The effects of movement velocity, mass displaced, and task certainty on associated postural adjustments made by normal and hemiplegic individuals.

Abstract

SUMMARY The activation times for trunk and leg muscles were examined in normal and left hemiplegic subjects who raised their right arms at different velocities in self-paced or reaction time conditions. Activity in these postural muscles preceded arm displacement, and they were activated in a similar sequence during all types of rapid movements. The presence and sequencing of associated postural adjustments were more variable during slow movements.Movement of an extremity, such as the arm, causes dynamic forces to be applied to the trunk, and these will act on the multisegmented kinematic chain between the shoulder and the base of support. The forces acting between a moving arm and the trunk are complex, but they must include linear centrifugal forces, inertial reactive forces, and torsional movements. In addition to the inertial reactions, the movement may cause a static displacement of body mass with respect to the support base, such that a postural adjustment will be necessary to maintain stability by keeping the center of mass over the vertical projection of the supporting base. If stability is to be maintained during voluntary movement, it is likely that neurally controlled postural adjustment or stabilisation must be produced by muscular activity, as a supplement to reactive forces provided by structures such as the ligaments. The required muscular activity could be controlled in two ways: (1) it could be centrally programmed, as part of the total motor act, or (2) it could be initiated reflexly by the consequences of the muscular contractions and/or the movement.Belen'kii et al' recorded the electromyographic (EMG) activity of the anterior deltoid and several muscles in the trunk and lower extremities in standing normal individuals who rapidly raised their arm

Three-dimensional angular kinematics of the lumbar spine and pelvis during running

“…It is possible that the angular rotations of the lumbar spine and pelvis during running occur as a consequence of the rapid movements of the lower limbs. Rapid limb movements are known to perturb the trunk due to both generation of reactive forces and the additional displacement of the centre of mass resulting from a change in body configuration (Bouisset & Zattara, 1981;Horak, Esselman, Anderson, & Lynch, 1984). Hodges, Cresswell, and Thorstensson (1999) and Hodges, Cresswell, Daggfeldt, and Thorstensson (2000) found that, in response to rapid upper limb movement, the trunk displayed characteristic movements that occurred both prior to or coincident with the onset of limb movement (preparatory motion) and after the onset of limb movement due to the reactive forces (resultant motion).…”

Modulation of grip force with load force during point-to-point arm movements

“…For example, anticipatory adjustments to cope with intersegmental forces resulting from arm movement have been reported in remote body segments as well as within the same limb. Horak et al (1984) have shown that when subjects raise their arm, activity in trunk and leg muscles precedes the arm movement. When the subject was asked to move faster or to lift heavier loads, these postural muscles became active earlier relative to the onset of arm displacement.…”

The influence of cellist's postural movements on their musical expressivity

“…Parmi ces paramètres, la vitesse du mouvement prévu semble particulièrement les influencer , Horak 1984. En effet, les APAs n'apparaitraient qu'à partir d'un certain seuil de vitesse, et disparaitraient pour les mouvements trop lents.…”

“…Ces résultats trouvent un écho intéressant avec plusieurs travaux sur les mouvements de personnes en situation de handicap moteur. En effet, les données obtenues sur des sujets paraplégiques 2 [Do 1985], hémiplégiques 3 [Horak 1984] ou parkinsoniennes [Bazalgette 1987] 4 révèlent que certains de leurs ajustements posturaux naturels ne s'effectuent pas correctement lors d'un mouvement intentionnel (comme celui du bras par exemple), et qu'en conséquence la vitesse de ce mouvement se trouve être réduite [Bouisset 1991]. A propos des parkinsoniens, Bazalgette a notamment montré que si la vitesse des mouvements intentionnels de bras était supérieure en position assise que debout, la valeur maximale de cette vitesse correspondait au seuil à partir duquel les APAs 5 (Ajustements Posturaux Anticipateurs) apparaissent chez les sujets sains.…”