GRip Assessment for Protocol Enhancements (GRAPE) in Older Adults - PROJECT SUMMARY/ABSTRACT Maximal handgrip strength (HGS) is considered a convenient and reliable measure of muscle function. Current protocols for assessing HGS focus exclusively on achieving maximal grip force; however, maximal strength is only a single characteristic of muscle function. Given that muscle function is multivariable, maximal HGS, as a measure of muscle function, could be incomplete. Other important aspects of muscle function such as bilateral coordination, explosiveness, submaximal force control, neuromuscular steadiness, strength asymmetry between limbs, and resistance to fatigue are overlooked in HGS assessments. Yet, deficiencies in each of these aspects are associated with health conditions linked to poor muscle function. Evaluating these additional aspects of muscle function, alongside maximal HGS, could improve how we conveniently assess muscle function and support the development of a new HGS protocol that could be utilized in clinical and translational research settings. This may aid in the discovery of processes that better predict age-related disability and disease, which will strengthen relevant screenings, better operationalize muscle function, and initiate opportunities for interventions to target specific characteristics of muscle function for successful aging. This work will advance how we assess muscle function by pursuing the following three specific aims: 1) evaluate the correlations of hand dominance and test-retest reliability for maximal HGS, bilateral HGS coordination, rate of HGS force development, submaximal HGS force control, neuromuscular HGS steadiness, HGS asymmetry, and HGS fatigability in older adults; 2) determine the multivariate relationships between maximal HGS, bilateral HGS coordination, rate of HGS force development, submaximal HGS force control, neuromuscular HGS steadiness, HGS asymmetry, and HGS fatigability to derive one or more HGS principal components in older adults; and 3) examine how maximal HGS, bilateral HGS coordination, rate of HGS force development, submaximal HGS force control, neuromuscular HGS steadiness, HGS asymmetry, and HGS fatigability are associated with knee extension strength, timed-up-and-go, short physical performance battery, gait speed, and 400-meter walk in older adults. Each HGS measure will be collected with digital handgrip dynamometers and accelerometers. Participants will also complete physical performance measurements to determine the study outcomes. This work has the potential to fundamentally transform clinical practice by better identifying the onset and progression of the disabling process with a new muscle function assessment. Our contribution is innovative because it could reveal that other characteristics of muscle function, when examined in HGS protocols, may not be related to maximal HGS and thereby could be more robustly associated with clinically relevant health outcomes. Ultimately, this research could improve the prognostic utility of muscle function assessments in clinical and translational research settings for preventing age-related disability and disease.
