Assessing the Reliability of Handheld Dynamometry and Ultrasonography to Measure Quadriceps Strength and Muscle Thickness in Children, Adolescents, and Young Adults.

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. 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. 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). The results of this study suggest quadriceps muscle strength and thickness measurements using HHD and ultrasonography are reliable in children, adolescents, and young adults.