Objective: To identify the relationship between the location of motor points of gastrocnemius and soleus and the skin surface landmarks.

Method: Compound muscle action potentials (CMAPs) of each lattice of gastrocnemius and soleus in 11 healthy subjects were recorded. Standardized reference lines were made as follows: 1) a horizontal reference line (popliteal crease) and 2) a vertical reference line drawn between mid-points of the horizontal reference line and inter-malleolus connection line. The CMAPs were mapped horizontally and vertically 1cm width to the standardized reference lines. Location of motor points was mapped to the skin surface in the ratio of length of the vertical and horizontal reference lines.

Results: The motor point of medial head of gastrocnemius was located at 41.0⁑6.1% distal and 54.6⁑19.2% medial to the mid-point of horizontal reference line. The location of the motor point of the lateral head of gastrocnemius was 35.7⁑5.2% distal and 48.5⁑15.1% lateral, respectively. In the soleus, the motor point was at 68.6⁑8.0% distal and 10.5⁑9.0% lateral, respectively.

Conclusion: The motor point of the lateral head of gastrocnemius was located more proximally relative to medial head, and the motor point of soleus was located at slightly lateral side of the vertical reference line. The author concluded that mapping of motor points of the gastro-soleus muscles would increase accessibility in performing phenol motor point block or botulinum toxin injection for management of spasticity or abnormal tonicity of the ankle.

Keywords :Motor point, Surface mapping, Gastrocnemius muscle, Soleus muscle