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Dear colleagues, thought I'd kick-off this discussion with a question:
I understand that the corticospinal pathway has a bias toward upper limb extension rather than flexion. Clinically, performing reaching activities in standing can be (?more) effective compared to sitting, providing the patient has sufficient postural control to manage standing. Could this be largely because we are biasing the CNS toward a global pattern of extension (i.e. standing) which then promotes better access to upper limb extension, or because other pathways are involved (VST and RST) then it doesn't matter necessarily what postural set the patient is in?
Hi Nic,
Thanks for your question.
You are correct in your understanding that the corticospinal (CST) system has a bias towards digit extension (as opposed to overall UL extension) based on the literature to date, however, we are learning more all the time about the role of the corticoreticulospinal system (CRSS) in hand function, particularly the role of the CRSS in gross digit flexion.
For me, there is a difference between the facilitation of digit extension and the facilitation of UL reach, however, digit extension will facilitate an UL reach pattern as we know from the literature that we create digit and wrist extension as the initial precursor to the UL reach pattern.
With respect to developing UL reach in standing vs. sitting, this is directly related to the level of anticipatory postural control (APA) available to the client. The development and acquisition of the standing posture will require a level of vestibulospinal (VS) and CRSS activation. Our APA demand is higher in standing, and if appropriately facilitated into standing the client will be receiving appropriate sensory information for the maintenance of equilibrium in standing. Therefore, APA's may be more readily accessible to the client in standing vs. sitting allowing them to posturally stabilize their trunk and shoulder girdle in order to potentiate an UL reach pattern.
However, there is no question that if the client is appropriately facilitated into standing, their overall extensor kinetic chain is being facilitated from a heel-up initiative and, therefore, there will be potential carryover into extension in the UL.
So, the clinical question is: Is the reach pattern impaired due to specifc UL impairments? Or, is the reach pattern impaired due to the loss of postural control of the trunk and shoulder girdle? Or, both? It is the clinical rationale that underlies these questions in a particular client which will determine the optimal posture to treat the client. For example, the facilitation of supine with the maintenance of heel loading may be more effective in the facilitation of UL reach than using the posture of standing, if the client does not yet have sufficient postural control for stand. Likewise, stand down, side lie, forward lean sit are also potential treatment postures for the facilitation of reach depending upon the individual client presentation.
Hope this helps, and happy to discuss further 🙂
Julie
