Response: Commentary on the effects of hypoxia on energy substrate use during exercise.

Background: A recent commentary has been published on our meta-analysis, which investigated substrate oxidation during exercise matched for relative intensities in hypoxia compared with normoxia. Within this commentary, the authors proposed that exercise matched for absolute intensities in hypoxia compared with normoxia, should have been included within the analysis, as this model provides a more suitable experimental design when considering nutritional interventions in hypoxia.

Main Body: Within this response, we provide a rationale for the use of exercise matched for relative intensities in hypoxia compared with normoxia. Specifically, we argue that this model provides a physiological stimulus replicable of real world situations, by reducing the absolute workload undertaken in hypoxia. Further, the use of exercise matched for relative intensities isolates the metabolic response to hypoxia, rather than the increased relative exercise intensity experienced in hypoxia when utilising exercise matched for absolute intensities. In addition, we also report previously unpublished data analysed at the time of the original meta-analysis, assessing substrate oxidation during exercise matched for absolute intensities in hypoxia compared with normoxia.

Conclusion: An increased reliance on carbohydrate oxidation was observed during exercise matched for absolute intensities in hypoxia compared with normoxia. These data now provide a comparable dataset for the use of researchers and practitioners alike in the design of nutritional interventions for relevant populations.