Cardio-respiratory responses to hiit: Evidence of persistent physiological stress during recovery

High-Intensity Interval Training (HIIT) represents one of the most effective and widely used exercise strategies for improving cardio-respiratory fitness and inducing metabolic adaptations. The aim of the present study was to analyze the acute cardio-respiratory and ventilatory responses induced by a circuit-based HIIT protocol in physically active women.

Materials and methods

The study included 24 female participants (age: 24.37 ± 6.63 years; height: 167.25 ± 5.34 cm; weight: 66.08 ± 12.17 kg; sports experience: 4.8 ± 2.4 years). The experimental protocol consisted of a circuit-based HIIT training session involving repeated intervals of high-intensity exercise alternated with short recovery periods. Cardio-respiratory parameters were assessed before exercise, during exercise, and after a 10-minute recovery period using the Spirobank II Smart spirometer. The analyzed variables included heart rate (HR), peripheral oxygen saturation (SpO₂), Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV1), Maximum Voluntary Ventilation (MVV), and rating of perceived exertion (Borg scale).