Improving the Muscle Strength and Endurance of College Students Using a Combined Plyometric and 4X4 High Intensity Interval Training (HIIT) Protocol

This study evaluated the efficacy of a 3-week combined plyometric and 4x4 HIIT protocol on lower body strength and endurance among untrained male maritime college students, and explored participants' lived experiences to inform program enhancement. An explanatory mixed-method design was employed with 120 untrained male first-year maritime college students at the university, assigned equally to an experimental group and a control group. The experimental group underwent a progressive 3-week combined plyometric and 4x4 HIIT intervention, while the control group followed the standard physical education curriculum. Eight indicators were assessed, four tests to measure strength and four endurance measures. Paired t-test was used for quantitative analysis, while Braun and Clarke's thematic analysis was applied to focus group discussion data. The experimental group demonstrated statistically significant improvements across all eight indicators compared to the control group. Notable gains included an increase in 1RM Back Squats, improvement in Vertical Jump, significant gain in Standing Long Jump, and an improvement in Wall Sit duration. Qualitative analysis revealed six emergent themes: (1) Physical Challenge and Initial Adaptation Difficulties, (2) Perceived Enhancement of Physical Capabilities, (3) Psychological Empowerment Through Achievement, (4) Social Bonding and Peer Support, (5) Navigating the Intersection of Training and Academics, and (6) Sustained Motivation and Future Training Aspirations. The combined plyometric and 4x4 HIIT protocol significantly enhanced lower body muscular strength and endurance in untrained male college students within a compressed 3-week timeframe. The qualitative findings underscored the importance of progressive program design, peer support mechanisms, and holistic development in optimizing training outcomes. The study established the combined protocol as a time-efficient, evidence-based training modality suitable for integration into college physical education programs and recommends its institutionalization as a core component of fitness curricula for first-year college students.