An amateur marathon runner presented with symptoms of thoracic outlet syndrome after long distance running. He complained of numbness on the C8 and T1 dermatome bilaterally. There were also symptoms of heaviness and discomfort of both upper limbs and shoulder girdles. These symptoms could be relieved temporarily by supporting both upper limbs on a rail or shrugging his shoulders. The symptoms and signs would subside spontaneously on resting. An exercise provocative test and instant relief manoeuvre, which are the main diagnostic tests for this unusual case of "dynamic" thoracic outlet syndrome, were introduced.