Now that spring has officially sprung, maybe it's time you spring yourself free from air-conditioned gyms. The best gym on Earth -- also known as the great outdoors -- awaits with lots of fresh air and fresh terrain -- the stuff working out on the treadmill can't give you.

But if you're thinking about taking your runs outdoors, there are a few things to keep in mind:

• Running outside is more difficult than running on the treadmill -- it's not just in your head! So take it slow and work up your pace gradually.
• Please your knees. Running on pavement is not great for your joints, so consider heading to an outdoor track or on a grassy area. If possible, head out of the city and take on some trails.
  
• Don't wear yourself out -- you'll be more prone to injury.
  
• Be wary of the elements -- always wear sunscreen and bring something breathable but waterproof -- you never know what kind of weather could pop up!
• Stretch. Before and after. And as always, drink lots of water!
  

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