When the Miles Start to Bite: Ultra-Endurance Injuries from Shin Stress to Foot Blisters

Ultra-endurance events push the body into territory most people never visit: back-to-back marathon distances, multi-day stage races, hundred mile runs, long-distance treks, and ultra trail races.

You accumulate:

• Tens of thousands of steps
• Hours of repetitive loading on hard or uneven ground
• Heat, sweat, moisture, and grit inside shoes
• Sleep deprivation and decision fatigue

Under this kind of stress, certain problems show up again and again. Two of the most common and performance-destroying are:

• Shin stress injuries (often medial tibial stress syndrome, commonly called shin splints, and the spectrum towards tibial stress fracture)
• Foot blisters and skin breakdown, which are among the top reasons for medical visits in ultramarathons

On top of this, ultra-endurance athletes also face internal threats like exercise associated hyponatremia, gastrointestinal problems, and heat-related illness.

Understanding how these injuries develop—and how to prevent and manage them—is essential if you want to enjoy long events and protect your long-term health.

Medial tibial stress syndrome is an overuse injury where the bone and soft tissues along the inner border of the shin bone become overloaded. It is characterised by exercise-induced pain along the lower two thirds of the tibia and sits on a continuum that can progress to tibial stress fracture if ignored.

Studies suggest:

• Exercise-induced shin pain accounts for about 10–20 percent of injuries in runners and up to 60 percent of lower limb overuse injuries.
• Up to 70 percent of runners may develop some form of overuse injury, including medial tibial stress syndrome, over a one-year period.

In ultra-endurance events, where training volume and race distance can be extreme, shin pain is practically a predictable risk if load is not managed.

Key drivers of medial tibial stress syndrome and related bone stress injuries include:

• Rapid increase in mileage or climbing, especially downhill
• Repetitive impact on hard or cambered surfaces
• Biomechanical factors such as overpronation, weak calf muscles, or hip weakness
• Inadequate recovery between long or intense sessions
• Low bone density or energy deficiency in some athletes

Ultra runners often ramp up distance and back-to-back long runs too quickly, or stack heavy training on top of busy work and life stress. The shin bone and attached tissues simply do not get enough time to repair.

During training or an event, watch for:

• Diffuse aching or burning along the inner border of the shin that starts with running or walking and settles with rest
• Pain that is worse at the beginning of a run, eases as you warm up, and then returns later in the session
• Tenderness when you press along a broad zone of the inner shin

These are classic features of medial tibial stress syndrome. [Image of medial tibial stress syndrome anatomy]

A key danger in ultra-endurance athletes is pushing through this pain for weeks. Over time, the pain may:

• Localise to a smaller area
• Persist even at rest or at night
• Be painful when hopping on that leg

These changes can signal a developing tibial stress fracture, which is a more serious injury that usually requires a significant break from running and sometimes use of a boot or crutches.

For most athletes, the best strategy is to act early rather than waiting for a scan to confirm a fracture. Evidence-informed steps include:

• Reducing running volume, especially long and downhill runs, for several weeks
• Substituting low-impact cross-training such as cycling or deep-water running
• Strengthening calf muscles, intrinsic foot muscles, and hip stabilisers
• Checking footwear for wear and appropriate support
• Considering a gait assessment to address biomechanical overload

If shin pain is focal, severe, or persists despite deloading, medical review and imaging such as magnetic resonance imaging or bone scan are important to rule out stress fracture.

Foot blisters are one of the most common injuries in long-distance and ultra-endurance events. Research has shown:

• Blister incidence in marathons has been reported as high as 39 percent.
• In multistage ultramarathons, reports show blister rates between 76 and 100 percent and foot care accounting for up to 74–76 percent of all medical visits.
• A history of previous blisters is one of the strongest risk factors for new blister formation in ultramarathon trail runners.

Blisters are often dismissed as “minor,” yet they can completely change gait, trigger compensation injuries, and force withdrawals from long events.

Blisters are caused by repetitive friction and shear forces between layers of skin when the outer surface remains relatively fixed against sock or shoe while deeper layers move. Moisture, heat, and small debris make this worse.

Common factors in ultra-endurance events:

• Swelling of the feet over many hours, making shoes effectively “smaller”
• Socks that hold moisture or wrinkle
• Grit and small stones entering shoes on trails or sand
• Downhill running, which pushes toes against the front of the shoe
• Long stages without opportunities to change socks or attend to hot spots

Areas most often affected include the heel, ball of the foot, under the big toe joint, and between the toes.

Evidence and expert consensus suggest several effective strategies:

1. Footwear fit and gait assessment
   • Get professionally fitted shoes with enough length and volume to allow for swelling.
   • Consider gait analysis to correct excessive pronation or other biomechanics that cause pressure points.
2. Moisture management
   • Use moisture-wicking socks (synthetic or wool blends rather than cotton).
   • Consider double-layer socks or toe socks for some runners.
   • Change socks at aid stations or stage ends, especially in hot or wet conditions.
3. Friction reduction
   • Apply lubricants or anti-chafing products to common hot spot areas.
   • Use protective patches such as moleskin, hydrocolloid dressings, or tape on high-risk areas before the race starts.
4. Gradual load build-up
   • Increase weekly distance gradually so that calluses form in a controlled way without thick, hard callus build-up that can crack.
5. Debris control
   • Use gaiters in sandy or rocky terrain.
   • Check and clear shoes regularly during training runs and races.

