Monitoring human neuromusculoskeletal system performance during spacesuit glove use: A pilot study

Abstract

This paper presents an application of system-based modeling to monitor the performance of the human neuromusculoskeletal (NMS) system during spacesuit glove use. Autoregressive moving average models with exogenous inputs (ARMAX) were used to characterize the dynamics of the NMS system and track its changes over time during two types of fatiguing tasks: isometric grasping and repetitive opening and closing of the hand. Features extracted from the joint time-frequency distributions of surface electromyography (sEMG) signals, collected from flexor and extensor muscles of the forearm, were inputs to the ARMAX models. Biomechanical data, either hand grip force or fingertip displacement, were outputs to the model. A quantitative metric that compares one-step ahead prediction errors of the model over time, called the Freshness Similarity Index (FSI), was utilized to track the rate at which an individual's NMS system behavior diverges over the course of the fatiguing tasks. Data collected from a single subject was employed to validate the monitoring methodology. Results showed that the FSI displayed statistically significant increasing trends for each of the tasks performed, indicating the growing dissimilarity between the subject's NMS system at a rested state and subsequent periods throughout the test. Furthermore, trends in the FSI exhibited consistency across multiple days of testing, the resolving power to distinguish differences in prescribed work load and glove features, and the ability to identify the accumulation of residual fatigue from consecutive trials of a task. As such, the FSI metric clearly characterized the rate at which the individual's performance degraded over time and succinctly represented the manifestation of fatigue. With impending plans for planetary and lunar explorations on the horizon, tracking an astronaut's physiological status will be essential for ensuring mission safety and success. Thus, the presented methodology, which successfully demonstrated the capacity to detect changes in an individual's performance while wearing a spacesuit glove, could be extended to assess full-body health status in real-time, identify the onset of abnormal or degraded performance, and evaluate fitness-for-duty during manned space exploration.