Your First Half or Full Marathon, Getting the Body Ready

Story

Connected to · 6

cofactor · 3

Glycogen supercompensation
The second half of a full marathon runs on the glycogen in your legs: in endurance events over about 90 minutes, exhaustion usually arrives together with very low muscle glycogen, and starting with more can postpone fatigue by about 20%; in runs of 60 to 90 minutes the extra glycogen goes unused. Eating somewhat more starchy food for a few days before the race is enough to raise glycogen, without starving first and then flooding.
Gut during exercise
Sugar eaten during a long run has to pass through transporters on the cells of the small intestine before it reaches the muscles; that door has a ceiling, and the excess stays in the gut and causes bloating and diarrhea, so eating more is not always better. The gut can be trained, too: in a randomized trial of 25 runners, eating sugary gels or food repeatedly while running over two weeks cut gut symptoms by about 60%.
Zone 2 training
Endurance training increases the mitochondrial enzymes in muscle, so at the same pace you can use more fat and less glycogen, and glycogen is exactly what runs short in the second half of a marathon. Endurance athletes who train a lot do about 80% of their training at low intensity; this describes how athletes train, and applying it to novices is an inference.

contrast · 3

Running for beginners
Adding distance for a first half marathon follows the same logic as starting to run: the heart and lungs catch up within weeks, tendon and bone far more slowly. Among runners preparing for a half marathon, those who suddenly raised their weekly distance by 20% to 60% had more injuries in the first 21 days, while following a rule of adding 10% a week did not reduce injuries in a randomized trial of novices.
Electrolyte powders
In a long race, drinking more than you lose is more dangerous than running short of salt: it dilutes the sodium in your blood, which is exercise-associated hyponatremia. Sports drinks are hypotonic too, so drinking too much of them is not protective, and when fluid intake is excessive, extra salt cannot prevent it. At the finish of the 2002 Boston Marathon, 13% of runners had hyponatremia, linked to weight gain during the race and finishing in more than 4 hours.
Exercising in the Heat
Headache, nausea or a change in mental state during or after a long race may be heat illness, or it may be hyponatremia from drinking so much that blood sodium is diluted; a bystander cannot tell them apart, and the two can occur together. Any change in mental state is an emergency: call emergency services now, cool the person on the spot in hot weather, and if they have been drinking all along and weigh more rather than less, give them nothing more to drink.

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Stop 1/6

Ready for a half after three months?

THE SHORT ANSWER

The heart, lungs and muscle metabolism catch up within weeks while tendon and bone take months; how fast you can add distance depends on the slowest part to adapt, and what to avoid is a sudden big jump in weekly distance.

WHO IT'S FORFor healthy runners a few months in who want to enter a first half or full marathon; anyone already injured should deal with the injury first.

WHAT IT MEANS FOR YOU

Count the weeks left before the race, then decide whether to enter the half or run a shorter race first.
Chest pain or tightness, or fainting, during exercise, or confusion or vomiting after drinking a lot of water, means stopping and calling emergency services now; in the second case, stop drinking water too.

EVIDENCEGUIDE 2 · REVIEW 4 · RCT 1 · COHORT 2 · OPEN 2 · MECH 1

Where it stops:No trial directly answers whether a few months of running is enough for a half; the link between distance and injury comes from observational studies, and a ready-made percentage rule did not reduce injuries in a trial.

READ THE ORIGINAL

The heart and lungs catch up within weeks while bone and tendon work on a scale of months, so how fast you can add distance depends on the slowest part to adapt. Seven to 10 days into endurance training, the enzymes in the mitochondria (the small structures in cells that produce energy) in your muscles have clearly increased, and a rise in maximal oxygen uptake can be measured within 3 weeks. Yet the core of an adult Achilles tendon is barely renewed for decades, and the tendon training studies pooled in one all lasted at least 8 weeks.

So when you have run for three months, your longest run is 10 kilometers, and you wonder whether you can go straight to a half marathon, the real question is whether your legs have had enough time. No trial has answered it directly; among runners preparing for a half marathon, those whose weekly distance jumped suddenly got injured more in the first few weeks.

This story is for people who have been running for a few months and want to enter their first half or full marathon; the chapters on fuel also apply to long rides.

A step you can take today: count how many weeks are left before the race, then decide whether to enter the half or run a shorter race first.

If you get chest pain or tightness, or faint, while exercising, or become confused or start vomiting after drinking a lot of water, stop and call emergency services now; in the second case, stop drinking water too. See Signs to stop right away.

Educational content, not medical advice — consult a clinician.

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