physical exertion
This does not have the same meaning as physical activities or physical exercise. You must improve your English vocabulary, specially in the synonym usage aspect.
This essay will first outline
Points will be deducted for the non-existence of your writer's opinion. You will not receive points for the writer's opinion section because you did not provide any cause and solution presentation as a part of the thesis statement of this paragraph. Without the thesis statement, there is no writer's opinion.
The causes were well developed in the presentation. Using a reference to adult and children exercise problems was a nice touch. However, the solutions presentation feels rushed and under developed. It would have been better for your score if you had a specific adult and children solution presented also. That way the cohesiveness of the discussion paragraphs would have been maintained and the C+C and GRA scores would have been increased.