Final answer:
If your hematocrit level drops from 51% to 45%, you would expect that your performance in endurance events may decline, as there are fewer red blood cells to deliver oxygen to your working muscles.
Step-by-step explanation:
When your hematocrit level decreases, it means that the proportion of red blood cells in your blood is lower. Red blood cells carry oxygen to your muscles during endurance events like distance running and cycling. Therefore, if your hematocrit level drops from 51% to 45%, you would expect that your performance in endurance events may decline, as there are fewer red blood cells to deliver oxygen to your working muscles.