Assessment of Cross Talk Between Fine Wire EMG from Soleus and Surface EMG from the Gastrocnemius

Objectives: To assess the extent of cross talk betweendeep and superficial muscle using fine wireelectromyography (EMG) and surface EMG and toassess the correct location of the inserted fine wires inthe targeted muscles.Design: Observational.Setting: Movement analysis laboratory, Department ofPhysical Medicine and Rehabilitation (PMR), ChristianMedical College (CMC), Vellore.Participants: 12 healthy volunteersMain Outcome Measures: (i) timing of the EMG fromthe fine wires and surface electrodes during differentfunctional tasks, (ii) movement in response to stimulationthrough the fine wires, (iii) cross-correlation of the finewire EMG with the surface recorded EMG.Methods: EMG sampling was done with fine wireelectrodes in the soleus and with surface electrodes onthe gastrocnemius from healthy subjects. Crosscorrelation and fine wire stimulation was done to assessthe extent of cross talk between the two groups and assessthe accuracy of fine wire placement.Results: In 9 out of 12 subjects, the EMG timing (method1) and cross-correlation (method 2) strongly indicatedthat the fine wires were in the Soleus when compared tothe surface electrodes which were over theGastrocnemius. In the remaining three subjects (subjects1, 3 and 4) the fine wires were probably in theGastrocnemius.Conclusions: The Gastrocnemius and the Soleus musclesperform almost the same actions of plantar flexion butthere are differences in their temporal and spatial firingpatterns, as shown in the results above. These differencesand the location of the fine wire electrodes have beendetermined using cross correlation and stimulation throughthe fine wire.