Poortvliet PC, Tucker KJ, Hodges PW. Changes in constraint of proximal segments effects time to task failure and activity of proximal muscles in knee position-control tasks.
Clin Neurophysiol 2012;
124:732-9. [PMID:
23102994 DOI:
10.1016/j.clinph.2012.09.025]
[Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Revised: 09/24/2012] [Accepted: 09/30/2012] [Indexed: 11/27/2022]
Abstract
OBJECTIVE
Maintenance of a limb position against external load (position-control) fails earlier (time to task failure: TTF) than maintenance of identical force against rigid restraint (force-control). Although possibly explained by physiological differences between contractions, we investigated whether less constraint of movements in other planes and proximal segments (commonly less in position-control tasks) shortens TTF.
METHODS
Seventeen adults (32±7 years) contracted knee extensor muscles to task failure in a position-control task, with and without constraint of motion in other planes and proximal segments, and a force-control task with constraints. Electromyography of knee extensors, their antagonist and hip muscles was recorded with force/position.
RESULTS
TTF was shorter for position-control without (161±55 s) than with constraint (184±51 s). Despite identical constraint, TTF was shorter in position- than force-control (216±56 s). Muscle activity and position variability at failure was greater without constraint.
CONCLUSION
Constraint of motion of proximal segments and other planes increases position-control TTF with less muscle activity and variability. As TTF differed between force- and position-control, despite equivalent constraint, other factors contribute to shorter position-control TTF.
SIGNIFICANCE
Results clarify that differences in the TTF between position- and force-control tasks are partly explained by unmatched restriction of motion in other planes and proximal segments.
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