Lactic Acid, Hydrogen, and What is Really Cause Your Muscles To Burn

Imagine you are in the middle of a workout…at Fierce 2.0 of course! You are going for a set of Barbell Back Squats for 12 reps. You get to rep 7 and you start to experience this burning feeling in your muscles. You push through the last 5 reps and re-rack the bar, legs feeling like they’re on fire. What is the first thing you attribute this burning sensation to? Lactic Acid, right? Well, this actually is not correct. Hydrogen is the real culprit.

Most of you are in disbelief that all those years of people telling you that lactic acid buildup causes your legs to feel like they’re ablaze. To understand why hydrogen is to blame, we must look at the bioenergetics (flow of energy in a biological system) of the muscle.

When you exercise, there are four main systems that allow your muscles to be fueled and continue working:

  • the ATP-CP or Phosphagen system
  • Anaerobic or Fast Glycolysis
  • Aerobic or Slow Glycolysis
  • and Beta Oxidation.

When you begin exercising, the first system that turns on is the ATP-CP system. This system uses an ATP (Adenosine Triphosphate) molecule that undergoes hydrolysis (reaction using water) to form ADP (Adenosine Diphosphate), an inorganic phosphate molecule, a hydrogen ion, and energy. This breakdown of ATP is the driving force behind muscular contraction. While about 50-60% of the ATP stored in the muscle can be used up within 10 seconds (especially during high intensity exercise), there is now a massive concentration of Hydrogen within the muscle. This causes what’s known as exercise-induced metabolic acidosis. The concentration of Hydrogen is so great that is lowers the pH (how acidic or basic an environment is) of the muscle. Seeing as all organs in the human body operate within a specific pH, when that specific pH is exceeded, the muscle begins to malfunction. This is when the feeling of pain and the burning sensation begins.

Wait, you may be asking, what about lactic acid? Lactic acid is actually a misnomer. The second system that kicks in during exercise is called Fast Glycolysis. Its main source of fuel will be glycogen (the stored form of glucose). There are only two reactions that need to be brought to light. The second to last reaction in Glycolysis transforms Phosphoenolpyruvate into Pyruvate with the assistance of Pyruvate kinase. This reaction actually causes a rise in pH, creating a more basic or alkaline environment; the opposite of acidic like the ATP breakdown. Pyruvate is then either shuttled into the Krebs Cycle to create more ATP or converted into Lactate through an enzyme called lactate dehydrogenase. This Lactate substrate is what people know as lactic acid. Lactate is actually very useful. It can be converted into glucose via a process called gluconeogenesis.

Luckily for you, the human body is very adept and adaptable. The more a person becomes conditioned, the more your muscles can deal with the increased concentration of Hydrogen. The biggest factor helping keep your muscles working as your conditioning increases is your body’s acid-base buffering system. Your body will increase the amount of buffer (solution used to neutralize acid or base) within a given system. Usually, the buffer will be sodium bicarbonate.

So the next time you wish to curse something for your muscle burning sensation, remember, it’s not Lactic acid. It’s the most abundant element in the universe: Hydrogen.