Temporal Changes in Anthropometric Circumferences and Bioimpedance-Derived Body Composition During Eight Weeks of Reformer Pilates in Young Women Without Regular Exercise Participation

Background: Evidence on Pilates-related body composition is inconsistent, and few studies track changes during programs. Objective: To assess body mass, bioimpedance-derived body-fat percentage and muscle mass, and seven circumferences at baseline, week 4, and week 8 of supervised Reformer Pilates. Methods: Twenty-two women aged 18–24 years who had not exercised regularly in the previous six months completed an 8-week program (two 50–60-min sessions weekly). Repeated-measures ANOVA with Greenhouse–Geisser correction was used; Holm adjustment covered 10 outcomes, with Bonferroni-adjusted pairwise comparisons and Friedman sensitivity tests. Results: Body mass, body-fat percentage, and muscle mass showed no significant time effects (Holm-adjusted P=.952, 1.000, and 1.000). All seven circumferences showed significant time effects (Holm-adjusted P≤.041). Baseline-to-week-8 reductions ranged from 0.95 cm (arm) to 5.32 cm (abdomen). Abdominal circumference decreased from 83.55±8.35 to 78.23±6.23 cm (adjusted P<.001; partial η²=.515). No week-4-to-week-8 comparison remained significant. Conclusions: During this uncontrolled program, several circumferences decreased, but body mass and bioimpedance-derived estimates showed no significant time effects. Most detectable circumference differences were evident by week 4.