Oh, I don't disagree at all, athletic is great --
but athletic the way, e.g., I remember being that at age, say, 7 or 8, when running all day, climbing trees, biking, swimming, just having no reason in my bones to sit still didn't harm me one bit. That's because athleticism that comes from the spontaneous joy of movement is never spending more than you can afford to spend. It is quite naturally and smoothly regulated by your internal "coaches" -- your feelings, senses, emotions, or in TCM terms, your Po.
Not so when one decides in the head to work towards accomplishing an athletic goal -- e.g., running a marathon, doing cardio towards the latest medical fad's idea of health or mass media's, of beauty. This is the kind of decision that doesn't come from the spontaneous joy of movement, and the internal coaches are summarily fired, people just ignore what their bodies are telling them and are forcing the latter to do what the head has decided, "it's for your own good, body, so why don't you just shut up and obey!"
Of course if one's resources of qi and jing are sufficient, either because they are backed up by specific good practice or because one got plenty at birth and hasn't yet lived long and hard enough to dip into them too deeply, there's no harm in doing things athletic towards any other goal than the sheer purposeless joy of movement of a healthy child (and an adult of any age who managed to preserve it.) Also, someone who hasn't moved in a long time will benefit from giving himself/herself any kind of kick to get going -- but this kick is going to have to come from yi anyway!

Athletes with an ax to grind, with a goal, an agenda (that is coming from other sources than one's own body asking for the pleasure of movement and competence in that and a sense of suppleness), also have to give themselves a willpower kick to do what they do -- and that's zhi, the kind of will that depletes the Kidneys (and jing...) when used as the source of momentum to get going. In other words, what I'm trying to say is,
the inner meaning of movement is the ultimate deciding factor in whether it's going to benefit or harm, you can't judge by external behavior only. Qi is interesting in that it is not unconscious and not meaningless. Qi is the medium and messenger of meaningful change. Changing the size of one's biceps or accommodating the latest fads implanted in one's head by pop culture is seldom meaningful enough for qi to get involved in any useful way... It will resist -- and if one overcomes this resistance with li, it will dwindle. But, by the same token, if it is guided by yi toward a goal qi itself finds meaningful -- then of course it's a different story. As the classics put it, "use the mind of tao, not the human mind" -- and you'll be fine no matter what you do. Qi uses the mind of tao...