The Real Reason Injuries Happen in Marathon Prep (And How to Prevent Them)

You’ve got your Winter/Spring season mapped out.

Your official 16-week plan starts in February.

Right now you’re sharpening speed, building power on hills, layering in tempo, and keeping volume intentionally controlled.

It’s a smart setup. Exactly what a well-designed build should look like.

But there’s a hidden trap here, one that I see runners fall into every single year.

It's around the 3–6 week mark, the little signs show up:

A tug in your calf.

A tight quad.

A cranky, achy shin.

A hip that's suddenly tight and “doesn’t feel right.”

You take a rest day.

Maybe two.

And it somehow turns into a whole week.

But when you try running again?

The same problem is still there.

This isn’t bad luck. This is predictable. Which means it’s completely fixable.

What you're experiencing is what's called a "training load error".

Which is fancy scientific way of saying your body has experienced an accumulation of micro-damage from your new training plan. Training hard isn't the problem; your body's ability to heal, recover, and adapt in time is.

As a result, a week of rest days has gone by and your niggles are refusing to leave.

Let’s break down exactly why this is happening and what to do so this doesn’t snowball into a January injury that derails your entire season.

The Hidden Lag Between Training Load Spikes and Injury (And Why It Always Catches Runners Off Guard)

Here’s the part most runners never realize until they’re deep in the frustration cycle:

Running injuries don’t happen on the day you “did too much.”

They show up 3–6 weeks after a training load spike.

That lingering calf tightness you’re feeling now?

That weird tug in your knee?

That shin that feels “off” during hill workouts?

Those didn’t start today.

They started weeks ago when your training load quietly increased faster than your body could adapt.

Why injuries lag behind your training changes

When you increase your running load (speed, hills, volume, intensity, etc), your tissues begin taking on more mechanical stress.

This is completely normal and is called microdamage.

Over time, with recovery, tissues adapt and get stronger. You can still hit your paces, finish your longs; however...

If the spike is too abrupt, your muscles, tendons, and bones begin playing catch up between the amount of training-induced damage occurring and what can be repaired.

If the microdamage builds and accumulates, your tissues hit their capacity limit.

That’s when the niggle, or the injury, finally shows up.

This is why we swear, as runners, that our injury “came out of nowhere.”

In reality, it didn’t.

It just took a few weeks to finally rear it's ugly head.

Training load is more than just mileage

Most runners think “training load” only relates to how many miles you’re running.

But that's only one piece.

There are four different loads your body is managing at all times:

1. Volume: miles per week

2. Intensity: speedwork, hills, tempos, strides etc

3. Frequency: how often you run and how much recovery exists between sessions

4. Global Stress: poor sleep, under-fueling, work stress, life stress

The reality: these all stack on top of each other.

So if mileage stays the same but intensity rises? Your load still spikes.

If you’re fueling poorly while doing faster workouts? Same thing: a load spike.

If sleep quality and quantity tanks? You got it, another spike.

This is exactly why the 10% rule is one of the most misleading pieces of running “advice” on the internet.

Why the 10% rule completely fails runners

The 10% rule only measures volume, not intensity, not frequency, not stress, not terrain.

You could increase mileage by only 5% but add "spikes" such as tempo workouts, track sessions, and hill repeats in the same week…and your tissues experience way more than a 10% spike in load.

Conversely, you might increase mileage by 12% but keep everything easy...and be totally fine.

This is why runners get confused:

“I followed the 10% rule… and still got injured.”

Because the rule only measures one part (the mileage) while your body is managing all of them.

The real model that explains everything: Load vs Capacity

Every muscle, tendon, and bone has a load it can tolerate (capacity).

When your applied load (training stress) exceeds that capacity repeatedly…you enter the injury zone.

Here's our formula for how running injuries happen:

Too much load + not enough capacity = niggles → injuries.

Where most runners go wrong is with rest days.

Because it makes sense, right? Have pain that's becoming a niggle? Stop and rest because...

Rest removes pain. But it also removes load capacity

This isn't to say rest days are bad! But when applied the wrong way for too long, you actually end up with the opposite results of what you're looking for.

Because here's the truth:

Rest doesn’t fix the underlying load problem. It can actually makes it worse.

I know. It feels backwards. But this is the missing puzzle piece behind 90% of early-season injuries.

When you rest, your pain usually decreases.

This feels like progress…until you start running again.

Why?

Because of this classic cycle:

“My calf this feels weird, like it's being pulled to the point of straining. I’ll skip today.”

“My hip flexor is tight and painful, especially when I push off with my toes in my stride. I’ll take another day.”

“Okay one more rest day, maybe two for this hamstring to finally calm down.”

Comes back to running; pain is still there (or worse)

Result? “Fine, I’ll take a full week off.”

This DOES NOT mean don't take rest days.

