Running · 5 min read
The half marathon is run at or very near the second lactate threshold, which makes it the road distance where one measurement explains more of your performance than anywhere else.
By Chris Gkoufas, DVOTION Labs ·
A marathon is run below the second threshold — comfortably below it for most runners, because three or four hours above it is not available to anyone. A half is run at it, or within a few seconds per kilometre of it.
That difference changes what the training is for. In a marathon the threshold sets a ceiling you deliberately stay under, and much of the race is decided by fuelling, economy and how long you hold a fraction of your capacity. In a half, the threshold is the pace. Raise it and the race gets faster; do not, and it does not.
It is the cleanest relationship between a single physiological measurement and a race result in distance running, which is why the half is the distance where testing changes training most directly.
The obvious conclusion — train at half marathon pace often — is the wrong one, and it is the most common error at this distance.
Work at or near the second threshold is productive and it is expensive. A programme built around frequent race-pace running accumulates fatigue faster than it produces adaptation, and the usual result is a runner who feels flat for a block and races slightly worse than their training suggested.
The distribution the research supports is most volume genuinely easy, a smaller proportion hard, and threshold work as a deliberate and limited component rather than the default intensity. That structure depends entirely on the easy work being easy — and easy is defined by the first threshold, not by feel.
For a half marathon, LT2 tells you what to race at and LT1 tells you whether the training around it is sustainable.
Running easy days above the first threshold is the most reliable way to arrive at a threshold session unable to do it properly. The fatigue is subtle, cumulative, and it presents as the hard sessions gradually becoming harder rather than as an obvious problem — which is why it persists for months in programmes that look sensible on paper.
When the first threshold is measured rather than assumed, the easy pace it produces is frequently slower than the runner has been training at. Applying it is uncomfortable for a fortnight and is usually the change that makes the rest of the block work.
Running economy is the oxygen cost of running at a given speed, and it varies substantially between runners with similar aerobic capacity. Over a half marathon, a difference in economy translates directly into a difference in the pace sustainable at the same physiological cost.
It is influenced by biomechanics, neuromuscular characteristics and training history, and it is the determinant most often ignored because it is the least visible on a watch. A runner whose threshold is high and whose race times lag behind it is frequently an economy problem rather than a fitness one.
That is where movement and force data earn their place alongside the physiology — not as an alternative to endurance testing, but as the explanation when the endurance numbers do not account for the race result.
For most runners a half marathon sits between about seventy and a hundred and twenty minutes, which is the region where carbohydrate availability begins to matter without being decisive.
Below roughly an hour it is largely irrelevant. Beyond ninety minutes it starts to be worth planning. In between, whether it matters depends on your glycogen status at the start more than on the race itself, which makes what you did the day before more important than what you carry.
Hydration follows the same logic. Sweat losses over ninety minutes are real and rarely decisive in temperate conditions, and become a genuine factor in a warm race. Knowing your own sweat rate is more useful for a hot half than a cool one, which is a narrower claim than the one usually made for it.
Twelve to sixteen weeks out, so the zones direct the block rather than describe it. That is also roughly the interval over which a threshold change becomes measurable, so a test at the start and a test before the next build gives you a genuine comparison rather than day-to-day noise.
The useful protocol is a blood lactate profile and a maximal respiratory test in the same appointment, run separately so neither interrupts the other. The ventilatory and lactate thresholds are independent readings of related transitions, and for a race run at threshold, having both agree is worth more than having one of them precisely.
A recent race gives you a good estimate of what you could do on that day in those conditions, which is not the same as where your thresholds sit. It also gives you one point rather than the two boundaries the training is built between, and it carries the weather and the course with it.
Less often than most half marathon programmes suggest. Threshold work is productive and costly, and its benefit depends on arriving at it recovered — which is a function of how easy the easy days genuinely are.
Below about an hour, rarely. Beyond ninety minutes, usually worth planning. In between it depends more on your glycogen status at the start than on the race, so what you ate the day before matters more than what you carry.
That pattern usually points at economy or at pacing rather than at fitness. Economy is influenced by biomechanics and neuromuscular factors, which is what movement and force data describe — and it is the determinant least visible from training data alone.
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