This paper investigates the relationship between physical fatigue and quality by testing the effect of
different operator fatigue levels to their accuracy when performing a cognitive task. Groups of
participants performed a cognitive task at different levels of fatigue, measured by desired heart rates of
80, 105, 130 and 155 beats per minute (bpm). Heart rates other than 80 bpm were achieved by asking the
participants to ride a static bicycle. The cognitive task was filling a beaker with water to a desired volume,
that is 200 ml. The outcome volumes of the filled up beakers were measured, compared to the desired
volume, and then analyzed with regression to six functions, each of which, the mean squared error (MSE)
was computed. The function with the smallest SME is chosen as the best fit function. Our experiment
shows that the relationship between quality and physical fatigue best fits in an exponential function.