Arm raising in humans under loaded vs. unloaded and bipedal vs. unipedal conditions - Université Paris Nanterre Access content directly
Journal Articles Brain Research Year : 1999

Arm raising in humans under loaded vs. unloaded and bipedal vs. unipedal conditions

Abstract

The aim of the present experiment was to study the central organization of equilibrium control during arm raising in the frontal plane. Nine adult subjects five seniors and four young adults were asked to raise their right arm to a horizontal position in the frontal plane in two support conditions bipedal vs. unipedal and two load conditions unloaded vs. a 3.5-kg load added on the moving hand . No instructions were given concerning the movement speed. The movements were performed at about half the maximum speed achievable under reaction time conditions. The final lateral center of mass CM position 1 s after the movement offset, and the time course of the CM shift during the movement were studied in the four experimental conditions, using a CM compensation index. The electromyographic. EMG pattern of the main muscles involved in the movement performance and in the postural control were studied in three out of nine subjects during movements performed at two velocities at the preferred speed and as fast as possible . The results indicate that 1 the CMshift remains minimized in the frontal plane during the time course of the arm movement and during the final stabilization of the arm regardless of the stance and load conditions; 2 the time course of the CM compensation index remains stable during the first 400 ms after the movement onset, decreasing late in the movement and increasing again at the end of the stabilization stage. A modelisation suggests that the time course is the result of the interaction of two controls: a first one, putative feedforward, starting early and decreasing with time and a second one, putative feedback, starting late in the movement and increasing with time; 3 both early and late index values are influenced by the support and load conditions, the highest index values being observed during unipedal stance and load conditions; 4 activation of quadratus lomborum QL contralateral to the raising arm is time locked with the deltoidus activation of the raising arm in both fast and slow movements: this contralateral QL activation corresponds to an anticipatory postural adjustment APA aimed at minimizing the CM shift.

Dates and versions

hal-04559792 , version 1 (25-04-2024)

Identifiers

Cite

Sylvie Vernazza-Martin, N Martin, M Cincera, A Pedotti, J Massion. Arm raising in humans under loaded vs. unloaded and bipedal vs. unipedal conditions. Brain Research, 1999, 846 (1), pp.12-22. ⟨10.1016/s0006-8993(99)01846-6⟩. ⟨hal-04559792⟩
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