Hello Geordiejonna,

I would like to know few other thing about your problem, if you are OK with that.
You said that the you noticed muscle weakness during the section at the gym... did you feel it during the warming up or during your sets?
A part from weakness on the muscle you have listed, any other symtom?
Do you have any neck pain?
Do you feel any weakness on your hand too? Can you extend fingers and wrist or have you got some difficulty on doing that too?
Any Pins and needle or funny sensation on the back of your arm, middle finger or little finger and inner aspect of arm and forearm?
Where did you had your flu stab? Right or left arm? where exactly?
How is it progressing since the onset? was the onset pretty acute or more insidious? And if insidious can you roughly say in how many days your weakness built up?

Thanks a lot