Blair McEachnie-George's List: PE

Circulatory System

The cardiac muscle surrounding the heart hypertrophies, resulting in thicker, stronger walls and therefore increases in heart volumes. The more blood pumped around the body per minute, the faster Oxygen is delivered to the working muscles.
The number of red blood cells increases, improving the bodies ability to transport Oxygen to the muscles for aerobic energy production.
The density of the capillary beds in the muscles and surrounding the heart and lungs increases as more branches develop. This allows more efficient gaseous exchange of Oxygen and Carbon Dioxide.
The resting heart rate decreases in trained individuals due to the more efficient circulatory system.
The accumulation of lactic acid is much lower during high-levels activity, due to the circulatory system providing more Oxygen and removing waste products faster.
Arterial walls become more elastic which allows greater tolerance of changes in blood pressure.
Respiratory System

The respiratory muscles (Diaphragm/intercostals) increase in strength.
This results in larger respiratory volumes, which allows more Oxygen to be diffused into the blood flow.
An increase in the number and diameter of capillaries surrounding the alveoli leads to an increase in the efficiency of gaseous exchange.
Muscle

Increased numbers of mitochondria (the cells powerhouse) means an increase in the rate of energy production.
The muscles, bones and ligaments become stronger to cope with the additional stresses and impact put through them.
The amount of myoglobin within skeletal muscle increases, which allows more Oxygen to be stored within the muscle, and transported to the mitochondria.
Muscles are capable of storing a larger amount of glycogen for energy.
Enzymes involved in energy production become more concentrated and efficient to aid the speed of metabolism.