Robert Wilczewski

Background: The Body Shape Index (ABSI) and somatotype components represent different approaches to assessing body morphology. This study aimed to examine the associations between physical activity, sedentary behaviour, sleep duration, ABSI, and somatotype components in young adults. Methods: A cross-sectional study was conducted among 371 university students from Poland and Slovenia (202 men and 169 women; mean age: 21.46 ± 1.07 years). ABSI and somatotype components were determined based on anthropometric measurements. Data on physical activity, sedentary behaviour, and sleep duration were obtained using a seven-day activity record. Associations were assessed using Spearman’s rank correlation coefficients and multiple linear regression models adjusted for sex, age, and country of origin. Results: Weak negative correlations were observed between walking time and ABSI (r_s = −0.135; p < 0.01) and between sleep duration and mesomorphy (r_s = −0.111; p < 0.05). Additional weak associations were identified in analyses conducted separately for women and men. After adjustment for potential confounders, walking time was positively associated with endomorphy (β = 0.158; p = 0.009) and mesomorphy (β = 0.117; p = 0.041), and negatively associated with ectomorphy (β = −0.192; p = 0.002). All significant associations were characterized by small effect sizes. No significant associations were found for ABSI in the primary adjusted model for the total sample. Conclusions: Despite the small magnitude of the observed associations, different patterns of associations were observed for ABSI and the somatotype profile, reflected by the combined pattern of its endomorphic, mesomorphic, and ectomorphic components. However, the identified associations were few in number and weak in strength; therefore, further research is needed to better explain their significance in young adult populations.

Background: Body mass index (BMI) is widely used as a simple anthropometric indicator, but its functional relevance to physical fitness in physically active populations, such as Physical Education students, remains debated. Aim: This study examined the association between BMI and selected components of physical fitness in Physical Education students, considering sex and country differences. Methods: A cross-sectional study was conducted among undergraduate Physical Education students from Poland and Romania (n = 515; mean age: 21.64 ± 1.34 years). BMI was calculated from measured height and body mass and analyzed as both a continuous and categorical variable. Physical fitness was assessed using three Eurofit tests evaluating upper-limb movement speed, trunk muscular endurance, and lower-limb explosive power. Analyses included correlation methods and multiple linear regression models with subgroup analyses, interaction terms, and quadratic BMI terms to assess nonlinearity. Results: Associations between BMI and fitness components were small in magnitude and inconsistent (r = −0.28 to 0.143; β = −1.614 to 0.005) and varied across tests and subgroups. No significant interaction effects by sex or country were observed, as interaction terms were not statistically significant, and no clear nonlinear relationships were identified. Sex and country were significantly associated with performance levels, whereas BMI contributed only marginally to explaining variability (ΔR² = 0.005–0.011). Conclusions: BMI showed limited and inconsistent associations with the assessed fitness components in this relatively homogeneous group of Physical Education students. It should be interpreted cautiously as a functional indicator and complemented with more precise measures of body composition and physical fitness.