I don't know, but I know lots of paid ways.

Here are some good ones:

1) Video Marketing
Rank your videos in Youtube and link back to your website

2) Forum Marketing
Find and Contribute to fitness forums and get links back to your website

3) SEO
Get organic search traffic, by using SEO strategies

4) Blog Commenting
Comment great comments on fitness blogs, and you get links back to your website

5) Social Sharing
Get people to share your stuff, to multiply traffic

6) Ad Swaps
Trade traffic by leveraging your email list, to get new traffic.

Hope this helps

I would utilize forum and video marketing.

Sign up to various forums in your niche and contribute quality information to the community and attempt to drive traffic through that. With video marketing, you can create some fitness/athletic videos and put a link in the description and at the end of the video. By establishing yourself as an authority on YouTube and on forums, you will be able to drive traffic very easy a few months down the line.

Use social media. Know where your audience gather and offer a free gift.

You can never go wrong with niche forum marketing...

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There are a boat load of ways to drive traffic to your site for free. Facebook posting, YouTube videos, countless social media sites and blog sites, and so on. I post on many of these sites: IBO Toolbox, Google+, Referral Key, DailyMotion, Blogger.com, and a host more. Free organic traffic does take a little longer but if you stay with it, you can see success. I would also search Google for Health / Fitness blog sites that you can post to as well. Hope this helps....

The best free way is to get on social media and start sharing interesting content.

Things like videos and fitness memes will get sharing and bring you lots of traffic.

The one thing I have noticed, that most of the biggest fitness people on twitter share boatloads of stuff--mostly pictures and again memes--so if you want to bring in the traffic,

Start putting out a lot of stuff and the traffic will come.