gives information about what the speaker thinks and feels.
Explanation:
In the end, after describing what happened, the author describes what the speaker is feeling "dazed, clutching my brow" and thinking "All of us writhing on the ground for one reason or another". That's a great way to conclude since it not only is very clear and put together, it ties nicely all characters involved, since all kids end up laying on the floor, even if it's for different reasons.
The effect is more endurance. The cause of that effect would be the regular aerobic exercise. If you're looking for just one word, it would most likely be "regular."