The higher oxygen consumption during multiple short intervals is sex-independent and not influenced by skeletal muscle characteristics in well-trained cyclists.

It has been suggested that time spent at a high fraction of maximal oxygen consumption (% V˙ O(2max)) plays a decisive role for adaptations to interval training. However, previous studies examining how interval sessions should be designed to achieve a high % V˙ O(2max) have exclusively been performed in males. The present study compared the % V˙ O(2max) attained during three different 6 × 8 min interval protocols, in female (n = 11; V˙ O(2max), 62.5 (6.4) mL · min(-1)·kg(-1)) and male (n = 8; V˙ O(2max), 81.0 (5.2) mL · min(-1)·kg(-1)) cyclists. Mean power output during work intervals were identical across the three interval protocols, corresponding to the cyclist's 40 min maximal effort (PO(40min)): (1) 30 s intervals at 118% of PO(40min) interspersed with 15 s active recovery at 60% (30/15), (2) constant pace at 100% of PO(40min) (CON), and (3) altering between 60 s intervals at 110% and 60 s at 90% of PO(40min) (60/60). Additionally, the study explored whether the m. vastus lateralis characteristics of the cyclists (fiber type proportion, capillarization, and citrate synthase activity) were associated with the % V˙ O(2max) attained during the interval sessions. Overall, mean % V˙ O(2max) and time ≥90% of V˙ O(2max) were higher during 30/15 compared to CON (86.7 (10.1)% and 1123 (787) s versus 85.0 (10.4)% and 879 (779) s, respectively; both p ≤ 0.01) and 60/60 (85.6 (10.0)% and 917 (745) s, respectively; both p ≤ 0.05), while no difference was observed between 60/60 and CON (both p ≥ 0.36). During interval sessions, % V˙ O(2max) and time ≥90% of V˙ O(2max) did not differ between sexes. Skeletal muscle characteristics were not related to % V˙ O(2max) during interval sessions. In conclusion, well-trained cyclists demonstrate highest % V˙ O(2max) during 30/15, irrespective of sex and skeletal muscle characteristics.