Evaluation of forearm fatigue during EVA pressure glove work

This study investigated the combined use of three measurement techniques to monitor fatigue in forearm muscles during pressure glove work. Pressurized gloves are a component of the spacesuit used by shuttle astronauts during extravehicular activities (EVA). The study was conducted to specifically evaluate and compare the effects of pressure and non-pressure components of the glove on work and fatigue. Ten healthy male subjects were recruited to perform a constrained task of repetitively squeezing a custom hand-grip dynamometer adjusted for constant resistance. Surface electromyographic (EMG) signals from two muscles of the forearm (m. extensor carpi ulnaris (ECU) and m. flexor digitorum superficialis (FDS)) were recorded concurrently with mechanical work and subjective fatigue. Measurements were made before, during, and after the repetitive gripping task. Each subject performed the test under three conditions: (1) bare hand, (2) gloved-hand without a pressure differential, and (3) gloved-hand with a pressure differential equal to the normal operating pressure of the shuttle glove. The results demonstrated that the three measurement procedures provided complementary information about the interrelationship between glove characteristics, muscle function, and work productivity. The EMG results from the FDS muscle indicated that the resistance offered by the glove materials provided a component of fatigue that was compounded by the presence of differential pressure. Although not muscle specific, measurements of work output and subjective fatigue supported this finding. In contrast to the FDS, the EMG results from the ECU muscle indicated that this muscle was less fatigued overall and less sensitive to the test conditions. Although high inter-subject variability precluded a statistically significant effect of test condition on the EMG results from the ECU muscle, 8 of the 10 subjects had higher EMG manifestations of fatigue for bare hand work than for either gloved-hand condition. We interpret these findings as evidence that the stiffness of the glove may have provided support to the wrist, thereby reducing the amount of fatigue present in this muscle during the work task. The study findings demonstrate the feasibility of using this multidimensional approach to fatigue measurement when evaluating other work-related tasks.