Experimental Brain Research

, Volume 193, Issue 3, pp 351–359 | Cite as

Common input to different regions of biceps brachii long head

  • Benjamin K. Barry
  • Michael A. Pascoe
  • Stephan Riek
  • Richard G. Carson
  • Roger M. Enoka
Research Article


The purpose of the experiment was to compare the level of synchronization exhibited by pairs of motor units located within and between functionally distinct regions of the biceps brachii muscle. Pairs of single motor units were recorded from seven subjects using separate electrodes located in the lateral and medial aspects of the long head of biceps brachii. Participants were required to exert a combination of flexion and supination torques so that both motor units discharged at approximately 10 pps for ≥200 s and the level of motor unit synchronization could be quantified. When motor unit recordings were sufficiently stable at the completion of this synchrony task, a series of ramp contractions with multiple combinations of flexion and supination torques were performed to characterize the recruitment thresholds of the motor units. Common input strength (CIS) was significantly greater (< 0.01) for the within-region pairs of motor units (0.28 extra sync. imps/s, n = 26) than for the between-region pairs (0.13 extra sync. imps/s, n = 18), but did not differ significantly for the 12 within-region pairs from the lateral head and 14 from the medial head (0.27 vs. 0.29 extra sync. imps/s; = 0.83). Recruitment thresholds were measured for 33 motor units, but there was only a weak association between CIS and the respective recruitment patterns for motor unit pairs (n = 9). The present investigation provides evidence of a differential distribution of synaptic input across the biceps brachii motor neuron pool, but this appears to have minimal association with the recruitment patterns for individual motor units.


Motor unit Recruitment Synchronization Compartmentalization Elbow flexors 



This research was supported by: Australian Research Council to SR and RGC, National Health and Medical Research Council to RGC, and NIH (NS042734) to RME.


