Synthyroid dose is dependent on your body weight. If you significantly loose your weight the dose can be reduced.
After severe stress
, use of anabolic steroids
, severe illness your TSH
can be abnormally low , which is not a sign of improvement in TSH. Regular exercise wont affect your TSH if your weight is relatively stable. You can go back to your work outs.
Hope I have answered your querry,
Dr Ajish TP