Explain how the illustration represents the cellular respiration reaction.

1) So if I understand your question correctly. The graph shows a Thermodynamic representation of a  exothermic reaction. Cellular respiration is an exothermic reaction you are taking your products ie) Glucose and turning it into a simpler carbon molecule. The redox reactions that occur during this process of cellular respiration are what give the cell the energy needed to live. This extraction of energy through the redox reaction gives us the lower energy product that we see on the graph.

2) Muscles can get over the "hump" or activation energy to preform the reaction through a catalyst. Also the muscle can increase the rate at which a reaction occurs kinetically by increasing the temperature, the amount of reactant present in the muscle, etc.

Hope this helps!