Among the forms of physical activity that have the potential to improve health, biking is a traditionally popular sport in Italy. To improve performance and health, while limiting the risk of adverse effects of exercise and overtraining, the practice of biking at both competitive and recreational levels requires the definition and monitoring of an individualised optimal training “dose” (defined by duration, intensity and frequency). The definition of adequate exercise intensity and the implementation of an individualised training dose require the accurate determination of the individual fitness level. The concept of “critical intensity” (CI) has been widely used to assess fitness. The bike version of the Conconi test is a submaximal incremental “field” test that allows a low-cost and simple identification of the power output at CI, based on the use of an accurate ergometer and heart rate deflection point. Yet the correspondence with the reference techniques, the optimal protocol in relation with specific subject’s characteristic (sex, age, fitness) remain elusive. Specifically, data on older and women cyclists are completely missing. In this context, the ergometer “Magnetic Days” (MD, ORF srl) could allow the evaluation on a large scale of different types of cyclists. Portability, low weight/bulk, low cost and high accuracy of load quantification are the most interesting features of this equipment. ORF is interested in developing and implementing evidence-based protocols for optimal and individualised testing and training, to be applied to professional and recreational cyclists of both sexes and different ages. Therefore, the aim of the present study is to develop and validate the optimal incremental testing protocol for CI determination based on heart rate deflection point in male and female cyclists of different ages and fitness levels.