How can lactic acid disrupt muscle contraction

This brief review presents 1 a short history of our understanding about lactic acid that explains the early acceptance of a causal relationship between lactic acid and fatigue, 2 evidence to show the temperature dependence of acidosis-induced changes and the beneficial effect of acidosis, and 3 a proposal that lactate production retards, not causes, acidosis.

These findings require us to reevaluate our notions of lactic acid, acidosis and muscular fatigue. Already have an account? Login in here. Journal home Advance online publication Journal issue About the journal. Keywords: lactate , lactic acidosis , temperature , pH. Article overview. I have vivid memories of joining my dad as he laid on the ground with his legs elevated after a long run or intense biking session.

My dad had been taught what many people believed about lactic acid: that it was a cause of fatigue and muscle soreness, and that it had to be removed in some way to help you recover and avoid soreness. As a young athlete, I often heard these same things being echoed by my coaches and I believed it to be true.

The soreness that you feel in your muscles post-workout is due to microscopic tears in the muscle tissue that rebuilds to help you get stronger. So, what is this lactic acid everyone was going on about? What does it do, and do I need to get rid of it? Read on to find out. Most people associate lactic acid with intense exercises, like sprinting or heavy lifting, and rightly so.

Lactic acid is a by-product of glycolysis, one of the metabolic processes the body uses to produce energy during intense exercise. Lactic acid is the collective term used to describe the lactate and hydrogen ions that are by-products of this process. Lactic acid is formed within the muscle cells during glycolysis to clear the cells of accumulating pyruvate, a by-product of glycolysis. While still in the muscle cells, the hydrogen ion is what is responsible for lowering the pH of the muscle tissue, making it more acidic.

This decrease in the muscle pH, known as acidosis, can lead to some of the burning sensations felt in the muscles during intense exercise. The good news, however, is that lactic acid is more of a helper to our muscles since it ultimately provides energy. The lactate is often recycled and used as energy, which is much needed during bouts of intense exercise.

Lactic acid is produced during bouts of high-intensity exercise as your body works hard to produce the energy that it needs to sustain the activity. Our bodies use adenosine triphosphate ATP as a primary energy source. During bouts of high-intensity exercise, like sprints or heavy loads during lifting, the body relies on the ATP-PC and Glycolytic systems glycolysis for quick energy because they produce ATP at faster rates than the Oxidative system.

The glucose for glycolysis can be provided by the blood supply, but is more often converted from glycogen in the muscle fibers. If glycogen stores in the muscle fibers are expended, glucose can be created from fats and proteins. However, this conversion is not as efficient. Pyruvate is continually processed into lactic acid. With pyruvate accumulation, the amount of lactic acid produced is also increased. This lactic acid accumulation in the muscle tissue reduces the pH, making it more acidic and producing the stinging feeling in muscles when exercising.

This inhibits further anaerobic respiration, inducing fatigue. Glycolysis alone can provide energy to the muscle for approximately 30 seconds, although this interval can be increased with muscle conditioning.

While the pyruvate generated through glycolysis can accumulate to form lactic acid, it can also be used to generate further molecules of ATP. Mitochondria in the muscle fibers can convert pyruvate into ATP in the presence of oxygen via the Krebs Cycle, generating an additional 30 molecules of ATP. Cellular respiration is not as rapid as the above mechanisms; however, it is required for exercise periods longer than 30 seconds.

Cellular respiration is limited by oxygen availability, so lactic acid can still build up if pyruvate in the Krebs Cycle is insufficient. Cellular respiration plays a key role in returning the muscles to normal after exercise, converting the excess pyruvate into ATP and regenerating the stores of ATP, phosphocreatine, and glycogen in the muscle that are required for more rapid contractions.

Muscle fatigue refers to the decline in muscle force generated over sustained periods of activity or due to pathological issues. Muscle fatigue has a number of possible causes including impaired blood flow, ion imbalance within the muscle, nervous fatigue, loss of desire to continue, and most importantly, the accumulation of lactic acid in the muscle. Long-term muscle use requires the delivery of oxygen and glucose to the muscle fiber to allow aerobic respiration to occur, producing the ATP required for muscle contraction.

If the respiratory or circulatory system cannot keep up with demand, then energy will be generated by the much less efficient anaerobic respiration. In aerobic respiration, pyruvate produced by glycolysis is converted into additional ATP molecules in the mitochondria via the Krebs Cycle. With insufficient oxygen, pyruvate cannot enter the Krebs cycle and instead accumulates in the muscle fiber. With pyruvate accumulation, lactic acid production is also increased.

This further inhibits anaerobic respiration, inducing fatigue. Lactic acid can be converted back to pyruvate in well-oxygenated muscle cells; however, during exercise the focus in on maintaining muscle activity.