Neuromuscular adaptations in ankle plantar flexor and dorsiflexor in persons with spinal cord injury

• Objective: Spinal cord injury (SCI) could lead to sensory-motor impairment of varying degree. After the injury, multiple neurophysiological changes occur, altering the neural motor control strategies. This study aims to assess the neuromuscular adaptations in the ankle plantar flexor and dorsiflexor muscles after the SCI by examining the electromyography (EMG) and motor unit parameters during sub-maximal voluntary isometric contractions and comparing these parameters to a control cohort. Methods: High-density EMG (HD-EMG) signals of tibialis anterior and soleus were recorded simultaneously with ankle joint torque during repeated sub-maximal (20% and 50% of the maximal torque) isometric voluntary contractions. Torque parameters such as normalized torque and coefficient of variation of torque during sustained contraction, EMG parameters such as amplitude and intramuscular coherence, as well as motor unit parameters such as motor unit discharge rates, recruitment thresholds, and coefficient of variation of the inter-spike intervals, were analyzed within the SCI and control groups. Results: We found that the SCI group, on average, had significantly weaker plantar flexor but not dorsiflexor muscles than the control group. Despite the increased variation of soleus motor unit inter-spike intervals post-SCI, both groups maintained constant sub-maximal torques with similar variability. However, the SCI group required up to 40.2% higher normalized EMG amplitudes to achieve the same torque level as the control group. Additionally, intramuscular coherence was found to be lower (up to 38.1% in TA and 34.6% in SOL) in the SCI group compared to the control group in the alpha frequency band during sustained sub-maximal isometric contractions. At higher force levels (50% MVC), motor units were recruited and de-recruited at lower thresholds in both muscles and fired at lower rates in the tibialis anterior muscle post-SCI. Conclusion: Through the analysis of these parameters, we observed altered force production and modulation strategies post-SCI. The observed combination of the motor unit and EMG parameter changes may indicate reduced common neural drive within the muscle and a possible shift towards larger motor units and in both TA and SOL muscles. Significance: The results of this study contribute to the knowledge of the neurophysiological modifications in the ankle dorsiflexors and plantar flexors following the SCI, which may aid future research on SCI rehabilitation.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Neurologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Neurology (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Medicinteknik -- Annan medicinteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Medical Engineering -- Other Medical Engineering (hsv//eng)

Nyckelord

neurophysiology

neuromuscular control

spinal cord injury

Medicinsk teknologi

Medical Technology

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