From 30-pound walks to bone health claims, the internet’s latest fitness trend is heavy on hype—and back pain.

The 6-6-6 challenge involves walking for 60 minutes at 6 a.m. or p.m., warming up and cooling down for six minutes. Here's ...

At one point, over 74,000 videos were shared under the #SkinnyTok hashtag, many of which portrayed extreme calorie deficits and regular body checks as users documented their shrinking bodies.