Cardiorespiratory Measures of Workload during Continuous Manual Performance

Abstract

Twelve subjects (six female) participated in a study designed to experimentally separate the effects of physical and cognitive effort on cardiac and pulmonary measures of workload. Cardiac (heart rate and variability), respiratory, and forearm muscle activity were measured while subjects performed a single-axis continuous manual tracking task. The central processing demands of the task were varied by changing the tracking system order over three levels: pure velocity, a combination of velocity and acceleration, and pure acceleration. The physical demands of the task were varied by requiring subjects to track either high or low amplitude sum-of-sines disturbance. RMS tracking error, subjective ratings, heart rate, and forearm muscle activity were sensitive to, but did not differentiate, the cognitive and physical manipulations; these measures increased as both tracking order and disturbance gain increased. However, the respiration measures dissociated under the physical and cognitive manipulations. Respiration rate increased with tracking order but not disturbance gain, while respiration amplitude increased with disturbance gain but not tracking order. Also, spectral power measures of respiratory activity and of cardiac activity at the respiration frequency (i.e., respiratory sinus arrythmia) dissociated for disturbance gain: respiratory power increased while cardiovascular power decreased as a function of increasing disturbance gain. These results verify the utility of a multiple-measures approach to the assessment of workload, and suggest the inclusion of respiration and cardiorespiratory interactions as workload measures.