Glossary

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Labyrinthine Righting Reflex
When proprioceptors of the inner ear are stimulated, a reflexive response causes the neck muscles to bring the head to a normal position.

Lactate Threshold
The workload that causes lactate production to exceed the rate of lactate removal by the liver. The threshold usually occurs at about 50% to 80% of VO2 Max. Athletes with better endurance have been detected with higher anaerobic thresholds.

Lactate Turnover
The rate of lactate removal from the blood. Lactate or lactic acid is not a waste product. In aerobic conditions lactate is converted back to glucose and also glycogen by a process called the Cori Cycle.

Lactic Acid
Related to pyruvate because it is pyruvate with extra hydrogen atoms. It is the reduced form of pyruvate. Lactic acid increases as exercise intensity increases and not enough oxygen is available for the final acceptance of hydrogen in the Electron Transport System. Hydrogen ions back up the system. First, hydrogen atoms bound to NAD+ (nicotinamide adenine dicnucleotide) accumulate. Next, pyruvate temporarily accepts hydrogen to form lactic acid. Lactic acid is rapidly diffused into the blood where it is buffered to lactate. In the presence of sodium bicarbonate, lactic acid reacts to produce sodium lactate and carbonic acid. Carbonic acid dissociates to release hydrogen ion to the extracellular fluids.

Lateral Dominance
The preference to use a particular hand, foot, eye or ear on one side rather than the other. The preference may be the same for all of the above or it may be mixed in an individual.

Law of Acceleration
Newton's Second Law of the three laws of motion. F = ma. The acceleration of a body is directly proportional to the resultant force applied to it and parallel in direction to this force. Also, the acceleration from a given force is inversely proportional to the mass of the body.

Law of Action-Reaction
Newton's Third Law of the three laws of motion. To every action there is always opposed an equal reaction; or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.

Law of Inertia
Newton's First Law of the three laws of motion. Every body persists in its state of rest or of uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.

Low Density Lipoprotein (LDL)
The "bad cholesterol" because it is the form of cholesterol that tends to end up on blood vessel walls.

Lean Body Mass
The mass of the body that does not include storage fat. Lean body mass equals bone, muscle and essential fat area, such as part of organs and skin.

Length-Tension Relationship
The correlation of the length of a muscle stretch and the tension produced by the muscle. Higher tension is created when the muscle is near its resting length. There is an optimal length for the best cross-linking of the contractile elements of the muscle. Too much or too little stretch minimizes the connections of the contractile elements.

Lever System
Three classes of levers, all of which involve a fulcrum, a resistance and an outside influential force. (1) In the First Class Lever the Fulcrum lies between the Effort and the Resistance (e.g., Extension of the head/neck, Triceps Pressdown). (2) In the Second Class Lever the Resistance lies between the Fulcrum and the Effort (e.g., Standing Calf Raising Body Weight with Plantar Flexion. (3) In the Third Class Lever the Effort lies between the Fulcrum and the Resistance (e.g., Biceps Curl, Elbow Flexion).

Limited Channel Processing
Hypothesis that there is a limit to how much stimulus can be received simultaneously and then performance declines.

Line of Pull
The line of action of a contracting muscle.

Lipolysis
The catabolism of fat (e.g., triglyceride to glycerol and fatty acid).

Lordosis
The forward curvature of the lumbar spine. Some refer to the normal lumbar spinal curve as lordosis, while some consider lordosis to describe an excessive curve.

Lumbar
The region of the spinal column between the thoracic region and the sacral region. The lower back.

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