Share Post:
A marathon will expose everything you have neglected. The 26.2 miles do not care about your intentions or your confidence. They respond only to the work you have done beforehand, and when that work is missing, the body pays a price that enthusiasm cannot cover.
People sign up for marathons for many reasons. Some want to prove something to themselves.
Others get swept into charity commitments or bucket list ambitions. The gap between registering and actually preparing for the distance often goes unaddressed until race day arrives. By then, the problems have already been set in motion.
Running a marathon without adequate preparation is a medical risk. It is also an unnecessary one, given how predictable the consequences tend to be.
What Happens to the Heart Under Unprepared Stress
The cardiovascular system handles sustained endurance effort through adaptations that develop over months of consistent training. An untrained heart working at marathon intensity for several hours operates outside its conditioned capacity.
Data from 29 million marathon and half-marathon finishers in the United States between 2010 and 2023 recorded 176 cardiac arrests during races.
Full marathons had a cardiac arrest rate of 1.01 per 100,000 finishers, compared to 0.27 per 100,000 for half-marathons. Coronary artery disease accounted for 52% of cases where the cause could be identified. Men experienced higher rates than women, and most cardiac arrests occurred during the final quarter of the race.
The last few miles are when fatigue peaks and the body’s compensatory mechanisms begin to fail. Runners without a training base push through warning signs because they have no frame of reference for what those signs mean.
Fueling Strategy and the Untrained Body
Marathon runners who skip structured preparation often fail to account for how their bodies will process nutrition during prolonged effort.
Products like running gels for athletes, electrolyte drinks, and energy chews require testing over weeks to determine tolerance and timing. An unprepared runner who consumes unfamiliar fuel mid-race risks gastrointestinal distress, compounding the physical strain.
This becomes dangerous when combined with existing hydration problems. Research found 13% of tested runners had hyponatremia, with 0.6% at critical levels. Sodium imbalance worsens when runners drink excessively without matching electrolyte intake, a problem proper training would have revealed.
Muscle Breakdown and Kidney Damage
Marathon running places heavy demands on skeletal muscle. When training has not conditioned the muscles to handle prolonged stress, fibers break down and release their contents into the bloodstream.
This condition, exertional rhabdomyolysis, sends myoglobin into circulation, where it can accumulate in the kidneys.
Heat and dehydration make this worse. Studies of ultra-marathon runners found 57% demonstrated myoglobinuria after races, indicating muscle protein in the urine. Untrained runners face compounded risk because their muscles have not been exposed to the kind of repeated stress that builds resilience.
The kidneys can handle some myoglobin load. They cannot handle excessive amounts, especially when blood flow is already compromised by dehydration.
Acute renal failure is a real possibility. It requires hospitalization and, in severe cases, dialysis.
The Problem with Pain Relievers
Some runners take anti-inflammatory medications before or during races, hoping to manage discomfort.
This creates additional risk. NSAIDs reduce blood flow to the kidneys, which are already under strain from exertion and fluid loss. Combining these drugs with marathon effort amplifies the likelihood of kidney injury.
Research has identified NSAID use as a factor that increases susceptibility to both rhabdomyolysis complications and hyponatremia. Trained runners learn through trial what their bodies can and cannot tolerate. Untrained runners often make decisions based on what seems logical rather than what has been tested.
Why Slower Finishers Face Higher Risks
| Factor | What Happens | Resulting Risk |
| Time on course | 4+ hours of continuous exertion | Greater cumulative strain on the heart, muscles, and joints |
| Sweat loss duration | Prolonged fluid loss | Dehydration and electrolyte imbalance |
| Fluid consumption window | Extended drinking over many hours | Increased hyponatremia risk when sodium replacement is inadequate |
| Muscle loading | Repetitive impact without conditioning | Higher risk of stress fractures and tendinopathies |
| Relative intensity level | Near-max effort for untrained runners | Sustained elevated heart rate and early glycogen depletion |
| Fatigue accumulation | Builds continuously with limited recovery | Breakdown of form, coordination, and protective mechanisms |
| Injury probability | Rises with exposure time | Overuse injuries that may appear days or weeks later |
Those who take more than 4 hours to finish a marathon face an elevated risk for several conditions. Longer time on the course means more time sweating, more time consuming fluids, and more opportunity for electrolyte imbalance to develop.
It also means more cumulative stress on joints, tendons, and muscles that have not been prepared for the load.
Slower paces do not necessarily mean lower intensity. An untrained runner moving at a 12-minute-per-mile pace may be operating at near-maximum effort for their fitness level. Heart rate stays elevated. The body pulls from limited glycogen stores.
Fatigue compounds over hours in ways that a fit runner finishing in 3 hours would not experience.
Injuries That Sideline Runners for Months
Beyond the acute medical events, unprepared marathon attempts frequently result in overuse injuries.
Stress fractures develop when bones have not adapted to repetitive impact. Tendinopathies in the Achilles, patellar, and IT band regions occur when connective tissue is loaded beyond its current tolerance.
These injuries do not always present during the race itself. Some manifest in the days and weeks following, when the accumulated damage becomes apparent. Recovery can take months. Some runners never return to the sport.
What Proper Preparation Actually Requires
A reasonable marathon training plan covers 12 to 20 weeks, depending on the runner’s starting fitness.
It includes progressive increases in weekly mileage, long runs that peak near 20 miles, and recovery periods built into the schedule. It also includes nutrition testing, hydration strategies, and enough time to identify problems before race day.
None of this can be compressed or shortcut. The body adapts on its own timeline. Pushing that timeline creates the conditions for injury and medical emergency.
Running a marathon without adequate preparation is a choice. It is one made easier by the accessibility of race registration and the encouragement of well-meaning friends.
But the consequences remain physiological, and physiology does not negotiate.
