Hi,
Lets see where to start...

EMG s can be negative but you can still have TOS - it is not a definitive test. just means your nerves aren't damaged yet..
plus it tests the major nerves and not the sensory nerves??{i think that is one reason so many have neg EMGs but still have TOS}

Have you had any cervical spine MRI or xrays ??
- to check for extra c ribs or c spine problems?
that is the next step

start working to correct that posture now
did chiro have any thoughts for that?
mine does PT therapies for me as well as adjustments
low level laser, IF stim { type of elect muscle stimulation}, ultra sound, trigger point massage etc

check our useful stickys too...

we can help you figure it out