Abstract

Investigations about voluntary movements mainly concern their speed and accuracy, or are based an the notion that biological systems minimize costs at the resonant frequency of a hybrid pendulum, as well as at preferred frequencies in repetitive tasks. We focussed the problem whether voluntary movements are controlled by an universal optimal frequency-amplitude combination, or whether this is individually chosen. Which regimen is more appropriate, unpaced oscillations with given amplitudes, or paced oscillations with free amplitude. The work was done with a brushcutter (a portable, combustion engine powered tool). Assuming fixed costs, the amplitude should be larger the slower is the oscillation. Experiment: i) Estimation of individually preferred frequencies when executing unpaced voluntary oscillation movements with prescribed sectors. ii) Movement amplitude was free, but 3 frequencies were imposed: an individually base-line frequency, -15% and -25% , or base-line frequency, +15% and +25%, respectively. Either amplitude (i) or oscillation time (ii) was taken as independent variable, performance as dependent variable. The prescribed increased amplitudes were attained to very well. Oscillation frequency decreased when amplitude increased, but performance increased in spite of longer time periods. Individually chosen combinations of frequencies and amplitudes varied highly. Working at decreased frequencies increased the amplitude somewhat, but decreased performance since amplitudes did not increase accordingly. Working at increased frequencies decreased the amplitude, but performance remained constant, because of equivalent amplitude reduction. Interindividual variability was high for both working conditions. A hypothesis of fixed costs cannot be verified, as long as metabolic costs are unknown. Verf.-Referat