I'm the first to admit a little extra rest and sleep can cause wonders.

But we can't ignore the physiology of when you stop loading your tissues for a prolonged period of time, such as 7 days, that they begin losing strength, stiffness, and load tolerance, meaning...they lose capacity.

So the second you return to “normal” running, your tissues immediately get overwhelmed again. And this is how a niggle now becomes an injury.

Why “Just Resting” Makes Your Niggles Worse (Not Better)

The Point: Rest is Not Rehab

Rest is only step one. And even then, very short-term.

What your tissues need is progressive overloading because did you know?

Depending on exactly what you've injured, determines what kind of, or application of, strength training you need to successfully rehab your running injury and return to running stronger than ever.

What to Do Instead (So You Actually Stop the Niggle Cycle)

The key to getting back to running as soon as possible and stronger than before so you avoid a repeat running injury, is you to match the fix to the tissue.

Because not all running injuries need the same approach.

• Injured tendons respond to slow, heavy, controlled lifting

• Injured Muscles respond to heavy lifting within an RPE of 8 to build strength + power

• Bones respond to fewer, but heavier and FAST reps.

  
  

This is why generic rehab fails.

This is why “I stretched it” doesn’t work.

This is why clamshells are not a positive personality trait.

You need the right exercise, the right tempo, and the right dose for injured tissue to heal and come back stronger than before.

And why the runners who rely on stretching, massage guns, and foam rolling stay stuck.

If it’s a tendon niggle....

Think Achilles, patellar tendon (runner's knee), posterior tib, even plantar fascia pain...

You need slow, heavy, capacity-building strength, not stretching, scraping, or resting.

What works:

• Lifting heavy, in elongated positions that place that tendon in stretched position

• Using slow and controlled reps with 3-4 sets, 4-10 reps

• Making sure you use a 6 second lifting phase meaning, 3 secs into the rep and 3 seconds out

• Not being scared of next-morning flairs: manage this by reducing SETS. NOT LOAD. Addressing and lowering volume can be an effective fix.

• Here are 2 exercises I would use to fix repeat Achilles tendon pain:

Why: Because tendons only care about high load and they only heal or remodel ONLY under slow, heavy tension. Anything less will feel good temporarily but won’t change the tissue.

If it’s a muscle niggle...

Think hamstring, gastroc, hip flexor strain, or quad tightness...

You need to challenge your muscles with strength and power, not only rest because muscle is smart and will continue to adapt the more we load it. And as a result, it’s very volume dependent.

What works:

• Heavy strength work at an RPE of 7-9 (NOT failure all the time as this WILL leave you too sore and tired to run)

• Adding in eccentric-biased training when you feel you've hit a plateau

• 2–3 days per week with 3-4 sets of 8-12 reps

• Here are 2 exercises I would use to fix repeat hip pain that feels like ITB pain but in reality is actually a result of weak glutes:

Why: Because superior strength gains also come from heavier loads. We don't want only muscle hypertrophy (bigger muscles). We also want greater muscle force capability.

If it’s a bone-loading issue

Think shin splints (MTSS), bone stress injuries, stress fractures etc...

This requires the most strategy because bone is sensitive to both underloading and overloading.

What works:

• Bone likes to be loaded fast (not slow) with high loads to elicit bone gains.

• Using few, fast, and heavy reps is best BUT but they need to HEAVY and need to be more than what the runner will typically experience during everyday life and running in order to prepare their injured bone for return to run

• 4 sets of FAST + HEAVY Squats (will demonstrate below)

• 3-5 reps @ 85-90% 1 rep max for 12 weeks, 3x/week program

• Here are some examples of fast-loading strength exercises I would use for runners struggling with repeat bone stress injuries such as shin splints:

Why: Bone doesn’t respond to stretching, massage, or mobility. It responds to the stimuli of muscles pulling on the bone from all directions during strength exercises but also requires the physiological stimuli of impact from plyometrics.

WRAPPING UP

Here’s the simple truth:

Rest days are helpful and necessary. Use them. But alone, they will NOT fix your injury lurking beneath the surface.

You need the right kind of loading.

Because when you load the injured tissue properly:

• pain decreases

• load tolerance increases

• running gets easier

• intensity in speed work or hills sprints becomes sustainable again

• and niggles stop coming back

  
  

THIS is how runners stay healthy between now and February when marathon plans kick off.

THIS is how you prevent the “I was fine until week 6 and then everything fell apart” cycle.

And THIS is why I’ve given you the exact example exercises I’d prescribe to a runner dealing with repeat stress reactions, repeat Achilles pain, and constantly tight calve muscles or hip flexors so you can plug them directly into your own strength work without guessing.

So until next time running fit fam....

Dare to Train Differently,

Marie Whitt, PT, DPT // @dr.whitt.fit