This quality analysis of test-retest reliability and validity (PART 1) serves as a basis for a further sensitivity analysis, whereby in a second step, a database with valid personalised age-, sex- and activity-related reference values for the respective measurement instrument, considering chronic concomitant diseases, is to be generated. The objectives of this study are therefore to 1) assess the test-retest reliability (intrasubject and intersession) and validity of JAMAR© Hydraulic and JAMAR© Smart dynamometers and Martin Vigorimeter (PART 1) and 2) undertake a sensitivity analysis providing valid personalised reference values for precision medicine (PART 2).~Thus, no study has yet comprehensively investigated all relevant influencing factors in a single and thus homogeneous study setting, so bias can be expected from this alone. The findings of this two-step study should enable physicians and therapists to compare the grip strength measurements of their patients with normative values in relation to their age, sex and activity group, as well as to any underlying chronic diseases that may be present. This allows realistic treatment and training goals to be set and patient performance to be interpreted.
Maximum isometric grip strength (MIGS) is a cost-effective, easily accessible, valid and reliable outcome measure for assessing upper body strength in both, adults and children. The the JAMAR Hydraulic Hand Dynamometer is the current gold standard for measuring MIGS. For certain age- and activity-groups, alternative devices may be more appropriate. To date, the quality criteria (test-retest-reliability and validity) of the JAMAR Smart Hand Dynamometer and the Martin Vigorimeter compared to the current gold standard are not yet investigated. Furthermore, no reference values for different age-, sex-, or activity level groups exist with regard to underlying disease entities for these three devices.