Cellular respiration is the metabolic process by which a cell produces usable energy in the form of ATP. In order to accomplish this cells require Glucose and Oxygen to form the reaction which produces ATP and the byproducts of Water and CO2.
In reality its a complex topic however this is the basic form.
It prepares to fight danger or run from it. It identifies the primary source of danger.
Proteins function optimally at a specific temperature. So if you get too hot or too cold, biochemical reactions in your body start to function less well. If the situation becomes extreme enough, they can cease to function well enough to sustain life.
Warm-blooded animals have an advantage over cold-blooded ones in that their bodies automatically try to maintain the optimal termperature for things in their bodies to function. Cold-blooded animals depend on the environmental temperature to do this for them. That's why reptiles are very sluggish when they're cold, but will "wake up" when they get warm.
The cost to this benefit is that metabolically, warm-blooded animals require a lot more fuel to run their bodies. It's very energy-intensive to maintain a constant body temperature. Cold-blooded animals require far less fuel than warm-blooded ones relative to their size.
The way that proteins operate in a specific temperature is also true of the pH in your body which is also very tightly maintained.
Your heart rate before exercising would probably be the at rest rate of say about 50-60 beats per minute whereas immediately after exercise it could easily be say 115-130 and depending on age there is an optimum heart rate for each age range which decreases somewhat with age. Timing for a full minute your heart rate is best as it will give the actual count whereas if you just do it for 10 seconds and then multply by 6 it would assume it will be consistent whereas it could decrease during the minute so the actual measured count for a full minute is more accurate.
