Commercially made exercise testing equipments are designed for testing adults with greater exercise capacity and relatively large minute ventilation compared to pediatric population. As the size of breaths becomes smaller and irregular, as in small children with pulmonary diseases, measurement delay errors may introduce errors to the final results in the exercise testing system. For this reason, a custom made Exercise System was built at the Exercise Laboratory Department at the Hospital for Sick Children. It incorporates a special algorithm that corrects measurement delay errors caused by small breaths. The algorithm calculates the lag time of the expired breath to reach the sampling port and re-aligns the gas concentration reading in time with the corresponding real-time recording of the breath. The Exercise System is currently used for clinical and research purposes. The system shows satisfactory results for adult testing; however, the system requires validation of increase in accuracy of results for testing in pediatrics, especially for ill patients with very small tidal volumes. The main objective of this study is to demonstrate that incorporating the lag time in the algorithm to process and calculate the oxygen (0₂) consumption improves the accuracy of the results in small children exercise testing. In addition, investigate the theory and operation of the Exercise System and document the system designs and testing results for publishing purposes.