Replenishing the Lactic Acid Source (Lactacid Oxygen Debt)

After exercise, lactic acid built up in the tissues must be removed; this is accomplished through the aerobic system. A good cool-down helps by keeping the aerobic system somewhat elevated during initial recovery. Many tissues of the body can aerobically metabolize lactate:

a. Skeletal muscle active during an exercise bout (Hatta et al, 1989) b. Skeletal muscle inactive during an exercise bout (Kawalchuk et al, 1988) c. Cardiac muscle (Hatta et al, 1989) d. Kidney (Hatta et al, 1989) e. Liver (Rowell et al, 1966) f. Brain (Nemoto et al, 1974)

Fate of accumulated lactate (one account, pages 328):

• ~60% is aerobically metabolized (Gasser & Brooks, 1979).
• ~40% is converted to glucose and protein; a small portion is excreted in urine and sweat (Ingjer, 1969).

A more detailed account (page 604, Fleck & Kraemer, 1997) gives:

• ~18% reconverted to glycogen or glucose in the liver and muscle.
• ~72% used as a fuel source in skeletal muscle and other organs (heart, brain, liver, kidneys).
• ~8% converted to protein in the liver.
• ~2% excreted in sweat and urine.

Half-life of the lactic acid system (the lactic-acid portion of the oxygen debt):

• ~50% cleared at 25 minutes (Hermansen et al, 1976)
• ~95% cleared at 1 hour 15 minutes

Accumulated lactate is removed from the blood more quickly if the muscles active during the exercise bout perform light activity afterward (Hildebrandt et al, 1991).

• Lactate is mostly metabolized aerobically; cleared via active/inactive muscle, heart, kidney, liver, brain.
• Account A: ~60% aerobically metabolized; ~40% → glucose/protein (small part excreted).
• Account B: ~18% → glycogen/glucose; ~72% fuel; ~8% → protein; ~2% excreted.
• Half-life: ~50% at 25 min; ~95% at 1 h 15 min.
• Light activity (active recovery) speeds blood lactate removal.