Background <p>Physical activity is essential for maintaining a healthy lifestyle; however, various psychological and physiological barriers can hinder participation. University students represent a high-risk group due to academic workload and social pressures. This study aimed to investigate barriers to physical activity participation among university students in the context of fatigue, motivation, and body composition determinants.</p> Methods <p>The study employed a cross-sectional and observational design, and a total of 552 individuals with a mean age of 20.5 ± 2.1 years were included in the analysis. Data were collected through a demographic information form, the Barriers to Physical Activity Scale, the Chalder Fatigue Scale, and the University Student Motivation Scale. Body composition was assessed using a bioelectrical impedance analysis device. In addition to descriptive statistics, Pearson’s correlation analysis was used to examine relationships between variables, and multiple linear regression was applied to determine the effects of predictor variables.</p> Results <p>Higher levels of fatigue were associated with increased perceptions of both personal (<i>r</i> ≈ .28) and social barriers (<i>r</i> ≈ .21), indicating that fatigue is a significant psychological constraint on physical activity participation. While intrinsic motivation demonstrated a protective effect (β=–0.22), extrinsic motivation (β = 0.19) and amotivation (β = 0.27) were linked to heightened perceptions of barriers. Furthermore, higher body fat percentage emerged as the strongest physiological predictor (β = 0.29), underscoring the critical role of body composition in shaping behavioural barriers.</p> Conclusion <p>In conclusion, barriers to physical activity among university students are influenced by both psychosocial dynamics and body composition characteristics. Strategies aimed at enhancing intrinsic motivation, while reducing fatigue and body fat, may substantially contribute to overcoming barriers in this age group.</p>