Experimental Brain Research

, Volume 180, Issue 3, pp 509–516 | Cite as

Motor unit conduction velocity during sustained contraction of the vastus medialis muscle

  • Nosratollah Hedayatpour
  • Lars Arendt-Nielsen
  • Dario Farina
Research Article


The aim of the study was to analyze motor unit conduction velocity at varying force of the vastus medialis muscle during sustained contraction. Surface (8-electrode array) and intramuscular (two wire electrodes) EMG signals were recorded from the distal part of the dominant vastus medialis muscle of ten healthy male subjects. The subjects sat on a chair with the knee 90° flexed and performed seven 180-s long contractions at forces in the range 2.5–30% of the maximal voluntary contraction force. For each force level, the discharge patterns of the newly recruited motor units with respect to the previous force level were identified from the intramuscular recordings and used as trigger for averaging the surface EMG signals. Motor unit conduction velocity was estimated from the averaged surface EMG. Average discharge rate at which motor units were analyzed was the same for each force level (mean ± SD, 8.3 ± 0.8 pulses per second). Motor unit conduction velocity at the beginning of the contraction and its rate of change over time increased with force (P < 0.05). Conduction velocity at the beginning of the contraction estimated from the interference surface EMG (4.44 ± 0.66 m/s) and from single motor units (4.75 ± 0.56 m/s) were positively correlated (R 2 = 0.46; P < 0.0001) but significantly different (P < 0.05). The results indicate that single motor unit conduction velocity and its rate of change during sustained contraction, assessed at a fixed discharge rate, depend on force level.


Multi-channel EMG Conduction velocity Motor unit 



Grants: The Danish Technical Research Council (Program “Centre for Neuroengineering (CEN)”, contract number 26-04-0100) partly supported the study.


