Final answer:
Deep breathing is the step that promotes relaxation in static stretching, facilitating the body's relaxation response and enhancing the effectiveness of the stretch. Hence, option (c) is correct.
Step-by-step explanation:
The step that promotes relaxation in static stretching is deep breathing. When you're engaged in static stretching, taking deep, diaphragmatic breaths helps the body to relax, which can improve the effectiveness of the stretch and counteract the natural tendency of the muscle to resist elongation. In contrast, intense muscle contractions, rapid shallow breathing, and dynamic and rapid movements are not associated with the relaxation necessary during static stretches.
During diaphragmatic breathing, the diaphragm contracts and allows for a full and expansive breath, which facilitates the relaxation of the muscles. This type of breathing is contrasted with shallow, costal breathing which does not promote relaxation in the same way. Particularly in the context of stretching, deep breathing helps to enable the parasympathetic nervous system, which is responsible for the 'rest and digest' state, thereby allowing the muscles to relax further.