A Tale of 2 Wheels

Figure 1. Biomechanical Adaptation of the Hip Flexors and Iliac Vessel Entrapment From Psoas Muscle Hypertrophy (A) Repetitive hip flexion and engagement of the psoas muscle during training and cycling can result in muscle hypertrophy, with subsequent compression of adjacent vascular structures leading to iliac artery endofibrosis or deep vein thrombosis of the iliac vein on the affected side. (B) The biomechanics of cycling affecting psoas muscle hypertrophy include increased vector forces during hip flexion (yellow arrow) from clip-on pedaling style (upward stroke motion and power transmission) and hyperflexion of the hip joint at the highest point of the pedaling stroke (red arrows) favored by extreme aerodynamic riding positions, as seen during time trialing and triathlon disciplines. Ao = aorta; IVC = inferior vena cava.