Comparative Effects of High-Intensity Interval Training and Low-Intensity Steady-State Exercise on Anthropometric Outcomes and Psychophysical Well-Being: A Pilot Study

Background: Comparative evidence for the effectiveness of High-Intensity Interval Training (HIIT) and Low-Intensity Steady-State (LISS) exercise derived from real-world settings using standardized anthropometric assessments and subjective perception measures remains limited. This pilot study aimed to compare the effects of 12 weeks of HIIT and LISS on anthropometric outcomes assessed through ISAK measurements and on post-intervention subjective perceptions. Methods: Twenty-four physically active adults (n = 12 HIIT; n = 12 LISS) completed a 12-week supervised training program with three sessions per week. Exercise intensity was monitored by heart rate (HIIT: 80–95% HRmax; LISS: 60–70% HRmax). Anthropometric measurements were performed according to ISAK guidelines at baseline and after 4, 8, and 12 weeks. Subjective perceptions were assessed post-intervention using a structured questionnaire. Data were analyzed using parametric or non-parametric tests, as appropriate. Results: Both HIIT and LISS showed significant reductions over time in body mass, BMI, fat mass, and waist and hip circumferences (p < 0.001), with no between-group differences for the primary endpoint. Endomorphy decreased and ectomorphy increased significantly in both groups. A significant group × time interaction was observed for muscle mass (p < 0.001), favoring preservation or slight increases in HIIT. Post-intervention, psychological well-being was higher in LISS (p = 0.002), whereas perceived physical performance improvements were greater in HIIT (p = 0.002–