Neuromechanical interference of posture on movement: evidence from Alexander technique teachers rising from a chair

Abstract

While Alexander technique (AT) teachers have been reported to stand up by shifting weight gradually as they incline the trunk forward, healthy untrained (HU) adults appear unable to rise in this way. This study examines the hypothesis that HU have difficulty rising smoothly, and that this difficulty relates to reported differences in postural stiffness between groups. A wide range of movement durations (1–8 s) and anteroposterior foot placements were studied under the instruction to rise at a uniform rate. Before seat-off (SO) there were clear and profound performance differences between groups, particularly for slower movements, that could not be explained by strength differences. For each movement duration, HU used approximately twice the forward center-of-mass (CoM) velocity and vertical feet-loading rate as AT. For slow movements, HU violated task instruction by abruptly speeding up and rapidly shifting weight just before SO. In contrast, AT shifted weight gradually while smoothly advancing the CoM, achieving a more anterior CoM at SO. A neuromechanical model revealed a mechanism whereby stiffness affects standing up by exacerbating a conflict between postural and balance constraints. Thus activating leg extensors to take body weight hinders forward CoM progression toward the feet. HU's abrupt weight shift can be explained by reliance on momentum to stretch stiff leg extensors. AT's smooth rises can be explained by heightened dynamic tone control that reduces leg extensor resistance and improves force transmission across the trunk. Our results suggest postural control shapes movement coordination through a dynamic “postural frame” that affects the resistive behavior of the body.

Lighten Up

“…Because the two sets of instructions we used had markedly different effects on postural sway, alignment, and movement smoothness, we conclude that the effects were not due to attention to the body, per se , or even solely to the increase in standing height. These results are consistent with previous results indicating that long-term training in the AT improves subtle control of axial tone and of coordination between the legs and torso, 21,51 and they suggest that how one conceives of postural uprightness affects how one stands and moves, and that this influence can be harnessed for rehabilitative purposes.…”

Human Postural Control

“…However, muscle length changes may also evoke involuntary shortening reactions (compliant posture behavior) or elicit postural adjustments of other “remote” muscles not being primarily stretched (Andrews et al, 1972 ; Gurfinkel et al, 1989b ). A dynamic “postural frame,” that is inherently incorporated in posture and movement coordination, may account for the resistive or compliant behavior of the body (Cacciatore et al, 2014 ). In this respect, Bernstein's ( 1940 ) interpretation of muscle tone seems more functional, as the degree of readiness for movement related to movement as a state is related to an action, or as a precondition is related to an effect.…”

Self-efficacy and self-care-related outcomes following Alexander Technique lessons for people with chronic neck pain in the ATLAS randomised, controlled trial

“…Training in the Alexander Technique has been shown to increase dynamic postural muscle tone [ 21 ], and improve movement coordination and balance [ [22] , [23] , [24] ]. These movement and balance changes are thought to result from the altered postural tone [ 25 ]. Research studies, often using qualitative methods, have reported improvements in psychological well-being, mood and confidence, as well as reduction in performance-related anxiety following one-to-one Alexander lessons [ [20] , [26] , [27] , [28] ].…”