title: Coordination of hand grip and load forces in uni- and bidirectional static force production tasks.
abstract: The purpose of the study was to explore the differences in coordination of grip (G) and load forces (L) in a unidirectional and bidirectional bimanual static force production task. Subjects (N=10) exerted oscillatory isometric L profiles against an externally fixed hand-held device, modulated either in pure tension (unidirectional) or in alternating tension and compression (bidirectional) at a rate of either 1.33 or 2.67 Hz. The unidirectional task revealed a high level of coordination of both the ipsilateral (i.e., G and L of each hand) and contralateral pairs of forces (two Gs and two Ls) as assessed by correlation and stability of force ratios. The bidirectional task demonstrated a low level of inconsistently modulated Gs with respect to the change of L, which resulted in a deteriorated coordination, particularly between the ipsilateral forces. The overall effect of task on the force coordination was higher than the effect of frequency suggesting that the higher frequency of G modulation required in the bidirectional task is not likely to be the main cause of the observed phenomenon. We interpret these differences by a relative simplicity of the control mechanisms of the unidirectional task based on a single synergy of G and L muscles that allows simultaneous coordination of both the ipsilateral and contralateral forces. Due to the switching between two distinctive synergies involving G muscles, the bidirectional task could possess a higher control complexity causing a decoupled coordination of the ipsilateral forces, while retaining the coordination of contralateral forces at a relatively high level.
authors.affiliation: Human Performance Laboratory, Department of Health, Nutrition, and Exercise Sciences, University of Delaware, 547 S. College Avenue, Newark, DE 19716, USA. jaric@udel.edu
authors.forename: Slobodan
authors.initials: S
authors.lastname: Jaric
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Russell
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Collins
authors.forename: Rahul
authors.initials: R
authors.lastname: Marwaha
mesh_terms: D000328:Adult; D005260:Female; D006225:Hand / Q000502:physiology*; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010812:Physical Stimulation / Q000379:methods; D004856:Postural Balance / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D013314:Stress, Mechanical; D013647:Task Performance and Analysis; D016474:Weight-Bearing / Q000502:physiology*