Like "The Six Million Dollar Man," today's teens are bigger, stronger, and faster. But they're also more likely to be underweight. Huh?

A study in the online journal BMC Public Health reveals two major shifts in teen bodies. Norwegian researchers compared data from teens analyzed in 1966-69 to teens in 1995-97 to determine how factors like height, weight, and body mass index changed over time.

Firstly, adolescents appear to be increasing in height and weight, with a higher BMI (body mass index) over all. This increased BMI could signal better nutrition, which means teens are getting heavier because they aren't malnourished. However, it could also mean that teens are eating too much and not getting enough exercise, signaling obesity.

By contrast, while the upper BMI percentile is increasing, the lower BMI percentile is decreasing. In other words, the thinnest 1990s teens had a lower BMI than the thinnest teens from the 1960s. This data also signals a wider disparity of body types, with teens generally falling into one of two extremes: obese or underweight.

It's important to note that this data does not include current teens - but judging by teen shows like "Gossip Girl," this underweight issue isn't just a 1990s anomaly.