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

n=19 well-trained cyclists: 11 women (VO2max 62.5 ± 6.4 mL/kg/min) and 8 men (VO2max 81.0 ± 5.2 mL/kg/min); m. vastus lateralis biopsy for fiber type proportion, capillarization and citrate synthase activity.

Three 6 × 8 min interval protocols with identical mean power during the work intervals, equal to the cyclist's 40-min maximal effort (PO40min):

Recovery between the 8-min blocks is not described in the abstract.

%VO2max and time ≥90% VO2max (primary outcomes):

30/15 exceeds both formats for time ≥90% VO2max — ~28% more than CON at identical mean power.

Sex differences:

Muscle characteristics (biopsy):

Inference, not tested: 30/15 intervals create high-frequency oscillation — every 30 s the load exceeds PO40min by 18%, and the 15-s recovery is too short for VO2 to fall much, so cumulative time near VO2max grows. The absence of any link to fiber type, capillarization or citrate synthase suggests the difference is not peripheral; the paper measured the association, not the mechanism.

Acute study — no data on chronic adaptations with regular 30/15 use. Large between-subject SDs (e.g. 1123 ± 787 s) — the format effect is consistent, the absolute time is not. Menstrual cycle in women not controlled. Single target power (100% PO40min) — other intensities not tested. Small sex sub-groups (11 and 8).