Cardiovascular fitness, measured through Resting Heart Rate (RHR) and Maximal Oxygen Uptake (VO2 Max), is critical for optimizing athletic performance. High-Intensity Interval Training (HIIT) and Fast Continuous Training (FCT) are two aerobic conditioning modalities widely used to improve cardiovascular efficiency, but their comparative effects remain insufficiently studied in adult competitive athletes. This study aimed to compare the effects of an 8-week HIIT and FCT program on RHR and VO2 Max in adult athletes, thereby evaluating the efficacy of each training modality in enhancing aerobic performance. A randomized controlled trial design was employed involving 90 adult athletes (45 males and 45 females, aged 21-26), randomly located into three groups: HIIT (n=30), FCT (n=30), and Control (n=30). RHR and VO2 Max were assessed during pre- and post-intervention using Polar H10 monitors and Vmax Encore Metabolic Cart, respectively. Data were analysed using ANCOVA (Analysis of Covariance) to control for pre-test differences, followed by Tukey’s post-hoc comparison. Post-intervention results revealed statistically significant improvements in both RHR and VO2 Max across the training groups (p < 0.05). The HIIT group exhibited the most significant reduction in RHR (62.72 bpm) and the highest increase in VO2 Max (52.12 ml/kg/min), outperforming both FCT (RHR = 65.06 bpm; VO2 Max = 49.40 ml/kg/min) and the Control group (RHR = 70.32 bpm; VO2 Max = 41.28 ml/kg/min). Effect sizes were large for both RHR (η² = 0.950) and VO2 Max (η² = 0.982), indicating robust model fit. The findings confirm that both HIIT and FCT are effective in improving cardiovascular parameters among adult athletes, with HIIT demonstrating superior efficacy in a shorter duration. These results support the strategic incorporation of HIIT in training regimens aimed at maximizing aerobic performance and cardiovascular health.

Keywords: High-Intensity Interval Training, Fast Continuous Training, Resting Heart Rate, Maximal Oxygen Uptake, Cardiovascular Fitness, Adult Athletes, Aerobic Capacity, Athletic Performance, Cardiorespiratory Fitness, Training Intervention, Exercise Physiology.

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Source of Funding:

This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Competing Interests Statement:

The authors declare that they have no conflict of interest.

Consent for publication:

The authors declare that they consented to the publication of this study.

Authors' contributions:

All the authors took part in literature search, review, analysis, and manuscript writing equally.

Ethical Approval:

This study was reviewed, and formal ethical approval was waived by the Institutional Ethics Committee of Swarnim Gujarat Sports University, as it involved routine training interventions with no invasive procedures or risk to subjects.

Informed Consent:

Informed consent was obtained from all participants, who were briefed about the nature, purpose, and voluntary nature of their participation.

Acknowledgement:

The authors express their sincere gratitude to the athletes from the participating sports academies for their enthusiastic cooperation and commitment throughout the study. Special thanks are extended to the faculty and staff of the Swarnim Gujarat Sports University, Gujarat and Regional College of Physical Education, Panisagar, for their logistical and administrative support.