In addition, since isometric exercises are done in a static position, they won't help improve speed or athletic performance. They can be useful, however, in enhancing stabilization â maintaining the position of the affected area â since muscles often contract isometrically to aid in stabilization.
Etiology. Most (85-95%) substernal thyroid masses represent benign goiter. Historically, goiters have generally occurred because of iodine deficiency, although this is now observed primarily in developing nations.
1 Lymphadenopathy mediastinal â An enlargement of the lymph nodes. 2  Pericardial cyst â A benign growth that results from an out-pouching of the pericardium (the heartâs lining). 3  Thyroid mass mediastinal â Usually a benign growth, such as a goiter. 4  These types of tumors can occasionally be cancerous.