Afactor that plays an important role in determining how strenuously and when you exercise

Your weight will be a factor to consider since the heavier you are the more your muscles will have to work to perform an activity that other find easy.

Another factor to consider is the altitude. When you are closer to sea level it is easier to perform physical activity but when you are in higher altitudes, then your body struggles to breath and oxygenate your muscles and therefore you have to take your muscles to the limit.

both anaerobic and aerobic respiration use glucose (or other carbohydrates), proteins and lipids to produce atp and nadh. cell uses those energy molecules, obtained from food and   breaks them down during the chemical reactions of respiration. in anaerobic respiration, nadh is regenerated to nad+ by enzymes lactate dehydrogenase (lactate is produced, e.g. in muscle cells) or by alcohol dehydrogenase where ethanol is produced (alcohol fermentation), while in aerobic respiration, electrons from nadh are deposited in the mitochondria to regenerate nad+ (electron transport chain. anaerobic respiration produces 2 atp per molecule of glucose compared to aerobic respiration where about 38 atp molecules are produced.

b - the respond is innate and varies over time.

good luck!