Grip surface affects maximum pinch force

Objective: The aim of this study was to investigate whether people change their isometric pinch grip generation depending on the surface they gripped. Specifically, the effect of grip surface friction condition on (a) maximum force produced in the direction normal to the contact surface, (b) fluctuation of normal force, and (c) the digit force's angular deviation from the direction normal to the grip surface was quantified.Background: Isometric pinch grip has been traditionally thought to be independent from the friction condition between the finger and gripped surface, which may be questionable.Method: For this study, 12 healthy participants performed maximum isometric pinch grip exertion on high-friction rubber and low-friction paper surfaces. Maximum normal force, normal force variance, and digit force's angular deviation from the normal direction were quantified.Results: Pinch grip on the high-friction rubber surface was associated with 10% greater maximum normal force and 50% reduced normal force variance, compared with the low-friction paper surface (p <.05). Digit force's angular deviation was not significantly different between the two surface friction conditions.Conclusion: The data support that people do change their pinch grip generation (maximum normal force and normal force variance) depending on the surface they gripped, potentially by using sensory feedback. The results of this study demonstrate that even a simple isometric pinch grip (no lifting associated) is affected by grip surface friction.Application: Grip surface condition should be considered for clinical assessments, biomechanical investigation, and motor control studies to ensure consistency in measurements and validity of comparisons.