A state of good fitness is related to a better health state and a lower mortality risk. In the German Health Interview and Examination Survey for Adults (DEGS1), aerobic fitness was measured among adults between 18 and 64 years old using a submaximal cycle ergometry test. The total sample comprised 5,263 persons, amongst those 3,111 were categorized as being test-qualified according to the Physical Activity Readiness-Questionnaire. There were 3,030 persons who absolved a submaximal exercise test according to the exercise protocol of the WHO (25/25/2). The test-participation rate was 57.2 % in relation to the total sample and 97.4 % among test-qualified persons. Apart from the continuous heart-rate monitoring, capillary blood was taken prior to starting the test and at the end of each workload stage for performing blood lactate analyses. The test ended when 85 % of the age-predicted maximal heart rate was exceeded. In all 11.9 % of the tests were terminated earlier, the mean exercise duration was 10.8 min, and the anticipated submaximal exertion in the highest workload stage was on average achieved with a mean of 15 on the 20-point RPE scale. The nationwide data can now be used for the national health monitoring system, epidemiological research and for the calculation of reference values. An English full-text version of this article is available at SpringerLink as supplemental.