Which of the following is a technique used to express or validate how a client feels when he or she is working during exercise?

RPE method is the correct answer.

The Rating of Perceived Exertion scale (1 - 10) is a technique used to measure how hard your body is working while doing some exercise. On this scale, the rating are related to the rate of the heart, which corresponds to how hard our hearts are working to get blood moving through our bodies.