Abstract
BackgroundPeople with brain or neural injuries, such as cerebral palsy or spinal cord injury, commonly have joint hyper-resistance. Diagnosis and treatment of joint hyper-resistance is challenging due to a mix of tonic and phasic contributions. The parallel-cascade (PC) system identification technique offers a potential solution to disentangle the intrinsic (tonic) and reflexive (phasic) contributions to joint impedance, i.e. resistance. However, a simultaneous neurophysiological validation of both intrinsic and reflexive joint impedances is lacking. This simultaneous validation is important given the mix of tonic and phasic contributions to joint hyper-resistance. Therefore, the main goal of this paper is to perform a group-level neurophysiological validation of the PC system identification technique using electromyography (EMG) measurements.MethodsTen healthy people participated in the study. Perturbations were applied to the ankle joint to elicit reflexes and allow for system identification. Participants completed 20 hold periods of 60 seconds, assumed to have constant joint impedance, with varying magnitudes of intrinsic and reflexive joint impedances across periods. Each hold period provided a paired data point between the PC-based estimates and neurophysiological measures, i.e. between intrinsic stiffness and background EMG, and between reflexive gain and reflex EMG.ResultsThe intrinsic paired data points, with all subjects combined, were strongly correlated, with a range of r = [0.87 0.91] in both ankle plantarflexors and dorsiflexors. The reflexive paired data points were moderately correlated, with r = [0.64 0.69] in the ankle plantarflexors only.ConclusionAn agreement with the neurophysiological basis on which PC algorithms are built is necessary to support its clinical application in people with joint hyper-resistance. Our results show this agreement for the PC system identification technique on group-level. Consequently, these results show the validity of the use of the technique for the integrated assessment and training of people with joint hyper-resistance in clinical practice.
Highlights
People with brain or neural injuries, such as cerebral palsy or spinal cord injury, commonly have joint hyper-resistance
We investigated the neurophysiological validity of an online PC algorithm, which disentangles the intrinsic and reflexive contribution to joint impedance
We have shown the neurophysiological validity of the PC system identification technique on group-level through the evaluation of an online PC algorithm
Summary
People with brain or neural injuries, such as cerebral palsy or spinal cord injury, commonly have joint hyper-resistance. Diagnosis and treatment of joint hyper-resistance is challenging due to a mix of tonic and phasic contributions. A simultaneous neurophysiological validation of both intrinsic and reflexive joint impedances is lacking This simultaneous validation is important given the mix of tonic and phasic contributions to joint hyper-resistance. People with brain or neural injuries, such as cerebral palsy or spinal cord injury, commonly have an increased joint resistance (or ’hyper-resistance’) [1]. This joint hyper-resistance can severely impair both walking ability and functional independence. Botulinum neurotoxin injections reduce both involuntary background activation and spasticity, and the ability to perform voluntary muscle contractions [3, 4]
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