Biomechanics

By Amanda Brunner

Cardiovascular Health

While we all know exercise is good for the 'ol ticker, the heart is a tricky organ. After all, if more exercise was always healthier then people wouldn’t collapse in cardiac arrest while doing vigorous exercise like shoveling snow, biking up steep hills, or aggressive running.

First a little bit of medical fact to consider. Intense aerobic exercise increases blood flow which in turn increases oxygen delivery to active muscles. Vasodilatation in the muscles opens more capillaries while vasoconstriction diminishes blood flow where it is not needed. In other words- strenuous activity results in increased blood flow to the muscles being used and a decline of blood to the rest of the body. Respiratory movements and skeletal muscle activity increases venous return to the heart. As venous return to the heart increases, ventricular walls stretch, stimulating them to contract with greater force. Heart rate increases as well.

A conditioned biker experiences an increase in heart pumping efficiency, blood volume, blood hemoglobin concentration, and mitochondria in muscle fibers which ultimately improves oxygen delivery to muscle tissue. An athlete’s heart typically changes in response to these increased demands and may enlarge up to 40 percent or more.

The cardiovascular system responds slowly and steady to change. It does not react well to sudden demands but rather it needs a steady buildup in exercise frequency and intensity. A person who leads a sedentary life may actually cause harm if they were to do vigorous exercise; sudden strain can increase the risk of cardiac arrest whereas an individual with the same body type and age who exercises on a regular basis would benefit from the same activity. The recommended amount of exercise for a beginner is 30 minutes 3 times a week.

A proper exercise regimen should elevate hear rate up to between 70 to 85 percent of its theoretical maximum. There is a simple calculation to determine theoretical maximum and that is to subtract your age from 220. Once established, consider what 70 to 85 percent of this number would be and aim to maintain this number as a steady heart rate while exercising.

It is a very common mistake among mountain bikers to attempt too much too quickly. It is wise to start off cruising flat trails then to slowly move up to the more difficult runs throughout the season to allow the heart time to expand for the increased load.