Recording of Exertion and Bio-Signals During Mental Strain: Relationship between Subjective and Objective Stress Parameters

Background Changes in the modern world of work place ever increasing demands on employees. This in turn is reflected in an increase in perceived mental strain at the workplace. Current research develops methods to improve the self-management of mental stress in everyday work. The presented study aims to analyze the five mental strain phases and their specific times during a state of strain. Furthermore, we analyze the relationship between the subjective feeling of exertion and objectively recorded bio-signals (heart rate and skin conductance) during cognitive load under laboratory conditions. We assume that there is phase-dependent mental strain and that, under moderate mental load, we can find correlation between the subjective perception of exertion (CR 10 scale according to Borg) and the objectively recorded parameters. Material and methods The bio-signals heart rate and skin conductance measured by the NeXus-10 MKII as well as the perception of exertion represented by the CR 10 scale according to Borg were recorded at a simulated cognitive load system, called RehaCom. Furthermore, the NASA TLX Scale reported the total perceived exertion oft he subjects. The test persons subjects (female, N=30, age: 34.3 years old (+/- 3.2)) were given tasks testing their ability to pay attention and react, the difficulty of which gradually increases over five load levels. Results The comparison of the basline measurement with the five mental strain levels showed a significantly higher subjective mental strain (CR-10 scale, p<0.01) as well as higher heart rates and a higher skin conductance for the five mental strain phases compared to the baseline measurement. Further analysis of the strain levels showed significantly different values (p <= 0.01) for the comparison of the first minute of exertion with the last minute. The total mental load was rated by the test persons as medium mental strain with 53.3 +/- 13.5 (NASA TLX scale 0: very low - 100 very high). There was also a significant correlation between the CR-10 scale and the skin conductance values (beta=0.21, p<0.001) which, however, turned out to be insignificant for the heart rate (beta=0.02, p=0.21) Conclusion The correlation, albeit weak, between subjective and objective parameters underlines the need for a more individual and comprehensive analysis in order to comprehend the complexity of mental strain, especially in moderate cases. Further investigations should aim at a relation to subjective load parameters such as CR-10 Borg scale in order to supplement the mere observation of the bio-signals.