The short answer
Prepare your feet for a 100K by rehearsing the whole system: shoe and sock fit, lacing, swelling allowance, moisture, debris, terrain, toenail care, hot-spot response and any tape or lubricant you actually plan to use. Change one element at a time and test it during progressively longer race-specific sessions.
Paper-tape trials in ultramarathon settings have reported conflicting results: one study found a protective effect at taped sites, while an earlier trial did not find significant overall prevention.1 That is the right lesson—tape may help some sites and athletes, but it is not a universal shield.
Start with the source of friction
A blister is not simply “bad socks.” Look for the repeated interaction:
- shoe too short, narrow, loose or unstable;
- sock seam, fold or retained moisture;
- debris inside the shoe;
- lacing that allows sliding or compresses the foot;
- downhill braking or side-hill movement;
- water crossings and slow drying;
- swelling during long duration;
- callus edge, nail contact or another focal pressure point.
Trail-running injury reviews describe blisters and skin problems among a wider set of race issues, but incidence and risk estimates vary by event and methods.4 Use your own repeated hot-spot location as the immediate problem to solve.
Build a foot map
After selected long sessions, inspect both feet in good light and record:
| Zone | What you felt | What changed during the session |
|---|---|---|
| Toes and nails | Contact, pressure, tenderness | Descents, swelling, shoe length |
| Forefoot | Heat, rubbing, numbness | Sock moisture, width, debris |
| Arch | Edge pressure or tape irritation | Insole, seam, adhesive |
| Heel | Lift, rub or pressure | Lacing, heel hold, sock thickness |
| Ankle | Collar or gaiter irritation | Debris, shoe collar, terrain |
Photograph only for your own comparison or clinician if appropriate. Do not diagnose infection or tissue injury from an online image.
Test the base system first
Before adding tape, powder or lubricant, establish a stable shoe-sock combination.
Shoe
- Enough room for the foot under expected duration and descent.
- Secure enough that the foot does not repeatedly slide.
- Used on similar terrain before the event.
- Lacing that can be adjusted without creating numbness.
- No new race-week model or size guess.
Sock
- Smooth fit without folds.
- Material and thickness tested when wet and dry.
- Compatible with the shoe’s volume.
- Spare pair only if the event plan and prior tests justify it.
The “best” combination is the one that remains comfortable and controllable in your conditions, not the one with the most technical features.
A four-rehearsal progression
Rehearsal 1: one-variable test
Use an easy hour on familiar terrain. Change only the sock, lacing or other selected variable. Stop if numbness, sharp pain or skin damage begins.
Rehearsal 2: moisture test
Where safe and realistic, test the system in rain, humidity or a controlled wet section. Do not create dangerous cold exposure. Record drying, bunching and hot spots.
Rehearsal 3: descent and swelling test
Use a longer trail session with representative descents. Check toe contact, heel hold and lacing before and after swelling. The 100K downhill progression should already make the terrain dose recoverable.
Rehearsal 4: aid-station treatment
At a planned stop, practise removing debris, drying where possible, changing socks or applying the exact previously tested protection. Time the sequence, but do not rush skin inspection.
If you test tape
Use a conservative protocol:
- choose one known hot-spot area;
- test the tape on intact skin during a short session;
- learn how the adhesive behaves with sweat and water;
- check edges for new friction;
- remove it carefully according to product guidance;
- stop if skin becomes irritated, painful or damaged.
The larger paper-tape trial used site-specific application and does not show that taping every surface is better.1 The earlier null trial reinforces that context, application and individual response matter.2 Adhesive allergy, fragile skin, diabetes, circulation problems or existing wounds need individual clinical guidance.
Use a hot-spot response ladder
Do not wait for severe pain if a repeatable hot spot appears.
Level 1: sensation only
Slow down, check lacing and note the location. If the sensation resolves and the skin remains intact, continue cautiously.
Level 2: persistent rubbing
Stop in a safe place. Remove debris, smooth the sock, adjust fit and use only a previously tested protection.
Level 3: visible blister or skin damage
Use event medical support or a clinician-appropriate plan. Do not cut, drain or medicate based on a generic internet instruction.
Level 4: infection or circulation concern
Spreading redness, warmth, pus, red streaking, fever, marked swelling, color change, loss of sensation or severe pain needs prompt medical assessment.
Do not ignore nails and swelling
Keep nails managed with enough time for irritation to settle before the event. Sudden aggressive trimming can create its own injury. Repeated nail trauma often points back to shoe length, descent technique, swelling or lacing.
Ultra events can produce substantial foot and ankle complaints, but published findings do not identify one prevention system for every athlete.3 Test the interaction, not just the product.
Make a minimal race kit
Build it from verified needs:
- spare socks if your rehearsal showed a clear benefit;
- previously tested tape or lubricant;
- a small clean drying item where rules and logistics allow;
- event-permitted blister care handled by trained staff where appropriate;
- a bag for waste;
- the location of event medical support.
Do not carry a pharmacy of unfamiliar products. A kit cannot compensate for a shoe that repeatedly damages the same area.
Fueling, heat and cognition still matter
Foot decisions become harder when an athlete is depleted, overheated or cognitively fatigued. Ultramarathon nutrition guidance supports an individualized, rehearsed plan, not waiting for a foot problem to force the first stop.6 Heat acclimation should be progressive and planned.7
Use the aid-station rehearsal to put the foot check into a stable stop sequence. The goal is early, calm correction—not proving you can ignore damage.
What not to claim
- Tape does not guarantee blister prevention.
- A shoe that worked for one athlete is not proven for another.
- Toughening the feet does not justify training through open wounds.
- Pain tolerance is not skin integrity.
- A single dry run does not validate wet-race use.
- An online guide cannot identify infection, fracture or nerve injury.
This guide is educational, not medical advice. Seek qualified care for concerning skin, nail, nerve, circulation or infection symptoms, and use event medical staff during the race.
Choose 100K trail in 26weeks.ai so terrain, long-run and recovery work can adapt around what your training actually shows. Start training with 26weeks.ai.
References
- Lipman GS, et al. Paper tape for foot-blister prevention in ultramarathons: randomized trial. 2016. (PubMed)
- Lipman GS, et al. Paper tape and foot-blister prevention in ultramarathon runners. 2014. (PubMed)
- Scheer V, et al. Foot and ankle injuries in ultramarathon runners. 2023. (PubMed)
- Viljoen CT, et al. Injury and illness among trail runners: systematic review. 2021. (PubMed)
- Scheer BV, et al. Foot-blister incidence and associated factors in ultramarathon running. 2014. (PubMed)
- Tiller NB, et al. ISSN position stand: ultramarathon nutrition. 2019. (PubMed)
- Racinais S, et al. Exercise-heat acclimation and heat-illness prevention. 2013. (PubMed)
- Garbisu-Hualde A, Santos-Concejero J. Limiting factors during an ultra-marathon. 2020. (PubMed)