When you die, you go back to the start of the level, or the last checkpoint you touched. Another side effect of this is a reset in the cycles of arrows/blades/spikes, it takes some seconds before the cycles start.

You can make good use of it by suicide (pressing 'r') right after touching certain checkpoints, to reset and delay the cycles and make the next section easier.

Also (irrelevant to the speedrun itself), suicide does not count as a death, for the tracking of in-game achievements.