STRENGTHS AND LIMITATIONS OF THIS STUDY
fatigue
ADVERSE EVENTS, COLD
This is the largest study to date assessing the safety and tolerability of exercising wearing a face mask.The randomised cross-over design ensured that the effect of any fatigue from exercise was equal between mask types.Some participants exercised outdoors and during cold weather when pulse oximeters were sometimes slow to provide readings, and this may have resulted in a recovery in oxygen levels and an underestimate of effect size.We collected a limited amount of non-invasive physiological data and did not collect data on measures such as end-tidal carbon dioxide or muscle oxygenation.We only included healthy young adults who exercised regularly in this study to minimise the risk of serious adverse events, but this may limit the generalisability of our findings to the wider population.