Let me guess, you saw someone in one of these forms of media with an incredible body, and said to yourself, "I want to look like that!" And boom a spark of motivation ignited a fire in you to start doing!
So with this new found charismatic enthusiasm you religiously, pound away pouring sweat in hopes of the new body featured in the magazine. If your motivation kept you going for more than 3 weeks, you may start noticing some changes (However, any increase in activity will do this), and that of course refuels your motivation, so you keep pounding away. Then all of a sudden the results stopped coming, what gives?
First of all, these are all patch work trendy exercises, that's why editors post them. There is no real personalized programming or progressions for you body to adapt too.
Secondly, intensity...there is no real way to gauge it within the media realm, at first the exercises seem challenging, then before you know it, you are just haphazardly going through the motions (especially after the 20th time going through the same exercise video). Apex-fitness.com overcomes this hurdle by timing safe exercises, to constantly challenge intensity! Studies have shown exercisers who follow more intense workouts yield better results than those who exercise at moderate intensities.
Thirdly, you most likely are performing the exercise wrong! It never ceases to amaze me, that after performing the exercise, instructing the exercise, and guiding clients through the exercise, how many clients do it wrong after a few repititions on their own. Your body wants to take the path of least resistance, in doing so, once prime muscles become fatigued, synergistic or auxiliary muscles will take over, leading to muscle imbalances, dysfunctional arthrokinetics (joint malfunction), and/or postural deviations all of which can lead to injury either chronic or acute.
I know we are in the age of Internet enlightenment and DIYer's, but when it comes to efficiency and your health, you just can't beat a trainer, even if it's only for a session or two a month to help keep you on track and injury free.