Most people who exercise regularly have heard about the problems lactic acid build-up in major muscles can cause. Muscle fatigue, cramping, and reduced performance have all been tied to increased levels of lactic acid in the affected muscles. This week in SciTech Watch we take a look at the results of new research on lactic acid’s role in metabolism and exercise. It seems lactic acid can be your friend.
Exercise physiologists tell us that lactic acid is a by-product of metabolism in muscle cells as they do work. When lactic acid, also known as lactate, builds up to too high a level the muscle’s functioning is impaired or performance reduced. Lactic acid is considered a waste product that must be flushed out of the muscle to keep its performance at high levels.
Now results from 30 years of metabolic research at the University of California, Berkley are painting a strikingly different picture of lactic acid’s role in metabolism. The two methods which a muscle uses to do work have been found to be linked together rather than being two distinct methods, as thought previously. The two methods, anaerobic metabolism and aerobic metabolism are now believed to be linked together and the link is lactate.[ADBLOCKHERE]
When muscle cells convert carbohydrates to energy they do so in an oxygen-free cycle called the glycolytic pathway. This method produces lactate as a by-product. The lactate is flushed out into the blood stream for reuse or disposal. During intense exercise, a second energy production method, the oxidative pathway, becomes active. This method uses oxygen and lactate to provide more energy for muscle work. Thus the lactate produced by the glycolytic pathway is used by the oxidative pathway as fuel to produce additional energy.
As people exercise regularly, the muscle cells are exposed to elevated levels of lactate. Repeated exposure to elevated levels of lactate triggers muscle cell adaptations producing the ability to use lactate as a second energy source rather than treating lactate as a waste product. Many athletes use interval training to achieve high levels of performance. Interval training works because the short bursts of intense activity cause spikes in lactate levels which encourage the activation of the oxidative pathway.
George Brooks, UC Berkeley professor of integrative biology, has been performing experiments on frogs and muscle metabolism over the last ten years. His research indicates that the mitochondria in cells are the sites where oxidative metabolism is occurring. Further, interval training increases the number of lactate transporter molecules found in mitochondria. Lactate levels measured during endurance training indicated that lactate levels in the blood were decreasing even though cells were producing the same amounts of lactate. Two scientific papers on this subject provide direct evidence of a complex of proteins inside a cell whose function it is to collect lactate and transport it to the mitochondria for use by the oxidative metabolism pathway.
The first paper by Professor Brooks is in press for the American Journal of Physiology, Endocrinology and Metabolism, was published online in January. The second paper will be published in the near future. Professor Brooks, and colleagues Takeshi Hashimoto and Rajaa Hussien did their research at UC Berkeley’s Exercise Physiology Laboratory. An overview of Professor Brooks’ work is available at the EurekAlert web site.