Outline the nine main factors determining heart rate.

1. Age: Heart rate tends to decrease with age, with infants having the highest heart rates and older adults having lower heart rates.

2. Fitness level: Individuals who are physically fit typically have lower resting heart rates compared to those who are sedentary.

3. Gender: Women tend to have slightly higher resting heart rates compared to men.

4. Body size: Larger individuals tend to have lower resting heart rates compared to smaller individuals.

5. Medications: Certain medications, such as beta blockers, can lower heart rate.

6. Stress and emotions: Stress, anxiety, and strong emotions can increase heart rate.

7. Body temperature: Heart rate tends to increase with higher body temperature, such as during exercise or when experiencing a fever.

8. Hormones: Hormones such as adrenaline can increase heart rate in response to stress or physical activity.

9. Health conditions: Certain health conditions, such as thyroid disorders or heart disease, can affect heart rate.

Nine Main Factors Determining Heart Rate:

1. Autonomic Nervous System:
- Sympathetic activation increases heart rate (fight-or-flight response).
- Parasympathetic activation decreases heart rate (rest-and-digest response).

2. Hormones:
- Epinephrine (adrenaline) increases heart rate.
- Thyroid hormones increase heart rate.
- Insulin decreases heart rate.

3. Electrolytes:
- Potassium and magnesium decrease heart rate.
- Calcium increases heart rate.

4. Body Temperature:
- Increased body temperature increases heart rate.

5. Age:
- Heart rate is generally higher in children and decreases with age.

6. Exercise:
- Exercise increases heart rate as oxygen demands increase.

7. Blood Pressure:
- Increased blood pressure can increase heart rate.

8. Blood Volume:
- Decreased blood volume can decrease heart rate.

9. Heart Conditions:
- Heart disease, arrhythmias, and other heart conditions can affect heart rate.