This study investigated the predictive strength of perceived competence and enjoyment on students' physical activity and cardiorespiratory fitness in physical education classes. Participants (N = 307; 101 in Grade 6, 96 in Grade 7, 110 in Grade 8; 149 boys, 158 girls) responded to questionnaires assessing perceived competence and enjoyment of physical education, then their cardiorespiratory fitness was assessed on the Progressive Aerobic Cardiovascular Endurance Run (PACER) test. Physical activity in one class was estimated via pedometers. Regression analyses showed enjoyment (R2 = 16.5) and perceived competence (R2 = 4.2) accounted for significant variance of only 20.7% of physical activity and, perceived competence was the only significant contributor to cardiorespiratory fitness performance (R2 = 19.3%). Only a small amount of variance here leaves 80% unaccounted for. Some educational implications and areas for research are mentioned.