Unlocking Your Full Potential: The Lactate Shuttle Explained
In running culture, “lactate” has been misunderstood for decades. It gets blamed for heavy legs, burning quads, and that familiar moment when pace suddenly feels expensive. But lactate itself isn’t the villain. In many ways, it’s the opposite - a valuable energy currency your body uses to keep you moving when intensity rises.
The lactate shuttle is one of the most useful performance concepts a runner can understand. Not because it turns you into a physiology nerd, but because it changes how you train: where you place your easy runs, why threshold matters, and why aerobic fitness makes “hard” feel less hard.
Let’s break it down simply, properly, and in a way you can apply immediately.
Lactate: Clearing Up the Biggest Myth
First, the myth: lactate causes fatigue.
What you actually feel in hard running (the burn, the loss of smoothness, the rising discomfort) is more closely linked to the accumulation of hydrogen ions (increasing acidity) and a cascade of other stress signals. Lactate production happens alongside that process, so it gets blamed by association.
In reality, lactate is a protective and useful by-product of anaerobic energy production. When you accelerate, surge, or hold a demanding effort, your muscles need energy quickly. One of the fastest ways to produce that energy is through glycolysis (breaking down glucose). Under high intensity, glycolysis can outpace your ability to process the end-products aerobically, so the body converts pyruvate into lactate.
That conversion isn’t a mistake, it’s a solution. Lactate helps keep energy production moving forward, buys time under pressure, and provides a transportable fuel that can be used elsewhere in the body.
“Lactate isn’t failure — it’s the body finding a way to keep going.”
A Mako athlete during a controlled threshold session.
What Is the Lactate Shuttle?
The lactate shuttle is the process of moving lactate from where it’s produced to where it can be used.
Think of it like this: one muscle is working hard and producing lactate rapidly. Instead of that lactate “pooling” as useless waste, your body moves it into the bloodstream and transports it to tissues that can use it efficiently, including:
- Other muscle fibres (especially more aerobic, fatigue-resistant fibres)
- The heart (which readily uses lactate as fuel)
- The liver (where lactate can be converted back into glucose via the Cori cycle)
So lactate becomes a courier - a way of relocating energy from the busiest areas to places that can process it. That’s why elite endurance athletes can operate at high speeds for longer: they’re not “avoiding” lactate. They’re producing it and using it more efficiently.
The performance implication is huge: the goal is not zero lactate. The goal is efficient lactate recycling.
“The best runners don’t produce less lactate. They recycle it faster.”
Why Aerobic Fitness Makes the Lactate Shuttle Better
Aerobic fitness isn’t just “good for distance.” It upgrades the entire system that manages intensity. When aerobic capacity improves, the lactate shuttle becomes more efficient in three major ways.
1) Improved Oxygen Delivery
As your aerobic system develops, your cardiovascular delivery improves: greater stroke volume, better capillarisation, and improved oxygen transport to working muscles. That means a larger percentage of your energy can be produced aerobically at a given pace.
When oxygen supply meets demand more effectively, you rely less on high-rate anaerobic glycolysis. Lactate still appears — but the system is calmer, more controlled, and easier to sustain.
2) Enhanced Mitochondrial Function
Mitochondria are where aerobic energy production happens — and they’re also where lactate can be used as fuel. With consistent aerobic training, mitochondria become more numerous and more efficient. This increases your capacity to convert lactate back into usable energy.
In practical terms: the fitter your aerobic system, the more “space” you have to process lactate without tipping into runaway fatigue.
3) Faster Lactate Clearance and Distribution
Aerobic training improves the transport and uptake mechanisms involved in moving lactate between tissues. The body becomes better at shuttling lactate away from the most stressed fibres and toward tissues that can use it.
That’s why aerobic fitness often looks like “staying smooth” at faster paces. It’s not just mental toughness — it’s improved internal logistics.
A Mako athlete in steady-state effort, relaxed stride, controlled breathing
Where “Threshold” Fits In (And Why Most Runners Misuse It)
Threshold training is often marketed as the magic zone, the “sweet spot” where you become faster without needing to sprint. That’s mostly true, but only if you understand what threshold work is trying to achieve.
