Leontien Martha Henrica Petronella Zijlaard-van Moorsel is a Dutch retired racing cyclist. She was a dominant cyclist in the 1990s and early 2000s, winning four gold medals at the Olympic Games and holding the hour record for women from 2003 until 2015.

The hour record is the record for the longest distance cycled in one hour on a bicycle from a stationary start. Cyclists attempt this record alone on the track without other competitors present. It is considered one of the most prestigious records in cycling. Since it was first set, cyclists ranging from unknown amateurs to well-known professionals have held the record, adding to its prestige, romance and allure. There is now one unified record for upright bicycles meeting the requirements of the Union Cycliste Internationale (UCI). Hour-record attempts for UCI bikes are made in a velodrome.