The maximum speed which you can sustain without slowing down because of fatigue. Critical velocity, or V-CRIT, is dependent on distance; the longer the distance the slower the V-Crit. so it is the highest speed you can hold for the rest of the distance still to be swum. If you go faster than that, physiology being what it is, you will have to slow down more than you have speeded up and, mathematics being what it is, your average speed will be slower. As the distance still to be swum shortens the highest speed you can hold rises, therefore you NEGATIVE SPLIT the swim. Let's repeat that; as the distance still to be swum shortens the highest speed you can hold rises. You should, therefore, always be accelerating and there should never be a time when you could go faster and still accelerate. Most world records have been set using negative split strategies. The limiting factor to critical velocity in a well-conditioned swimmer is the ability of the muscle fibers, nerve endings and pain tolerance to deal with the amount of LACTIC ACID in the muscles.

The velocity at critical flow. Also called sonic velocity.

Mean velocity of flow when flow is at critical depth.