By measuring respiration, you can tell something about the quality of breathing, such as frequency, intensity and duration. It is also possible to give an indication about the location of predominant breathing movement. Measure abdominal (B) or thoracical (A) breathing rate and relative depth of breathing.
The major muscle involved in active breathing is the diaphragm. As we inhale, the diaphragm contracts and pushes down the stomach to create a larger space in the chest and air moves into the lungs. To exhale, the diaphragm must relax, it raises upwards, compressing the chest and lungs, and lets the air flow out. To measure respiration, we usually place a respiration sensor over the abdomen, as this is associated with relaxed breathing. With every breath, the sensor measures the relative expansion and contraction of the belly. Place the sensor over the thorax to measure chest breathing.