Lets do some math. Usain Bolt could do 12.5 meters per second (in a short burst, not the whole 100 meters). At that speed, the "mass increase" is about a factor of 8.7 x 10^-16. For a 100 kg person (a bit on the large side), that's about 0.087 nanograms, or the mass of one human red blood cell, or one tiny tiny drop of sweat.
Of course, this increase is lost as soon as you stop running.