Lactate Overview

Lactate: More Than a Waste Product

• Lactate has more important functions than just being a metabolic waste product.

Enantiomers of Lactate

• Enantiomers are molecules that are mirror images of each other.
• The predominant form in the human body is the L+ version.

Lactate and Exercise Intensity

• With increasing exercise intensity, more lactate is produced through fast glycolysis.
• Lactate threshold can be determined through:
  • Visual determination.
  • Dmax method (drawing a linear line and then looking at the perpendicular line with the greatest distance).
  • Onset of blood lactate accumulation (set at $4$ mmol).

Lactate as a Signaling Molecule

• Low Intensity Exercise:
  • Role in norepinephrine release and glucose metabolism.
  • Increase ventilation and vasodilation.
• Moderate to High Intensity:
  • Continuing effects on norepinephrine, glucose metabolism.
  • Mimics hypoxic environments.
• Severe Intensity:
  • Signals pain receptors.

Lactate Production Under Aerobic Conditions

• There is some evidence that suggests small amounts of lactate are produced even under fully aerobic conditions.

Lactate Shuttle Hypothesis

• Lactate can be uptaken by different cells and tissues because it is shuttled to them.
• Glucose is broken down into pyruvate.
• Pyruvate can also be converted to lactate via the enzyme lactate dehydrogenase.

Lactate Shuttling

• Lactate can be shuttled from one muscle fibre to another and also various parts of the body.
• Fast twitch fibres (producers of lactate) -> slow twitch muscle fibres.
• Lactate can be shuttled into the circulation where it can travel to the lung, heart, brain, liver and kidneys.

Lactate and the Cori Cycle

• Pyruvate and lactate formed in the muscle can circulate in the bloodstream to the liver and kidney.
• There carboxylic acids can be synthesised to form glucose.

Lactate's Influence on Exercise-Related Adaptations

• $HIF-1$ (hypoxic inducible factor one) activates signals which favour lactate production.
• Lactate also indirectly affects $HIF-1$.
• $PGC$ one alpha (a master switch of HIT adaptations) controls lactate transport, but lactate also affects alpha.

Lactate as a Signaling Molecule (Detailed)

• Lactate might influence the lungs to increase pulmonary ventilation during exercise.
• Thought to increase blood vessel formation through angiogenesis.
• Impact on tumour cells by reducing the amount of tumor genesis or the creation of tumor cells.
• Myokines: cytokines and other peptides that are produced, expressed and released by muscle fibres and exert either autocrine, paracrine or endocrine effects.
• Exokines: released in response to acute or chronic exercise.