Experimental Brain Research

, Volume 197, Issue 1, pp 1–13 | Cite as

Prehension synergies: a study of digit force adjustments to the continuously varied load force exerted on a partially constrained hand-held object

  • Jason Friedman
  • Mark L. Latash
  • Vladimir M. Zatsiorsky
Research Article


We examined how the digit forces adjust when a load force acting on a hand-held object continuously varies. The subjects were required to hold the handle still while a linearly increasing and then decreasing force was applied to the handle. The handle was constrained, such that it could only move up and down, and rotate about a horizontal axis. In addition, the moment arm of the thumb tangential force was 1.5 times the moment arm of the virtual finger (VF, an imagined finger with the mechanical action equal to that of the four fingers) force. Unlike the situation when there are equal moment arms, the experimental setup forced the subjects to choose between (a) sharing equally the increase in load force between the thumb and VF but generating a moment of tangential force, which had to be compensated by negatively co-varying the moment due to normal forces, or (b) sharing unequally the load force increase between the thumb and VF but preventing generation of a moment of tangential forces. We found that different subjects tended to use one of these two strategies. These findings suggest that the selection by the CNS of prehension synergies at the VF-thumb level with respect to the moment of force is non-obligatory and reflects individual subject preferences. This unequal sharing of the load by the tangential forces, in contrast to the previously observed equal sharing, suggests that the invariant feature of prehension may be a correlated increase in tangential forces rather than an equal increase.


Finger forces Hand Moment Prehension Synergy 



The study was in part supported by NIH grants AG-018751, NS-035032, and AR-048563.


  1. Arimoto S, Tahara K, Yamaguchi M, Nguyen P, Han M (2001) Principles of superposition for controlling pinch motions by means of robot fingers with soft tips. Robotica 19(1):21–28CrossRefGoogle Scholar
  2. Bernstein NA (1996) On dexterity and its development. In: Latash ML, Turvey MT (eds) Dexterity and its development. Erlbaum Publ., Mahwah, pp 3–244Google Scholar
  3. de Freitas P, Krishnan V, Jaric S (2007) Force coordination in static manipulation tasks: effects of the change in direction and handedness. Exp Brain Res 183(4):487–497PubMedCrossRefGoogle Scholar
  4. Gao F, Latash ML, Zatsiorsky VM (2006) Maintaining rotational equilibrium during object manipulation: linear behavior of a highly non-linear system. Exp Brain Res 169(4):519–531PubMedCrossRefGoogle Scholar
  5. Gorniak SL, Zatsiorsky VM, Latash ML (2009) Hierarchical control of static prehension: II. Multi-digit synergies. Exp Brain Res 194(1):1–15PubMedCrossRefGoogle Scholar
  6. Hermsdörfer J, Blankenfeld H (2008) Grip force control of predictable external loads. Exp Brain Res 185(4):719–728PubMedCrossRefGoogle Scholar
  7. Johansson RS, Riso R, Häger C, Bäckström L (1992) Somatosensory control of precision grip during unpredictable pulling loads. I. Changes in load force amplitude. Exp Brain Res 89(1):181–191PubMedCrossRefGoogle Scholar
  8. Kang N, Shinohara M, Zatsiorsky VM, Latash ML (2004) Learning multi-finger synergies: an uncontrolled manifold analysis. Exp Brain Res 157:336–350PubMedCrossRefGoogle Scholar
  9. Kostyukov A (1998) Muscle hysteresis and movement control: a theoretical study. Neuroscience 83(1):303–320PubMedCrossRefGoogle Scholar
  10. Latash ML, Kang N, Patterson D (2002) Finger coordination in persons with Down syndrome: atypical patterns of coordination and the effects of practice. Exp Brain Res 146:345–355PubMedCrossRefGoogle Scholar
  11. Pataky TC, Latash ML, Zatsiorsky VM (2004) Tangential load sharing among fingers during prehension. Ergonomics 47(8):876–889PubMedCrossRefGoogle Scholar
  12. Santello M, Soechting JF (2000) Force synergies for multifingered grasping. Exp Brain Res 133(4):457–467PubMedCrossRefGoogle Scholar
  13. Shim JK, Latash ML, Zatsiorsky VM (2004) Finger coordination during moment production on a mechanically fixed object. Exp Brain Res 157(4):457–467PubMedCrossRefGoogle Scholar
  14. Shim JK, Latash ML, Zatsiorsky VM (2005a) Prehension synergies in three dimensions. J Neurophysiol 93(2):766–776PubMedCrossRefGoogle Scholar
  15. Shim JK, Latash ML, Zatsiorsky VM (2005b) Prehension synergies: trial-to-trial variability and principle of superposition during static prehension in three dimensions. J Neurophysiol 93(6):3649–3658PubMedCrossRefGoogle Scholar
  16. van Groeningen C, Nijhof EJ, Vermeule FM, Erkelens CJ (1999) Relation between torque history, firing frequency, decruitment levels and force balance in two flexors of the elbow. Exp Brain Res 129(4):592–604PubMedCrossRefGoogle Scholar
  17. Zatsiorsky (2002) Kinetics of human motion. Human Kinetics, Champaign, ILGoogle Scholar
  18. Zatsiorsky VM, Gregory RW, Latash ML (2002) Force and torque production in static multifinger prehension: biomechanics and control. I. Biomechanics. Biol Cyber 87(1):50–57CrossRefGoogle Scholar
  19. Zatsiorsky VM, Gao F, Latash ML (2003) Prehension synergies: effects of object geometry and prescribed torques. Exp Brain Res 148(1):77–87PubMedCrossRefGoogle Scholar
  20. Zatsiorsky VM, Latash ML, Gao F, Shim JK (2004) The principle of superposition in human prehension. Robotica 22:231–234CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Jason Friedman
    • 1
  • Mark L. Latash
    • 1
  • Vladimir M. Zatsiorsky
    • 1
  1. 1.Department of KinesiologyThe Pennsylvania State UniversityUniversity ParkUSA

Personalised recommendations