In scientific applications, we use ergonomic principles initially on the design of human-machine interfaces and in product design. The ergonomic design of the physical and psycho-social environment of Man-Machine Systems is also very important as they affect human performance. But in any case, we have to consider what human being pays if we ignore scientific principles to apply in every kind of Man-Machine System design. If we can group the complexity of interrelationships among different parameters in this type of system it gives us the opportunity to use fuzzy logic. For different kinds of human performance problems fuzzy logic seems to be very flexible to solve them.