Exertional calf pain at kilometer five - Finding the cause.

A 23-year-old professional distance runner with several years of exertional calf pain was diagnosed with a unique mixed type III and functional popliteal artery entrapment syndrome (PAES). Surgical reduction of the obstructing tissue allowed her to return to professional running. This case highlights the importance of including PAES in the differential for chronic intermittent lower extremity claudication and outlines the work-up required to diagnose this vascular obstruction in younger athletes.