Those who frequent my class have probably never heard me mention energy or chakras. The reason being that these concepts have been so superficially disseminated into our pop culture as to render them almost entirely cliche. Catch phrases like "feel the energy" or "open your third eye" often make new-age fluff of subtle ancient truths.
Yogic teachings establish that we have both a physical body and an energy body, the latter having "centers" or chakras; however, the correlation between our physical and energy bodies is not as linear as is generally made out to be.
For instance, back-bending encourages an opening across the chest which some would contend correlates to an opening of the fourth or "heart" chakra. The fourth chakra is associated with our capacity for kindness, compassion and love. The theory being that by opening our chests we are increasing our capacity for these desirable attributes.
Not necessarily so. If we are going about our back-bends in an overly forceful or inconsiderate way then, regardless of how impressive the physicality, no "heart" opening is taking place. There is certainly a connection between our physical and energy bodies and engaging our physical body can have an affect on our energy body but the link between the two is perhaps more nuanced then direct.
I think of it like this: If there was ever a time in your life, even just a moment, however fleeting or passing it may have been, when you felt that everything was exactly as is supposed to be. When life felt like it was in total harmony. In that moment, your chakras were perfectly aligned. There may be any number of things you might do that would help encourage and maintain some degree of this state. Hatha Yoga is particularly constructive in this regard.
Practically speaking, the term energy simply refers to how something feels. Engaging breath and body, eating, sleeping, having friends and lovers, basically everything we do and think is playing into the equation of our experience and is expressed in how we feel and behave, or our energy body.
Ultimately, the quality and intention with which we engage the forms, be they asana or other, is what determines the affect. In many respects, the form is irrelevant. As I once heard U.G. Krishnamurti say, "Your physical body is your physical body and your energy body is your energy body."
When these concepts are made out to be something esoteric or super-natural and end up being the punchline on a TV sitcom, we become blinded to what is merely natural and inherent to all of us.