Unravelling the biological roles of reactive oxygen species (ROS) is challenging (Murphy et al. 2011). There are three key challenges: (1) the global term ‘ROS’ subsumes chemically diverse free radical and non‐radical species making it difficult to attribute a particular effect to a particular species; (2) nutritional antioxidants often fail to react appreciably with key ROS (e.g. superoxide anion, O2.−) at the desired time and place; and (3) measuring ROS is a perennial difficulty because their short half‐lives (usually in the order of milliseconds) can preclude direct detection (Murphy et al. 2011). It is unsurprising, therefore, that few suspected biological roles of ROS have been confirmed in humans, especially in an exercise context that presents its own unique experimental challenges. For example, debate still exists as to whether ROS regulate key adaptive responses to exercise (Margaritelis et al. 2016).