INS and type 2 diabetes mellitus: This study compared the acute effects of one single session of 100% O2 (HBO) with one of 21% O2 ambient air (control condition, CON), both delivered at 240 kPa compression, with regards to the following variables: (1) tissue-specific glucose metabolism during endogenous (fasting) insulinaemia; (2) tissue-specific insulin sensitivity during hyperinsulinaemic–euglycaemic clamp conditions; (3) skeletal muscle and WAT mitochondrial capacity, oxidative stress and antioxidant capacity; and (4) insulin signalling in skeletal muscle of humans with type 2 diabetes (Fig. 1 and ESM Table 1).