Physiological Responses to Treadmill HIIT with Fixed vs Self-Selected Recovery without Feedback in Runners

This dataset contains cardiopulmonary exercise data (gas exchange and heart rate) processed to 5-second averages and blood lactate values collected during a treadmill high-intensity interval training (HIIT) protocol performed under three recovery strategies: - HIIT 1:0.5 — 2 min work / 1 min passive rest - HIIT 1:1 — 2 min work / 2 min passive rest - Self-selected — passive rest duration chosen by the runner, without time or heart-rate feedback Design: - Within-subject crossover: each participant completed all three conditions in counterbalanced order (1–2 weeks between visits). - Each session: 6 × 2-min work bouts at constant speed, 1% incline, with passive standing rest between bouts. - Gas exchange + HR recorded continuously; exported here as 5-second means. - Lactate measured discretely during recovery time points (see variables below).