**Category:** Physiology  
**Subtype:** Exercise Physiology  
**Problem Description:** The problem involves measuring physiological indicators of a group of students at two different times: before and immediately after running 1000 meters. The task is to determine how many physiological indicators decrease after the exercise compared to before. Specifically, it asks about heart rate and the duration of one heartbeat cycle.  

**Indicators to Consider:**  
- I. Heart Rate  
- II. Body Temperature  
- III. Duration of One Heartbeat Cycle  

**Question:** How many of these indicators decrease after running 1000 meters?  
**Options:**  
A. 1  
B. 2  
C. 3 (Note: The option for body temperature is not explicitly mentioned in the question but is included in the list.)