My guest today is Mark Burnley, PhD from the University of Kent, in the UK. His principle interests concern endurance physiology, specifically the oxygen uptake and metabolic responses to exercise and the power-duration relationship. For example, he was part of the group that first validated the 3-minute all-out test to estimate critical power. He's spent much of his career questioning why a large fraction of our exercise capacity is unsustainable. In other words, we can only maintain exercise when the intensity is less than 20-30% of our ability to generate force…why do we have so much additional capacity when we can't sustain it?