Like pretty much everyone else, I set some fitness goals heading into 2025. I decided it was time to get serious about cardio, and I’ve actually been really consistent. Running has become a regular part of my workout routine.
Since I’m always in the gym, the treadmill naturally became my go-to at the end of every workout. I was comfortably knocking out five-mile runs multiple times a week.
Then my fiancé convinced me to run outside with her.
I figured it would be no big deal. I was feeling great about my endurance, so I assumed I was more than ready. But not even a quarter mile in, that confidence started to fade. I was huffing and puffing like a madman. It felt like my first time exercising in years. Outside running was kicking my ass.
Back when I used to go on random runs outside and struggled, I always blamed it on not being in “running shape.” But now, after months of racking up consistent mileage on my Nike Run app, I knew that excuse didn’t really work anymore.
So, I started looking into it. Why does running outside feel so much harder than running on a treadmill?
1. Outdoor Running Demands Better Form
When you’re outside, your body has to create all the force to move forward. That means your glutes, hamstrings, calves, and core are putting in serious work. Running outdoors requires strong form and powerful movement from your backside muscles to keep you going efficiently.
On a treadmill, the moving belt helps carry you forward, so your muscles don’t have to work as hard. This can actually shorten your stride and reduce how much your body is engaging certain muscles, especially in your hips and legs. If you’re always running on a treadmill, your glutes, hamstrings, and stabilizing muscles might not get the attention they need. Over time, this can lead to muscle imbalances, especially when paired with tight hip flexors or a weaker core.
2. Outdoor Terrain Is Tougher on Your Joints
Treadmills are designed to absorb some of the impact from your steps, which makes them easier on your joints. That’s helpful if you’re recovering from an injury or dealing with any kind of joint pain.
Outside, the ground is a lot less forgiving. Whether you’re running on pavement, dirt trails, or gravel, your body has to handle more of the shock. This added impact makes outdoor runs feel tougher, even if your pace and distance are the same.
3. You Lose Predictability and Control
One of the best things about treadmill running is that you control everything. You set the speed, the incline, and sometimes even the temperature. Once you hit start, you just keep up with the belt.
Running outside is a whole different story. The terrain changes, the weather plays a role, and you’re constantly adjusting. Hills, wind, uneven sidewalks, and even dodging people or bikes can make things more challenging.
Your body has to respond to all of these little shifts, which activates more muscles and demands more energy. Your ankle and foot stabilizers, for example, work harder outside. So do your hip muscles, which help you adjust to the changing ground.
Conclusion
Running five miles on a treadmill and five miles outside might look the same on your fitness tracker, but they’re not the same experience. Even if you play with the incline or speed on the treadmill, it doesn’t match the variability and challenge of solid ground.
That said, both have their place. Outdoor running is more physically demanding, but many people enjoy it more. The changing scenery, fresh air, and sense of freedom help it feel less boring.
On the other hand, treadmill runs can feel mentally harder because of the repetition. You’re literally staring at the same thing the whole time.
Personally, I think both are useful. If you can run outside, do it. But if the weather, your schedule, or nagging injuries get in the way, the treadmill is still a great way to get your miles in.
At the end of the day, the best run is the one you actually do.
