by Lactic Acid: Why fatigue sets in during exercise and how it affects the body
What is lactic acid?
Lactic acid is a colorless, water-soluble organic acid with the chemical formula C3H6O3. It is produced as a byproduct of anaerobic glycolysis – a process that generates energy in our muscles during intense exercise without sufficient oxygen supply. When oxygen is limited or muscles are working too intensely, glucose gets broken down via glycolysis to produce ATP for energy in an anaerobic (without oxygen) pathway. This leads to the buildup of lactic acid within the muscle tissue.
Lactic acid buildup causes muscle fatigue
As lactic acid concentration rises within muscles during exercise, it causes the muscles to fatigue faster. This is because lactic acid decreases the pH within muscle cells, making it more acidic. The increased acidity interferes with muscle contractions by inhibiting enzymes involved in muscle function. It also displaces calcium ions from troponin C protein – an important protein responsible for muscle contraction. Both these effects cause the muscles to tire quickly, resulting in the sensation of fatigue and stitches in active muscles. This protective mechanism forces the body to slow down or stop exercise to allow lactic acid levels to return to normal.
Lactic acid clears out after exercise stops
Once exercise stops, oxygen supply resumes to the working muscles. At this point, lactic acid starts getting cleared out from muscles through two main pathways. First, it gets converted back to pyruvate which then re-enters the Krebs cycle in mitochondria to be oxidized completely. Secondly, lactic acid gets transported through the bloodstream to the liver where it gets converted back to glucose through a process called gluconeogenesis. This regenerated glucose can then be used as fuel by other tissues or stored as glycogen in the liver and muscles. Within a few hours after exercise ends, normal lactic acid levels get restored in the body.
Effects of long-term elevated lactic acid
Chronic elevation of lactic acid levels due to intense long-duration exercises can potentially cause muscle damage over time. Prolonged high acidity in muscle cells leads to protein denaturation and breakdown. It also impairs calcium handling in muscles interfering with muscle contraction and relaxation. This can result in muscle soreness, stiffness and reduced muscle function. High lactic acid post exercise may also delay muscle recovery since it impedes protein synthesis needed for repair. However, regular interval training helps muscles adapt by enhancing their capacity to clear lactic acid quickly, delaying fatigue onset.
Lactic acid and performance enhancement
Certain types of training that promote lactic acid buildup like high-intensity interval training have performance-enhancing effects. They help muscles develop greater lactic acid buffering ability via increased mitochondria and enzymes involved in lactic acid shuttling. This allows muscles to work at a higher intensity for longer before fatigue sets in. Studies also show such training elevates hormone levels like human growth hormone responsible for muscle growth. Overall, exercising at the lactic acid threshold induces physiological and metabolic adaptations helping boost sports performance, strength and endurance over time.
Effects on cardiovascular health
Interestingly, lactic acid produced during exercise also has positive effects on cardiovascular health. Short-chain fatty acids like lactic acid activate receptors in the liver and intestines that stimulate secretion of gut hormones like GLP-1 hormone. This hormone lowers blood pressure and improves insulin sensitivity, reducing heart disease risk factors over the long term. Lactic acid also triggers anti-inflammatory responses and increases mitochondrial biogenesis in heart muscles imparting a protective effect. However, diabetic patients may experience slightly elevated blood lactic acid post-workout which needs to be monitored.
In summary, lactic acid is an important regulator of muscle fatigue during high-intensity exercise. While it causes muscles to tire quickly, regular interval training enhances the body’s lactic acid clearance capacity bringing performance benefits. It also confers cardiovascular protection when exercise is done in moderation. A balanced lifestyle including diet and rest allows the body to derive optimal advantages from lactic acid buildup during bouts of exercise.
