Answer: The organizational structure used in this sentence is cause and effect.
Step-by-step explanation: The cause-and-effect organizational pattern consists in stating why something happened and which were the consequences of that event. This organizational structure is generally used in expository or argumentative essays. In the sentence provided, the writer presents a cause or the reason why something happened ("I hit a big rock while mountain biking"), as well as the results or consequences of that action ("This knocked me off my bike" and "I hurt both my elbows when I landed").