  1. Athwal GS, Steinmann SP, Rispoli DM (2007) The distal biceps tendon: footprint and relevant clinical anatomy. J Hand Surg [Am] 32:1225–1229CrossRefGoogle Scholar
  2. Barry BK, Riley ZA, Pascoe MA, Enoka RM (2008) A spinal pathway between synergists can modulate activity in human elbow flexor muscles. Exp Brain Res 190:347–359PubMedCrossRefGoogle Scholar
  3. Bremner FD, Baker JR, Stephens JA (1991) Effect of task on the degree of synchronization of intrinsic hand muscle motor units in man. J Neurophysiol 66:2072–2083PubMedGoogle Scholar
  4. Butler JE, Gandevia SC (2008) The output from human inspiratory motoneurone pools. J Physiol 586:1257–1264PubMedCrossRefGoogle Scholar
  5. Butler TJ, Kilbreath SL, Gorman RB, Gandevia SC (2005) Selective recruitment of single motor units in human flexor digitorum superficialis muscle during flexion of individual fingers. J Physiol 567:301–309PubMedCrossRefGoogle Scholar
  6. Cavallari P, Katz R (1989) Pattern of projections of group I afferents from forearm muscles to motoneurones supplying biceps and triceps muscles in man. Exp Brain Res 78:465–478PubMedCrossRefGoogle Scholar
  7. Christou EA, Rudroff T, Enoka JA, Meyer F, Enoka RM (2007) Discharge rate during low-force isometric contractions influences motor unit coherence below 15 Hz but not motor unit synchronization. Exp Brain Res 178:285–295PubMedCrossRefGoogle Scholar
  8. Conway BA, Halliday DM, Farmer SF, Shahani U, Maas P, Weir AI, Rosenberg JR (1995) Synchronization between motor cortex and spinal motoneuronal pool during the performance of a maintained motor task in man. J Physiol 489(Pt 3):917–924PubMedGoogle Scholar
  9. Cope TC, Sokoloff AJ (1999) Orderly recruitment tested across muscle boundaries. Prog Brain Res 123:177–190PubMedCrossRefGoogle Scholar
  10. Dartnall TJ, Nordstrom MA, Semmler JG (2008) Motor unit synchronization is increased in biceps brachii after exercise-induced damage to elbow flexor muscles. J Neurophysiol 99:1008–1019PubMedCrossRefGoogle Scholar
  11. Datta AK, Stephens JA (1990) Synchronization of motor unit activity during voluntary contraction in man. J Physiol 422:397–419PubMedGoogle Scholar
  12. Datta AK, Farmer SF, Stephens JA (1991) Central nervous pathways underlying synchronization of human motor unit firing studied during voluntary contractions. J Physiol 432:401–425PubMedGoogle Scholar
  13. De Luca CJ, Roy AM, Erim Z (1993) Synchronization of motor-unit firings in several human muscles. J Neurophysiol 70:2010–2023PubMedGoogle Scholar
  14. De Troyer A, Kirkwood PA, Wilson TA (2005) Respiratory action of the intercostal muscles. Physiol Rev 85:717–756PubMedCrossRefGoogle Scholar
  15. Eames MH, Bain GI, Fogg QA, van Riet RP (2007) Distal biceps tendon anatomy: a cadaveric study. J Bone Joint Surg Am 89:1044–1049PubMedCrossRefGoogle Scholar
  16. Ellaway PH (1978) Cumulative sum technique and its application to the analysis of peristimulus time histograms. Electroencephalogr Clin Neurophysiol 45:302–304PubMedCrossRefGoogle Scholar
  17. Ellaway PH, Murthy KS (1985) The origins and characteristics of cross-correlated activity between gamma-motoneurones in the cat. Q J Exp Physiol 70:219–232PubMedGoogle Scholar
  18. English AW, Letbetter WD (1981) Intramuscular “compartmentalization” of the cat biceps femoris and semitendinosus muscles: anatomy and EMG patterns. Abstr Soc Neurosci 7:557Google Scholar
  19. Epstein M, Wong M, Herzog W (2006) Should tendon and aponeurosis be considered in series? J Biomech 39:2020–2025PubMedCrossRefGoogle Scholar
  20. Ettema G, Styles G, Kippers V (1998) The moment arms of 23 muscle segments of the upper limb with varying elbow and forearm positions: implications for motor control. Hum Mov Sci 17:201–220CrossRefGoogle Scholar
  21. Farmer SF, Bremner FD, Halliday DM, Rosenberg JR, Stephens JA (1993a) The frequency content of common synaptic inputs to motoneurones studied during voluntary isometric contraction in man. J Physiol 470:127–155PubMedGoogle Scholar
  22. Farmer SF, Swash M, Ingram DA, Stephens JA (1993b) Changes in motor unit synchronization following central nervous lesions in man. J Physiol 463:83–105PubMedGoogle Scholar
