Validity and reliability of Eforto®, a system to (self-)monitor grip strength and muscle fatigability in older persons

IntroductionWe developed Eforto (R), an innovative system for (self-)monitoring of grip strength (GS) and muscle fatigability (Fatigue Resistance (FR = time until GS decreased to 50% of maximum during sustained contraction) and grip work (GW = area under the strength-time curve)). The Eforto (R) system consists of a rubber bulb that is wirelessly connected to a smartphone-based application, and a telemonitoring platform. The aim was to evaluate the validity and reliability of Eforto (R) to measure muscle fatigability.MethodsCommunity-dwelling older persons (n = 61), geriatric inpatients (n = 26) and hip fracture patients (n = 25) were evaluated for GS and muscle fatigability. In community dwellers fatigability was tested twice in the clinic (once with Eforto (R), once with Martin Vigorimeter (MV), standard analog handgrip system) and for six consecutive days as a self-assessment at home with Eforto (R). In hospitalized participants, fatigability was tested twice using Eforto (R), once by a researcher and once by a health professional.ResultsCriterion validity was supported by good to excellent correlations between Eforto (R) and MV for GS (r = 0.95) and muscle fatigability (FR r = 0.81 and GW r = 0.73), and no significant differences in measurements between both systems. Inter-rater and intra-rater reliability for 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).Discussion/conclusionWe established the criterion validity and reliability of Eforto (R) in older community-dwelling persons and hospitalized patients, supporting the implementation of Eforto (R) for (self-)monitoring of muscle fatigability.