INTRODUCTION: The ability to produce steady muscle contraction force is affected by the contraction intensity. Whether and how the steadiness of contraction will be affected by the muscle activity of the contralateral limb requires further study.
AIM: To determine 1) whether the steadiness in precision contractions of one limb would be affected by muscle contractions of the contralateral limb; and 2) whether the motor unit firing rate (MUFR) would be affected by muscle contractions of the contralateral limb.
METHOD: Twelve healthy volunteers (6 M and 6 F, age range 20-‐35 years) performed 12 s static knee extensions at 10% and 30% of the maximal voluntary contraction (MVC) force using the left leg, while the right leg was at rest or performed static knee extensions at 10% or 30%MVC 6 s after the commencement of the left leg contraction. The steadiness of contraction was assessed by the standard deviation (SD) of force variation against the target level. Motor unit action potentials were recorded from the left vastus lateralis muscle using a custom-‐made high-‐impedance quadrafilar needle electrode, and identified using custom-‐written software for multichannel spike recognition (Kamen et al. 1995). An average of 154 motor units from each subject was analysed. The MUFR for each spike train was calculated for the first 6 s and the second 6 s period of each contraction. ANOVA with repeated measures and post-‐hoc analysis with Bonferroni adjustment were performed to evaluate the main effect of individual conditions (ie. left leg force, right leg force and unilateral vs bilateral) and interactions between these conditions.
RESULTS: A significant effect (P
CONCLUSION: This study provided new evidence indicating that the steadiness of muscle force production could be affected by muscle contraction of the contralateral limb. The MUFR and its variation were also affected by the muscle contraction in the contralateral limb.