When we exercise at high intensities we often feel a burning in the muscle. This burning sensation is lactic acid building up in the muscle tissue. When all the oxygen is depleted from the cell hydrogen atoms increase forming lactic acid. Once lactic acid accumulates enough in the cell, muscle contractions cease. After training people associate their sore muscles to lactic acid still being in the muscle tissue. The pain is due to DOMS (delayed onset muscle soreness), which I will discuss later. For this discussion I will be talking about lactic acid and its effect on the cells of the body as a result of intense exercise.
When lactic acid, the product of glycolysis (the anaerobic phase of carbohydrate metabolism), accumulates to high levels in blood and muscle, fatigue sets in. Therefore, full recovery from exercises in which maximal amounts of lactic acid have accumulated involves the reduction of lactic acid levels from both the blood and skeletal muscles that were active during the preceding exercise period.
Several important questions related to this process that need answering are 1. How long does it take to remove the accumulated lactic acid, 2. What factors influence the speed of lactic acid reduction, 3. What happens to the lactic acid, and 4. What is the relationship between the removal of lactic acid during recovery and the slow-recovery phase?
Speed of Lactic Acid Removal
The time course of the removal of lactic acid from blood and muscle is 5-60 minutes, respectively. During sub maximal, but heavy, exercise, in which the accumulation of lactic acid is not as great, less time is required for its removal during recovery.
Effects of Exercise during Recovery on Speed of Lactic Acid Removal
When a person rests throughout the duration of the recovery period this is known as rest-recovery.
However, lactic acid can be removed from blood and muscle more rapidly following heavy to maximal exercise by performing light exercise rather than by resting throughout the recovery period. Such a recovery is referred to as exercise-recovery, or active recovery, and is similar to the warm-down procedures that most athletes have practiced for many years. A study (Belcastro, Bonen) was done years ago that determine the effects of the exercise recovery on lactic acid removal. They had subjects run 1 mile on 3 separate days. Three different recovery periods were used 1. Rest, 2. Continous exercise consisting of jogging at a self-selected pace and, 3. Intermittent exercise of the kind normally practiced by athletes. Both exercise-recoveries resulted in substantial increases in the rate of lactic acid removed from the blood. The removal rate was fastest during the continuous jogging recovery. This information suggests that athletes should exercise continuously throughout the recovery period rather than intermittently, which is their normal practice. Lactic acid, rather than being removed should be thought as a fuel source for muscle and as a source for the partial regeneration of liver and muscle glycogen.
How much exercise should be performed during recovery to promote optimal lactic acid removal? The answer to this question is for untrained subjects, the recovery exercise that produces the fastest or optimal rate of removal of blood lactic acid is one in which the oxygen consumption (VO2) is between 30 and 45% V02 max, or 1.0 to 1.5 liters per minute, or 15 to 20 milliliters per kilogram of body weight per minute. With trained subjects performing recovery exercise consisting of running or walking, it has been shown that lactic acid removal is optimal at intensities between 50 and 65% V02 max (Belcastro, Bonen). The major reason for this difference is probably related to the state of training of the subjects than to the difference in exercise modes (running walking versus bicycling). In other words, the higher the fitness level (with greater mitochondria density, blood perfusion, and enzyme capacities), the higher the recovery exercise intensity for optimal lactic acid removal.
One more point. When the intensity of the recovery exercise is either below or above the optimal limits, lactic acid is removed more slowly. In fact, when the intensity of the recovery exercise is greater than 60% VO2 max the removal rate of lactic acid is actually less than that during rest-recovery. The reason for this is that during the recovery exercise itself, more lactic acid is being produced than is being removed.
Elite middle-distance athletes often appears to follow the procedure of maintaining an active recovery near the 70% VO2 Max for the first few minutes, then dropping to 40% VO2 max for the later recovery period.
Daryl Conant, M.Ed.
tags: lactic acid, bodybuilding, Daryl Conant, Ron Kosloff, Vince Gironda