Cycling at the Olympics - how it works for BMX:
32 men, 16 women
Held on a circuit of 320-370m, which features an 8m-high start ramp and various corners and jumps.
Contact between riders often occurs during racing and crashes are frequent.
Each competitor has one time trial run over the circuit, with the better time determining his or her seeding for the quarter-finals (men) and the semi-finals (women).
The men's quarter-finals are held over five runs, with points for places on each run.
After three runs, the best two riders from each quarter-final progress to the semi-finals.
The remaining riders compete in the final two quarter-final runs and the best two from each quarter-final also progress to the semis.
The semis follow a three-run format. The top four riders from each semi-final advance to the final, where the medals are decided over one run.