Journal of Computational Neuroscience

, Volume 22, Issue 3, pp 347–361 | Cite as

Analysis of the effects of firing rate and synchronization on spike-triggered averaging of multidirectional motor unit torque

  • Jason J. KutchEmail author
  • Nina L. Suresh
  • Anthony M. Bloch
  • William Z. Rymer


Spike-triggered averaging (STA) of muscle force transients has often been used to estimate motor unit contractile properties, using the discharge of a motor unit within the muscle as the triggering events. For motor units that exert torque about multiple degrees-of-freedom, STA has also been used to estimate motor unit pulling direction. It is well known that motor unit firing rate and weak synchronization of motor unit discharges with other motor units in the muscle can distort STA estimates of contractile properties, but the distortion of STA estimates of motor unit pulling direction has not been thoroughly evaluated. Here, we derive exact equations that predict that STA decouples firing rate and synchronization distortion when used to estimate motor unit pulling direction. We derive a framework for analyzing synchronization, consider whether the distortion due to synchronization can be removed from STA estimates of pulling direction, and show that there are distributions of motor unit pulling directions for which STA is insensitive to synchronization. We conclude that STA may give insight into how motoneuronal synchronization is organized with respect to motor unit pulling direction.


Spike-triggered averaging Motor unit Pulling direction Firing rate Synchronization 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. An, K. N., Ueba, Y., Chao, E. Y., Cooney, W. P., & Linscheid, R. L. (1983). Tendon excursion and moment arm of index finger muscles. Journal of Biomechanics, 16, 419–425.PubMedCrossRefGoogle Scholar
  2. Andreassen, S., & Baron, E. (1983). Estimation of motor unit twitches. IEEE Transactions on Biomedical Engineering, 30, 742–748.PubMedCrossRefGoogle Scholar
  3. Binder, M. D., & Powers, R. K. (2001). Relationship between simulated common synaptic input and discharge synchrony in cat spinal motoneurons. Journal of Neurophysiology, 86, 2266–2275.PubMedGoogle Scholar
  4. Bremner, F. D., Baker, J. R., & Stephens, J. A. (1991a). Correlation between the discharges of motor units recorded from the same and from different finger muscles in man. Journal of Physiology, 432, 355–380.PubMedGoogle Scholar
  5. Bremner, F. D., Baker, J. R., & Stephens, J. A. (1991b). Variation in the degree of synchronization exhibited by motor units lying in different finger muscles in man. Journal of Physiology, 432, 381–399.PubMedGoogle Scholar
  6. Bremner, F. D., Baker, J. R., & Stephens, J. A. (1991c). Effect of task on the degree of synchronization of intrinsic hand muscle motor units in man. Journal of Neurophysiology, 66, 2072–2083.PubMedGoogle Scholar
  7. Buchthal, F., & Schmalbruch, H. (1970). Contraction times and fibre types in intact human muscle. Acta Physiologica Scandinavica, 79, 435–452.PubMedCrossRefGoogle Scholar
  8. Calancie, B., & Bawa, P. (1986). Limitations of the spike-triggered averaging technique. Muscle & Nerve, 9, 78–83.CrossRefGoogle Scholar
  9. Datta, A. K., & Stephens, J. A. (1990). Synchronization of motor unit activity during voluntary contraction in man. Journal of Physiology, 422, 397–419.PubMedGoogle Scholar
  10. Deluca, C. J., Roy, A. M., & Erim, Z. (1993). Synchronization of motor-unit firings in several human muscles. Journal of Neurophysiology, 70, 2010–2023.Google Scholar
  11. Farmer, S. F., Halliday, D. M., Conway, B. A., Stephens, J. A., & Rosenberg, J. R. (1997). A review of recent applications of cross-correlation methodologies to human motor unit recording. Journal of Neuroscience Methods, 74, 175–187.PubMedCrossRefGoogle Scholar
  12. Fetz, E. E., & Cheney, P. D. (1980). Postspike facilitation of forelimb muscle-activity by primate corticomotoneuronal cells. Journal of Neurophysiology, 44, 751–772.PubMedGoogle Scholar
  13. Fuglevand, A. J., Winter, D. A., & Patla, A. E. (1993). Models of recruitment and rate coding organization in motor-unit pools. Journal of Neurophysiology, 70, 2470–2488.PubMedGoogle Scholar
