Muscle fitness and physical function in children and adolescents with newly diagnosed cancer.

Background and aims: Maintaining muscle health is crucial for children undergoing cancer treatment. However, the extent of impairments during the early stages of treatment remains sparsely investigated. Therefore, we investigated muscle fitness-muscle strength, muscle power, and muscle endurance-and physical function in children with newly diagnosed cancer compared to community controls. Methods: We compared parameters of muscle strength (assessed by isometric knee-extension, bench press and handgrip strength), muscle power and physical function [by countermovement jump and timed-up-and-go (TUG)], and lower body strength and muscle endurance [by 30 and 60-second sit-to-stand test (STS)] between children with newly diagnosed cancer (age 6-17.9 years) and community controls. Children with cancer were assessed within 31 days of treatment initiation. Results: We included 123 children with cancer (58% boys; median age 12 years, IQR 8-15), assessed within a median of 9 (IQR 6-14) days after cancer treatment initiation, and 221 community controls (61% boys; median age 12 years, IQR 9-14). All outcomes were significantly lower in children with cancer compared with community controls except handgrip strength. Knee extension strength was 15.8% lower (mean diff.: -5.46 kg, 95% CI: -9.98; -0.93, Conclusions: Children with cancer have impaired muscle fitness and physical performance within the first month of treatment. Our results suggest that rehabilitation should be implemented early during treatment to counteract further loss of muscle strength, muscle power, and muscle endurance, with the potential to support motor development and maintain sense of normality.