Prologue: discourse concerning two conventional sciences

The form of the Discorsi of Galileo Galilei is used here to emphasize the three aspects of research objects. The point of view of the user (Simplicio), the theoretician (Salviati) and the experimenter (Sagredo). Two technical aspects of the papers which have been presented in the three Biomechanics Supplements of Injury [volumes 30(1), 31(2), and 31(3)] are discussed by these three interlocutors: i. The confidence intervals of the number of cases in the epidemiological studies, which should be high enough to reveal significant differences (i.e. a total of about 2,000 patients to show that an improvement in treatment reduces the infection rate); ii. The importance of the deformation for the quantification of the deleterious effect of stress protection, whereby it is shown that the size of the subject (small animal vs human) is non-linearly related to the effect, as was already disclosed by Galilei 367 years ago--but which is still not yet well understood by the nonmechanic.