Your cardiovascular fitness (or lack thereof) is what you feel when you get winded climbing a flight of stairs or briskly walking from Point A to Point B. It’s the ability of your body to use vessels such as veins and arteries to carry oxygen to and from the heart and muscles, and efficiently extract that oxygen from the blood to make energy.
In contrast, your muscular strength (or lack thereof) is what you feel if you dropped to do 10 pushups or tried to move a big rock while gardening in your backyard.
So if cardiovascular fitness and muscular strength are so different, can weight training improve your cardio?
The answer is yes! Here’s why:
When you lift weights, receptors on the blood vessels in your working muscles vasodilate (get bigger) to allow more blood flow to the working muscle. At the same time, the contracting muscles “milk” blood back towards the heart, which increases the blood that the heart is able to pump with each beat. Both these mechanisms can improve your cardiovascular fitness.
When you lift weights, your body must rapidly burn up glucose to use as a fuel, and a byproduct of using glucose for energy is the formation of a molecule called pyruvate. This is one of the body’s main energy sources during aerobic activity, and through weight training, your body learns how to produce it and use it more efficiently.