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If you run several times per week and then go to the gym to do light squats, lunges and endless sets of 15–20 reps, there’s a good chance your strength training is just giving you… more endurance work.
And this is one of the biggest mistakes recreational runners make with strength training.
There’s still a strange idea in running that heavy weights are dangerous.
“I don’t want to get bulky.”
“I need muscular endurance, so I should do high reps.”
“I run long distances, so I should lift light weights for 15–20 reps.”
It sounds logical.
But your running already gives you thousands and thousands of low-force repetitions — you already run.
So what should strength training actually do for a runner? Make you stronger.
That sounds obvious, but it changes how you should train.
A major review published in Sports Medicine — “Optimizing Resistance Training for Sprint and Endurance Athletes: Balancing Positive and Negative Adaptations” — looked specifically at how resistance training can help, and potentially hurt, sprint and endurance athletes.
One of its key practical recommendations for endurance athletes was surprisingly simple:
Lift relatively heavy. Keep the volume under control. And you usually don’t need to train to failure.
When researchers talk about “heavy” strength training, they’re often talking about loads around 85% of your one-rep max or above. That doesn't mean you need to constantly test your maximum. There’s a much easier way to think about it.
Imagine you choose a weight you could lift for roughly six good repetitions.
Instead of fighting through rep six, seven and eight until your soul leaves your body, you might do four or five clean reps and stop.
You got the heavy stimulus. You didn't create unnecessary fatigue. And you can still run tomorrow.
If Monday's strength session destroys Tuesday's interval session, we haven't magically made you a better runner because your quads were sore.
Training only works when the pieces work together.
Here's the funny part. You already train muscular endurance. It's called running.
Every stride is another repetition. If you go out for a 10 km run, your legs don't exactly suffer from a shortage of repetitive work.
Strength training can therefore fill a different gap.
Instead of asking: “How can I make my legs tired in the gym?”
Ask:
How can I make every stride "cheaper"?
If your maximum force capacity increases, the force required for each normal running stride becomes relatively less demanding. That is a very different goal from simply surviving four sets of 20 squats.
This is probably the biggest fear we hear from runners.
Heavy barbell appears. Runner immediately imagines gaining 10 kg and turning into a bodybuilder by Friday.
That's not how it works.
The bigger concern highlighted in the review is high resistance-training volume, particularly large amounts of work performed close to or at failure. That style of training creates a stronger hypertrophy stimulus.
And for an endurance athlete, deliberately chasing maximum muscle size isn't necessarily useful. Extra body mass has an energetic cost when you have to carry it for kilometres. The effect is especially relevant when additional mass is further away from the body — for example in the lower leg.
But this isn't an argument against strength training. It's an argument against programming a runner like a bodybuilder.
The research reviewed suggests that combining endurance work with sensible resistance training usually produces relatively modest increases in lean mass, while the benefits of resistance training often outweigh the potential disadvantages. PubMed Central (PMC)
Muscles aren't the only thing adapting. Heavy strength training can also affect your tendons.
A stiffer Achilles tendon can store and return force differently during ground contact, potentially helping the muscle-tendon system operate more economically during running.
Think less: muscles working harder every stride.
And more: a stronger spring system transferring force efficiently.
This is one reason strength training isn't just something runners should tolerate because somebody told them it's “good for injury prevention.” It can potentially contribute directly to how efficiently you run.
For a recreational runner, two well-designed strength sessions per week can already be plenty.
A session might include something like:
The exact exercises matter less than the principle.
Good technique. Meaningful resistance. Low-to-moderate volume. No pointless grinders.
And if you're new to lifting, don't jump straight to 85% loads because you read it on the internet.
Learn the movements first. Build gradually. Then make them heavy.
You absolutely can do both.
But if improving your running is currently a priority, your CrossFit training should complement it rather than compete with it. That might mean keeping the strength work heavy and purposeful while occasionally reducing extra leg volume in the conditioning.
If you've got a hard running interval session tomorrow, doing 150 walking lunges tonight probably isn't a personality test you need to pass.
Likewise, you don't automatically need to remove squats, deadlifts or Olympic lifting because you're preparing for a half marathon. Often the opposite is true.
You just need to manage load, volume and fatigue.
Runners don't need the gym to give them more endurance. Running already takes care of that pretty well.
Your strength training should give you something different: more force, stronger tissues, better neuromuscular capacity and potentially better running economy — without creating unnecessary mass and fatigue.
So the next time someone tells you runners should only lift tiny weights for 20 reps, remember: You don't need to make strength training look like running.
You need it to make you a stronger runner.
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