Relation between the perception of the aerobic capacity and the VO 2max in firemen. For a fireman, knowing whether he is fit enough for his job implies regulating the intensity of the rescue without causing premature body fatigue. Therefore, the main purpose of this study is to determine the real aerobic capacity in a sample of firemen, based on the VO 2máx , and to compare it with two self-report measures: the subjective appraisal of aerobic capacity and the appraisal of the physical exercise carried out. Thus, 37 firemen from Asturias took part in this study and performed effort tests on a treadmill, measuring their heart frequency and VO 2máx consumption. Of the firemen, 94.4% who obtained a VO 2máx below 43 ml/min/kg (the minimum advised to perform their job effectively) considered their aerobic capacity to be <<high>> or <<very high>>. This might be influenced by the lack of feedback on their aerobic capacity, as their training is voluntary and self-planned. Therefore, it is highly recommended to program specialized training and to carry out periodical tests to provide feedback about aerobic capacity.