Limit Cycle Properties of Rhythmic Forearm Movements

The kinematics of 1- and 2-armed rhythmic forearm movements were examined using the methodology and limit cycle modeling strategy of B. A. Kay, J. A. S. Kelso, E. L. Saltzman, and G. Schōner (1987) . As frequency was paced from 1 to 6 Hz (in steps of 1 Hz), amplitude decreased in all 7 participants, whereas peak velocity showed different trends for different participants. The data of 2 of the 7 participants could be described with Kay et al.'s model. To account for the data of the remaining 5 participants, a new model was proposed with a dissipative structure involving a frequency-dependent Rayleigh term and a standard Van der Pol term. For 2 of these 5 participants, the coefficient of the Van der Pol term was not significantly different from zero. Contrary to Kay et al.'s model, the new model suggests that the energy bookkeeping of rhythmic forearm oscillations is affected by the frequency of movement.