Hi Lucy,
When you use the pronator teres technique you can see the individual heads independently.
In the long axis if you scan slightly towards the floor you see the long head and towards the roof the short head.
In the short axis the one closer to the ulna is the long head.
This is the great advantage of this technique. You can seperate the heads and see the enthesis , tendons and MTJ all with one technique.
Using the cobra technique the collagen that presents to you is the long head as it wraps further around the radial tuberosity.
Using the cotton reel technique you don’t see any insertions, however you can see both tendons and follow them to their MTJ.
If you slide the transducer slightly towards the hand you see short head and towards the elbow you see the long head.
Steve.