Experimental Brain Research

, Volume 175, Issue 4, pp 584–595 | Cite as

Low-frequency common modulation of soleus motor unit discharge is enhanced during postural control in humans

  • G. Mochizuki
  • J. G. Semmler
  • T. D. Ivanova
  • S. J. GarlandEmail author
Research Article


The maintenance of quiet stance requires the activation of muscles bilaterally. The soleus muscles in each leg share a common function in standing; that is, each muscle acts to control antero-posterior (AP) sway on its own side. We sought to determine the extent to which oscillations in motor unit discharge were related in motor unit pairs of the soleus muscles during postural and voluntary isometric tasks, both within and between legs. Subjects stood quietly for 5 min or performed a voluntary isometric plantarflexion contraction in a seated position. During the postural tasks, the excursions of AP sway between legs were highly correlated (ρ = 0.86 ± 0.06). The strength of common modulation of motor unit discharge rates was assessed using time- and frequency-domain analyses. The time-domain common drive analysis revealed that the strongest correlation in motor unit discharge modulation occurred in the postural task with unilateral pairs (ρ = 0.71 ± 0.13) being more strongly correlated than bilateral pairs (ρ = 0.50 ± 0.16). Common modulation of motor unit discharge was lowest for the voluntary tasks, with ρ = 0.38 ± 0.11 and 0.16 ± 0.08 for unilateral and bilateral pairs, respectively. Similarly, the frequency-domain coherence analysis demonstrated an identical ordering effect, with the largest maximum pooled coherence occurring during standing posture in unilateral (0.070 at 1.6 Hz) and bilateral (0.055 at 1.6 Hz) recordings, whereas minimal coherence was observed in the voluntary task in both unilateral and bilateral recordings within the 0–5 Hz range. These results indicate that in the soleus muscle, common modulation of motor unit discharge is greater during postural tasks than during voluntary isometric tasks and can be observed in both bilateral and unilateral motor unit pairs. Differences in the extent of co-modulation of motor unit discharge between tasks may be attributed to either differences in the descending control or differences in the proprioceptive input between postural and isometric tasks.


