I came into this from the lifting side.
So I understand the hesitation.
You finally have a squat you are proud of. Your legs are growing. Training is moving.
Then somebody tells you to start running.
Sounds like a great way to make your quads tired for no reason.
Except it does not have to work like that.
Start with less running than your lungs want
This is the annoying part.
Your cardio can improve faster than your feet, calves, shins, and knees get used to running.
You go out for 20 minutes. Feels fine.
Next week you decide 35 sounds reasonable.
Then you add a third run because breathing was not even that hard.
Two weeks later something below the knee starts complaining.
I would rather start with two easy runs and let the boring stuff catch up.
Twenty to thirty minutes.
Then another easy run later in the week.
Do that long enough that it feels normal before turning the plan into a running hobby with a lifting problem.
Your first runs should be embarrassingly easy
Lifters are bad at this because effort feels productive.
Hard set? Good.
Heavy bar? Good.
Easy jog where you can talk the whole time?
Feels like you forgot to train.
That is fine.
You are trying to add aerobic work without creating another hard lower-body session.
If you cannot talk in full sentences, slow down.
If a hill turns the run into a grind, walk the hill.
Nobody is giving out medals for keeping the watch under a certain pace on an easy Tuesday.
The Zone 2 guide goes deeper on that.
Running counts when you plan leg volume
I know that sentence sounds obvious.
Still worth writing.
If you squat Monday, run Tuesday, deadlift Thursday, and run Saturday, your legs did not only train Monday and Thursday.
The runs were work too.
That does not mean cut every leg accessory the second you buy running shoes.
It means watch what happens as mileage grows.
If lower-body performance keeps sliding while running volume keeps climbing, I would look at the total week before blaming the squat program.
I would protect the big lifting days
If strength is still the priority, I want the important lower-body sessions getting a decent version of your legs.
That means I am not putting hard intervals the night before heavy squats just because Wednesday was the only blank square on the running calendar.
Easy running gives you a lot more freedom.
An easy run after upper body?
Usually easy to live with.
An easy run later in the day after lower body?
Can work if your stride still looks normal and the run stays easy.
Hard running gets treated like hard training.
Do not add mileage and intensity together
This is how a simple running plan turns into a mess.
You add a third run.
Make the long run longer.
Then add intervals because easy running got boring.
All in the same two weeks.
Your lifting stayed exactly the same too, obviously.
Now everything hurts and every workout feels harder.
Pick one change.
Let your body deal with it.
Then decide whether you need another.
Will you lose strength?
You might have some days where strength feels worse.
That is different from actually losing all the strength you built.
Bad sequencing, too much running too quickly, poor fueling, and carrying fatigue into lower-body work can all make a session look worse.
A couple easy weekly runs are a very different thing from high-mileage race training.
If you eventually want to run a lot, the tradeoffs get bigger.
That is okay.
You just need the lifting plan to admit that the running exists.
When I would finally add faster running
Once two or three easy runs feel normal.
Your lifting is still moving.
Your feet and shins are not yelling at you.
Then maybe threshold work or intervals earn a spot if your goal needs them.
Maybe they do not yet.
Running faster is not the automatic next level of being serious.
It is another training tool.
Use it when you have a reason.
If you want the full weekly layout, start with Hybrid Athlete Training. If you are trying to understand what the different paces are for, read Running Pace Zones.