  23. Henneman E, Somjen G, Carpenter DO (1965) Functional significance of cell size in spinal motoneurons. J Neurophysiol 28:560–580PubMedGoogle Scholar
  24. Herrmann U, Flanders M (1998) Directional tuning of single motor units. J Neurosci 18:8402–8416PubMedGoogle Scholar
  25. Katz R, Penicaud A, Rossi A (1991) Reciprocal Ia inhibition between elbow flexors and extensors in the human. J Physiol 437:269–286PubMedGoogle Scholar
  26. Keen DA, Fuglevand AJ (2003) Role of intertendinous connections in distribution of force in the human extensor digitorum muscle. Muscle Nerve 28:614–622PubMedCrossRefGoogle Scholar
  27. Keen DA, Fuglevand AJ (2004a) Assessment of synchrony in motor unit pools with different presumed levels of corticomotoneuronal input. Abstr Soc Neurosci #992.5Google Scholar
  28. Keen DA, Fuglevand AJ (2004b) Common input to motor neurons innervating the same and different compartments of the human extensor digitorum muscle. J Neurophysiol 91:57–62PubMedCrossRefGoogle Scholar
  29. Keen DA, Fuglevand AJ (2004c) Distribution of motor unit force in human extensor digitorum assessed by spike-triggered averaging and intraneural microstimulation. J Neurophysiol 91:2515–2523PubMedCrossRefGoogle Scholar
  30. Kilbreath SL, Gandevia SC (1994) Limited independent flexion of the thumb and fingers in human subjects. J Physiol 479(Pt 3):487–497PubMedGoogle Scholar
  31. Kilbreath SL, Gorman RB, Raymond J, Gandevia SC (2002) Distribution of the forces produced by motor unit activity in the human flexor digitorum profundus. J Physiol 543:289–296PubMedCrossRefGoogle Scholar
  32. Kim M-S, Masakado Y, Tomita Y, Chino N, Pae YS, Lee K (2001) Synchronization of single motor units during voluntary contractions in the upper and lower extremities. Clin Neurophysiol 112:1243–1249PubMedCrossRefGoogle Scholar
  33. Kirkwood PA, Sears TA, Stagg D, Westgaard RH (1982a) The spatial distribution of synchronization of intercostal motoneurones in the cat. J Physiol 327:137–155PubMedGoogle Scholar
  34. Kirkwood PA, Sears TA, Tuck DL, Westgaard RH (1982b) Variations in the time course of the synchronization of intercostal motoneurones in the cat. J Physiol 327:105–135PubMedGoogle Scholar
  35. Mattei B, Schmied A, Mazzocchio R, Decchi B, Rossi A, Vedel JP (2003) Pharmacologically induced enhancement of recurrent inhibition in humans: effects on motoneurone discharge patterns. J Physiol 548:615–629PubMedCrossRefGoogle Scholar
  36. McIsaac TL, Fuglevand AJ (2007) Motor unit synchrony within and across compartments of the human flexor digitorum superficialis. J Neurophysiol 97:550–556PubMedCrossRefGoogle Scholar
  37. McKiernan BJ, Marcario JK, Karrer JH, Cheney PD (1998) Corticomotoneuronal postspike effects in shoulder, elbow, wrist, digit, and intrinsic hand muscles during a reach and prehension task. J Neurophysiol 80:1961–1980PubMedGoogle Scholar
  38. Monti RJ, Roy RR, Hodgson JA, Edgerton VR (1999) Transmission of forces within mammalian skeletal muscles. J Biomech 32:371–380PubMedCrossRefGoogle Scholar
  39. Naito A, Shindo M, Miyasaka T, Sun YJ, Morita H (1996) Inhibitory projection from brachioradialis to biceps brachii motoneurones in human. Exp Brain Res 111:483–486PubMedCrossRefGoogle Scholar
  40. Naito A, Shindo M, Miyasaka T, Sun YJ, Momoi H, Chishima M (1998) Inhibitory projections from pronator teres to biceps brachii motoneurones in human. Exp Brain Res 121:99–102PubMedCrossRefGoogle Scholar
  41. Nielsen J, Kagamihara Y (1994) Synchronization of human leg motor units during co-contraction in man. Exp Brain Res 102:84–94PubMedGoogle Scholar
  42. Nordstrom MA, Fuglevand AJ, Enoka RM (1992) Estimating the strength of common input to human motoneurons from the cross-correlogram. J Physiol 453:547–574PubMedGoogle Scholar
  43. Palmer E, Ashby P (1992) Corticospinal projections to upper limb motoneurones in humans. J Physiol 448:397–412PubMedGoogle Scholar
  44. Reilly KT, Schieber MH (2003) Incomplete functional subdivision of the human multitendoned finger muscle flexor digitorum profundus: an electromyographic study. J Neurophysiol 90:2560–2570PubMedCrossRefGoogle Scholar
