Outside of a potential fall due to unsteady outdoor footing, landing wrong on your foot can cause strains and other injuries. If you've been doing much of your running on a treadmill, your body is used to a nearly even and constant stride. Should you run outside, your risk of an injury from even a minor misstep would be higher because the small muscles, tendons and ligaments of your ankle haven't been forced to get used to a variety of landings. (i.e.: sharp turns, curbs, uneven pavement, trails, etc.)
More: 6 Tips to Tackle Any Terrain
Wind Resistance: Even in ideal outdoor conditions you run against air resistance; you don't get inside, so the paces you run on a treadmill are a bit easier than they would be outside. To negate this, you can put the treadmill incline up to 1.5 percent to account for lost wind resistance and make the paces comparable to those run outdoors.
With these key elements in mind, you can adapt your training as need be. If you're doing much of your running indoors, make sure to supplement with extra hamstring-strengthening exercises.
To safeguard your ankles, work on balance and mobility drills such as balancing on one leg on a Bosu ball or pillow. After you can hold there, test your balance further by moving your arms or reaching down with your opposite arm towards the foot you are balancing on. This will build strength in the ankle area.
More: 4 Exercises to Strengthen Ankles
How to Transition Between Indoor and Outdoor Running
If you have been doing nearly all of your training indoors, you need to be especially cautious as you begin to move back outside. You need to transition gradually in order to avoid a resulting injury. So start with one or two of your easy, shorter runs per week outside and build from there; you can also split runs up—some miles can be completed on the treadmill and the rest outside.
Of course it works both ways: If you're moving from all outdoor running to more treadmill running, rely on the gradual transition method.
More: Avoid Treadmill Mistakes
As we head into the winter months, if the wind is hollering, the snow has left your running route only navigable by snow-shoe, or you need a training partner who doesn't care if you're tired and would like to slow down, the treadmill can be your respite.
More: 5 Tips for a Better Treadmill Workout
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