09/03/2026
Lactate isn’t a waste product when running, It’s a fuel
For years people were told lactate was the thing that made your legs burn and forced you to slow down. But modern exercise physiology shows the opposite.
When you run hard, your muscles break down glucose through glycolysis to produce energy. One of the byproducts of this process is lactate. Instead of being useless, lactate becomes a valuable energy shuttle.
That lactate leaves the working muscle cells and enters the bloodstream. From there it can be transported to other muscles, the heart, and even back into the same muscle fibres.
Slow twitch muscle fibres and the heart are especially good at taking up lactate and converting it back into energy inside the mitochondria. The liver can also convert lactate back into glucose through a process called the Cori cycle.
In simple terms, when intensity increases your body creates lactate, moves it around the body, and reuses it as fuel to keep producing energy.
The better trained you are, the better your body becomes at clearing and reusing lactate. That is why endurance training improves what we call lactate threshold.
So lactate isn’t the enemy.
It’s part of the engine that keeps you moving faster for longer.