Threshold is best viewed as the highest intensity you can sustain while maintaining a relatively stable internal environment, where lactate production and lactate clearance stay in balance. The moment the effort rises beyond that point, lactate (and the wider fatigue signal) accumulates faster than you can manage, and pace becomes time-limited.
The common mistake is turning threshold sessions into mini races. When runners push threshold too hard, they shift into a more anaerobic environment, which changes the training stimulus. Instead of improving lactate turnover and aerobic efficiency, they create excessive fatigue and need longer recovery (often at the cost of consistent weekly volume).
Good threshold training should feel controlled, sustainable, and repeatable. If you finish a threshold session shattered, you probably weren’t training threshold. Instead you were probably training your ability to suffer.
Training Strategies That Improve Lactate Shuttle Efficiency
The lactate shuttle improves primarily through aerobic development and smart exposure to controlled intensity. You don’t need complicated workouts — you need the right distribution of stress.
1) Keep Easy Runs Easy
This is the unglamorous foundation. Long, slow running (often referred to as Zone 1–2) creates prolonged exposure to aerobic conditions. It encourages mitochondrial development, capillarisation, and improved fat oxidation — all of which reduce reliance on fast glycolysis at moderate speeds.
The biggest mistake runners make is running easy days too hard. That turns the week into a constant grey zone — stressful enough to accumulate fatigue, not specific enough to drive the best adaptations.
If you want a better lactate system, you need a bigger aerobic engine. Easy running is where it’s built.
2) True Threshold Work (The Sweet Spot)
Threshold training teaches the body to manage lactate intelligently, producing it, transporting it, and using it without compromise. The key is staying in the correct zone.
Examples (choose one approach):
- Tempo blocks: 2–3 × 8-10 minutes at controlled sub - threshold effort, 2–3 minutes easy between
- Threshold intervals: 4–6 × 1 mile (or 6 - 10 × 1 km) at threshold, short recoveries
Threshold should feel like you’re working hard, but not fighting for survival. You should finish knowing you could have done more.
3) Consistency Over Complexity
The lactate shuttle improves through repeated exposure over weeks and months. A single session doesn’t change you. A season of consistent aerobic training does.
This is where runners often lose the plot: chasing novelty rather than building a base. The physiology is predictable. The discipline is the hard part.
How You’ll Notice It’s Working
When the lactate shuttle becomes more efficient, performance changes in subtle but unmistakable ways:
- Hard paces feel smoother - less tension, less fighting
- You recover faster between reps and sessions
- Late-race pace is more available because you’ve preserved internal control
- Surges don’t destroy you - you can change gears and settle again
In other words, your system becomes less reactive. You stop “hanging on” and start “holding pace.”
Coach’s Insight
When athletes tell me they “need to improve lactate threshold,” they often mean they want to suffer less at faster paces. And that’s fair enough. However they think working above threshold is the solution. I can tell you now the solution is rarely more intensity - it’s better structure.
The best athletes with the best lactate systems focus on building through disciplined easy running, well-controlled threshold work, and consistency. Not hero workouts. Not weekly time trials. Just intelligent training repeated long enough for the body to adapt.
If you’re stuck in a cycle of feeling flat, constantly sore, or unable to hit paces you “should” be able to, the issue is often that your week is too hard too often. Lactate management improves when your easy days actually restore you and your hard days are appropriately targeted.
Final Takeaway
The lactate shuttle is not a fringe concept, it’s a core performance mechanism. Lactate is fuel, and the ability to transport and reuse it separates runners who fade from runners who finish.
Build aerobic fitness, respect easy running, and treat threshold as a controlled training zone and not a proving ground. Over time, you won’t just run faster. You’ll run faster with more control.
If you want deeper guidance on structuring your weeks for endurance, recovery, and performance, explore the Mako Lab for practical resources designed to make training simple, scientific, and sustainable.
If you enjoyed this article, why not take the next step?
