Determination of optimal grip span between a bicycle handlebar and a brake lever by using a two-dimensional biomechanical hand model

In this study, optimal grip span between a bicycle handlebar and a brake lever was determined by a twodimensional biomechanical hand model. A three-step process was applied: (1) develop a two- dimensional biomechanical hand model, (2) determine input data for hand model simulation, and (3) conduct mathematical simulation. In the first step, in order to estimate tendon forces, joint constraint forces and total gripping support force at the metacarpal, a mathematical static hand model was developed based upon the hand anatomy and static equilibrium conditions. In the second step, US 50%ile hand length was selected as target population from the 1988 US Army data, and grip postures for five participants(average hand length = 18.2 cm and SD = 0.8) were measured to get joint angles( θ₁, θ₂, and θ₃ ) which are required for the hand model simulation, by using a dynamometer having adjustable grip spans such as 4, 5.2, 6.4, 7.6, and 8.8 cm. In the third and final step, mathematical simulation was conducted to determine an optimal grip span. Consequently, on given external load(grip force), 100 N, both total tendon forces and total gripping support force of the metacarpal showed monotonically increasing trend while grip span broadening from 4 to 8.8 cm. Also, minimum of both total tendon force and total gripping support force at the metacarpal was achieved at 4 cm grip span.