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typically 1/4 (strength emphasis) or 1/2 lap (power emphasis). They can be done seated to develop seated strength and low cadence power.

Technique and timing are critical to a good gate start.  There's many ways to get out of the gate and a lot of practice is required.

Key things to remember - the standing start has much in common with the deadlift or the (power) clean.  The head is up and looking forward, the chest high, hips forward once the rider has escaped from the gate and the upper body is held rigid.  Often it's helpful to hold your breath for the first few pedal strokes (like a deadlift or a clean or a squat) to help keep the torso rigid.

Typical Powertap data (14y/o female, 86")

Trivia : We don't know why these are called K1's, the term is an East European one of unknown exact origin, if you know the answer, curious minds would like to know.