Studies of marathon training cohorts report injury rates between 50 and 90% across a single training block. Most of those injuries trace back to a small set of preventable errors, not bad luck or genetics. The seven mistakes below show up in study after study, and each one has a corrective fix that is well-known to coaches and sports medicine clinicians. Avoiding even three of these errors typically separates a smooth training block from a derailed one.
1. Excessive Weekly Mileage Increases
The single biggest cause of running injury is a sudden jump in training volume. Recent research on running-related injuries suggests that the danger often comes from one outsized session rather than from steady weekly increases, with single-run spikes above 110% of the longest run from the prior month producing a 64% rise in overuse injury risk. The standard advice to cap weekly mileage growth at around 10% works as a soft target, but the more important rule is to avoid one-day surges that the body has not seen before.
A safer approach is to add 10 to 15% per week to total mileage and avoid pushing any single long run more than two miles past the previous longest run. Stress fractures and tendinopathies cluster in athletes who break both rules at once.
2. Skipping Strength Work
Running alone does not build the muscle strength needed to absorb impact and maintain form across late-race miles. Hip, glute, and core weakness produce the compensatory patterns that trigger knee pain, Achilles tendon issues, and IT band problems. Two short strength sessions per week, focused on single-leg work, hip abduction, and core stability, reduce injury rates in trial data by 30 to 50%.
The standard objection is time. The standard answer is that strength work pays back its time cost through fewer missed weeks of training. A skipped 30-minute lift session is cheap. A six-week injury layoff is not.
3. Inadequate Long-Run Fueling
Most runners underfuel their long runs. The published target is 40 to 80 grams of carbohydrate per hour for sessions over 90 minutes, yet survey data from amateur marathon training cohorts show the average actual intake closer to 20 grams per hour. The mismatch produces glycogen depletion in the final miles of long runs, which trains the body to bonk rather than to absorb fuel.
Practice with the exact race-day fuel during long runs is the standard fix. The gut adapts to higher carbohydrate intake across weeks of progressively raised dosing. Race day is the worst time to find out that 80 grams per hour produces stomach cramps that 40 grams did not.
4. Running Easy Days Too Hard
The 80/20 rule, which calls for 80% of weekly running at conversational easy pace and 20% at moderate or hard intensity, holds up across decades of training science. Most amateur runners flip this ratio, running their easy days at a moderate-hard pace because it feels productive and looking at finishing splits is more rewarding than logging slow miles.
The cost is fatigue accumulation that limits the quality of the genuinely hard sessions. The fix is humility on easy days. If a planned easy day registers a heart rate within 10 beats of the threshold pace, the day should be slower. The Guardian feature on the run-walk method covers one extreme version of this fix, where easy days alternate run intervals with walk intervals to keep the average heart rate genuinely low.
5. Hydration and Electrolyte Errors
The most common race-week hydration error is overdrinking plain water in the final 24 hours, which dilutes blood sodium and shows up as a heavy, sluggish feeling on race morning. The most common in-training error is undertraining the hydration plan during long runs, leaving race day as the first time the runner uses sports drinks or salt tablets at the planned dose.
Most runners adapt fastest to using an electrolyte powder on every long run during the build, with the same product, the same flavor, and the same dose they plan to use on race day. The salt and fluid combination that suits a runner is partly individual, and the only way to dial it in is to test the plan repeatedly under training conditions. The Intermountain Healthcare guide on marathon training advises a similar approach, with the pre-race week reserved for rehearsing what already works rather than introducing new variables.
6. Improper Tapering
Most amateur runners taper by reducing both volume and intensity. The intensity cut is the mistake. Three weeks of slow easy mileage with no fast running leaves the legs feeling flat on race morning. The professional approach reduces volume by 40 to 60% across three weeks while keeping the threshold runs, race-pace efforts, and short fast strides at full speed. The total time on the legs drops, but the neuromuscular system stays sharp.
The other taper mistake is panic mileage. A runner who feels undertrained in the final week often crams in extra runs that produce only fatigue. The race result depends on what was banked across the previous 12 weeks. Adding mileage in the final 7 to 10 days does not raise fitness and can produce minor injuries that derail the race.
7. New Equipment on Race Day
Race-day surprises usually come from new shoes, new gear, new fuel, or new pre-race meals. Each one introduces an unknown variable into the most stressful athletic effort the runner will produce all year. The standard rule, repeated across every coaching guide, is to use only equipment and food that have been tested across at least two long runs. The AARP feature on training tips for older runners makes the same point, with extra emphasis on shoe rotation to avoid breaking in fresh foam in the final weeks.
The shoe failure mode is the most painful. Carbon-plated racing shoes fit tighter than training shoes for some runners, and the first marathon in a new pair produces blisters that early-mile runners would have caught during a 20-mile training run. The Orthopaedic & Spine Center of the Rockies guide on marathon training injuries notes that race-day equipment changes are one of the predictable causes of finish-line breakdowns.
What the Pattern Reveals
The seven mistakes share a common shape. Each one is the result of doing more, doing harder, or doing newer than the training plan calls for, in the belief that extra effort or extra novelty will buy a faster finish time. Most often, the opposite is true. Trained runners who hit moderate weekly increases, restraint on easy days, practiced fueling and hydration, careful taper, and tested race-day gear post the fastest times relative to their fitness level. The discipline is not glamorous, and the cost of breaking it is paid in injury weeks, missed sessions, and disappointing race finishes that the runner will trace back to a single avoidable mistake from the training block.
