Does the number of trials affect the reliability of handgrip strength measurement in individuals with intellectual disabilities?

The main objectives of this study were to examine which testing protocol (one/two/three trials) and method (best/average value) used for determining maximal handgrip strength is more reliable for individuals with intellectual disabilities (ID) and to compare the reliability and variability of maximal handgrip strength measurement between individuals with ID and healthy individuals. Twenty individuals with ID (18.7±3.3 years) and 20 healthy individuals (18.5±3.4 years) performed six separate sessions. During these sessions, the participants' maximal handgrip strength was evaluated using three protocols with different number of trials (one/two/three). In individuals with ID, the protocols with one and two trials were less reliable (ICC=0.78-0.95; SEM%=9-21) than the protocol with three trials (ICC=0.94-0.96; SEM%=8-10) whereas in healthy individuals all protocols were equally reliable (ICC=0.95-0.99; SEM%=1.9-4.9). In individuals with ID, the mean of three trials (ICC=0.96, SEM=1.19-1.35kg, SEM%=8.2-8.7) had slightly higher reliability than the best of three trials (ICC=0.94, SEM=1.47-1.75kg, SEM%=9.2-10.1). Furthermore, the variability of maximal handgrip strength measurement was about twofold higher in individuals with ID (CV=37-45%) vs. healthy individuals (CV=21-23%). Maximal handgrip strength can be measured reliably in young individuals with ID using the mean of three trials as the most reliable approach for the determination of maximal handgrip strength.