By this do you mean he is quite fit - but he has palpitations often, or he is unfit and has palpitations?
All in all there are many medical conditions that he could have and some are very hard to track down in the early stages. Particularly worrisome is the loss of voice along with the muscle weakness - these, while very rare, particularly at his age, could be early signs of ALS, “Lou Gehrig’s” or some other motor neuron condition. He should definitely be checked over thoroughly by a neurologist along with appropriate blood panels including auto-immune markers. Muscle twitching/weakness and voice and/or swallowing issues, are some of the initial signs of these conditions.
There are also many more mild conditions, of course, including simple fatigue (psychological and mental) from medical school. In Chinese Medicine this might translate as Spleen Qi Deficiency and/or Lung Qi Deficiency. But proper diagnosis by a practitioner in your area would be the only way to know for sure. For general information on those patterns you could read, My Spleen is What? and My Lungs Are What?.
These are not normal symptoms, however, so I would heavily pursue analysis from both western and eastern perspectives and start with treatment. Whatever this is the normal stress of medical school will likely not help it very much.
Technically speaking he can be helped with Chinese Medicine regardless, but proper diagnosis is key.