This paper describes clinical trials which are aimed to understand the relationship between blood glucose level changes and physical activity in type 1 diabetics. Also, the paper introduces our study, including the protocol and preliminary statistics on the collected data. Our study observes type 1 diabetic individuals in everyday living conditions. During the study, the subjects log their insulin intake, physiological status (circadian rhythm, menstruation, stress), nutrient and fluid intake, and medication intake by means of electronic diaries. In addition, heart rate is automatically collected from a wearable device. The data will be used to investigate the effect of physical activity on blood glucose levels, e.g. for virtual patient system model development ("digital twin"), to develop and refine physical activity detection, and to refine blood glucose prediction.