Endurance exercise induces cardiovascular adaptations; the athletic phenotypes of the heart and arteries are well characterised, but few studies have investigated the effects of chronic exercise on the venous system. The aim of this study was to describe the anatomy and function of lower limb deep and superficial veins in athletes compared to controls. Endurance-trained athletes and untrained controls (13 males, 7 females per group) were examined utilising ultrasound to measure vein diameter and flow, and air plethysmography to assess calf venous volume dynamics and muscle pump function at rest, during a single step, ambulation (10 steps) and after acute treadmill exercise (30 min ~80% age-predicted heart rate maximum). Diameters of 3 of the 7 deep veins assessed were larger in athletes (P≤0.0167) and more medial calf perforators were detectable (5 vs. 3, P=0.0039). Calf venous volume was 22% larger in athletes (P=0.0057), calf muscle pump ejection volume and ambulatory venous volume after 10 steps were both greater in athletes (20 and 46% respectively, P≤0.0482). Following acute exercise, flow recovery profiles in deep and superficial veins draining the leg were not different between groups, despite athletes performing ~four times more work. After exercise, venous volume and ejection volume were reduced by ~20% in athletes with no change in controls (interaction P≤0.0372) and while ambulatory venous volume reduced, this remained greater in athletes. These findings highlight venous adaptations that compensate for the demands of regular endurance exercise, all of which are suited to enhance flow through the lower limb venous system.
