Every week I talk to runners who are deep into their marathon block.

And almost every week, someone asks me the same question:

“Should I race in carbon shoes?”

Last week I had that exact conversation with a runner preparing for his first marathon. Smart, motivated, aiming for a sub-2:55. He’d been doing most of his training in the Saucony Endorphin Speed 5 and now he wanted to know whether it was time to make the jump to a carbon plate.

He told me exactly what most runners say:

And he’s right. Carbon shoes can help.
But what most first-time marathoners don’t realize is this:

Carbon shoes don’t just make you faster. They change the way forces travel through your body, and unless you condition your body for those forces, the marathon will expose every weakness.

Let me explain.

Biomechenical shifts

If you go from something like the Speed 5 into a true carbon racer, you’re not just switching foam and plates. You’re changing your mechanics.

Here’s what happens whether you feel it or not:

1. Increase in ground reaction force (GRF).

This is the “pop” runners love. But it also means your calves, quads, and ankles take more load every single step.

2. Your stride length quietly increases.

The plate stiffens your foot and the foam rebounds harder. This energy return pushes you forward and generates a slight increase in stride length.

3. Your cadence usually drops a little.

Longer steps = fewer steps per minute. Lower cadence increases impact per step. Multiply that by 42 kilometers and it can become rough out there.

None of this is “bad.”

It’s just different. And different requires adaptation.

Training in carbon.

This runner told me he might test them in a speed session or two. Good idea, but not enough.

Short reps tell you how fast the shoe is.
Long runs tell you whether your body can keep up with the shoe.

The marathon doesn’t care how the shoe feels at 5K pace. The marathon cares how your calves, quads, stabilizers, and foot mechanics hold up after two hours in racing shoes.

This is why experienced marathoners can get away with using carbon shoes more easily. They have already been conditioned for the fatigue and know they can maintain form throughout the race. First-timers don’t have that luxury.

If you want the performance boost while minimizing the chance at late-race collapse, you need exposure to carbon racing shoes. For a marathon, that means long sessions, not just long runs.

This is what I recommend for first-time marathoners switching to carbon:

Run 4–5 long sessions in your race shoes.

Not easy long runs.
Not “try it for the last 5K.”

I’m talking about the kind of runs that actually teach your body what racing will feel like.

These sessions are as much about fitness as they’re about load tolerance, mechanical stability, and the way your stride behaves under fatigue in a stiff, high-stack shoe.

A lot of runners don’t understand that part until they’re walking at 34 km wondering where their quads went.

Carbon shoes work (extremly well), but you need to train your body to handle the loads. For shorter races (up to 10 miles), you can get away with them. But for half and full marathon races, you need practise in them.

My gait analysis service breaks down your mechanics and shows you which carbon shoes match your stride. If you want personalized shoe guidance before race day, book a session.

Thank you for reading,

Tim 👟