Aims: Muscle strength testing is a core aspect in the pediatric physical and occupational therapy clinical examination and evaluation, and quadriceps muscle strength is associated with the ability to perform gross motor skills. The aim of this study was to assess the reliability of handheld dyamometry (HHD) and ultrasonography to measure quadriceps muscle strength and thickness in children, adolescents, and young adults. Methods : In 30 participants (6–26 years), without motor impairment, quadriceps strength was measured with HHD in seated and supine with the knee flexed to 90° and 35°. Rectus femoris (RF) and vastus lateralis (VL) muscle thickness was measured using ultrasonography. Typical error of measurement (TEM), coefficient of variation (CV%), and intra-class correlation coefficient (ICC) were used to assess the error and reliability of measures. Results : The average CV% among three trials of strength testing was 7.07%–9.94% and improved when using the top two trials (4.49%–5.61%). The average TEM was 2.21 Nm for strength and 0.03 cm for muscle thickness. Intra-rater and inter-rater reliability of muscle thickness was good to excellent (0.91–1.00). Conclusions: The results of this study suggest quadriceps muscle strength and thickness measurements using HHD and ultrasonography are reliable in children, adolescents, and young adults.

Purpose: To explore muscle properties, gross motor performance, and quality of life (QoL) in children with sickle cell disease (SCD) compared with controls and to assess relationships among these outcomes. Methods: A cross-sectional study of 24 children assessed muscle properties including: knee extension strength by dynamometry; vastus lateralis (VL) and rectus femoris (RF) muscle thickness by ultrasonography; and VL and RF neuromuscular activation (rate of muscle activation [RoA]) by electromyography (EMG). Gross motor performance and QoL were assessed by standardized tests and questionnaires. Results: Children with SCD had impaired knee extension strength, VL EMG RoA, gross motor performance, and QoL compared with children without SCD. Relationships among muscle properties, gross motor performance, and QoL were identified. Conclusions: These findings indicate that comprehensive muscle properties, gross motor performance, and QoL assessments should be considered to support and develop individualized physical therapy plans for children with SCD.

Children with hematologic and oncologic health conditions are at risk of impaired skeletal muscle strength, size, and neuromuscular activation that may limit gross motor performance. A comprehensive assessment of neuromuscular function of these children is essential to identify the trajectory of changes in skeletal muscle and to prescribe therapeutic exercise and monitor its impact. Therefore, this review aims to (a) define fundamental properties of skeletal muscle; (b) highlight methods to quantify muscle strength, size, and neuromuscular activation; (c) describe mechanisms that contribute to muscle strength and gross motor performance in children; (d) recommend clinical assessment measures; and (e) illustrate comprehensive muscle assessment in children using examples of sickle cell disease and musculoskeletal sarcoma.