Comment: difference between assessment of upper limb movement and upper limb associated reactions during walking

Abstract

Background: While walking, people swing their arms in a specific pattern. This specific arm swing pattern during walking has shown to have a beneficial effect on gait as it reduces walking energy cost and optimizes balance. In several patient populations the arm movements can be directly affected (e.g. in patients with acquired brain injury (ABI)), which in turn has a negative effect on their gait pattern, balance and energy cost of walking. Maintext: InDecember 2019, Kahn et al. published a paper in JNER concerning thequantification of upper limb associated reactions (ARs) during walking in peoplewith ABI. ARs are defined as “an effort-dependent phenomenon causing aninvoluntary increase in upper limb muscle tone, with awkward and uncomfortablepostures”. These upper limb ARs appear often in patients with ABI and can havean important effect on their gait. The authors calculated kinematic measuresusing three-dimensional gait analysis relating to range of motion, variabilityand mean position over the gait cycle for the different upper limb joints(shoulder, elbow, wrist) during self-selected steady-state walking. Based ondifferences they found between an ABI cohort and healthy control cohort, theauthors concluded that they were able to quantify ARs during walking in thispopulation. This calculation, however, is not specific for upper limb ARs. Infact, the authors calculated general measures of arm posture (e.g. mean positionover the gait cycle) or arm movement (e.g. range of motion and variability)during gait. Previous research has already indicated that other factors thanARs can influence the posture or movement of the arm during gait in patientswith brain injury, such as voluntary compensations for gait instability andcontractures or spasticity of upper arm muscles. Yet, it is not possible to disentanglethe different causes of the altered arm posture during steady-state walkingbased on the proposed measures. Conclusion: The kinematic arm measures proposed by Kahn et al. (J Neuroeng Rehabil 16(1):160, 2019) are not adirect measure of ARs, but provide a quantification of overall deviation of armposture or movement during gait. Depending on the specific study design thesemeasures may provide insights in ARs.