Hammering Does Not Fit Fitts' Law.

Area of Science:

• Biomechanics
• Neuroscience
• Robotics

Background:

• Human movement is complex and difficult to replicate in machines or fully restore in impaired individuals.
• Current models of motor control often use simplified tasks that don't capture real-world complexities like impacts.

Purpose of the Study:

• To investigate human motor control during a periodic impact task (hammering).
• To compare existing motor control models with experimental data and propose a new model.
• To assess the robustness of human motor control to variations in tool dynamics.

Main Methods:

• Recorded impact forces and kinematics from 10 subjects hammering nails.
• Varied hammering frequencies and hammer properties (mass, face area).
• Developed a feedforward optimal simulation with a neuromechanically inspired cost function.

Main Results:

• Humans demonstrated robustness to minor changes in hammer dynamics.
• The optimal simulation model successfully reproduced experimental data.
• A new logarithmic model of movement distance versus time showed superior fit (R² ≥ 0.99) compared to Fitts' Law (R² ≥ 0.88).

Conclusions:

• Human motor control appears to operate on optimal principles.
• Fitts' Law may not be universally applicable to periodic impact tasks.
• The proposed logarithmic model offers a better explanation for movement control in such tasks.