Resumen: This study aimed to investigate the effects of a physical activity intervention, based on self-determination theory and the transtheoretical model, on university students in the contemplation stage. Participants: 42 students, in the contemplation stage at baseline, were randomly assigned to an experimental group (16 women, 2 men; M age = 19.1 ± 1.15) and a control group (18 women, 2 men; M age = 20.1 ± 5.7). Methods: Physical activity was measured at different moments by accelerometry. Other cognitive variables were measured by self-reported scales. Results: We did not find any significant increases in students’ physical activity in favor of the intervention group. Intragroup analyses indicate that the intervention has an effect on physical activity (moderate-to-vigorous physical activity), basic psychological needs, and intrinsic and extrinsic motivation. Conclusions: Results partially demonstrate that applying social cognitive theories seems to be effective in improving physical activity and cognitive variables in university students in the contemplation stage Idioma: Inglés DOI: 10.3390/ijerph16224368 Año: 2019 Publicado en: International journal of environmental research and public health 9, 16 (2019), 4368 [13 pp.] ISSN: 1661-7827 Factor impacto JCR: 2.849 (2019) Categ. JCR: PUBLIC, ENVIRONMENTAL & OCCUPATIONAL HEALTH rank: 32 / 169 = 0.189 (2019) - Q1 - T1 Categ. JCR: PUBLIC, ENVIRONMENTAL & OCCUPATIONAL HEALTH rank: 58 / 193 = 0.301 (2019) - Q2 - T1 Categ. JCR: ENVIRONMENTAL SCIENCES rank: 105 / 264 = 0.398 (2019) - Q2 - T2 Factor impacto SCIMAGO: 0.739 - Health, Toxicology and Mutagenesis (Q2) - Public Health, Environmental and Occupational Health (Q2) - Pollution (Q2)