Linking the evidence base to my practice: Arm muscle synergies, hand shaping, reach and grasp function.

Author, Katie Sutton (Bobath Tutor Trainee BBTA)

Upper limb recovery remains a priority in neurological rehabilitation research and clinical practice, owing to its fundamental role in functional independence and the complexity of upper limb biomechanics. The upper limb is characterised by multiple degrees of freedom and refined dexterity, making targeted therapy particularly challenging.

The Bobath Concept has long recognised the interdependence between upper limb function and postural control. Central to this approach is the understanding that the hand and shoulder are functionally linked, stability at the shoulder can improve the dexterity within the hand, but gaining increased sensory stimulation and enhancing single digit activity in the hand can facilitate muscle activation and promote stabilisation around the shoulder complex.

Historically, this clinical observation has not been linked to the literature. However, over the past decade, increased focus has been placed on the control of functional tasks such as reach and grasp, particularly through the study of muscle synergies.

A pivotal study by Tanzarella et al. (2024) examined the synergistic motor control involved in reaching and identified distinct synergy pairs. Of particular interest, one synergy pair demonstrated a notable correlation between posterior deltoid activation and specific hand-shaping movements, including thumb abduction, index finger extension, and little finger flexion. The action of these three movements is the fundamental basis for posturing the hand in order to gain the appropriate shape to go around the object to be grasped. The posterior deltoid acts as a stabiliser around the shoulder to provide the stability required to maintain the posture and direction of the arm whilst reaching.

The results of the EMG activity supports the concept of facilitating the reaching pattern from the hand with the goal of increasing the stabilisation around the shoulder in order to gain a placing response which is unique to the Bobath concept. It also supports the notion that gaining a contactual hand orientating response (CHOR) and loading through the hand can have a significant impact on shoulder and trunk stability in all functional tasks.

Another synergy pair identified was the ‘closing the hand while grasping’ synergy and this positively correlates with muscle activity of the triceps which extend the elbow in the act of stretching the arm. This is supported by previous studies that have identified that the aperture of the hand closes and shapes to the object prior to the upper limb reaching its destination. This would suggest that the closing of the hand can influence triceps activity and again highlights the importance of shaping within the hand and the influence of the intrinsic muscles. Shaping the arches of the hand and improving the stability of the hand is a fundamental principle within the Bobath concept and has been something I have always been conscious of incorporating into my treatment sessions. This paper has highlighted to me the importance of the timing of the grasp in relation to the reach and how small adjustments in the hand posture can aid elbow extension.

Overall there are distinct arm, forearm and hand synergies. This study highlights the fact that specific muscle activity around the shoulder predict hand pre-shaping during reaching an object to grasp it, and that vice versa, different hand postures can influence the activity around the shoulder. In fact, for the grasping and manipulation of different objects, the modality of reaching changes accordingly and in different parts of the reaching, and hand shape changes in line with the function of the object handled. However post stroke what we often see is a very flexed, abducted upper limb that cannot adapt to the demands of the task.

In clinical practice this highlights the importance of not only of being able to create stability around the trunk and shoulder for improved hand function but also being able to shape the hand itself and gain appropriate posturing in order to be able to lead the reach pattern and reduce the flexion and abduction component in order to maximise the potential of the upper limb.

If you would like to learn more about how to develop your practical hands-on rehabilitation skills for your patients upper limb recovery, have a look at the BBTA website for our exciting courses. www.bbta.org.uk.

Ref: Arm muscle synergies enhance hand posture prediction in combination with forearm muscle synergies. Tanzarella et al 2024 J. Neural Eng. 21 026043