The act of running over a short distance at the greatest possible speed. Because of physiology, a runner's near-top speed cannot be maintained for more than 3 combat rounds (36 seconds) due to the depletion of phosphocreatine stores in the muscles. Even at amateur sprinting speeds, however, this can cover a considerable distance.
As a combat round is inconveniently long and vague where sprinting distances are concerned (in an Olympic race, reaction time, block clearance and achieving a speed of maximum acceleration all occur in a 4-second interval), the actual distance covered by a sprinter is broken down by action points expended rather than in terms of rounds.
Further, the highest speed possible by a character will be limited by any baggage or items the character may carry. In game terms (rather than reality, as I am lacking useful tables that can be applied to role-playing encumbrance), this will translate as a 40% reduction in potential distance covered per action point lost due to encumbrance the character carries. Since this will quickly reduce 'sprinting' speed to below normal speed, it may be presumed that when the character is able to move at a faster rate through combat running, it and the character's 'sprinting' speed should be seen as equal. The rule treats the matter this way to suspend any idea that sprinting ability is a form of combat superiority.