Although the principal cause of IC is reduced blood flow to the lower limbs relative to increased demand during exercise, the pathophysiology of IC is not completely understood. For example, limb haemodynamics does not closely correlate with clinical presentation or the limitations in peak exercise performance. Haemodynamic measures of the severity of PAD, such as the ankle-brachial systolic blood pressure index (ABI) and blood flow by strain gauge plethysmography, are poor predictors of exercise capacity in patients with IC.