The Organization and Control of Intra-Limb Anticipatory Postural Adjustments and Their Role in Movement Performance

Abstract

Anticipatory Postural Adjustments (APAs) are commonly described as unconscious muscular activities aimed to counterbalance the perturbation caused by the primary movement, so as to ensure the whole-body balance, as well as contributing to initiate the displacement of the body center of mass when starting gait or whole-body reaching movements. These activities usually create one or more fixation chains which spread over several muscles of different limbs, and may be thus called inter-limb APAs. However, it has been reported that APAs also precede voluntary movements involving tiny masses, like a flexion/extension of the wrist or even a brisk flexion of the index-finger. In particular, such movements are preceded by an intra-limb APA chain, that involves muscles acting on the proximal joints. Considering the small mass of the moving segments, it is unlikely that the ensuing perturbation could threaten the whole-body balance, so that it is interesting to enquire the physiological role of intra-limb APAs and their organization and control compared to inter-limb APAs. This review is focused on intra-limb APAs and highlights a strict correspondence in their behavior and temporal/spatial organization with respect to inter-limb APAs. Hence it is suggested that both are manifestations of the same phenomenon. Particular emphasis is given to intra-limb APAs preceding index-finger flexion, because their relatively simple biomechanics and the fact that muscular actions were limited to a single arm allowed peculiar investigations, leading to important conclusions. Indeed, such paradigm provided evidence that by granting a proper fixation of those body segments proximal to the moving one APAs are involved in refining movement precision, and also that APAs and prime mover activation are driven by a shared motor command.

Do Grade II Ankle Sprains Have Chronic Effects on the Functional Ability of Ballet Dancers Performing Single-Leg Flat-Foot Stance? An Observational Cross-Sectional Study

“…Recently, a few studies pointed out that a crossover effect of injuries can exist, especially tendinitis, from one side to the other [38,39]. While it is not clear the mechanism of action of this crossover effect (e.g., central nervous system or anticipatory postural adjustments [40]), it still could be a possible confounder of our results as the pathological and healthy side could be similar because of it. Our study arrived to a different conclusion than a similar 2011 study [25]; however, we focused on a more selective group of subjects who had only grade II ankle injury.…”

Peer Review #2 of "Anticipatory Postural Adjustments and kinematic arm features when postural stability is manipulated (v0.2)"

“…Second, the upward acceleration of the arm produces a forward trunk tilting that can be counteracted when sitting with support but is more difficult when no support is added on the feet. So, APAs not only serves the whole-body equilibrium to the movement initiation, but are also concerned to provide the correct postural set to obtain the correct movement (Cavallari et al, 2016).…”

Cough-Anal Reflex May Be the Expression of a Pre-Programmed Postural Action

“…APAs may also precede movements of tiny masses, like a brisk flexion of the index-finger when performed in a seated position (Caronni and Cavallari, 2009 ). In this case, they are named intra-limb APAs as the fixation chain is limited to muscles acting on proximal joints (Cavallari et al, 2016 ). Taking into account the small mass of the moving segments, and the fact that this movement cannot affect the whole-body balance, the role of intra-limb APA has been attributed to the precision of the final movement (Bruttini et al, 2016 ).…”

“…Taking into account the small mass of the moving segments, and the fact that this movement cannot affect the whole-body balance, the role of intra-limb APA has been attributed to the precision of the final movement (Bruttini et al, 2016 ). Note also that despite the different aim, inter- and intra- limb APAs share many behavioral properties: they are distributed to muscles of the same limb in which the movement occurs, precede the onset of the voluntary movement, are polarized according to the task direction in space, are scaled to the amplitude of the perturbation and adapt to changes in the postural requirement of the task (Cavallari et al, 2016 ).…”

“…Returning to the cough-anal reflex/response question, an important family of pre-programmed muscle contractions has been well documented when studying voluntary movements: these anticipatory adjustments play a fundamental role in whole body and segmental postural control (Bouisset and Do, 2008 ; Cavallari et al, 2016 ), so that they are referred to as anticipatory postural adjustments (APAs). By analogy, we propose that also the sphincter control may belong to the family of the pre-programmed actions , and in this view, the cough-anal reflex may be interpreted as an APA on the thoraco-abdominal compartment.…”