Quantifying muscle strength, size, and neuromuscular activation in adolescent and young adult survivors of musculoskeletal sarcoma: Identifying correlates and responses to functional strengthening

Background: Medical and surgical treatment for musculoskeletal sarcoma (MSS) place survivors at risk for impairments in muscle properties including muscle strength, muscle size, and neuromuscular activation. The purpose of this study was to explore muscle properties, gross motor performance, and quality of life (QoL) and the changes in response to a 6-week functional strengthening intervention (PT-STRONG) in MSS survivors of childhood cancer (CCS). Methods: Eight lower extremity MSS CCS (13–23 years old) performed baseline testing and three completed PT-STRONG. Participants completed measurements of knee extension strength using handheld dynamometry, vastus lateralis (VL) and rectus femoris (RF) muscle thickness using ultrasonography at rest, and neuromuscular activation using electromyography during strength testing and a step-up task. Participants also completed gross motor and QoL assessments. Results: Compared with the non-surgical limb, MSS CCS had lower surgical limb knee extension strength, VL muscle thickness, and RF step-up muscle rate of activation (RoA). Compared with normative values, MSS CCS had decreased bilateral knee extension strength, gross motor performance, and physical QoL. Positive correlations among muscle strength, muscle thickness, and gross motor performance were identified. After PT-STRONG, MSS CCS had improvements in VL muscle thickness, VL and RF RoA duing step-up, gross motor performance, and physical QoL. Conclusions: Positive association between larger muscle thickness with greater knee extension strength, and higher knee extension strength with better gross motor performance indicate that comprehensive physical therapy assessment and interventions that identify and target impairments in muscle properties to guide clinical decision making should be considered for MSS CCS into survivorship.