Thoracic Outlet Syndrome (TOS)
is characterized by a compression of the artery, vein, brachial plexus at the scalenes (muscles of the neck), or pectoralis minor part of the axilla (under your armpit).
Symptoms may include heaviness in hands or numbness and tingling in the hands.
Poor posture, overexertion during exercise, and improper breathing habits can aggravate Thoracic Outlet Syndrome by causing further compression of your neurovascular bundle.
Scar tissue build-up after mastectomy surgery can also cause TOS symptoms that result in increased swelling of the arm.