Muscle cramping is a common problem encountered by athletes and non athletes alike. Defined as painful involuntary skeletal muscle contractions, cramps may be categorized as either non exercise related or exercise related. Traditionally, such cramping was believed to arise from dehydration, electrolyte imbalances (including magnesium, potassium and sodium),accumulation of lactic acid, or low cellular energy levels.

Mammalian and avian hearts have four chambers two atria and two ventricles.Amphibians and reptiles, by contrast, have a three-chambered heart. The three-chambered heart consists of two atria and one ventricle.Fish possess the simplest type of true heart a two-chambered organ composed of one atrium and one ventricle.

The lymphatic system is a complex system of fluid drainage and transport, and immune response and disease resistance. Fluid that is forced out of the bloodstream during normal circulation is filtered through lymph nodes to remove bacteria, abnormal cells and other matter. This fluid is then transported back into the bloodstream via the lymph vessels. Lymph only moves in one direction, toward the heart.