A Study on Reliability and Concurrent Validity of a Load Cell Device in a Prototype Exercise Machine for Lower Limb Strengthening in Children with Cerebral Palsy
Abstract
This study aimed to evaluate the reliability and concurrent validity of a load cell device installed at the center of the footpad in a prototype exercise machine for lower limb strengthening in children with cerebral palsy. The device was tested using ten levels of constant weight (10–100 kilograms) placed on the footpad and compared with measurements obtained from a standard scale. Two testing rounds were conducted, separated by a seven-day interval, with each weight level was measured three times per round. Data analysis using the Intraclass Correlation Coefficient: ICC(3.1) demonstrated excellence reliability (ICC = 0.999, 95%CI: 0.985–1.000, p<0.001) and excellent validity in both rounds (ICC = 1.000, 95%CI: 0.997–1.000, p<0.001; and ICC = 1.000, 95%CI: 0.998–1.000, p<0.001). In addition, Bland–Altman plot analysis indicated a high level of agreement between the load cell and the standard scale, with most differences lying close to the mean line and remaining within the 95% limits of agreement across both rounds. These findings indicate the suitability of the load cell device as a quantitative research instrument for measuring weight and assessing lower limb muscle performance, particularly in monitoring treatment outcomes and developing effective exercise programs for children with cerebral palsy.
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