Once a blister forms, the goal is to limit further damage and prevent infection. Good field care includes:

• Stopping early when you feel a “hot spot” and applying tape or padding before a full blister develops
• For intact blisters, using donut-shaped padding to offload the area and keeping the roof intact where possible
• If a blister must be drained for functional reasons, using sterile technique and keeping the overlying skin as a natural dressing, then covering with an appropriate dressing
• Watching for signs of infection such as spreading redness, increased pain, or pus, which need medical review

For multi-day events, proactive foot care at the end of each stage is as important as nutrition and sleep.

While shin stress and blisters top the list, ultra-endurance athletes also face a range of musculoskeletal and internal problems.

Prolonged running or hiking causes repeated eccentric loading of muscles, especially in downhills and late-race stages. Laboratory studies in ultra-marathon runners show substantial muscle damage markers and reduced muscle function after long events.

Common clinical issues include:

• Calf muscle strains, particularly in under-trained or fatigued runners
• Achilles tendon and patellar tendon pain from repetitive loading
• Hip and iliotibial band pain from cumulative time on uneven or cambered surfaces

Strength training, gradual build-up of downhill running, and regular mobility work can help reduce these problems.

Ultra events last long enough that internal physiology becomes a major factor. Key issues include:

• Exercise associated hyponatremia – low sodium concentration in the blood due to excessive intake of hypotonic fluids, sometimes combined with large sweat sodium losses.
  • Symptoms can range from mild nausea and headache to confusion, seizures, and even death in severe cases.
  • It has been repeatedly documented in ultra-marathon case series.
• Gastrointestinal problems – nausea, vomiting, bloating, diarrhoea and abdominal cramps are among the most common reasons for runners failing to finish ultramarathons.
• Heat-related illness – when ultra events are held in hot, humid conditions, heat exhaustion and heat stroke become serious risks, especially if pace and clothing are not adjusted.

Carefully planned pacing, nutrition, and fluid strategies that are tested in training are crucial to minimise these risks.

For shin stress and other bone injuries, the research on medial tibial stress syndrome clearly highlights rapid, unplanned increases in training volume and intensity as a core cause.

Ultra-athletes should:

• Increase weekly distance gradually over months, not weeks
• Use cut-back weeks to allow for recovery
• Avoid stacking multiple very long or very intense sessions back to back without adaptation

To protect bones, tendons, and muscles:

• Use a year-round strength programme targeting calves, quadriceps, hamstrings, hips, and core
• Gradually include controlled downhill sessions so that the body adapts to eccentric load

This reduces both shin stress and overall muscle damage during long events.

For blister prevention, plan well before race day:

• Test shoes and socks on progressively longer runs, including in heat and on terrain similar to race conditions
• Trim nails, manage hard calluses, and keep skin supple with regular moisturising in the weeks before the event
• Identify hot spots in training and pre-tape those areas for the race

For internal issues:

• Avoid overdrinking plain water “just in case”; base fluid intake on thirst and conditions
• Use drinks and foods that provide some sodium, especially in hot events or if you sweat heavily
• Test all race fuels in training to identify gastrointestinal triggers
• Develop a flexible fueling plan that allows for slower intake during periods of nausea

Starting too fast is a classic trigger for both shin pain and general overuse during an ultra event. Aim for:

• Conservative pacing early, even if you feel fresh
• Short, quick steps on downhills to reduce braking forces on the shins
• Occasional walk breaks to vary loading patterns and give tissues a micro-rest

If you feel shin pain building during an event:

• Shorten stride and reduce downhill intensity
• Take brief walking segments on steep or hard-surface sections
• Consider using compression sleeves if you have found them helpful in training (though evidence is mixed)

If pain localises sharply, worsens with hopping, or makes weight-bearing difficult, this is a sign to stop and seek medical assessment rather than pushing on.

For blisters and hot spots:

• React early: stop at aid stations to check feet and adjust socks or shoes
• Apply tape, pads, or lubricant to irritated spots before they form large blisters
• Allow extra time in your race plan for quick foot-care interventions

This may feel “slow” in the moment, but it saves much more time and pain later.

During long events:

• Drink to thirst rather than sticking to a rigid “x cups per hour” target in all conditions
• Be cautious about taking in very large volumes of plain water without electrolytes, especially if you are a slower athlete with long race times.
• Take nausea, confusion, or sudden lethargy seriously—these can be signs of hyponatremia, heat illness, or other serious issues, not just “toughing it out.”

Ultra-endurance culture sometimes glorifies suffering, but there are clear situations where continuing is not worth the risk:

• Sharp, focal shin pain that worsens with each step or prevents hopping on that leg (possible stress fracture)
• Blisters with extensive skin loss, spreading redness, or signs of infection
• Neurological symptoms such as confusion, seizures, or severe headache (possible hyponatremia or heat stroke)
• Chest pain, severe shortness of breath, or sudden collapse

Ultra-endurance events will always be there next season; a tibial stress fracture, infected blister, or episode of severe hyponatremia can take you out of sport for months—or worse.

• Ultra-endurance events dramatically increase the risk of shin stress injuries and foot blisters, which are among the most common reasons for pain, performance loss, and medical visits.
• Medial tibial stress syndrome is an early warning sign of bone overload; if ignored, it can progress to stress fracture. Acting early with load management and strength work is crucial.
• Foot blisters are extremely common in ultra runners, but targeted strategies with footwear, socks, moisture management, and proactive foot care can significantly reduce incidence and severity.
• Internal problems such as exercise associated hyponatremia, gastrointestinal distress, and heat illness are serious threats in long events and require careful planning of pacing, nutrition, and hydration.

Ultra-endurance success is not just about mental toughness; it is about smart preparation and early attention to warning signs. Protect your shins, protect your feet, and respect the physiology behind very long efforts—so you can enjoy big adventures now and keep running, hiking, or racing for many years to come.