Don't think so. You can dare to very well write a detailed post on Fitness, even if its competetive. What you can actually do is (something the top ranking pages aren't doing) is write supporting articles (low competetion keywords) and point it to the pillar article that you wrote in the beginning. You won't get traffic from search but you sure can get traffic from internal links that are easy to rank on search (& if you've done your job right, you'd be ranking for the target keywords already)

Hope this helps.