Effects of lifestyle on health related physical fitness and skin condition in university students

A total of 259 university students were included in the baseline analysis, including 73 participants in the control group and 186 participants in the resistance training group. One participant had missing follow-up body composition data; therefore, 258 participants were included in the longitudinal phenotype transition analysis. A hierarchical principal component analysis was used to integrate the health-related fitness domain, consisting of handgrip strength, modified sit-up, 20-m shuttle-run, and sit-and-reach performance, with the body composition domain, consisting of body fat mass, body fat percentage, and skeletal muscle mass. The first principal component of the fitness domain explained 52.67% of the variance, and the first principal component of the body composition domain explained 68.58%. The final integrated health-related fitness score explained 84.02% of the variance in the two domain-specific component scores. K-means clustering identified three ordered integrated health-related fitness phenotypes: Low (n=90), Moderate (n=99), and High (n=70). The phenotypes demonstrated graded differences in the integrated score, muscular strength, muscular endurance, cardiorespiratory endurance, skeletal muscle mass, body fat mass, and body fat percentage. The three-cluster solution had an average silhouette coefficient of 0.602, and 1,000-iteration bootstrap analysis showed an overall agreement of 97.5% with the original cluster classification. Among the 258 participants with complete follow-up data, 230 participants (89.1%) remained in the same phenotype, 25 (9.7%) transitioned to a higher phenotype, and 3 (1.2%) transitioned to a lower phenotype. Phenotype transitions were significantly asymmetric (Bowker ?²=17.37, df=2, p<0.001), with upward transitions occurring more frequently than downward transitions. Linear mixed-effects model analysis of the integrated health-related fitness score showed a significant group-by-time interaction favoring the resistance training group (ß=0.139, 95% CI 0.047–0.230, p=0.003). Upward phenotype transitions occurred in 11.4% of the resistance training group and 5.5% of the control group. These findings indicate that integrating field-based fitness measures and bioelectrical impedance analysis-derived body composition variables provides a multidimensional framework for describing health-related fitness status and 16-week changes in university students. External validation in independent populations is required before broader application.