In this study we evaluate the validity and reliability of Eforto® to measure muscle fatigability. Community-dwelling older persons, geriatric inpatients and hip fracture patients were evaluated for grip strength (GS) and muscle fatigability. Criterion validity was supported by good to excellent correlations between Eforto® and Martin Vigorimeter, and no significant differences in measurements between both systems. Inter-rater and intra-rater reliability for grip work (GW) were moderate to excellent (intra-class correlation: 0.59–0.94). The standard error of measurement for GW was small for geriatric inpatients and hip fracture patients (224.5 and 386.5 kPa*s) and higher for community-dwellers (661.5 kPa*s). See more.