Someone showed me their core routine recently. Four minutes of planks, some crunches, a bit of bicycle kicking. They did it most days and had done for a year, and they wanted to know why their hip still dropped at the end of a long run.
Because none of that had anything to do with the problem.
Your trunk's job in endurance sport is not to move. It is to refuse to move while everything attached to it does.
What the Trunk Actually Does When You Run
Every stride, your arms swing one way and your legs swing the other. That produces a rotational force through the middle of your body, and something has to resist it or you would corkscrew down the road.
At the same time, the leg that has just landed is pushing up through the hip, and the pelvis wants to tilt and drop. Something has to stop that too.
Both of those are anti-movement jobs. Anti-rotation and anti-lateral-flexion. The trunk is behaving like a stiff transmission, taking force from the ground and delivering it to the point where it does something useful, and any energy that leaks out as trunk movement is energy you paid for and did not use.
So the quality you want is stiffness under load, not the ability to flex your spine repeatedly. A crunch trains spinal flexion, which is the opposite of the job.
Why Planks Stop Working
I have nothing against a plank. It is a reasonable starting point and it trains the right idea, which is bracing.
The problem is that it stops progressing almost immediately. Once you can hold sixty seconds, holding ninety trains endurance in a position you never adopt, and holding three minutes trains you to be good at holding planks. Meanwhile the actual demand in running is brief, repeated, asymmetric and under fatigue, which is nothing like a static hold on two elbows and two feet.
The fix is not longer. It is harder, and asymmetric.
What I Actually Programme
Loaded carries, first and most. A heavy suitcase carry, one weight in one hand, walking. Your whole lateral trunk is fighting to stop you folding sideways, under load, while you walk, which is about as close to the running demand as anything in a gym gets. Three lots of thirty metres a side.
Pallof press. Standing side-on to a cable or a band, press it straight out from your chest and resist the rotation. That is anti-rotation in its purest form, and most athletes find it far harder than they expect. Three sets of ten a side.
Dead bugs and bird dogs, done slowly. These teach you to hold a neutral spine while the limbs move independently, which is precisely the coordination running requires. The value is entirely in the control, so a fast set of twenty is worthless and a slow set of six is excellent.
Side plank with a leg lift, which turns a static hold into something the glute medius has to participate in.
And, honestly, the heavy compound lifts. A properly loaded split squat or a Romanian deadlift demands more of your trunk than any dedicated core exercise, because the load is real and the failure is obvious. Athletes who lift heavy twice a week need far less separate core work than they think.
The Part That Matters Most
Train it tired.
Your trunk does not fail at kilometre two. It fails at kilometre thirty, when the glutes have gone, the hip starts dropping, and the whole chain reorganises around the weakness. Testing or training it fresh tells you almost nothing about that.
So once a fortnight I put a short trunk circuit at the end of a hard session rather than at the start. Not for the strength stimulus, but so the athlete finds out what their bracing feels like when they are empty, and so it has been practised in the state it will actually be needed.
That is the one exception to my general rule about not doing quality work on tired legs, and it is deliberate.
The Bottom Line
Stop doing crunches and stop adding seconds to your plank. Carry heavy things in one hand. Resist rotation. Move your limbs slowly while your spine stays exactly where it is.
Ten minutes twice a week, plus your heavy lifts, and once a fortnight do it at the end of a session when you have nothing left, because that is when your trunk actually has to do its job.
