The sentence "measure what is measurable, and make measurable what is not so" (Galilei) can be seen as a postulate for using only objective physical or chemical methods in science to obtain hard data. Athletic fitness and health are complex states, however, including more than objective personality traits, described by hard data. Therefore, in the context of assessment of athletic fitness and health the questions arose: What does "measure" mean and how important are data that are immeasurable? Hard data are necessary, but not sufficient for assessment of all personality traits relevant for athletic fitness and health. Soft data are important as well. "Measure" in the context of athletic fitness and health should not only be restricted to physical or chemical methods, but should also include soft data, obtained by all systematic inside- and outside-observations using rating methods or only descriptions of qualitative items. For interpretation of both hard and soft data experience is necessary: this step of scientific work includes subjectivity in all cases. In order to gain experience, subjective methods must be trained, and this requires estimation of soft data and their appertaining methods, too. In conclusion, "measure" in the context of athletic fitness and health should include all objective and subjective methods for description of relevant personality traits.