Operator performance and localized muscle fatigue in a simulated space vehicle control task

Fourier transforms in a special purpose computer were utilized to obtain power spectral density functions from electromyograms of the biceps brachii, triceps brachii, brachioradialis, flexor carpi ulnaris, brachial is, and pronator teres in eight subjects performing isometric tracking tasks in two directions utilizing a prototype spacecraft rotational hand controller. Analysis of these spectra in general purpose computers established general agreement with previous studies, aided in defining muscles involved in performing the task, and yielded a derived measure potentially useful in predicting task termination. The triceps was the only muscle to show significant differences in all possible tests for simple effects in both tasks and, overall, was the most consistently involved of the six muscles. Monitoring of total average power in all muscles for contiguous sixteen-second intervals throughout each task provided consistent data useful in predicting task termination for all subjects. The total power monitored for triceps, biceps, and brachial is dropped to minimal levels across all subjects earlier than for other muscles. However, smaller variances existed for the biceps, brachioradialis, brachial is, and flexor carpi ulnaris muscles and could provide longer predictive times due to smaller standard deviations for a greater population range. The data for these muscles potentially provide information predictive of task termination up to approximately thirty-five seconds prior to the event. This technique of relatively non-obtrusive monitoring and analysis has potential practical utility in work station and tool design, physical training, medical applications, and extravehicular pressure-suited work activities for large scale space construction missions. Additional applied research must be conducted to identify derived measures sensitive to the needs of the designer and practically useful in design and real-time applications.