A 12-Week Pilot Study Comparing High-Intensity Interval Training and Peripheral Heart Action Training on ISAK-Based Anthropometric Outcomes and Perceived Psychophysical Well-Being in Young Adults

Background: High-Intensity Interval Training (HIIT) and Peripheral Heart Action (PHA) are widely used training modalities, but comparative longitudinal data using standardized anthropometric methods remain limited. Purpose: To compare within-group changes over 12 weeks of HIIT and PHA training on body composition and perceived psychophysical well-being in moderately active young adults. Methods: Twenty-four adults (12 males, 12 females; age 30.9 ± 3.5 years) were allocated to either HIIT or PHA in a non-randomized pilot study, based on training schedule availability and previous training routine, which may introduce selection bias. Training was performed three times per week for 12 weeks. Body composition was assessed using standardized ISAK anthropometry. Data were analyzed using linear mixed-effects models. Results: Significant effects of Time were found for body mass, BMI, sum of skinfolds, waist circumference, and endomorphy (all p < 0.05). Significant Time × Group interactions were observed for BMI, sum of skinfolds, waist circumference, and endomorphy (p < 0.05), indicating different adaptation patterns. HIIT showed greater reductions in selected skinfolds and higher perceived performance improvement (p < 0.001), whereas PHA showed greater increases in arm circumferences and mesomorphy (p < 0.01). Conclusions: Within-group improvements were observed in anthropometric/body composition indicators over time, with distinct longitudinal adaptation patterns between HIIT and PHA.