As we have discussed at length in the past, some of the fundamental physiological adaptations sought by endurance athletes through training occur in the mitochondria. A textbook will tell you that the mitochondria are the ‘aerobic powerhouses’ of cells; the sites of aerobic metabolism, and therefore metabolically where an endurance athlete makes their money. It has long been known that significant mitochondrial remodelling occurs in response to exercise (4), with increased size, number, and functionality of mitochondria observed following endurance training (5). This mitochondrial remodelling, and subsequent useful increase in the mitochondrial respiratory capacity, typically occurs as a result of mitochondrial biogenesis – the building of nice new mitochondria – and mitophagy – the break-down of damaged existing mitochondria.

A couple of recent studies have reported quite startling findings; namely, that short periods of very intense training actually...