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 (%$$O_2max) plays a decisive role for adaptations to interval training. However, previous studies examining how interval sessions should be designed to achieve a high %$$O_2max have exclusively been performed in males. The present study compared the %$$O_2max attained during three different 6 × 8 min interval protocols, in female (n = 11; $$O_2max, 62.5 (6.4) mL · min⁻¹·kg⁻¹) and male (n = 8; $$O_2max, 81.0 (5.2) mL · min⁻¹·kg⁻¹) cyclists. Mean power output during work intervals were identical across the three interval protocols, corresponding to the cyclist's 40 min maximal effort (PO_40min): (1) 30 s intervals at 118% of PO_40min interspersed with 15 s active recovery at 60% (30/15), (2) constant pace at 100% of PO_40min (CON), and (3) altering between 60 s intervals at 110% and 60 s at 90% of PO_40min (60/60). Additionally, the study explored whether the m. vastus lateralis characteristics of the cyclists (fiber type proportion, capillarization, and citrate synthase activity) were associated with the %$$O_2max attained during the interval sessions. Overall, mean %$$O_2max and time ≥90% of $$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, %$$O_2max and time ≥90% of $$O_2max did not differ between sexes. Skeletal muscle characteristics were not related to %$$O_2max during interval sessions. In conclusion, well-trained cyclists demonstrate highest %$$O_2max during 30/15, irrespective of sex and skeletal muscle characteristics.