  14. Keen, D. A., & Fuglevand, A. J. (2004a). Common input to motor neurons innervating the same and different compartments of the human extensor digitorum muscle. Journal of Neurophysiology, 91, 57–62.PubMedCrossRefGoogle Scholar
  15. Keen, D. A., & Fuglevand, A. J. (2004b). Distribution of motor unit force in human extensor digitorum assessed by spike-triggered averaging and intraneural microstimulation. Journal of Neurophysiology, 91, 2515–2523.PubMedCrossRefGoogle Scholar
  16. Kernell, D., Eerbeek, O., & Verhey, B. A. (1983). Relation between isometric force and stimulus rate in cat’s hindlimb motor units of different twitch contraction time. Experimental Brain Research, 50, 220–227.Google Scholar
  17. Komatsu. Y., Nakajima, S., Toyama, K., & Fetz, E. E. (1988). Intracortical connectivity revealed by spike-triggered averaging in slice preparations of cat visual-cortex. Brain Research, 442, 359–362.PubMedCrossRefGoogle Scholar
  18. Lim, K. Y., Thomas, C. K., & Rymer, W. Z. (1995). Computational methods for improving estimates of motor unit twitch contraction properties. Muscle & Nerve, 18, 165–174.CrossRefGoogle Scholar
  19. Mannard, A., & Stein, R. B. (1973). Determination of Frequency-response of isometric soleus muscle in cat using Random nerve-stimulation. Journal of Physiology-London, 229, 275–296.Google Scholar
  20. Matsumura, M., Chen, D. F., Sawaguchi, T., Kubota, K., & Fetz, E. E. (1996). Synaptic interactions between primate precentral cortex neurons revealed by spike-triggered averaging of intracellular membrane potentials in vivo. Journal of Neuroscience, 16, 7757–7767.PubMedGoogle Scholar
  21. Nordstrom, M. A., Miles, T. S., & Veale, J. L. (1989). Effect of motor unit firing pattern on twitches obtained by spike-triggered averaging. Muscle & Nerve, 12, 556–567.CrossRefGoogle Scholar
  22. Sandercock, T. G. (2005). Summation of motor unit force in passive and active muscle. Exercise and Sport Sciences Reviews, 33, 76–83.PubMedCrossRefGoogle Scholar
  23. Schmied, A., Vedel, J. P., & Pagni, S. (1994). Human spinal lateralization aassessed from motoneuron synchronization - dependence on handedness and meter unit type. Journal of Physiology-London, 480, 369–387.Google Scholar
  24. Semmler, J. G. (2002). Motor unit synchronization and neuromuscular performance. Exercise and Sport Sciences Reviews, 30, 8–14.PubMedCrossRefGoogle Scholar
  25. Stein, R. B., Yemm, R., French, A. S., & Mannard, A. (1972). New methods for analyzing motor function in man and animals. Brain Research, 40, 187–192.PubMedCrossRefGoogle Scholar
  26. Taylor, A. M., Steege, J. W., & Enoka, R. M. (2002). Motor-unit synchronization alters spike-triggered average force in simulated contractions. Journal of Neurophysiology, 88, 265–276.PubMedGoogle Scholar
  27. Thomas, C. K., Bigland-Ritchie, B., Westling, G., & Johansson, R. S. (1990b). A comparison of human thenar motor-unit properties studied by intraneural motor-axon stimulation and spike-triggered averaging. Journal of Neurophysiology, 64, 1347–1351.PubMedGoogle Scholar
  28. Thomas, C. K., Johansson, R. S., Westling, G., & Bigland-Ritchie, B. (1990a). Twitch properties of human thenar motor units measured in response to intraneural motor-axon stimulation. Journal of Neurophysiology, 64, 1339–1346.PubMedGoogle Scholar
  29. Thomas, C. K., Ross, B. H., & Stein, R. B. (1986). Motor-unit recruitment in human first dorsal interosseous muscle for static contractions in three different directions. Journal of Neurophysiology, 55, 1017–1029.PubMedGoogle Scholar
  30. Westling, G., Johansson, RS., Thomas, C. K., & Bigland-Ritchie, B. (1990). Measurement of contractile and electrical properties of single human thenar motor units in response to intraneural motor-axon stimulation. Journal of Neurophysiology, 64, 1331–1338.PubMedGoogle Scholar
  31. Yao, W., Fuglevand, R. J., & Enoka, R. M. (2000). Motor-unit synchronization increases EMG amplitude and decreases force steadiness of simulated contractions. Journal of Neurophysiology, 83, 441–452.PubMedGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • Jason J. Kutch
    • 1
    • 2
    Email author
  • Nina L. Suresh
    • 2
  • Anthony M. Bloch
    • 1
  • William Z. Rymer
    • 2
  1. 1.Department of MathematicsUniversity of MichiganAnn ArborUSA
  2. 2.Sensory Motor Performance ProgramRehabilitation Institute of ChicagoChicagoUSA

Personalised recommendations