"Principles of Exercise Physiology: Responses to Acute Exercise and Long-term Adaptations to Training"
This is an excellent article that reviews exercise physiology, the body's response to exercise, and long-term adaptation. It does a quick summary of basic information like muscle types, metabolic response (aerobic vs anaerobic), and the activities that activate each level of metabolism. One of the initial responses to exercise is the cardiovascular response. At first, stroke volume increases alone, but at 40-60% of the VO2max, cardiac output can only increase through increased heart rate. Tissues can also improve their oxygen content by increasing oxygen extraction from the blood (arterial-venous difference). Of course, blood pressure will be found to increase as well (systolic). Additionally, hydration is a well-known component of exercise and can have significant impact on exercise performance. Dr. Noakes, on the other hand, presents the opinion of hydration levels being overly criticized as the culprit in Lore of Running. His research has found hypoglycemia and hyponatremia to be the cause of decreased athletic performance far more frequently. Regular endurance exercise has been shown to have several effects on the body. Muscles have increased mitochondria size and capillary formation. This increases blood flow to the muscle and the cells' ability to extract/utilize oxygen. Plasma volume has also been shown to increase, thus, improving the viscosity of the blood, making it easier for it to flow through the body. The increased work load results in left ventricular hypertrophy, which leads to stronger contractions. For much more, check out the article yourself!
Rivera-Brown AM, Frontera WR. Principles of Exercise Physiology: Responses to Acute Exercise and Long-term Adaptations to Training (2012). PM&R: The Journal of Injury, Function, and Rehabilitation 4(11), 797-804.