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Modulation of finger muscle activation patterns across postures is coordinated across all muscle groups.
J Neurophysiol. 2020 Aug 01; 124(2):330-341.JN

Abstract

Successful grasp requires that grip forces be properly directed between the fingertips and the held object. Changes in digit posture significantly affect the mapping between muscle force and fingertip force. Joint torques must subsequently be altered to maintain the desired force direction at the fingertips. Our current understanding of the roles of hand muscles in force production remains incomplete, as past studies focused on a limited set of postures or force directions. To thoroughly examine how hand muscles adapt to changing external (force direction) and internal (posture) conditions, activation patterns of six index finger muscles were examined with intramuscular electrodes in 10 healthy subjects. Participants produced submaximal isometric forces in each of six orthogonal directions at nine different finger postures. Across force directions, participants significantly altered activation patterns to accommodate postural changes in the interphalangeal joint angles but not changes in the metacarpophalangeal joint angles. Modulation of activation levels of the extrinsic hand muscles, particularly the extensors, were as great as those of intrinsic muscles, suggesting that both extrinsic and intrinsic muscles were involved in creating the desired forces. Despite considerable between-subject variation in the absolute activation patterns, principal component analysis revealed that participants used similar strategies to accommodate the postural changes. The changes in muscle coordination also helped increase joint impedance in order to stabilize the end-point force direction. This effect counteracts the increased signal-dependent motor noise that arises with greater magnitude of muscle activation as interphalangeal joint flexion is increased. These results highlight the role of the extrinsic muscles in controlling fingertip force direction across finger postures.NEW & NOTEWORTHY We examined how hand muscles adapt to changing external (force direction) and internal (posture) conditions. Muscle activations, particularly of the extrinsic extensors, were significantly affected by postural changes of the interphalangeal, but not metacarpophalangeal, joints. Joint impedance was modulated so that the effects of the signal-dependent motor noise on the force output were reduced. Comparisons with theoretical solutions showed that the chosen activation patterns occupied a small portion of the possible solution space, minimizing the maximum activation of any one muscle.

Authors+Show Affiliations

Department of Biomedical Engineering, Catholic University of America, Washington, District of Columbia. Center for Applied Biomechanics and Rehabilitation Research, MedStar National Rehabilitation Hospital, Washington, District of Columbia. Department of Mechanical Engineering, Korean Advanced Institute of Science and Technology, Daejeon, Korea. Sensory Motor Performance Program, Rehabilitation Institute of Chicago (currently Shirley Ryan AbilityLab), Chicago, Illinois.Department of Biomedical Engineering, Illinois Institute of Technology, Chicago, Illinois.Sensory Motor Performance Program, Rehabilitation Institute of Chicago (currently Shirley Ryan AbilityLab), Chicago, Illinois. Department of Occupational Therapy, University of Illinois at Chicago, Chicago, Illinois.Sensory Motor Performance Program, Rehabilitation Institute of Chicago (currently Shirley Ryan AbilityLab), Chicago, Illinois. Department of Mechanical Engineering, University of Detroit Mercy, Detroit, Michigan.Sensory Motor Performance Program, Rehabilitation Institute of Chicago (currently Shirley Ryan AbilityLab), Chicago, Illinois. Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, Illinois. Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University, Raleigh, North Carolina. Department of Physical Medicine and Rehabilitation, University of North Carolina School of Medicine, Chapel Hill, North Carolina.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

32579416

Citation

Lee, Sang Wook, et al. "Modulation of Finger Muscle Activation Patterns Across Postures Is Coordinated Across All Muscle Groups." Journal of Neurophysiology, vol. 124, no. 2, 2020, pp. 330-341.
Lee SW, Qiu D, Fischer HC, et al. Modulation of finger muscle activation patterns across postures is coordinated across all muscle groups. J Neurophysiol. 2020;124(2):330-341.
Lee, S. W., Qiu, D., Fischer, H. C., Conrad, M. O., & Kamper, D. G. (2020). Modulation of finger muscle activation patterns across postures is coordinated across all muscle groups. Journal of Neurophysiology, 124(2), 330-341. https://doi.org/10.1152/jn.00088.2020
Lee SW, et al. Modulation of Finger Muscle Activation Patterns Across Postures Is Coordinated Across All Muscle Groups. J Neurophysiol. 2020 Aug 1;124(2):330-341. PubMed PMID: 32579416.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Modulation of finger muscle activation patterns across postures is coordinated across all muscle groups. AU - Lee,Sang Wook, AU - Qiu,Dan, AU - Fischer,Heidi C, AU - Conrad,Megan O, AU - Kamper,Derek G, Y1 - 2020/06/24/ PY - 2020/6/25/pubmed PY - 2020/6/25/medline PY - 2020/6/25/entrez KW - activation patterns KW - extrinsic and intrinsic hand muscles KW - index finger KW - motor control SP - 330 EP - 341 JF - Journal of neurophysiology JO - J. Neurophysiol. VL - 124 IS - 2 N2 - Successful grasp requires that grip forces be properly directed between the fingertips and the held object. Changes in digit posture significantly affect the mapping between muscle force and fingertip force. Joint torques must subsequently be altered to maintain the desired force direction at the fingertips. Our current understanding of the roles of hand muscles in force production remains incomplete, as past studies focused on a limited set of postures or force directions. To thoroughly examine how hand muscles adapt to changing external (force direction) and internal (posture) conditions, activation patterns of six index finger muscles were examined with intramuscular electrodes in 10 healthy subjects. Participants produced submaximal isometric forces in each of six orthogonal directions at nine different finger postures. Across force directions, participants significantly altered activation patterns to accommodate postural changes in the interphalangeal joint angles but not changes in the metacarpophalangeal joint angles. Modulation of activation levels of the extrinsic hand muscles, particularly the extensors, were as great as those of intrinsic muscles, suggesting that both extrinsic and intrinsic muscles were involved in creating the desired forces. Despite considerable between-subject variation in the absolute activation patterns, principal component analysis revealed that participants used similar strategies to accommodate the postural changes. The changes in muscle coordination also helped increase joint impedance in order to stabilize the end-point force direction. This effect counteracts the increased signal-dependent motor noise that arises with greater magnitude of muscle activation as interphalangeal joint flexion is increased. These results highlight the role of the extrinsic muscles in controlling fingertip force direction across finger postures.NEW & NOTEWORTHY We examined how hand muscles adapt to changing external (force direction) and internal (posture) conditions. Muscle activations, particularly of the extrinsic extensors, were significantly affected by postural changes of the interphalangeal, but not metacarpophalangeal, joints. Joint impedance was modulated so that the effects of the signal-dependent motor noise on the force output were reduced. Comparisons with theoretical solutions showed that the chosen activation patterns occupied a small portion of the possible solution space, minimizing the maximum activation of any one muscle. SN - 1522-1598 UR - https://www.unboundmedicine.com/medline/citation/32579416/Modulation_of_finger_muscle_activation_patterns_across_postures_is_coordinated_across_all_muscle_groups L2 - https://journals.physiology.org/doi/10.1152/jn.00088.2020?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -
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