The scientific community doesn't really now why a placebo does what it does… just that it does it… and how to make it do it… a placebo basically is just another term for empowering your self. So yeh basically this meditation's are a "placebo effect".
If you are feeling like you are getting stronger you probably are. Even believing you are getting stronger may make you stronger because thinking=energy and you give this energy a purpose. This is why believing yourself is half part of success.
Hail Satan and All Gods of Hell!