The calories we burn during exercise come from three different sources : carbohydrates, fat and proteins. The type of fuel our body uses during a workout depends on the nature of the activity performed.
(i) Which of the above mentioned fuel/fuels is (are) used in moderate cycling (10 miles/hour) workout ?
(ii) When is the cycling workout categorised as vigorous ? Which fuel does it burn then ?
(iii) Which is the least preferred source of energy during exercise ?
(iv) What is importance of exercise in our life ?

Explanation

(i) Both fat and carbohydrates (roughly `60 %` of the energy comes out from fat)
(ii) When cycling speed exceeds `10 miles//hour`, the workout is categorised as vigorous. At this level, the primary fuel shifts from fat to stored carbohydrates.
(iii) Protein is the least preferred source of energy during exercise. When glycogen stores (from carbohydrates) are low or depleted, as much as `10 %` of the fuel for exercise comes from proteins.
(iv) Lack of exercise results in obesity which is the mother of all diseases - hypertension, diabetes, heart diseases-to mention just a few.