Answer:
After changing the pronoun focus, the sentences can be:
Walking is one of the best forms of exercise because it helps one lose weight and improve one's cardiovascular systems while one enjoys being outside in the fresh air.
(Alternative answer - see the explanation below)
Walking is one of the best forms of exercise because it helps people lose weight and improve their cardiovascular systems while they enjoys being outside in the fresh air.
Explanation:
When writing formally, we must avoid permeating our texts with sentences that are too personal. Formal writing demands impersonality, which makes it sound more trustworthy and unbiased. Therefore, using the first person "I" should be avoided. One way to substitute it is by using the pronoun "one", as we did in the first answer above. Some people find it difficult to use "one". If that is the case, we can always use "you" or "people". These do not sound as formal as "you", but are still less personal and informal than "I".
