Races involve up to four riders racing anticlockwise round four laps of the track, the winner being the first across the line. The number of laps varies with the age of the riders but is usually 4 laps for a single race. Competitors use a lightweight single-speed bicycle equipped with a freewheel but without brakes, often a stripped-down mountain bike frame is adequate for beginners although specialist machines are used by the top racers. Riders slide their left foot along the track as they race round turns. Physical contact is legal and often necessary; clothing usually covers the whole body from the neck down, with padding for knees, elbows and hips; helmets are also required since their introduction in 1999. There has never been an accident in cycle speedway resulting in serious injury or death.