How Endurance Training Changes Your Heart and Body

Endurance training is an important way to improve how our heart and blood system work. In this post, we will explore how this type of training affects two key parts: stroke volume (SV) and cardiac output (CO). These are important for understanding how well our heart performs during exercise.

When we regularly do endurance training, our bodies become stronger and can handle more effort. One big change happens in stroke volume. Stroke volume is the amount of blood the left side of the heart pumps out with each beat.

For people who don’t exercise much, the average stroke volume is about 70 mL (milliliters) per beat. This can change based on age, gender, and fitness level. But for trained athletes, stroke volume can rise to around 120 mL per beat or even more!

Here are some reasons why this happens:

1. Stronger Heart Contraction: Endurance training helps the heart’s muscle work better, making it contract more strongly. This improvement is partly due to better handling of calcium in heart cells.

2. More Blood Filling the Heart: When we exercise, more blood returns to the heart. This happens because of increased blood volume and better blood flow from the veins. A well-known idea, the Frank-Starling mechanism, says that the more blood in the heart before it beats, the stronger the heartbeat, which increases stroke volume.

3. Less Resistance for Blood Flow: With regular training, blood vessels adjust to help the heart pump easier. Wider blood vessels make it easier for the heart to push blood out, improving efficiency.

When stroke volume increases, cardiac output also gets better. Cardiac output is the total amount of blood the heart pumps in one minute. We calculate it like this:

$$CO = SV \times HR$$

Here, $HR$ means heart rate. Trained athletes usually have a lower resting heart rate (around 40-60 beats per minute). But their higher stroke volume helps maintain or even boost cardiac output during exercise. Research shows that a well-trained athlete can reach cardiac outputs of 30-40 liters per minute, compared to about 20-25 liters per minute for untrained people.

Endurance training also brings several other benefits to the body:

• Increased Blood Volume: Training often raises the amount of blood plasma, which is important for a better stroke volume. More plasma means better blood return and filling of the heart.

• More Blood Vessels: Training encourages new blood vessels to form. This improves the delivery of oxygen and nutrients to muscles that are working hard.

• Better Oxygen Use: With more mitochondria in muscle cells, the muscles use oxygen more effectively, helping them work better.

• Hormone Changes: Regular endurance training also affects the nervous system, allowing for a calmer heart rate at rest and enabling a larger increase in stroke volume during exercise.

• Healthier Heart Structure: Long-term training leads to positive changes in heart structure, like a stronger left ventricle. This helps the heart fill up more and pump blood out more efficiently.

However, it’s important to remember that training too much without rest can cause problems, such as overtraining and heart issues.

In conclusion, endurance training greatly improves both the stroke volume and cardiac output of the heart. These changes help with exercise performance and overall heart health. Understanding how these adaptations happen shows us how our bodies meet the demands of physical activity and highlights the amazing effects of training on our health.