We aim to include 60 children and adolescents aged 10 to 19 years who have undergone successful treatment for leukemia or lymphoma. Based on randomization, they will either 1) commence 16 weeks of training with STEEL or 2) commence 16 weeks of circuit training. STEEL training involves exercises for major muscle groups using free weights, body weight, or tailored machines. Circuit training is structured similarly to previous training for the target group and includes exercises using body weight, exercise balls, and rings. The training takes place in local centers either with friends or with other participants in the project. Before starting participation in the project, the child/adolescent and their parents or guardians will receive information about late effects, diet, sleep, and exercise, providing guidance and support regarding the project elements. The effects of the two training modalities will be evaluated based on self-reported quality of life, muscle strength, muscle mass, bone mineral content, fitness, and markers of metabolic syndrome (BMI, waist circumference, blood pressure, and blood analysis).