title: Control of fingertip forces in young and older adults pressing against fixed low- and high-friction surfaces.
abstract: Mobile computing devices (e.g., smartphones and tablets) that have low-friction surfaces require well-directed fingertip forces of sufficient and precise magnitudes for proper use. Although general impairments in manual dexterity are well-documented in older adults, it is unclear how these sensorimotor impairments influence the ability of older adults to dexterously manipulate fixed, low-friction surfaces in particular. 21 young and 18 older (65+ yrs) adults produced maximal voluntary contractions (MVCs) and steady submaximal forces (2.5 and 10% MVC) with the fingertip of the index finger. A Teflon covered custom-molded splint was placed on the fingertip. A three-axis force sensor was covered with either Teflon or sandpaper to create low- and high-friction surfaces, respectively. Maximal downward forces (F(z)) were similar (p = .135) for young and older adults, and decreased by 15% (p<.001) while pressing on Teflon compared to sandpaper. Fluctuations in F(z) during the submaximal force-matching tasks were 2.45× greater (p<.001) for older adults than in young adults, and reached a maximum when older adults pressed against the Teflon surface while receiving visual feedback. These age-associated changes in motor performance are explained, in part, by altered muscle activity from three hand muscles and out-of-plane forces. Quantifying the ability to produce steady fingertip forces against low-friction surfaces may be a better indicator of impairment and disability than the current practice of evaluating maximal forces with pinch meters. These age-associated impairments in dexterity while interacting with low-friction surfaces may limit the use of the current generation of computing interfaces by older adults.
authors.affiliation: Department of Kinesiology, University of Wisconsin-Milwaukee, Milwaukee, WI, USA.
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Keenan
authors.forename: William V
authors.initials: WV
authors.lastname: Massey
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001324:Autoantigens / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D005260:Female; D005385:Fingers / Q000502:physiology*; D017276:Friction / Q000502:physiology*; D018737:Hand Strength / Q000502:physiology; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D013499:Surface Properties; D055815:Young Adult
chemical_list: D001324:Autoantigens; D018797:Cell Cycle Proteins; C086074:PCM1 protein, human