L-Carnitine --  a nutritional supplement claimed to increase the body’s capacity for burning fat. The Food and Drug administration does not evaluate the claims of nutritional supplements; while studies have shown it may help strengthen a weakened heart, but the supplement’s fat burning properties are doubted 
Lactate Threshold -- See “Anaerobic Threshold”

Lactic Acid – a chemical derived from the body’s process of extracting energy from carbohydrates, causes muscle fatigue and pain after a hard workout
Lateral – a shoes outermost side

Log – a documentation of your progress through workouts

Marathon – a long distance race of 42.195 kilometers or 26 miles, 385 yards

Master – runners 40 years old or older 

Maximum Heart Rate  – the fastest speed your “Heart Rate” may attain   

Medial – the inner arch of a foot or shoe

Medial Post – a denser wedge of midsole cushioning in the “Medial” region to provide “Pronation” control

Metric Mile – 1600 meters, the rounded metric distance closest to a standard mile or four laps around the 400 meter track, an actual mile is 1609 meters

Microfiber – a material made of small fibers tightly wrapped, valued for its quick drying, and wind and water resistance

Midsole – the segment of a running shoe in between the outsole and the running shoe’s upper, the layer of cushioning underneath the removable innersole 

Mile – 5,280 feet or 1,609 meters

Motion Control – a feature of the shoe’s construction intended to guide the foot’s form and movement, often in an attempt to correct “Pronation” problems  

Negative Splits – running the first half of a race at a slower pace than the second half