Vera Storm

• Lifestyle-related diseases such as cardiovascular diseases and musculoskeletal diseases are the leading cause of work disability and death worldwide. As regular physical activity and sufficient intake of fruit and vegetables play a key role in the prevention and treatment of such diseases, the promotion of these behaviours constitutes a major topic in health psychology. Yet approaches for multiple health behaviour change, as well as the incorporation of work-related outcomes, and quality of life warrant further research. The research questions were examined in one observational and three experimental studies in various settings (medical rehabilitation; primary prevention) and across different health behaviours (physical activity; fruit and vegetable consumption). The results of this thesis highlight the importance of incorporating quality of life and vocational outcomes in activity-based treatment programmes. The findings of this thesis further suggest that improving a person’s confidence in their abilities may not only set the stage for successful behaviour change by strengthening intentions, but may also diminish the negative effects of compensatory health beliefs. Finally, especially if accompanied by self-regulatory strategies such as self-efficacy and planning, increases in desired behaviour for even more than one behaviour may be reached. The findings show that web-based computer-tailored interventions for multiple health behaviours can be an effective means to improve habit strength for physical activity and fruit and vegetable consumption if they make use of such self-regulatory strategies. The practical implications for public health, medical rehabilitation, and workplace health promotion on changing employee’s health behaviours given may provide a promising basis for disease prevention, sustaining quality of life and employability, and reintegration of already sick-listed employees.