Exercise begins with skeletal muscle contraction, an active process that requires adenosine triphosphate (ATP) for energy. A small amount of ATP is present in the muscle when contraction begins. This ATP can be used and replenished to fuel about 15 seconds of intense exercise, after which point the muscle must generate more ATP through the process of cellular respiration. During cellular respiration, oxygen is used up when it combines with hydrogen to form water (oxidative phosphorylation). Thus, as a muscle's metabolism increases during exercise, the concentration of oxygen in the tissue decreases, while temperature, acid, and CO2 increase. These factors and the homeostatic sensors that detect them send out signals that result in local vasodilation, which shunts bloodflow from inactive tissues to the exercising muscles, where it is needed. Drag and drop each of the following terms to form a flow chart.

Person starts to exercise

Oxygen sensors cause local blood cell vessels to dilate

Skeletal muscle metabolism increase

Skeletal muscle oxygen demand increase

Blood delivery to the skeletal muscle increases is order to provide more oxygen