Metabolic By-products

The human body is a site of continuous metabolic processes that involve the breakdown and build-up of numerous substances. Both muscles and fascia, as integral components of this complex system, are deeply involved in metabolic activities and, consequently, in waste and fluid production and removal.

a. Lactic Acid

Lactic acid, or lactate, is a key by-product of anaerobic glycolysis, a metabolic process that occurs within muscle cells during intense exercise when the oxygen demand surpasses the supply (Robergs et al., 2004). Under these conditions, glucose or glycogen is metabolized into pyruvate, which is subsequently converted into lactate. Although lactate is often viewed as a ‘waste’ product, it’s also a valuable energy source, as it can be converted back into pyruvate and utilized by mitochondria for ATP production when oxygen becomes available. The accumulation of lactate, along with H+ ions, is associated with muscle fatigue and decreased muscle contractility, which was traditionally attributed to ‘lactic acidosis’. However, contemporary research indicates that this process is far more complex and involves multiple factors (Weston et al., 2014).

b. Carbon Dioxide

Carbon dioxide (CO2) is another significant by-product of cellular metabolism, formed in the mitochondria during the process of aerobic respiration. Oxygen is used to oxidize glucose, producing ATP, water, and CO2. The CO2 is diffused out of the muscle cells into the bloodstream, where it’s converted into bicarbonate and hydrogen ions. Bicarbonate acts as a buffer, helping to maintain the blood’s pH, while CO2 is carried to the lungs to be exhaled (Silverthorn, 2018). CO2 accumulation in tissues can lead to hypercapnia, which can disrupt the acid-base balance and negatively impact muscle function.

Fluid accumulation in fascia and muscles, often seen as edema, can be a result of several factors. These can include local inflammation due to injury or disease, changes in hydrostatic and osmotic pressures, and disruption of lymphatic drainage. Understanding these processes is essential to comprehend how the accumulation of metabolic by-products and fluids can impact muscle and fascial function and, consequently, mobility and performance.


  1. Robergs, R. A., Ghiasvand, F., & Parker, D. (2004). Biochemistry of exercise-induced metabolic acidosis. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 287(3), R502-R516.
  2. Weston, A. R., Myburgh, K. H., Lindsay, F. H., Dennis, S. C., Noakes, T. D., & Hawley, J. A. (1997). Skeletal muscle buffering capacity and endurance performance after high-intensity interval training by well-trained cyclists. European journal of applied physiology and occupational physiology, 75(1), 7-13.
  3. Silverthorn, D. U. (2018). Human physiology: an integrated approach. Pearson.