Concurrent Validity of Lower Limb Muscle Strength by Handheld Dynamometry in Children 7 to 11 Years Old

Context The assessment of pediatric muscle strength is necessary in a range of applications, including rehabilitation programmes. Hand-held dynamometry is considered easy to use, portable and low cost, but validity to measure lower limb muscle strength in children has not been assessed. Objective To determine the concurrent validity of lower limb torque from hand-held dynamometry (HHD) compared to isokinetic dynamometry (ID) in children age 7 to 11 years old. Design A descriptive assessment of concurrent validity of lower limb joint torques from HHD compared to ID. Methods Sixty-one typically developing children underwent assessment of maximal hip, knee and ankle isometric torque by HHD and ID using standardized protocols. Joint positions were selected to represent maximal strength and were replicated between devices. Concurrent validity was determined by Pearson’s correlation, limits of agreement, and Bland-Altman plots. Results Correlations between HHD and ID were moderate-to-large for knee extension (r 95%CI: 0.39 to 0.73), small-to-large for plantarflexion (r 95%CI: 0.29 to 0.67), knee flexion (r 95%CI: 0.16 to 0.59), hip flexion (r 95%CI: 0.21 to 0.57), hip extension (r 95%CI: 0.18 to 0.54), and hip adduction (r 95%CI: 0.12 to 0.56), and small-to-moderate for dorsiflexion (r 95%CI: -0.11 to 0.39) and hip abduction (r 95%CI: -0.02 to 0.46). Limits of Agreement for all joint torques were greater than 10% indicating large error in HHD measured torque compared to ID. A positive proportional bias was detected for plantarflexion, indicating that HHD underestimated torque to a greater extent in participants with higher torque values. Conclusions Maximal torque values from HHD and ID are consistent with those previously reported in the literature. Poor concurrent validity of HHD may have arisen from issues around joint position, joint stabilization and the experience of the tester to prevent an isokinetic contraction. Pediatric lower limb muscle strength assessed by hand-held dynamometry should be interpreted with caution.