Triathlons are timed in five sequential sections.
From the start of the swim to the beginning of the first transition (swim time). The use of flippers or other swim propulsion and flotation aids are illegal.
From the beginning of the first transition to the end of the first transition (T1 time).
From the start of the cycling to the end of the cycling leg (cycling time). The competitor's helmet must be donned before the competitor mounts the bike, and it must remain on until the competitor has dismounted.
From the beginning of the second transition to the end of the second transition (T2 time)
Finally from the start of the run to the end of the run, at which time the triathlon is completed.