Bollocks to that.
A slightly different view: It is possible to greatly enhance the efficiency of body movement. Aerobic exercise equipment can help one learn this. It allows you to study and experiment on your movement under controlled conditions. You can set it to some precise level then really optimize your movement pattern. The heart-rate monitors built in to the machines provide some feedback on your efficiency, so one objective is to try to lower your heart rate. The main objective however is to minimize pain, to feel as loose and relaxed as possible.
From this view, we are not neccessarily even trying to get fitter, just learning to use our bodies well. It makes sense to exercise for extended periods at a low level (eg a slow walk on the treadmill), while paying sustained attention to the sensations in your body. Only once you feel you've gotten into an optimal rhythm for a slow pace would you increase the settings (being careful not to reflexively tense in anticipation of the higher load!).
Sustained, directed attention is important. From this point of view, the TV and radio are counter-productive. Pain is not to be ignored or shoved aside, but neither is it necessary to "concentrate" and apply more effort to reduce pain. Attention but not concentration or extra work. There is no "try". Once you start looking, you start realizing just how many muscles there are in your body, and in how many different ways they may be employed to achieve even the simplest task. (ok, so maybe me taking pills that lengthen my attention-span is cheating a little :-o )
Attention can be either narrowly focussed on some particular body part, or widened into a gestalt of the full body. Both forms of attention (and levels in between) are valuable.
Direct attention where you wouldn't normally. Like your back and spine. There are an amazing number of degrees of freedom to your spine and back muscles. Holding all of them in your head at once is a juggling act requiring full attention.
Breathing method is important.
I've been trying this for a couple of weeks now. It feels like i have better posture, and i find i can employ the muscles in my back to help walk and climb stairs with much less effort.