Introduction: The VO[subscript 2] max test is the gold standard measure for aerobic fitness. A standardised treadmill protocol was developed years ago for individuals with Down syndrome but with variations in terms of starting speed, load increases and time spent at each stage. However, we realised that the most widely used protocol for adults with Down syndrome, trouble participants with high treadmill speeds. Consequently, the purpose of the current study was to determine whether an adapted protocol provided improved maximal test performance. Method: Twelve adults (33 ± 6 years) randomly performed two variations of the standardised treadmill test. Results: The protocol that added another incremental incline stage increase yielded a significant improvement in absolute and relative VO[subscript 2] peak, time to exhaustion, minute ventilation and heart rate max. Conclusion: A treadmill protocol with the addition of an incremental incline stage allowed for a significant improvement in maximal test performance.