pp 174–194
Loeb GE (1985) Motoneurone task groups: coping with kinematic heterogeneity. J Exper Biol 115:137–146
Masuda T, Sadoyama T (1988) Topographical map of innervation zones within single motor units measured with a grid surface electrode. IEEE Trans Biomed Eng 35:623–628
Moritani T, Muro M (1987) Motor unit activity and surface electromyogram power spectrum during increasing force of contraction. Eur J Appl Physiol 56:260–265
Moritani T, Gaffney FD, Carmichael T, Hargis J (1985) Interrelationships among muscle fiber types, electromyogram, and blood pressure during fatiguing isometric contraction. In: Winter DA et al. (eds) Biomechanics IX-A. Human Kinetics, Champaign, Ill., pp 287–292
Nagata S, Arsenault AB, Gagnon D, Smyth G, Mathieu PA (1990) EMG power spectrum as a measure of muscular fatigue at different levels of contraction. Med Biol Eng Comput 28:374–378
Petrofsky JS, Glaser RM, Phillips CA (1982) Evaluation of the amplitude and frequency components of the surface EMG as an index of muscle fatigue. Ergonomics 25:213–223
Riek S, Bawa P (1992) Recruitment of motor units in human forearm extensors. J Neurophysiol 68:100–108
Roy SH, DeLuca CJ, Schneider J (1986) Effects of electrode location on myoelectric conduction velocity and median frequency estimates. J Appl Physiol 61:1510–1517
Serres SJ de, Hebert LJ, Arsenault AB, Goulet C (1992) Effect of pronation and supination tasks on elbow flexor muscles. J Electromyogr Kinesiol 1:53–58
Solomonow M, Baten C, Smit J, Baratta R, Hermens H, D'Ambrosia RD, Shoji H (1990) Electromyogram power spectra frequencies associated with motor unit recruitment strategies. J Appl Physiol 68:1177–1185
Stulen FB, DeLuca CJ (1981) Frequency parameters of the myoelectric signal as a measure of muscle conduction velocity. IEEE Trans Biomed Eng 28:515–523
Vigreux B, Cnockaert JC, Pertuzon E (1979) Factors influencing quantified surface EMGs. Eur J Appl Physiol 41:119–129
Windhorst U, Hamm TM, Stuart DG (1989) On the function of muscle and reflex partitioning. Behav Brain Sci 12:629–681
Winter DA (1990) Biomechanics and motor control of human movements. Wiley Interscience, New York
Yang JF, Winter DA (1984) Electromyography amplitude normalization methods: improving their sensitivity as diagnostic tools in gait analysis. Arch Phys Med Rehabil 65:517–521
Zuylen EJ van, Gielen CCAM, Denier van der Gon JJ (1988) Coordination and inhomogeneous activation of human arm muscles during isometric torques. J Neurophysiol 60:1523–1548
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Caldwell, G.E., Jamison, J.C. & Lee, S. Amplitude and frequency measures of surface electromyography during dual task elbow torque production. Europ. J. Appl. Physiol. 66, 349–356 (1993). https://doi.org/10.1007/BF00237781
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00237781