Human Motor unit Posture Coherence Common drive 


  1. Adam A, De Luca CJ (2005) Firing rates of motor units in human vastus lateralis muscle during fatiguing isometric contractions. J Appl Physiol 99:268–280PubMedCrossRefGoogle Scholar
  2. Amjad AM, Halliday DM, Rosenberg JR, Conway BA (1997) An extended difference of coherence test for comparing and combining several independent coherence estimates: theory and application to the study of motor units and physiological tremor. J Neurosci Methods 73:69–79PubMedCrossRefGoogle Scholar
  3. Andreassen S, Rosenfalck A (1980) Regulation of the firing pattern of single motor units. J Neurol Neurosurg Psychiatry 43:897–906PubMedGoogle Scholar
  4. Bellemare F, Woods JJ, Johansson R, Bigland-Ritchie B (1983) Motor-unit discharge rates in maximal voluntary contractions of three human muscles. J Neurophysiol 50:1380–1392PubMedGoogle Scholar
  5. Brouwer B, Ashby P (1990) Corticospinal projections to upper and lower limb spinal motoneurons in man. Electroencephalogr Clin Neurophysiol 76:509–519PubMedCrossRefGoogle Scholar
  6. Brouwer B, Ashby P (1992) Corticospinal projections to lower limb motoneurons in man. Exp Brain Res 89:649–654PubMedCrossRefGoogle Scholar
  7. Davey NJ, Ellaway PH, Baker JR, Friedland CL (1993) Rhythmicity associated with a high degree of short-term synchrony of motor unit discharge in man. Exp Physiol 78:649–661PubMedGoogle Scholar
  8. De Luca CJ, Erim Z (2002) Common drive in motor units of a synergistic muscle pair. J Neurophysiol 87:2200–2204PubMedGoogle Scholar
  9. De Luca CJ, LeFever RS, McCue MP, Xenakis AP (1982) Control scheme governing concurrently active human motor units during voluntary contractions. J Physiol 329:129–142PubMedGoogle Scholar
  10. Dietz V, Horstmann GA, Berger W (1989) Interlimb coordination of leg-muscle activation during perturbation of stance in humans. J Neurophysiol 62:680–693PubMedGoogle Scholar
  11. Erim Z, Beg MF, Burke DT, De Luca CJ (1999) Effects of aging on motor-unit control properties. J Neurophysiol 82:2081–2091PubMedGoogle Scholar
  12. Farmer SF, Bremner FD, Halliday DM, Rosenberg JR, Stephens JA (1993) The frequency content of common synaptic inputs to motoneurones studied during voluntary isometric contraction in man. J Physiol 470:127–155PubMedGoogle Scholar
  13. Fitzpatrick RC, Gorman RB, Burke D, Gandevia SC (1992) Postural proprioceptive reflexes in standing human subjects: bandwidth of response and transmission characteristics. J Physiol 458:69–83PubMedGoogle Scholar
  14. Garland SJ, Miles TS (1997) Control of motor units in human flexor digitorum profundus under different proprioceptive conditions. J Physiol 502:693–701PubMedCrossRefGoogle Scholar
  15. Gatev P, Thomas S, Kepple T, Hallett M (1999) Feedforward ankle strategy of balance during quiet stance in adults. J Physiol 514:915–928PubMedCrossRefGoogle Scholar
  16. Halliday DM, Conway BA, Christensen LO, Hansen NL, Petersen NP, Nielsen JB (2003) Functional coupling of motor units is modulated during walking in human subjects. J Neurophysiol 89:960–968PubMedCrossRefGoogle Scholar
  17. Hayashi R, Miyake A, Jijiwa H, Watanabe S (1981) Postural readjustment to body sway induced by vibration in man. Exp Brain Res 43:217–225PubMedCrossRefGoogle Scholar
  18. Horak FB, Earhart GM, Dietz V (2001) Postural responses to combinations of head and body displacements: vestibular-somatosensory interactions. Exp Brain Res 141:410–414PubMedCrossRefGoogle Scholar
  19. Iyer MB, Christakos CN, Ghez C (1994) Coherent modulations of human motor unit discharges during quasi-sinusoidal isometric muscle contractions. Neurosci Lett 170:94–98PubMedCrossRefGoogle Scholar
  20. Kavounoudias A, Roll R, Roll JP (2001) Foot sole and ankle muscle inputs contribute jointly to human erect posture regulation. J Physiol 532:869–878PubMedCrossRefGoogle Scholar
  21. Keen DA, Fuglevand AJ (2004) Common input to motor neurons innervating the same and different compartments of the human extensor digitorum muscle. J Neurophysiol 91:57–62PubMedCrossRefGoogle Scholar
  22. Kim MS, Masakado Y, Tomita Y, Chino N, Pae YS, Lee KE (2001) Synchronization of single motor units during voluntary contractions in the upper and lower extremities. Clin Neurophysiol 112:1243–1249PubMedCrossRefGoogle Scholar
  23. Kuchinad RA, Ivanova TD, Garland SJ (2004) Modulation of motor unit discharge rate and H-reflex amplitude during submaximal fatigue of the human soleus muscle. Exp Brain Res 158:345–355PubMedCrossRefGoogle Scholar
  24. Loram ID, Maganaris CN, Lakie M (2005) Human postural sway results from frequent, ballistic bias impulses by soleus and gastrocnemius. J Physiol 564:295–311PubMedCrossRefGoogle Scholar
