Medically Reviewed by Dr. Tom Biernacki, DPM, FACFAS — Board-certified podiatrist & foot surgeon | Balance Foot & Ankle | Last updated: May 2026
The most common foot injuries in marathon training are plantar fasciitis, metatarsal stress fractures, black toenails (subungual hematoma), and Achilles tendinopathy. They typically occur during weeks 12–18 when mileage peaks above 40 miles/week. The 10% weekly mileage increase rule is the most evidence-based injury prevention strategy. Any foot pain that alters running gait during a long run warrants immediate podiatric evaluation — training through gait-altering pain accelerates injury severity.
The Marathon Training Injury Curve
Marathon training injuries follow a predictable pattern. The early weeks (1–8) rarely produce significant foot problems — volume is manageable and the body adapts. Weeks 9–14, as long runs extend past 16–18 miles, fatigue-related biomechanical breakdown begins. The injury peak for most programs occurs between weeks 14–20, when cumulative mileage reaches its highest point before the taper. Recognizing where you are in this curve allows you to intervene preventively rather than reactively.
High-Mileage Foot Injury Guide
| Injury | Typical Onset | Red Flag Signs | Action |
|---|---|---|---|
| Plantar fasciitis | Weeks 10–16 | Pain lasting >30 min into run | Reduce volume, stretch, podiatry eval |
| Metatarsal stress fracture | Weeks 14–20 | Pinpoint bony tenderness, worsens with hopping test | Stop running, same-day X-ray |
| Achilles tendinopathy | Weeks 8–14 | Morning stiffness >30 min; mid-tendon swelling | Heel drop protocol, reduce hills |
| Black toenail (subungual hematoma) | After 18–20 mile runs | Severe pain, pulsating pressure | Podiatry for nail trephination if painful |
| Posterior tibial tendon pain | Weeks 12–18 | Arch collapse worsening; inside ankle pain | Orthotics, motion control shoe, load reduction |
| Blisters / interdigital maceration | Any long run | Blood blisters, torn skin between toes | Body Glide, toe socks, half-size larger shoe |
Shoe Strategy for Marathon Training
Many marathon runners make the mistake of training in the same shoe model from week 1 to race day — but shoes compress and lose 40–60% of their midsole cushioning over 300–500 miles. In a 16–20 week program averaging 40 miles/week, you will log 640–800 miles. Most athletes should rotate two pairs during training and break in their race-day shoe on 2–3 long runs before the event. A half-size larger than your street shoe size accommodates foot swelling during long runs — essential for preventing black toenail and forefoot blister formation on 20-mile training days.
Watch: How to Cure Plantar Fasciitis Fast — the #1 Marathon Training Injury
Dr. Tom Biernacki covers the most effective treatment approaches for plantar fasciitis — the injury most likely to derail marathon training — and what actually works when you can’t afford to stop running:
The most common mistake marathon runners make is ignoring foot pain during peak training weeks because “the race is too close to stop now.” This reasoning leads to two outcomes: either the injury worsens and race participation becomes impossible, or the runner completes the race and develops a chronic condition (non-healing stress fracture, plantar fascia rupture, complete Achilles tear) that sidelines them for months post-race. If foot pain changes your gait during a long run, that is your body signaling structural overload — see a podiatrist before the next long run, not after the race. Intervening at week 14 saves the race; waiting until week 20 often cancels the next season.
Frequently Asked Questions
Can I run a marathon with plantar fasciitis?
Many runners complete marathons with managed plantar fasciitis — but “managed” is the key word. Strategies that allow continued training: cortisone injection 4–6 weeks before the race (not within 2 weeks — weakens the fascia temporarily); custom orthotics or over-the-counter arch supports in all shoes; night splints to prevent morning stiffness; pre-run calf and plantar fascia stretching; and anti-inflammatory protocol (ice after runs, targeted NSAIDs if cleared by your physician). If pain is severe enough to produce a visible limp during long runs, completing the marathon risks plantar fascia rupture — a 6–12 month recovery.
What is the hopping test and why does it matter for stress fractures?
The hopping test is a quick clinical screen for metatarsal stress fractures: stand on the affected foot and hop 5 times. If this reproduces sharp, localized pain in the metatarsal shaft, a stress fracture is strongly suspected and requires same-day X-ray. Many early stress fractures are X-ray-negative within the first 10–14 days — if clinical suspicion is high and X-ray is negative, MRI is the definitive test. Running through a suspected stress fracture risks converting a hairline crack to a complete fracture requiring surgical fixation — an automatic DNS for race day.
How do I prevent black toenails during long runs?
Black toenails result from the toe hitting the shoe’s toebox repeatedly during long runs. Prevention: wear running shoes a half-size larger than your street shoe size; keep toenails trimmed short and straight across; use moisture-wicking socks to reduce friction amplification; and consider toe sleeves or Bodyglide on the toes for runs over 16 miles. If a black toenail develops significant pressure pain during a run, it can be drained (trephinated) by a podiatrist in a quick in-office procedure — relief is immediate and the nail is preserved.
Should I see a podiatrist before starting marathon training?
A pre-training podiatric evaluation is particularly valuable if you: have had previous foot or ankle injuries; have flat feet or high arches; are a newer runner moving to your first marathon; or have diabetes or other conditions affecting foot health. A gait analysis and structural assessment can identify biomechanical vulnerabilities before they become injuries at mile 500. Custom orthotics prescribed before training begins — rather than mid-training when injury is present — are significantly more effective and less disruptive to your program.
How do I know if my foot pain during marathon training needs imaging?
Imaging is warranted when: pain is localized to a specific bony point (not diffuse arch or heel); the hopping test is positive; pain worsens with each mile of a long run rather than warming up; you have bony tenderness on palpation over the metatarsal shaft, navicular, or calcaneus; or pain is present at rest and not just with running. Balance Foot & Ankle has in-office digital X-ray at both locations — same-day results allow you to know within hours whether training can continue or requires modification.
Training for a Marathon and Dealing with Foot Pain?
Don’t let foot pain end your race. Same-day podiatric evaluation with in-office X-ray at Howell and Bloomfield Hills, MI. Dr. Tom Biernacki DPM — runner-focused podiatrist. Most insurances accepted.
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Dr. Tom Biernacki, DPM is a double board-certified podiatrist and foot & ankle surgeon at Balance Foot & Ankle Specialists in Southeast Michigan. With over a decade of clinical experience, he specializes in heel pain, bunions, diabetic foot care, sports injuries, and minimally invasive surgery. Dr. Biernacki is a member of the APMA and ACFAS, and his patient education content on MichiganFootDoctors.com and YouTube has reached over one million views.
- Plantar Fasciitis: Diagnosis and Conservative Management (PubMed)
- Plantar Fasciitis (APMA)
- Diagnosis and Treatment of Plantar Fasciitis (PubMed / AAFP)
- Heel Pain (APMA)