Fartlek --  Swedish for “speed play”; a workout schedule alternating aerobic walking with more intense anaerobic running, usually lasts for at least 45 minutes

Fast Twitch Muscle Fibers – as opposed to “Slow Twitch Muscle Fibers”; muscle cells which rapidly and forcefully contract, but tire quickly; these fibers thicken with exercise

Fat Burning – exercise which burns stored fat for energy instead of calories, while the exact intensity needed to burn fat is heavily debated, but generally more intense, shorter workouts burn more calories while longer slower paced workouts burn more fat. Burning either will lead to weight loss, though

Glucose – the basic form of sugar all “Carbohydrate” energy is initially converted into in order to travel through the bloodstream

Glycogen –the body’s main form of short-term energy storage; carbohydrates are stored in this form in the liver and muscles

Half-marathon – a race slightly less than 21.1 kilometers, or approximately 13.1 miles

Half-mile – slightly more than two laps around a 400 meter track, about 804.67 meters

Hamstring Injury – often referred to as a “pulled hamstring”, stretching, and/or microscopic tears in the tendons and muscle fibers at the back of the thighs 

Heart Rate – the frequency of the heart’s beating cycle
Heart Rate Monitor – equipment measuring the “Heart Rate” 

Hills – a workout involving running up and down a hill, sprinting up hill and jogging downhill; improves “Aerobic Capacity” and muscle strength