Low back pain (LBP) is a prevalent musculoskeletal condition that affects a large portion of the adult population globally, contributing to significant disability and economic burden. Clinical guidelines emphasize the biopsychosocial model for LBP management, which focuses on patient education, self-management, and interventions such as physical activity and exercise to promote recovery. Exercise therapy is considered effective for LBP management, though its success varies between individuals. Face-to-face physiotherapy is often combined with home-based exercises (HBE) to increase treatment dosage without adding extra costs. However, patient adherence to HBE is crucial for the effectiveness of HBE interventions, yet adherence remains a challenge and is difficult to measure accurately. Digital health technologies, such as smartphone apps, have the potential to support adherence to HBE. These technologies, when integrated with traditional physiotherapy, form blended care interventions that can enhance patient engagement, self-management, and exercise adherence. In light of this, the e-Exercise LBP intervention was developed, combining a smartphone app with face-to-face physiotherapy. The content of this intervention is tailored to the patient’s risk of developing persistent LBP and includes self-management themes, a tailored exercise program, and a goal-oriented physical activity module. To better understand adherence, the Exercise Adherence Scale (EXAS) was developed and tested for validity and reliability. The EXAS measures adherence to the frequency, intensity, and quality of HBE. The tool demonstrated good intrarater reliability but had lower interrater reliability. Using the EXAS, researchers could explore adherence patterns and their associations with clinical outcomes in patients with LBP. The research in this thesis also explored patient perspectives on using a smartphone app to support HBE. Qualitative interviews revealed that patients found the app acceptable and useful, particularly valuing its ease of integration into their daily routines. Key features of the app, such as video instructions, reminders, and self-monitoring, were considered beneficial. However, physiotherapists play an essential role in guiding patients on how to use the app effectively. A cluster randomized controlled trial was conducted to evaluate the effectiveness and cost-effectiveness of the e-Exercise LBP intervention compared to usual care. Both the intervention and usual care groups showed improvements in physical functioning, but no significant differences were found between the groups and for its cost-effectiveness. However, the e-Exercise LBP intervention significantly improved secondary outcomes like fear-avoidance beliefs and exercise adherence, particularly in high-risk patients. The research then identified three trajectories of adherence: declining, stable, and increasing adherence. Surprisingly, baseline patient characteristics did not predict adherence trajectories, highlighting the complexity of adherence behavior. Lastly, the research found no significant correlation between adherence levels and improvements in physical functioning or pain intensity, suggesting a more complex relationship between adherence and recovery from LBP than previously assumed. In conclusion, the research in this thesis emphasizes the importance of physiotherapists in supporting patient adherence and the value of using digital tools like apps to enhance treatment outcomes. However, adherence remains a complex issue, and further research combining quantitative and qualitative methods is necessary to better understand its role in LBP recovery.