"Aerobics" is the term coined by Dr. Kenneth Cooper in 1968 to describe sustained low to moderate cardiovascular exercise. Aerobic activities include jogging, cycling, rowing, swimming and group exercise classes such as step. Aerobic exercise offers a wide variety of benefits to your heart, lungs and muscles. Aerobic exercise affects your muscles in the long term as a result of your workouts and also in the short term while you exercise.
Increased Demand for Oxygen
As soon as you begin to exercise, your muscles increase their demand for essential oxygen. Fat, in the presence of oxygen, supplies the primary fuel for aerobic workouts. To meet your muscles' demand for more oxygen, your breathing rate and heart rate must increase. This results in your muscles getting warmer as oxygen-rich blood is pumped into them.
Your muscles are saturated with tiny thread-like veins called capillaries, which are one-cell thick to allow oxygen and other essential substances to diffuse from your blood and into your muscles. Aerobic exercise results in an increase of carbon dioxide, which must diffuse from your muscles and into your blood, ready for exhalation. To facilitate this increased exchange of gasses, your capillaries and other blood vessels in and around your muscles expand during exercise. This phenomenon is called vasodilation.
Increased Glycogen Stores
Aerobic exercise predominately uses fat for fuel, but a small amount of carbohydrates is also used, a fuel source stored in your muscles called glycogen, consisting of glucose molecules bound to water. Your glycogen stores increase in size as you get fitter and as a direct result of repeated aerobic workouts. Increased glycogen stores play a major part in increased muscular endurance -- a vital component in aerobic exercise.
Improved Muscular Endurance
Aerobic exercise typically uses a high volume of low-intensity muscular contractions. Your muscles are broadly made up of two types of muscle fibers: slow twitch and fast twitch. Aerobic exercise mostly uses your slow-twitch muscle fibers. Slow-twitch muscle fibers have a relatively poor ability to get bigger, but as a result of repeated aerobic workouts over time, they do increase in size very slightly and their work capacity increases significantly. In addition to muscle fiber improvements, cells within your muscles called mitochondria, which are responsible for producing the energy-yielding compound adenosine triphosphate, or ATP, increase in both size and number.
The combination of improved slow-twitch muscle fibers and more/larger mitochondria means your muscles are much slower to fatigue.