Marathon’s consist of running/jogging/sprinting long distances, so first off it would be a good idea to increase stamina, which would be done by jogging everyday, increasing your distance everyday. Stretch your calf muscles upper leg muscles to avoid cramps while running too.
Individuals need to adjust their physical activity to account for reduced flexibility, a loss of balance, as well as decreased energy levels as they age. As we see, there is a number of rather unwanted changes which happen with old age so the correct answer would be D - all of the above.
I guess its medical, if not, philosophical
Respect like caring of others feelings and doing them right.