Force control of pinch grip: Normative data of a holistic evaluation

Background: Pulp pinch (PP) is a vital hand movement involving muscle strength and sensory integration. Previous research has primarily focused on Maximal Voluntary Contraction, but PP encompasses broader parameters.

Purpose: This study aims to establish normative data for a comprehensive evaluation of thumb and index force control during PP, including endurance, precision, accuracy in unilateral PP, and force coordination in bilateral PP.

Study design: A cross-sectional study.

Methods: Three hundred and twenty eight healthy Italian cis-gender participants (169 females, 159 males) were enrolled in a multiparametric force control evaluation of pinch grip, consisting in: sustained contraction (SC: ability to maintain a stable contraction at 40% MVC, measured as the time until exhaustion), dynamic contraction (DC: the ability to modulate precisely and accurately force output to follow a dynamic force trace), bimanual strength coordination (BSC: the ability to coordinate in-phase bimanual forces at different combined magnitudes) tasks. The sample was divided per sex and stratified in five age groups taking into account hand dominance. Differences in tasks' results between age, sex and hand-dominance were analysed.

Results: Endurance (SC) was similar between younger and older adults (η² =0.047 (Females) and η² < 0.007 (Males)). Older adults exhibited lower precision (DC) and coordination (BSC) compared to young adults in both sexes (η² >0.16). Females demonstrated greater endurance (SC) but lower precision and coordination (BSC) compared to males (0.01 <η² <0.1). No hand dominance effect emerged in SC and DC.

Conclusions: Force accuracy and precision to modulate pinch force to perform a visual feedback force-matching task (DC) and force coordination between hands (BSC) worsen at increasing age. Hand dominance did not influence either endurance or precision of pinch grip in visual-feedback guided task.