Is The ‘1% Incline Rule’ Actually True?

Here’s the big question… is running on a flat treadmill bad for you? Will it damage your knees and break you down over time? If you aren’t already aware, this is a huge debate among runners. The reality is, there is a lot of misinformation about treadmills. Let me start by saying, as a personal trainer and kinesiologist, treadmills aren’t going to kill you! I’ve worked with many clients and I say the same thing over and over, this machine isn’t inherently good or bad, it’s just another tool. As long as you have a wide array of tools in your belt, you’ll be set up for a successful, injury-free running career.

When it comes to the ‘1% rule’, it’s not really that complicated. My rationale below may not be the flashy answer you’re looking for, but I care more about telling it as it is. Two of the biggest mistakes we make in running are overthinking and overtraining. This sport is much more intuitive than you may think. I hope my perspective can help you determine what your specific anatomy and training goals are best suited for.

Let’s jump into it!

Demystifying the Treadmill

Saying that running on a flat treadmill is bad for you is not necessarily true. Sure, if you have a history of knee pain, then another surface such as a track or chip trail will be more appropriate for you. For the majority of us, however, there is absolutely nothing wrong with running without an incline. The rumor that a flat treadmill is going to destroy your joints has been floating around for far too long. As long as you’re running within your abilities and doing it with proper technique, you will be just fine. Poor running form has a much stronger correlation to joint pain than the surface you’re running on, but that’s for another post.

Conclusion #1 — Running without an incline won’t destroy your knees if it’s done in moderation, but poor running form will.

That being said, we must ask the question, “Why wouldn’t you run with a slight incline?” In a study by Jones & Doust, it is stated that a “1% treadmill grade most accurately reflects the energetic cost of outdoor running.” The argument is that a slight increase in grade can compensate for the lack of air resistance and dynamics that cannot be achieved in an indoor setting. Additionally, that little bit of incline may feel better for certain individuals who have had severe joint pain in the past.

It’s such a subtle shift, but it can make your workouts feel more challenging and worthwhile over time. Just keep in mind that there is no ideal grade percentage for everyone, as this is going to be dependent on each individual's mechanics and goals for training. Anywhere within the range of 1–3% is typically a safe bet.

Conclusion #2 — Due to the energy demand benefits of incline running, we must ask ourselves, “Why not?”

If it feels like we’re getting into the nitty-gritty of running, it’s because we are. Why don’t take a step back for a moment? What’s far more important than your percentage of incline is the way you’re approaching running as a whole. One of the most valuable pieces of running advice I’ve ever received is to prioritize variety in training. This is for three critical reasons:

Variety is simply more fun and engaging.

Variety will ensure you’re not isolating yourself to the treadmill or concrete and consequently receiving an overuse injury.

Variety will make you a far more versatile runner.

What’s worked well for me is to balance time between running on the roads and trails. Everyone once in a while, I’ll mix this in with a treadmill session if I’m looking for a change of scenery, or the weather has turned sour. Whatever you do, make sure you’re switching up your running surfaces every once in a while. While running form is a more important variable, this is still a valuable strategy for fostering sustainability and health.

Conclusion #3 — What incline % you run with isn’t everything. Just listen to your body and do what feels challenging yet safe. What’s more important is that you’re not solely running on the treadmill. Variety is key!

In Closing,

If you take anything away from this article, let it be to not overthink your training! Will solely running on a no-incline treadmill hurt you over time? Most likely. Is it more productive to run at a slight grade? Yes. The more important lesson is that we should always be looking at the bigger picture. How are you spending the majority of your volume? Do you have enough variety in your weekly training? Is your body responding well to your current mileage and rest intervals?

Don’t buy into every piece of running advice you see on the web. What works for some may be detrimental for others. That’s the beauty of running. We’re all paving a different path to become the best athletes we can be. ‘Intuitive running’ may be an overused phrase, but I do believe it’s an important philosophy. Reflect on your training and listen to your own body, to run safely and effectively. How ever you choose to approach your running, ensure you’re doing it with balance and sustainability in mind. Oh, and there’s no reason why small doses of the treadmill can’t be part of this process.

I’ll say it over and over again… play the long game!