Everybody knows that lactic acid accumulates when we exercise at a high intensity, but there is much more to lactate than that. It plays an integral role in many of the bodys metabolic processes.


1. Lactic Acid is Always Present
Its always being produced. At rest your lactic acid levels will be about 1 millimoles/liter (mmol/L). As exercise intensity increases so does the production of lactic acid. Its not until you pass your anaerobic threshold that it reduces your efficiency. For most people this is approximately 4 mmol/L, or 70-80% of their VO2max.


2. Not Just Oxygen Deficiency
It is commonly thought that it is the lack of oxygen that causes the increased production of lactic acid. Whilst it is a contributing factor, it is the absence of the "carrier molecules" NAD (nicotinomide adenine dinucleotide) and FAD (flavin adenine dinucleotide) that have a much greater effect. They play the important role of transporting hydrogen into the cells for use in the production of energy. If they are not around, the hydrogen joins with pyruvate to produce lactic acid.


3. Lactic Acid as Fuel
Lactic acid is usually removed from the muscle tissue within 30 minutes after exercise. It is used by liver, heart, and kidney as a source of energy. The liver can also convert it back into glucose, where it is released into the bloodstream for muscle use. It can also be converted into glycogen for storage.


4. Fatigue and Lactic Acid
Most people know that increases in lactic acid causes a decrease in your ability to perform but few actually know how this occurs.
Firstly, youll have a decrease in energy. The increase in hydrogen reduces the production of ATP (energy) by inhibiting key ezymes involved in its production.
Secondly, your muscles wont be able to contract as often or with as much force. For a muscle to contract we need calcium to attach itself to binding sites within the muscle. The more calcium attached, the more forceful the contraction. The problem occurs because hydrogen competes with calcium for bindings sites.


5. Delayed Onset Muscle Soreness (DOMS)
Delayed Onset Muscle Soreness is the pain you feel in the muscle 24-48 hours after exercise. It was once thought that lactic acid caused this but it has now been proven wrong.
Its the excessive mechanical force which results in damage to the muscle or connective tissue. The body responds by repairing it and this stimulates sensory nerve endings which results in pain. This is why it usually occurs when you first start an exercise program, or when you train at an unusually high intensity.