Every spring, tens of thousands of Britons line up for the London Marathon, Manchester Marathon, Brighton and dozens of regional 26.2-milers — and a sizeable fraction limp to the start line injured, undertrained or overtrained. Marathon training mistakes are remarkably consistent year after year: the same errors sabotage first-timers and experienced runners alike. Having watched countless training cycles (and made most of these mistakes personally), here’s what to avoid — the errors that turn 16 weeks of dedication into disappointment.
Mistake 1: running every run too fast
The single most common marathon mistake: doing easy runs too fast. Around 80% of marathon training should be genuinely easy — conversational pace, where you could chat in full sentences. Most runners train in the grey zone: too fast to recover, too slow to build real speed. The result is perpetual fatigue, plateaued fitness and, eventually, injury or burnout. Elite marathoners run their easy days embarrassingly slowly; recreational runners should too.
The fix is discipline, not fitness. Learn your easy pace (roughly 60–90 seconds per kilometre slower than marathon pace for most runners) and defend it against your ego. Use the talk test on every easy run — if you can’t speak comfortably, you’re going too fast. Heart-rate monitors help, but perceived effort works fine. Counterintuitively, slowing your easy runs down is what allows your hard sessions to be truly hard, which is where the adaptations live. If you’re new to structured running, our beginner’s running guide establishes the easy-running habit that marathon training depends on.
Mistake 2: the long run errors (too long, too fast, too late)
The long run is marathon training’s cornerstone and its most abused session. Error one: making it too long. Beyond about 3–3.5 hours (roughly 30–32km for most runners), the injury risk and recovery cost outweigh the fitness benefit — yet runners routinely push to 35km+ “for confidence”. Error two: running it too fast. The long run should be easy-paced; racing it every Sunday is how you arrive at the start line exhausted. Error three: the longest run too close to race day — your final 30km+ effort belongs three weeks out, not ten days, because the taper needs time to convert training into freshness.
Also: practise everything on long runs. Fuelling strategy (which gels, how often, with water), kit (nothing new on race day — the most violated rule in marathon running), and pacing discipline. British marathons serve specific gel brands on course — check and train with them, or carry your own. Runners who “try something new on race day” feature in every marathon’s medical tent statistics. The TCS London Marathon’s training resources emphasise rehearsal for exactly this reason.
Mistake 3: skipping the taper (or tapering wrong)
After 14 weeks of building, the taper — 2–3 weeks of reduced volume before race day — feels wrong. Legs feel heavy, phantom niggles appear, and the urge to “test” fitness with a hard run is overwhelming. Runners who skip the taper arrive stale; runners who panic-train through it arrive injured. Trust the process: reduce volume by 40–60% over the final two to three weeks while keeping some intensity (short strides, a few marathon-pace kilometres) so legs stay sharp.
Taper madness (“taper tantrums”) is real and universal — irritability, convinced you’re losing fitness, obsessing over weather forecasts. Fitness doesn’t meaningfully decline in two weeks; freshness increases enormously. Don’t try new foods, don’t get a deep-tissue massage in race week (it can leave muscles sore), don’t start a new stretching regime. The taper is for sleeping, hydrating, carb-loading sensibly (no need for the old 10-plate pasta ritual — just eat normally with slightly more carbs for 2–3 days), and arriving at the start line bored and rested rather than heroic and broken.
Mistake 4: neglecting fuelling, hydration and the wall
“The wall” — glycogen depletion around 30–32km — is optional for well-fuelled runners and mandatory for under-fuelled ones. The mistake is training your legs for 16 weeks while ignoring your stomach. Practise taking on 60–90g of carbohydrate per hour during long runs (gels, chews, sports drink — whatever your stomach tolerates), starting from the first hour, not when you feel empty. By the time you feel the bonk, it’s too late.
Hydration needs rehearsal too, especially for spring marathons when an unseasonable warm day (increasingly common) catches runners out. Drink to thirst at water stations — don’t skip them all, don’t stop at every one either. And the week before: don’t try the “fat-loading” or exotic diet protocols from forums; eat familiar foods, slightly carb-heavier, and avoid anything that risks stomach trouble. Race-day fuelling disasters are almost always caused by novelty, not by the distance itself. Good everyday nutrition underpins the whole cycle — our healthy eating on a budget guide covers fuelling without expensive products.
Mistake 5: ignoring strength, rest and warning signs
Marathoners love running and neglect everything else — until something breaks. Two 20-minute strength sessions weekly (glutes, calves, core, single-leg work) prevent an enormous share of overuse injuries; the evidence for strength training reducing running injuries is strong. Rest days are training too — adaptations happen during recovery, and the runner who “can’t take a day off” is usually the one who can’t take three months off with a stress fracture either.
Learn to distinguish niggles from injuries. A niggle: mild, symmetrical, warms up and disappears during the run, gone afterwards. An injury: sharp, localised, worsening during the run, altering your gait, or persisting into the next day. Running through the former is fine; running through the latter is how 16 weeks becomes a DNS (did not start). The NHS running guidance and England Athletics both stress progressive loading and rest — unglamorous advice that works. And sleep: marathon training on 6 hours a night is building a house on sand.
The bottom line
To avoid the classic marathon training mistakes: run your easy days genuinely easy, cap long runs around 3–3.5 hours at easy pace three weeks out, respect the taper, rehearse fuelling and kit on every long run, and protect the whole cycle with strength work, rest days and honest injury assessment. The marathon rewards the boring, consistent runner — not the heroic one. Sixteen weeks of sensible training beats sixteen weeks of spectacular training followed by six weeks of injury every single time.
Frequently Asked Questions
How long should my longest marathon training run be?
About 30–32km or 3–3.5 hours, whichever comes first, run at easy pace three weeks before race day. Longer runs add injury risk without meaningful extra benefit.
What pace should my easy runs be?
Conversational — you should be able to chat in full sentences. For most runners that’s 60–90 seconds per kilometre slower than marathon pace. If in doubt, slow down.
Should I run the day before the marathon?
A very easy 15–20 minute jog with a few strides is traditional and fine, or complete rest — whichever you practised in training. Nothing new, nothing hard.
How do I avoid hitting the wall?
Take 60–90g of carbs per hour from early in the race, pace conservatively in the first half (most runners go out too fast), and rehearse your fuelling on long runs.
Can I walk during a marathon?
Absolutely — planned walk breaks (e.g., through water stations) are a legitimate strategy used by thousands of finishers, and run-walk often produces faster times than running until collapse.
