for a few milliseconds per stride, which can be caught on film, but such a short flight phase is said to be undetectable to the human eye. Athletes stay low to the ground by keeping their arms pumping low, close to their hips. If one sees a racewalker's shoulders rising, it may be a sign that the athlete is losing contact with the ground. What appears to be an exaggerated swivel to the hip is, in fact, a full rotation of the pelvis. Athletes aim to move the pelvis forward and to minimize sideways motion in order to achieve maximum forward propulsion. Speed is achieved by stepping quickly with the aim of rapid turnover. This minimizes the risk of the feet leaving the ground. Strides are short and quick, with pushoff coming forward from the ball of the foot, again to minimize the risk of losing contact with the ground. World-class racewalkers (male and female) can average under four and five minutes per kilometre in a 20-km racewalk. Distances Races have been walked at distances as short as at the 1920 Summer Olympics, and as long as 100 km (62.1 mi). The men's world record for the 50-mile race walk is held by Israeli Shaul Ladany, whose time of 7:23:50 in 1972 beat the world record that had stood since 1935. The modern Olympic events are the 20 km (12.4 mi) race walk (men and women) and 50 km (31 mi) race walk (men only). One example of a longer racewalking competition is the annual Paris-Colmar which is 450 to 500 km. Indoor races are 3000 m and 5000 m. Judges There are judges on the course to monitor form. Three judges submitting "red cards" for violations results in disqualification of the competitor. There is a scoreboard placed on the course so competitors can see their violation status. If the third violation is received, the chief judge removes the competitor from the course by showing a red paddle. For monitoring reasons, races are held on a looped course or on a track so judges get to see competitors several times during a race. A judge could also "caution" a competitor that he or she is in danger of losing form by showing a paddle that indicates either losing contact or bent knees. No judge may submit more than one card for each walker and the chief judge may not submit