So you been sprinting, Lily? Just a bit of cramp? So that's the lactic acid building up. When an athlete does too much or runs too vigorously, not enough oxygen can be delivered to the muscles.

When the researchers blocked the protein that imports lactic acid into cells, exhausted T cells gained a new lease on life ..

Often, a rider talking about the feeling of lactic acid buildup is referring to that heavy sense of muscular fatigue or ...

Davidson, R. G., Fildes, R. A., Glen-Bott, A. M., Harris, H., and Robson, E. B., Ann. Hum. Genet., 29, 5 (1965).