Which of the following is a commonly used test to measure flexibility?

The sit-and-reach test is a widely recognized method for assessing flexibility, specifically the flexibility of the lower back and hamstring muscles. This test is straightforward and involves reaching forward while seated with legs extended, which provides valuable insight into an individual's overall flexibility and ability to perform activities that require a good range of motion.

In contrast, options like the deadlift test, push-up test, and vertical jump test focus on strength and power rather than flexibility. The deadlift test primarily assesses strength, particularly in the lower body and core, while the push-up test evaluates muscular endurance and strength of the upper body. The vertical jump test measures explosive lower body power and is unrelated to flexibility assessment. These distinctions clarify why the sit-and-reach test is the appropriate choice for measuring flexibility.