Muscle Adaptation with Aerobic Training

The body is an amazing thing, the more I learn about it the more I am astonished at the way it works and changes. You can spend hours looking at the skeletal system, the nervous system, circulation and respiration systems. Looking at the muscles of the body these are split into 3 types: Skeletal muscle, Smooth muscle and Cardiac muscle.

Cardiac muscle, as you’ve guessed is the muscle type of the heart which is a phenomenal organ. A normal person’s heart beats over 100,000 times a day. Imagine a how much that would be in a lifetime? The heart is extremely strong, the heart wall can be over an inch thick in certain places. It also has been to be reliable, you don’t want this muscle to stop working! The great thing is the more it works (exercise) the stronger, the more reliable and efficient it gets.

Smooth muscle or involuntary muscle is the type of muscle which makes up your intestines, blood vessels and the stomach. This muscle type is more elastic, slower to contract, can hold contractions for a much longer period and is much more sensitive to temperature changes or chemical stimuli.

Skeletal muscle is the muscle type you’ll be most aware of, as they are under conscious control and they play a major part in body movement. Muscles are made up of fibres, you are born with a set amount of fibres, and these can not increase with training, although the structure and function can change with training.

Skeletal muscles are made up of two types of muscle fibre, slow twitch and fast twitch. Slow twitch fibres are red in colour because of high myoglobin (transports oxygen in the muscle, red in colour) content, narrower in diameters and are surrounded by capillaries. Fast twitch has two types type IIa and type IIb which are greater in size than slow twitch, have a less generous supply of capillaries, they are white or pale pink in colour an have a lower myoglobin content.

In strength training the fibres will increase in size, but my main interest is in aerobic training and the changes it makes to the muscle fibre types, mitochondrial function(part of the muscle fibres energy system), and oxidative ezymes(proteins which speed up the break down of nutrients for the energy system).

It has been shown that with aerobic exercise there are changes in the muscles. This includes change of the muscle fibre types, there is a transition of type II(strength) to type I(endurance). Although the amount of change is small, not more than a few percent there are also other changes within the muscle. A further change after prolonged periods of aerobic training is the increase of myoglobin in the muscle which increases the amount of oxygen available to the muscle, this can increase from 75% to 80%. Another effect is that an oxidative enzyme, succinate dehdrogenase (SDH) increases largely in number, it has been shown by anything up to 800% over seven months of continued training. This would increase the muscle ability to make energy much more efficiently during exercise.

This evidence really does show how the muscles adapts to the demands and stresses that they are put under and how over time they change to improve performance. When you are seeing improvement in your performance over time these are some of the things that taking place in your muscles to make your run, longer, faster and more efficiently.