Aerobic – literally “requiring oxygen”; most commonly used to describe a moderate intensity workout

Aerobic Capacity – a measurement of the largest amount of oxygen the body is capable of converting into energy (aka VO2max), or an exercise regimen intended to increase this amount

Aerobic Conditioning – exercise intended to increase the efficiency of the heart and lungs in the process of taking in oxygen and delivering it to the muscles

Amenorrhea --  a woman’s medical condition leading to the ceasing of menstruation; can be caused by overly exhaustive workouts

Anaerobic – the lack of oxygen, exercise of this type is often extremely intense

Athletes Helping Athletes (AHA) – a charity organization raising money for mentally and physically challenged athletes 

Anaerobic Capacity – the largest amount of energy the body can generate without needing oxygen, or an exercise regimen intended to increase this capacity 

Anaerobic Threshold – the point at which “Lactic Acid” quickly begins building up in the runner’s muscles, also called the “Lactate Threshold”
Anandamide – See “Runner’s High”