EMG-assessed paratonia: A novel approach to investigating motor response inhibition in healthy subjects

Abstract

Paratonia is an involuntary muscle activity that occurs during passive joint mobilization and is common in people with dementia. It includes oppositional paratonia, in which muscle activity resists passive movement, and facilitatory paratonia, in which it assists movement. This phenomenon reflects a defect in motor response inhibition. In a recently published paper, we demonstrated that paratonia can be detected using surface electromyography (EMG) not only in patients with dementia but also in healthy individuals, the majority of whom do not exhibit clinically observable paratonia. This finding suggests that EMG-assessed paratonia may provide a novel approach to studying motor response inhibition in healthy subjects. The present study investigates this possibility for the first time. We recruited 120 healthy subjects under the age of 30, divided equally into three groups: sedentary, amateur, and professional athletes with low, moderate, and high levels of physical activity, respectively. Paratonia was assessed in the triceps and biceps brachii muscles during passive forearm movements performed manually. The results indicate that paratonia is more pronounced during fast and continuous passive movements, with facilitatory paratonia being more prevalent than oppositional paratonia. It is also more pronounced in the biceps than in the triceps. These findings, which mirror those previously observed in patients with dementia, suggest a similarity between paratonia in healthy subjects and those with cognitive impairment, supporting the hypothesis that paratonia in healthy individuals represents a form of impaired motor response inhibition. Furthermore, the comparison between groups showed that paratonia decreased with increasing physical activity, being least evident in athletes, more noticeable in amateurs, and most pronounced in sedentary individuals. This pattern confirms a key feature of motor response inhibition that has been shown in studies using traditional methods. Overall, our findings suggest that EMG-assessed paratonia provides a new method for studying motor response inhibition in healthy individuals.

Fig 1

(A) Depicts passive elbow flexion and extension movements performed either in a continuous or discontinuous manner, synchronized with metronome beeps. (B) Shows the detection of the facilitatory form of EMG-assessed paratonia in the biceps brachii during passive flexion and in the triceps brachii during passive extension. Conversely, the oppositional form of EMG-assessed paratonia is observed in the biceps brachii during passive extension and in the triceps brachii during passive flexion.

Fig 2. TREND flow diagram.

Description of study population recruitment.

Fig 3. Facilitatory and oppositional EMG-assessed paratonia in the biceps brachii (blue) and triceps brachii (red) during passive elbow flexion and extension at different metronome velocities (40 BPM vs. 100 BPM).

Fig 4. Facilitatory and oppositional EMG-assessed paratonia in the biceps brachii (blue) and triceps brachii (red) muscles during passive elbow flexion and extension, comparing discontinuous and continuous passive movements.

Fig 5

Facilitatory and oppositional EMG-assessed paratonia in the biceps brachii (left) and triceps brachii (right) muscles during passive elbow flexion and extension.

Fig 6

Facilitatory and oppositional EMG-assessed paratonia in the biceps brachii (top row) and triceps brachii (bottom row) muscles during passive elbow flexion and extension across three groups: professional athletes, amateurs, and sedentary individuals.

Fig 7

Facilitatory and oppositional EMG-assessed paratonia in the biceps brachii (top row) and triceps brachii (bottom row) muscles during passive elbow flexion and extension across different sports: basketball, tennis, running, and swimming.