How I Ran a Sub-3 Marathon at 45: Structured Training, Carb Loading and Race-Day Fuelling

Breaking three hours in the marathon is a goal that lives rent-free in the head of every serious recreational runner. The pace required — 4:15 per kilometre, 6:51 per mile — is unforgiving. You don’t get a comfortable mile. You get 26.2 miles of “stay on it.” At 45, the margin gets thinner every year you wait.

This April I crossed the line at the adidas Manchester Marathon in 2:55:10. Here’s how I structured the training and the fuelling that carried me through.

Why structured marathon training matters more after 40

Masters runners (40+) recover slower and respond better to consistency than to volume spikes. The block that worked for me peaked at 111km in one week — built on rigid weekly architecture repeated for 14 weeks.

Each week had the same skeleton: Monday recovery, Tuesday speed, Wednesday strength plus easy run, Thursday easy, Friday rest, Saturday LT2 effort built around the local Parkrun, Sunday long run. Contents changed week to week as the block progressed; structure didn’t. That predictability is what lets you string together 14 productive weeks without injury — which, at 45, is the actual hard part.

Total training distance from 1 January to race day: 1,232km (765 miles). The block contained eleven long runs of 25km or more, including a 42.4km marathon simulation six weeks out from race day.

Using Structur to plan, sync and measure marathon fitness

Structur syncs directly with Garmin Connect, so every session lands in the platform automatically. The training plan lives alongside the actual data — every Sunday evening, did this week go to plan? gets answered with numbers, not gut feel.

The most useful metric Structur surfaced wasn’t pace — it was aerobic efficiency on easy runs (pace divided by heart rate). Lower is better. Across the 14 weeks that number dropped steadily, the cleanest signal that the engine is genuinely improving rather than just suffering harder. By the peak of the block, my easy runs were 15-20 seconds per kilometre faster at the same heart rate as in early February.

The three sessions that built sub-3 fitness

Three workouts I’d credit with the result:

The 42.4km long run on 8 March. Done at 4:45/km, six weeks from race day. Time on feet (3 hours 22 minutes) and the psychological weight of having already covered the distance once.

The 30.6km long run on 22 March at 4:15/km. At goal marathon pace, heart rate at 166bpm — comfortably below my lab-tested lactate threshold of 179bpm. The single best predictor of race readiness.

Tuesday 8×1km repeats at 3:32/km. Faster than my lab LT pace, building the speed reserve that made marathon pace feel comfortable rather than hard.

Carb loading for marathon performance: what I actually ate

Carb loading is one of the most evidence-backed practices in endurance sport, and one of the most poorly executed. The target is 8-12 grams of carbohydrate per kilogram of bodyweight per day for the two days before the race. For a 70kg runner that’s 560-840g per day. Most people massively undershoot.

Two days before Manchester, I logged 684g of carbs: porridge, mac and cheese, salmon with rice, custard creams, rice cakes and a litre of chocolate milk. Total: 4,418 calories.

The day before, I logged 607g of carbs: caramel waffles, margherita pizza, more rice with salmon, plus orange juice, tortilla chips, fizzy laces and Coca-Cola. Total: 3,717 calories.

That’s deliberately high in carbs and low in fibre — fibre sits in your gut on race morning. The “boring” foods (white rice, white bread, sweets) are doing real work: maxing out glycogen storage. You’ll feel slightly bloated. That’s the point. You’re storing fuel.

In-race marathon fuelling: SiS Beta Fuel every 25 minutes

The marathon fuelling target is 60-90g of carbs per hour, with research increasingly supporting the high end.

My strategy was simple and rehearsed: one SiS Beta Fuel gel (40g of carbs) 15 minutes before the start, then one every 25 minutes during the race. Sips of water at every aid station — not full cups, just enough to wash the gel down.

Roughly seven gels across 2:55 — around 280g of carbs, 95g per hour, at the upper end of what most runners can absorb. Beta Fuel uses a 1:0.8 maltodextrin-to-fructose ratio: glucose and fructose use different intestinal transporters, so combining them lets you take in more carbs per hour without overwhelming the gut.

Practising this exact protocol in training is non-negotiable. Every long run from 8 March onwards used the same gel, the same timing, the same water strategy. Race day was rehearsal, not experiment.

The race: a negative split built on data, not bravery

The race played out cleanly: first half 1:28:35, second half 1:26:40. A negative split of 1:55. The fastest kilometre of the entire marathon was km 35, in 3:55.

The training data had been telling me for weeks that I was capable of this. The discipline on race day was trusting it and not running off the start line at 4:02 pace when 4:10 was the right call. Average heart rate was 172bpm — below my lactate threshold — the marker of a well-paced effort.

What sub-3 at 45 actually takes

Structure. A plan you can follow, synced to a tool that tells you whether you’re on it. Long runs — lots, including one near the marathon distance. Specific sessions at specific paces, week after week. A carb load that feels excessive but is exactly what the science calls for. A rehearsed fuelling strategy you’ve used so often that race day is the easy bit.

Age is a factor, but it’s not the limiting one. Build the plan, track the data, eat the carbs, take the gels. Trust the work.

Train smarter for your next marathon. Structur syncs with Garmin Connect to plan, track and analyse every session of your training block — so you know whether you’re really on track for your goal time.

Sub-3 marathon FAQs