Introduction: The evaluation of flexibility is important to coaches to assess their players' flexibility status, predict future performance, and even detect talented players. The aim of this research was to develop a new flexibility test to examine the forward split in athletes. Material and methods: In this study, 15 gymnasts, 10 Taekwondo athletes, 5 football players, and 10 karate athletes (20 males and 20 females) volunteered for this experiment and were evaluated in a common movement pattern, the forward split. In the experimental condition, participants performed the forward split on a mattress using infrared sensor technology (IST test), and, afterward, they performed the forward split on a mattress without infrared sensor technology (N-IST test). Two trials of this procedure were conducted. Results: For concurrent validity, no significant difference in the average distances of the anterior superior iliac spine (ASIS) from the mattress in Trials I and II was found between the IST and N-IST tests-p = 0.664 and p = 0.710, respectively. Conclusions: The findings of this study confirm the concurrent and construct validity of the IST test, which was created to measure the height of the ASIS from the mattress in a forward-split test. Thus, this test can be used by coaches, athletes, and sports scientists to improve and monitor the forward-split tests of athletes in training programs.