The shape of the American body, both the real one and the imagined, appears to be undergoing yet another physical reexamination in the advertising world lately.

The Nike company, in an effort to market its sneakers to women who are anything but lean and mean, has launched an ad campaign that features “big butts” and “thunder thighs” and the defiantly proud women who own them. The ads are being praised on the one hand for finally celebrating the bodies of “real people” rather than the rail-thin “idealized” figures that fill the fashion magazines. Critics, however, say they know what a genuine big butt looks like and it’s definitely not the one pictured in the ad, which the text explains is a prominent gluteus maximus sculpted to athletic firmness by hours in the gym. Same with the so-called thunder thighs, which more closely resemble the muscular, toned legs of a an Olympic decathlete rather than the flabby ones women look at in the mirror each morning.

Industry experts say the Nike spots are part of a shift away from the unattainable bodies advertisers have always glorified to the more attainable ones found in the real world. The Dove brand is trying the same thing with cellulite cream ads that show “real” women of varying shapes and sizes posing in their underwear to reveal their “real curves.” A Chicken of the Sea tuna ad on TV features a beautiful woman who dashes into an elevator and exhales, showing us her “real-life” large belly.

These new mixed-message marketing ploys, of course, are just further proof that advertisers will go to any lengths – or widths, as it were – to lighten our wallets. Theirs is the business of manipulation, after all, so let the buyer beware. But this schizophrenic, media-driven approach to body image, a recent study suggests, may be tempting the most easily manipulated and vulnerable segment of the population – our youngsters – to take extreme measures in an effort to look good.

In the largest study done so far on adolescents’ views of their bodies, USA Today reported recently, one in eight boys and one in 12 girls admitted to using hormones and supplements in the past year to improve their appearance, strength and muscle mass.

Using a nationwide survey of 10,000 adolescents, the Harvard Medical School study published early this month in the journal Pediatrics revealed a “high rate of concern about body image in both boys and girls.” Teens from 12 to 18 who worry about how their bodies look, the study found, are much more likely than their peers to use hormones and dietary supplements to enhance their physiques. The potentially harmful products include everything from protein powders to growth hormone to steroids injected at least once a week to improve strength and appearance. The study’s lead researcher, Alison Field, urged us to think about body-image dissatisfaction in boys as well as girls. Both are strongly influenced by images in the media, she said, that are “unrealistically thin for girls and unrealistically muscular for boys.”

The most commonly used products were protein powders and shakes. Yet boys, mostly, also admitted in the survey to using such substances as creatine, amino acids, an amino-acid metabolite called HMB, growth hormone as well as anabolic steroids, which have known harmful health effects. Desperate measures, indeed, just to resemble celebrities and magazine models who often don’t look nearly as buff without the help of camera trickery and airbrushes.

“Parents have to help teens understand that they’re comparing themselves to an image that isn’t real,” a teen-health authority told USA Today.

Good advice, of course, provided the parents aren’t victims of the same delusion themselves.