  25. Marsden JF, Farmer SF, Halliday DM, Rosenberg JR, Brown P (1999) The unilateral and bilateral control of motor unit pairs in the first dorsal interosseous and paraspinal muscles in man. J Physiol 521:553–564PubMedCrossRefGoogle Scholar
  26. Masani K, Popovic MR, Nakazawa K, Kouzaki M, Nozaki D (2003) Importance of body sway velocity information in controlling ankle extensor activities during quiet stance. J Neurophysiol 90:3774–3782PubMedCrossRefGoogle Scholar
  27. Mauritz KH, Dietz V (1980) Characteristics of postural instability induced by ischemic blocking of leg afferents. Exp Brain Res 38:117–119PubMedCrossRefGoogle Scholar
  28. Mochizuki G, Ivanova TD, Garland SJ (2004) Postural muscle activity during bilateral and unilateral arm movements at different speeds. Exp Brain Res 155:352–361PubMedCrossRefGoogle Scholar
  29. Mochizuki G, Ivanova TD, Garland SJ (2005) Synchronization of motor units in human soleus muscle during standing postural tasks. J Neurophysiol 94:62–69PubMedCrossRefGoogle Scholar
  30. Moritz CT, Christou EA, Meyer FG, Enoka RM (2005) Coherence at 16-32 Hz can be caused by short-term synchrony of motor units. J Neurophysiol 94:105–118PubMedCrossRefGoogle Scholar
  31. Oda S, Moritani T (1995) Cross-correlation of bilateral differences in fatigue during sustained maximal voluntary contraction. Eur J Appl Physiol Occup Physiol 70:305–310PubMedCrossRefGoogle Scholar
  32. Person RS, Kudina LP (1972) Discharge frequency and discharge pattern of human motor units during voluntary contraction of muscle. Electroencephalogr Clin Neurophysiol 32:471–483PubMedCrossRefGoogle Scholar
  33. Peterka RJ (2002) Sensorimotor integration in human postural control. J Neurophysiol 88:1097–1118PubMedGoogle Scholar
  34. Rosenberg JR, Amjad AM, Breeze P, Brillinger DR, Halliday DM (1989) The Fourier approach to the identification of functional coupling between neuronal spike trains. Prog Biophys Mol Biol 53:1–31PubMedCrossRefGoogle Scholar
  35. Sears TA, Stagg D (1976) Short-term synchronization of intercostal motoneurone activity. J Physiol 263:357–381PubMedGoogle Scholar
  36. Semmler JG, Kornatz KW, Dinenno DV, Zhou S, Enoka RM (2002) Motor unit synchronisation is enhanced during slow lengthening contractions of a hand muscle. J Physiol 545:681–695PubMedCrossRefGoogle Scholar
  37. Semmler JG, Nordstrom MA (1998) Motor unit discharge and force tremor in skill- and strength-trained individuals. Exp Brain Res 119:27–38PubMedCrossRefGoogle Scholar
  38. Semmler JG, Nordstrom MA, Wallace CJ (1997) Relationship between motor unit short-term synchronization and common drive in human first dorsal interosseous muscle. Brain Res 767:314–320PubMedCrossRefGoogle Scholar
  39. Semmler JG, Sale MV, Meyer FG, Nordstrom MA (2004) Motor-unit coherence and its relation with synchrony are influenced by training. J Neurophysiol 92:3320–3331PubMedCrossRefGoogle Scholar
  40. Sturm H, Schmied A, Vedel JP, Pagni S (1997) Firing pattern of type-identified wrist extensor motor units during wrist extension and hand clenching in humans. J Physiol 504:735–745PubMedCrossRefGoogle Scholar
  41. Westgaard RH, De Luca CJ (2001) Motor control of low-threshold motor units in the human trapezius muscle. J Neurophysiol 85:1777–1781PubMedGoogle Scholar
  42. Winter DA, Patla AE, Prince F, Ishac MG, Gielo-Perczak K (1998) Stiffness control of balance in quiet standing. J Neurophysiol 80:1211–1221PubMedGoogle Scholar
  43. Winter DA, Patla AE, Rietdyk S, Ishac MG (2001) Ankle muscle stiffness in the control of balance during quiet standing. J Neurophysiol 85:2630–2633PubMedGoogle Scholar
  44. Winter DA, Prince F, Stergiou P, Powell C (1993) Medial–lateral and anterior–posterior motor responses associated with centere of pressure changes in quiet standing. Neurosci Res Commun 12:141–148Google Scholar
  45. Zattara M, Bouisset S (1988) Posturo-kinetic organisation during the early phase of voluntary upper limb movement. 1. Normal subjects. J Neurol Neurosurg Psychiatry 51:956–965CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • G. Mochizuki
    • 1
  • J. G. Semmler
    • 2
  • T. D. Ivanova
    • 3
  • S. J. Garland
    • 3
    • 4
    Email author
  1. 1.Centre for Stroke RecoverySunnybrook Health Sciences CentreTorontoCanada
  2. 2.Research Centre for Human Movement Control, School of Molecular and Biomedical ScienceThe University of AdelaideAdelaideAustralia
  3. 3.School of Physical Therapy, Rm 1588, Elborn CollegeUniversity of Western OntarioLondonCanada
  4. 4.Department of Physiology and PharmacologyThe University of Western OntarioLondonCanada

Personalised recommendations