Complex sentence: The syndrome also became known as "effort-induced thrombosis" in the 1960s, as it has been reported to occur after vigorous activity, though it can also occur due to anatomic abnormality such as clavicle impingement or spontaneously.
Split into simpler sentences: The syndrome also became known as "effort-induced thrombosis" in the 1960s, as it has been reported to occur after vigorous activity. Though it can also occur due to anatomic abnormality such as clavicle impingement or spontaneously.