Opponens pollicis silent period during a precision motor task with the isometric contraction of the ipsilateral knee extension.

Abstract

Objectives: To clarify the excitability of the central nervous system function via a difference in the feedback method, we examined the alterations in the duration of the silent period recorded from the opponens pollicis muscle during a precision motor task. This task involved isometric knee extension using visual feedback and verbal conduction. Design: Cross-sectional study with an A-B-A task-order design. Methods: 12 healthy adults (7 males and 5 females; mean age: 23.7 ± 2.1 years) participated in this study. SP was recorded from the opponens pollicis muscle during a precision motor task involving with isometric contraction during ipsilateral knee extension with constant torque by two kinds of feedback. The precision motor task was carried out as follows; Subjects maintained knee extension torque at a constant strength using the BIODEX SYSTEM 3 with 60° of knee flexion. The knee extension torque was set at 25% of individual maximum effort. We monitored the torque using two methods. The first method used subjects’ own visual feedback with gazing at the BIODEX screen (Task A). The second task featured torque adjustment by the examiner’s verbal instruction. Subjects’ eyes were bandaged to eliminate visual feedback (Task B). Silent period was recorded from the opponens pollicis muscle while subjects maintained ipsilateral isometric knee extension during an A-B-A task order. As a stimulus condition, a constant current rectangular wave with a frequency of 0.5 Hz and a duration of 0.2 ms, was added 16 times in the median nerve at the wrist with the intensity of supra-maximum, which maximal M wave was evoked. We compared the duration of silent period between tasks in each dominant and non-dominant side. Results: The duration of silent period on the dominant leg was 109.1 ± 5.2 ms (Task A), 105.2 ± 7.2 ms (Task B), and 107.6 ± 6.7 ms (Task A). And that on the non-dominant leg was 111.3 ± 6.1 ms (Task A), 105.9 ± 4.4 ms (Task B), and 109.3 ± 4.4 ms (Task A). There was no significant difference on the dominant leg side. However, during Task B on the non-dominant leg side, the duration of silent period was shortened (Tukey’s test, p = 0.01, 0.08). Conclusion: During less-skilled motor adjustment using the non-dominant leg, the motor control with verbal conduction and no visual feedback requires more afferent activation. In these cases, central nervous system function excitability associated with ipsilateral upper extremity increases, even if the task involves the lower extremity.