Exertional compartment syndrome can happen in most compartments, ie, muscle groups bound by inflexible structures, but cant happen in just one muscle. It usually/most often originates in the Anterior or Lateral compartments of the leg, since, as Taku said, those are strongly bound by the tibia and interossea membrane. However, in the lower leg, cyclists/runners are also susceptible to developing cs in the posterior and deep posterior compartments (ie calf).
There are described cases of cs in the thigh. The cases I have read about were almost all due to impact in contact sports (football etc) and were not, therefore, exertional(chronic) in etiology.
In rowers, canoeists, motorcrossers, you frequently get cs of the forearm. In theory, cs of the upperarm is possible, but I dont remember reading anything about it.
Francois is right about chronic(exertional) being 'the one for athlete', however, you can, if you dont take care of it, turn a chronic case into an acute situation.
I had exertional cs in the anterior and lateral compartments of the leg, and both compartments of the forearm, all bilaterally, had surgery to fix all of them, hence the info.
IMHO, I really dont think Tom has compartment syndrome.
Ziva