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Absorption - The process by which nutrients and other substances are transferred from the digestive system into the blood for transport throughout the body.
Adenosine triphosphate (ATP) - ATP is a high-energy compound that is primarily produced through the oxidation of fat and carbohydrates. When one of its phosphate groups is broken off, energy is released and adenosine diphosphate (ADP) is formed. This energy directly fuels the contraction of muscles.
Adenosine diphosphate (ADP) - Formed after a phosphate group is broken off from the high-energy compound ATP. This chemical reaction releases energy which is utilized by muscle cells for muscle contraction. The ADP that is formed during this chemical reaction can be converted back to ATP via the enzyme creatine kinase (see also: creatine phosphate).
Aerobic energy - Energy produced in the presence of adequate cellular oxygen availability. When exercising in a primarily aerobic state, the body utilizes carbohydrates and fats as energy sources to regenerate ATP for muscle contraction. Endurance exercise is primarily aerobic exercise, and the higher the exercise intensity, the more carbohydrate one uses to produce ATP. Scientifically, aerobic energy production is called oxidative phosphorylation.
Amino acids - The chemical building blocks that make up proteins. Ingested proteins are broken down into amino acids in the digestive tract. These amino acids are then used to make the specific types of protein needed in the body.
Anaerobic - When the availability of oxygen to cells is limited, the anaerobic energy system provides the majority of the ATP supply necessary for muscle contraction. When exercising in an anaerobic state, such as during a short sprint, the body primarily uses creatine phosphate and glucose stored in muscles (glycogen) as energy sources to quickly generate ATP. Short-burst, high-intensity exercise is considered anaerobic exercise, and results in high production rates of muscle lactate. Scientifically, anaer
Anorexia nervosa - An eating disorder characterized by extreme weight loss. Linked to body dysmorphic disorder, psychological issues, and obsessive fear of weight gain.
Antioxidants - Chemical substances that help prevent or slow free radical damage caused by oxidation of cells. Breathing, exercise, and exposure to oxidizing agents such as environmental pollutants, smoke, ozone, etc. causes oxidation, which in turn produces free radicals. Vitamins A, E, and C and the mineral selenium are just a few examples of antioxidants.