Why not both? During training and after the race. Both require our bodies to go through immense stress, and in some cases training is harder than the actual race since we usually take a taper and rest better before the race. Our bodies can’t tell the difference outside of nerves of race day, so why should we limit being in tip top shape to ONLY before or after the race?
Getting treatment before the race (and the weeks leading up to) will help our bodies recover faster and work out any pains and aches before our bodies learn to compensate. When they start to compensate, it could change many things including gait and other body mechanics that could lead to further injuries — imagine it like the first domino in a line of issues that gets worse if not fixed early on.
I recommend my patients to see me the week of and as soon as they can after their race. Doing so will put their body in an ideal state for the race, and reset any ailments or injuries that they might face during the race since we many people push and pour their efforts all out.
So should you come in before or after a race? Both.