  1. Andreassen S, Arendt-Nielsen L (1987) Muscle fibre conduction velocity in motor units of the human anterior tibial muscle: a new size principle parameter. J Physiol 391:561–571PubMedGoogle Scholar
  2. Arabadzhiev TI, Dimitrov GV, Dimitrova NA (2004) The cross-correlation and phase-difference methods are not equivalent under noninvasive estimation of the motor unit propagation velocity. J Electromyogr Kinesiol 14:295–305PubMedCrossRefGoogle Scholar
  3. Bigland-Ritchie B, Donovan EF, Roussos CS (1981) Conduction velocity and EMG power spectrum changes in fatigue of sustained maximal efforts. J Appl Physiol 51:1300–1305PubMedGoogle Scholar
  4. Castle NA, Haylett DG (1987) Effect of channel blockers on potassium efflux from metabolically exhausted frog skeletal muscle. J Physiol 383:31–43PubMedGoogle Scholar
  5. De Luca CJ, LeFever RS, McCue MP, Xenaius AP (1982) Behavior of human motor units in different muscles during linearly varying contractions. J Physiol (Lond) 329:113–128Google Scholar
  6. Farina D, Merletti R (2004) Methods for estimating muscle fibre conduction velocity from surface electromyographic signals. Med Biol Eng Comput 42:432–445PubMedCrossRefGoogle Scholar
  7. Farina D, Mesin L (2005) Sensitivity of surface EMG-based conduction velocity estimates to local tissue in-homogeneities–influence of the number of channels and inter-channel distance. J Neurosci Methods 142:83–89PubMedCrossRefGoogle Scholar
  8. Farina D, Muhammad W, Fortunato E, Meste O, Merletti R, Rix H (2001) Estimation of single motor unit conduction velocity from surface electromyogram signals detected with linear electrode arrays. Med Biol Eng Comput 39:225–236PubMedCrossRefGoogle Scholar
  9. Farina D, Arendt-Nielsen L, Merletti R, Graven-Nielsen T (2002) Assessment of single motor unit conduction velocity during sustained contractions of the tibialis anterior muscle with advanced spike triggered averaging. J Neurosci Methods 115:1–12PubMedCrossRefGoogle Scholar
  10. Farina D, Arendt-Nielsen L, Merletti R, Graven-Nielsen T (2004a) Effect of experimental muscle pain on motor unit firing rate and conduction velocity. J Neurophysiol 91:1250–1259PubMedCrossRefGoogle Scholar
  11. Farina D, Gazzoni M, Camelia F (2004b) Low-threshold motor unit membrane properties vary with contraction intensity during sustained activation with surface EMG visual feedback. J Appl Physiol 96:1505–1515PubMedCrossRefGoogle Scholar
  12. Farina D, Zagari D, Gazzoni M, Merletti R (2004c) Reproducibility of muscle-fiber conduction velocity estimates using multichannel surface EMG techniques. Muscle Nerve 29:282–291PubMedCrossRefGoogle Scholar
  13. Farina D, Arendt-Nielsen L, Graven-Nielsen T (2005a) Effect of temperature on spike-triggered average torque and electrophysiological properties of low-threshold motor units. J Appl Physiol 99:197–203PubMedCrossRefGoogle Scholar
  14. Farina D, Gazzoni M, Camelia F (2005b) Conduction velocity of low-threshold motor units during ischemic contractions performed with surface EMG feedback. J Appl Physiol 98:1487–1494PubMedCrossRefGoogle Scholar
  15. Gazzoni M, Camelia F, Farina D (2005) Conduction velocity of quiescent muscle fibers decreases during sustained contraction. J Neurophysiol 94:387–394PubMedCrossRefGoogle Scholar
  16. Henneman E (1957) Relation between size of neurons and their susceptibility to discharge. Science 126:1345–1347PubMedCrossRefGoogle Scholar
  17. Hogrel JY (2003) Use of surface EMG for studying motor unit recruitment during isometric linear force ramp. J Electromyogr Kinesiol 13:417–423PubMedCrossRefGoogle Scholar
  18. Jones DA (1981) Muscle fatigue due to changes beyond the neuromuscular junction. Ciba Found Symp 82:178–196PubMedGoogle Scholar
  19. Keenan KG, Farina D, Maluf KS, Merletti R, Enoka RM (2005) Influence of amplitude cancellation on the simulated surface electromyogram. J Appl Physiol 98:120–131PubMedCrossRefGoogle Scholar
  20. Keenan KG, Farina D, Merletti R, Enoka RM (2006a) Influence of motor unit properties on the size of the simulated evoked surface EMG potential. Exp Brain Res 169:37–49PubMedCrossRefGoogle Scholar
  21. Keenan KG, Farina D, Merletti R, Enoka RM (2006b) Amplitude cancellation reduces the size of motor unit potentials averaged from the surface EMG. J Appl Physiol 100:1928–1937PubMedCrossRefGoogle Scholar
  22. Knaflitz M, Merletti R, De Luca CJ (1990) Inference of motor unit recruitment order in voluntary and electrically elicited contractions. J Appl Physiol 68:1657–1667PubMedGoogle Scholar
  23. Kossler F, Lange F, Caffier G, Kuchler G (1991) External potassium and action potential propagation in rat fast and slow twitch muscles. Gen Physiol Biophys 10:485–498PubMedGoogle Scholar
  24. Masuda T, De Luca CJ (1991) Recruitment threshold and muscle fiber conduction velocity of single motor units. J Electromyogr Kinesiol 1:116–123CrossRefGoogle Scholar
  25. Masuda T, Miyano H, Sadoyama T (1985) The position of innervation zones in the biceps brachii investigated by surface electromyography. IEEE Trans Biomed Eng 32:36–42PubMedCrossRefGoogle Scholar
  26. Merletti R, Knaflitz M, De Luca CJ (1990) Myoelectric manifestations of fatigue in voluntary and electrically elicited contractions. J Appl Physiol 69:1810–1820PubMedGoogle Scholar
  27. Milner-Brown HS, Stein RB, Andyemm R (1973) Changes in firing rate of human motor units during linearly changing voluntary contractions. J Physiol (Lond) 230:37l–390Google Scholar
  28. Nishizono H, Kurata H, Miyashita M (1989) Muscle fiber conduction velocity related to stimulation rate. Electroencephalogr Clin Neurophysiol 72:529–534PubMedCrossRefGoogle Scholar
  29. Okajima Y, Toikawa H, Hanayama K, Ohtsuka T, Kimura A, Chino N (1998) Relationship between nerve and muscle fiber conduction velocities of the same motor unit in man. Neurosci Lett 28(253):65–67CrossRefGoogle Scholar
  30. Plonsey R, Barr RC (2000) Bioelectricity: a quantitative approach. Plenum Press, New YorkGoogle Scholar
  31. Pozzo M, Merlo E, Farina D, Antonutto G, Merletti R, Di Prampero PE (2004) Muscle-fiber conduction velocity estimated from surface EMG signals during explosive dynamic contractions. Muscle Nerve 29:823–833PubMedCrossRefGoogle Scholar
  32. Rainoldi A, Bullock-Saxton JE, Cavarretta F, Hogan N (2001) Repeatability of maximal voluntary force and of surface EMG variables during voluntary isometric contraction of quadriceps muscles in healthy subjects. J Electromyogr Kinesiol 11:425–438PubMedCrossRefGoogle Scholar
  33. Schneider J, Silny J, Rau G (1988) Noninvasive measurement of conduction velocity in motor units influenced by temperature and excitation pattern. In: Wallinga W, Boom HBK, DeVries J (eds) Electromyographical kinesiology. Elsevier, Amsterdam, pp 251–254Google Scholar
  34. Stalberg E (1966) Propagation velocity in human muscle fibers in situ. Acta Physiol Scand Suppl. 287:1–112PubMedGoogle Scholar

Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Nosratollah Hedayatpour
    • 1
  • Lars Arendt-Nielsen
    • 1
  • Dario Farina
    • 1
  1. 1.Center for Sensory-Motor Interaction (SMI), Department of Health Science and TechnologyAalborg UniversityAalborgDenmark

Personalised recommendations