Final answer:
Flexibility exercises, such as stretching, should be done before participating in activities like swimming, weightlifting, and yoga, but not before playing chess.
Step-by-step explanation:
Flexibility exercises, such as stretching, improve the range of motion of muscles and joints. Regular stretching helps people avoid activity-related injuries. Therefore, stretching should be done before participating in activities such as swimming, weightlifting, and yoga. However, stretching is not necessary before participating in a sedentary activity like chess.