  45. Reilly KT, Nordstrom MA, Schieber MH (2004) Short-term synchronization between motor units in different functional subdivisions of the human flexor digitorum profundus muscle. J Neurophysiol 92:734–742PubMedCrossRefGoogle Scholar
  46. Riek S, Bawa P (1992) Recruitment of motor units in human forearm extensors. J Neurophysiol 68:100–108PubMedGoogle Scholar
  47. Schmied A, Ivarsson C, Fetz EE (1993) Short-term synchronization of motor units in human extensor digitorum communis muscle: relation to contractile properties and voluntary control. Exp Brain Res 97:159–172PubMedCrossRefGoogle Scholar
  48. Sears TA, Stagg D (1976) Short-term synchronization of intercostal motoneurone activity. J Physiol 263:357–381PubMedGoogle Scholar
  49. Segal RL (1992) Neuromuscular compartments in the human biceps brachii muscle. Neurosci Lett 140:98–102PubMedCrossRefGoogle Scholar
  50. Semmler JG, Steege JW, Kornatz KW, Enoka RM (2000) Motor-unit synchronization is not responsible for larger motor-unit forces in old adults. J Neurophysiol 84:358–366PubMedGoogle Scholar
  51. 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
  52. Tanji J, Kato M (1973) Recruitment of motor units in voluntary contraction of a finger muscle in man. Exp Neurol 40:759–770PubMedCrossRefGoogle Scholar
  53. Taylor AM, Enoka RM (2004) Quantification of the factors that influence discharge correlation in model motor neurons. J Neurophysiol 91:796–814PubMedCrossRefGoogle Scholar
  54. ter Haar Romeny BM, Denier van der Gon JJ, Gielen CC (1982) Changes in recruitment order of motor units in the human biceps muscle. Exp Neurol 78:360–368PubMedCrossRefGoogle Scholar
  55. ter Haar Romeny BM, van der Gon JJ, Gielen CC (1984) Relation between location of a motor unit in the human biceps brachii and its critical firing levels for different tasks. Exp Neurol 85:631–650PubMedCrossRefGoogle Scholar
  56. Turker KS, Powers RK (2001) Effects of common excitatory and inhibitory inputs on motoneuron synchronization. J Neurophysiol 86:2807–2822PubMedGoogle Scholar
  57. Turker KS, Powers RK (2002) The effects of common input characteristics and discharge rate on synchronization in rat hypoglossal motoneurones. J Physiol 541:245–260PubMedCrossRefGoogle Scholar
  58. van Bolhuis BM, Medendorp WP, Gielen CC (1997) Motor unit firing behavior in human arm flexor muscles during sinusoidal isometric contractions and movements. Exp Brain Res 117:120–130PubMedCrossRefGoogle Scholar
  59. van Zuylen EJ, Gielen CC, Denier van der Gon JJ (1988) Coordination and inhomogeneous activation of human arm muscles during isometric torques. J Neurophysiol 60:1523–1548PubMedGoogle Scholar
  60. Wiegner AW, Wierzbicka MM (1987) A method for assessing significance of peaks in cross-correlation histograms. J Neurosci Methods 22:125–131PubMedCrossRefGoogle Scholar
  61. Windhorst U, Hamm TM, Stuart DG (1989) On the function of muscle and reflex partitioning. Behav Brain Sci 12:629–681CrossRefGoogle Scholar
  62. Winges SA, Santello M (2004) Common input to motor units of digit flexors during multi-digit grasping. J Neurophysiol 92:3210–3220PubMedCrossRefGoogle Scholar
  63. Yu WS, Kilbreath SL, Fitzpatrick RC, Gandevia SC (2007) Thumb and finger forces produced by motor units in the long flexor of the human thumb. J Physiol 583:1145–1154PubMedCrossRefGoogle Scholar
  64. Yucesoy CA, Koopman BH, Baan GC, Grootenboer HJ, Huijing PA (2003) Effects of inter- and extramuscular myofascial force transmission on adjacent synergistic muscles: assessment by experiments and finite-element modeling. J Biomech 36:1797–1811PubMedCrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Benjamin K. Barry
    • 1
    • 2
    • 3
  • Michael A. Pascoe
    • 1
  • Stephan Riek
    • 2
  • Richard G. Carson
    • 2
  • Roger M. Enoka
    • 1
  1. 1.Neurophysiology of Movement Laboratory, Department of Integrative PhysiologyUniversity of ColoradoBoulderUSA
  2. 2.Perception and Motor Systems Laboratory, School of Human Movement StudiesThe University of QueenslandBrisbaneAustralia
  3. 3.School of Medical SciencesThe University of New South WalesSydneyAustralia

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