Marathon prep: what actually changes your finish time

A marathon is not a longer half marathon. Most people don't fall apart at kilometre 32 because of fitness, but because they started too fast, ate too little during the race, and stacked their weeks badly for months beforehand. Here are the numbers, not the pep talk.

Mileage: boring and non-negotiable

If the goal is simply to finish, you want 40–55 km per week at peak, spread over 4–5 runs. Sub-4 hours realistically means 60–80 km. Build by the 10 percent rule: if this week was 40 km, next week is 44, not 55. Every fourth week is a down week, cut volume by 25–30 percent and keep the intensity.

A block runs 16–20 weeks if you're already running 25–30 km per week. Starting from zero, give yourself six months of consistent running first, then pick a race.

The three sessions that do the work

Long run

Once a week, building from 16 km to 30–32 km. Going past 32 km isn't worth it: the benefit flattens out and recovery eats three days. Run it 45–75 seconds per kilometre slower than goal marathon pace. Across the block, do 3–4 long runs over 28 km, and in at least two of them run the last 8–10 km at goal pace.

Tempo

20–40 minutes at a pace you could hold for about an hour in a race. Example: 15 minutes warm-up, 2 x 15 minutes tempo with 3 minutes easy jogging between, 10 minutes cool-down.

Intervals

6 x 800 m or 5 x 1000 m at 5 km race pace, with 2–3 minutes of easy jogging between reps. Once a week, and never in the same week as a 30 km long run if you recover slowly.

The rest of the week is 2–3 easy runs of 40–60 minutes at a pace where you can talk in full sentences. The general rule is 80/20: roughly 80 percent of total time easy, 20 percent hard. Injuries come from turning easy days into moderately hard ones.

Strength: twice a week, 30 minutes

Runners skip strength work and then wonder why the knee or the Achilles hurts. Two short sessions per week, on the day after a hard run, never the day before a long run:

• Squat or leg press: 3 sets x 6–8 reps, using a load where you'd have two reps left in the tank
• Romanian deadlift: 3 x 8
• Split squat or lunge: 3 x 8 per leg
• Calf raises, both straight-knee and bent-knee: 3 x 12 each
• Side plank: 3 x 30–45 seconds per side

Add 10 minutes of jumping two or three times a week: 3 x 10 bodyweight jumps or 3 x 60 seconds of skipping rope. That improves running economy, meaning less oxygen used at the same pace.

Fuel: the real reason for the wall

Glycogen stores last roughly 90–120 minutes of running. Everything past that has to be replaced on the move. Aim for 60–90 grams of carbohydrate per hour, and train your gut the way you train your legs: start at 30 g/h on long runs and add 10–15 g every two or three weeks.

Fluid: 400–800 ml per hour, more in heat. If you sweat heavily and leave white salt marks on your shirt, add 300–600 mg of sodium per litre. Breakfast 3 hours before the start: 1–2 g of carbohydrate per kilogram of body weight, so 70–140 g for a 70 kg runner, for example two slices of bread with honey plus a banana. In the last two days before the race, push carbohydrate to 8–10 g per kilogram; you'll gain 1–2 kg on the scale because water binds to glycogen, which is normal and useful.

Nothing new on race day. Not the gel, not the drink, not the shoes, not the breakfast.

Taper and race pacing

Last three weeks: volume minus 20 percent, then minus 40, then minus 60 in race week. Keep the intensity, just make the sessions shorter. Your final long run is three weeks out; the last two days are rest or 20 minutes easy.

The most common mistake is running the first 10 km 15–20 seconds per kilometre faster than planned. You pay for that between kilometre 30 and 38, with interest. Run the first 5 km 5–10 seconds slower than goal pace and cover the second half as fast as or faster than the first. For a realistic goal, multiply your half marathon time by 2.1, or by 2.15–2.2 if this is your first marathon.

When to see a doctor

• Chest pain or pressure, fainting, dizziness with nausea, or an irregular pulse while running: stop immediately and get checked, don't push through it.
• Pinpoint pain on a bone (shin, foot) that gets worse as you run and makes you limp: suspect a stress fracture, stop running and get imaging.
• Cola-coloured urine after a long run, with severe muscle pain and swelling: urgent, this can be rhabdomyolysis.
• Over 35 with a first marathon, plus smoking, high blood pressure, high cholesterol or family heart disease: get a check-up and a stress test before you start the block.
• Performance dropping for three weeks or more, constant fatigue, frequent colds, or loss of menstruation: check ferritin, vitamin D and whether you're eating enough at all.

The short version

• 40–80 km per week over 16–20 weeks, with a down week every fourth week and 10 percent build steps.
• One long run (up to 32 km), one tempo and one interval session per week; everything else easy, 80/20.
• Two 30-minute strength sessions per week: squat, deadlift, split squat, calves, planks, plus jumps.
• 60–90 g of carbohydrate and 400–800 ml of fluid per hour, rehearsed on long runs, nothing new on race day.
• Start the first 5 km slower than goal pace, taper for three weeks, and see a doctor immediately for chest pain or pinpoint bone pain.