Acute Hemodynamic Responses to Three Work-Matched HIIT Training Protocols in Trained Cyclists

Current literature indicates that studies comprehensively examining acute central and peripheral hemodynamic responses to different high-intensity interval training (HIIT) modalities in trained cyclists remain limited. Therefore, this study aims to compare the acute central cardiac output (Q), stroke volume (SV) and peripheral arteriovenous O2 difference (a−vO2diff) responses elicited by three distinct HIIT models and to determine which modality provides a greater acute stimulus to the respective physiological components. Twelve trained male cyclists (Level 3-4) participated in this study (age: 29.7 ± 5.3 years; maximal oxygen uptake (V̇O2max): 57.8 ± 4.1 mL·min-1·kg-1; body mass: 69.8 ± 6.0 kg). Acute hemodynamic responses were evaluated with three work- and effort-matched HIIT models administered in a randomised order: Long-HIIT (4×3 min work- 3 min recoveries), Short-HIIT (1 series of 15×43.5 sec work - 43.5 sec recovery), and Decreasing Power Output HIIT (DPO-HIIT; 6×114.5 sec work - 114.5 sec recovery). Q, SV, and a−vO2diff were measured using a non-invasive inert gas rebreathing method (N2ORB). Two-way repeated-measures analysis of variance revealed no significant main effect of the protocol for Q (F(2.000, 22.000)=1.966, p=0.178, ηp2=0.152), SV (F(2.000, 22.000)=0.790, p=0.446, ηp2=0.067), heart rate (HR) (F(2.000, 22.000)=0.620, p=0.547, ηp2=0.053), or a−vO2diff (F(2.000, 22.000)=1.586, p=0.227, ηp2=0.126). The Protocol × Time interaction was significant only for HR (F(2.467, 27.132)=4.561, p=0.014, ηp2=0.293). Consequently, while overall systemic stress remains matched, coaches and athletes can utilise these different HIIT structures interchangeably, which may allow for flexibility in endurance training prescription.