* Increased production of lactic acid (lactate): During intense exercise, especially when oxygen supply cannot keep up with energy demand (anaerobic metabolism), glucose is broken down to produce ATP (energy) and lactate. The accumulation of lactate is associated with increased hydrogen ions (H+), which lowers the pH.
* Production of carbon dioxide (CO2): Aerobic metabolism also increases during exercise, producing CO2. When CO2 dissolves in bodily fluids (including muscle tissue), it forms carbonic acid, which dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-), thus lowering pH.
* ATP hydrolysis: ATP is broken down to provide energy for muscle contraction. The hydrolysis of ATP releases hydrogen ions (H+), contributing to the decrease in pH.
* Release of hydrogen ions from other metabolic processes: Other metabolic processes in the muscle can also release hydrogen ions.
The drop in pH can contribute to muscle fatigue by interfering with various processes involved in muscle contraction, such as enzyme activity and ion transport.
However, it's important to note that the body has buffering systems to help mitigate the drop in pH, but during intense exercise, these buffering systems can be overwhelmed, leading to a more significant decrease in pH.