Lactic Acid
A substance caused by anaerobic training of the muscles, a build up prevents continuation of exercise, and a good example is 400 meter runners. Watch how they slow down during the last 100 meters of the race. 

Lat's
Abbreviation for Latissimus dorsi, the large muscles of the back that move the arms downward, backward and in internal rotation.

Lean Body Mass
Everything in the body except for fat, including bone, organs, skin, nails and all body tissue including muscle. Approximately 50-60% of lean body mass is water.

Lifestyle
Individual patterns of your typical life.

Lift Off
Assistance in getting weight to proper starting position.

Ligament
Strong, fibrous band of connecting tissue connecting two or more bones or cartilage or supporting a muscle, fascia or organ.

Lipids
All fats and fatty acids.

Lipoprotein
Fat carrying protein in the blood.

Lock Out
Partial repetition of an exercise by pushing the weight through only last few inches of movement.

Low Density Lipoprotein (LDL)
A core of cholesterol surrounded by protein, often referred to as bad cholesterol.

Lower Abs (lower abdominals)
Abbreviation for abdominal muscles below the navel.

Lumbar
Lower region of you spine, vertebrates L1 to L5. Used for bending and extending the body forward and back, with the aid of the abdominal and erector spinae muscles.