Article

Before altering the travel direction in normal gait, anticipatory activation in
trunk muscles is observed, followed by a top-down sequence of rotation of body
segments. Turning while pushing a cart is a more challenging task for the trunk
because of its low stiffness in pushing while walking and the interaction with
the high inertia of the cart. 12 healthy subjects pushed a 200 kg cart at
shoulder and hip height while making turns (gradual, sharp and unexpected sharp).
The normalized electromyogram amplitudes of left (right) lateral and anterior
external oblique muscle, and right (left) internal oblique muscle were averaged
to represent left (right) trunk rotator muscle activity. The baseline values of
trunk rotator muscle activity before the turn and the peak values after the turn
were determined. Additionally, peak values of hand forces, twisting moments and
twisting motions were assessed. Before turning, higher trunk rotator muscle
activity than in straight pushing without turning was only observed before making
a turn in the gradual or sharp turn conditions. After the turn, clockwise
twisting motion was associated with a clockwise twisting moment induced by the
reaction forces at the left hand. Anticipatory activation was initially absent in
the unexpected sharp turn, while bilateral trunk rotator muscle activity
increased after the turn, indicating co-contraction. In the unexpected turn
condition the combination of an uncontrolled twisting motion with delayed muscle
activation may increase the potential risk of low-back injury.
CI - Copyright (c) 2012 Elsevier B.V. All rights reserved.

Langue : ANGLAIS