Effects of High-Intensity Interval Training on Functional Fitness, Body Composition, and Quality of Life in Older Women: A Randomized Controlled Trial

High-intensity interval training (HIIT) has emerged as a time-efficient exercise strategy with potential benefits for older adults. However, evidence regarding its effects on functional fitness, body composition, and quality of life in older women remains limited. This randomized controlled trial included community-dwelling older women allocated to a HIIT group or a control group. The intervention consisted of a 65-week HIIT program (3 sessions/week), while the control group maintained usual activities. Functional fitness was assessed using standardized field-based tests, body composition was evaluated by bioelectrical impedance analysis, and quality of life was measured using the WHOQOL-BREF questionnaire. Pre- and post-intervention assessments were performed under standardized conditions. Data were analyzed using mixed ANOVA models, with significance set at p < 0.05. Compared with the control group, the HIIT group significantly improved aerobic capacity (2MST: +25.4 vs. −19.6 repetitions; p < 0.001), lower-limb strength (30s CST: +4.8 vs. −2.6 repetitions; p < 0.001), and mobility (TUG: −0.3 vs. +0.4 s; p < 0.001). Body composition improved with reductions in body fat percentage (−1.8% vs. +1.9%; p < 0.001) and visceral fat index (−0.6 vs. +0.3; p < 0.001), alongside increased total body water (+2.3% vs. −1.8%; p < 0.001). Quality of life improved significantly in physical, psychological, and environmental domains (p < 0.001). HIIT was associated with improvements in functional fitness, body composition, and quality of life, with no major adverse events reported. These findings support the use of HIIT as a practical intervention to enhance health and functional independence in aging populations.