Introduction Physical inactivity is a significant concern among undergraduate trainee teachers due to their demanding schedules and heavy workload, leading to adverse health consequences. Despite specializing in physical education (PE), many of these students lead sedentary lifestyles and do not engage in regular physical activity. This study investigates the relationship between the Task, Authority, Recognition, Grouping, Evaluation, and Time (TARGET) model, situational motivation, and physical activity adherence in PE among undergraduate trainee teachers. Methods The study involved 183 male and 237 female participants aged 18–23 years (mean age: 21.43 ± 1.50) from various Institutes of Teacher Education campuses. Data were collected using self-administered questionnaires: the TARGET Measures, the Situational Motivation Scale, and the Physical Activity Adherence Questionnaire. Descriptive analysis, independent-samples t-tests, one-way ANOVA, and two-way ANOVA were employed to analyze the data. Results Independent-samples t-tests revealed significant gender differences in perceived authority (p = 0.001), recognition (p = 0.033), grouping (p = 0.001), evaluation (p = 0.001), external regulation (p = 0.001), amotivation (p = 0.001), predisposing factors (p = 0.001), and enabling factors (p = 0.010). One-way ANOVA indicated a significant difference between the three teaching methods on intrinsic motivation (p = 0.006). Furthermore, between-subjects ANOVA revealed significant interactions: between Gender and Age on time (p = 0.026), and between Gender and Teaching Methods on authority (p = 0.031), external regulation (p = 0.041), and enabling factors (p = 0.035). Conclusion The findings suggest that implementing TARGET approaches within a mastery motivational climate is crucial for enhancing the motivation and adherence to physical activity among undergraduate trainee teachers in physical education.