Ventilatory Efficiency and End-Tidal CO₂ Kinetics During Active Recovery Following VT₂-Referenced Intermittent...

Backround and Objectives: Basketball performance is shaped by repeated high-intensity actions interspersed with brief recovery. Conventional continuous or strictly incremental testing may not fully capture short active-recovery dynamics relevant to stop-and-go sports. Material and Methods: This study applied a VT₂-referenced progressive-intermittent treadmill protocol and focused on 60-s active-recovery kinetics to describe effort tolerance in an applied basketball setting. Basketball players from Mureș County completed anthropometry (24 h pre-test, fasted) and a single laboratory visit. Pre-test training and diet were standardized for 48 h (submaximal training; predominantly carbohydrate intake). CPET was performed in 3-min stages (6.5 km·h^-1 start; +0.7 km·h^-1 per stage) and stopped at RER = 1.00 and/or blood lactate = 4.0 mmol·L^-1 (operational VT2). After 3 min active recovery, participants completed six 60-s high-speed bouts separated by 60-s active recovery intervals (AR1-AR6), with intensities prescribed at 120-180% of VT2-derived speed, followed by an 8-min active recovery. For each AR interval, linear regression over 0-60 s yielded slopes for VO₂, VO₂/HR, VCO₂, V̇E, VE/VO₂, VE/VCO₂, and PetCO₂. Results: VT₁ was determined at 2.29 m·s^-1 (VO₂ 32 mL·min^-1·kg^-1) and VT2 at 3.07 m·s^-1 (VO₂ 42 mL·min^-1·kg^-1). Maximal intermittent speed was 5.33 m·s^-1 (VO₂ 45.5 mL·min^-1·kg^-1; RER 1.06; PetCO₂ 38 mmHg). VO₂ differed across successive bouts (p = 0.0001), while PetCO₂ showed a small downward drift across repetitions. Peak indices (max speed, VE/VCO₂max, PetCO₂max, VEmax) were associated with phase-specific recovery slopes across early, mid, and late recovery periods (false discovery rate-adjusted correlations). Lactate decreased over 8 min, but lactate change rates were not associated with peak indices. Conclusions: The VT₂-referenced progressive-intermittent protocol appears feasible in basketball players and provides phase-dependent recovery information that complements conventional peak CPET outcomes, with potential relevance for applied team settings.