Untucking your tailbone: If your tailbone slopes down, as in the first picture, your too-tight hamstrings are preventing natural pelvic floor and glute strength from developing. Follow this step by step guide to squatting, to untuck your tailbone and reinstate the natural activity of the pelvic floor and gluteal muscle groups.
If you've never had your pelvic floor released, consider hunting down an integrative structural specialist: It's a weird sensation, for sure, and generally reveals a shocking revelation. While you might assume that this muscle web that acts as a "hammock" for your undercarriage would be stretched out (particularly if you've had kids), it's generally the opposite. on goop.com. http://goop.com/the-secrets-of-the-pelvic-floor/