How many backflips can you do? Wow, that many? Okay, you're way more impressive than us. But, how many can you do underwater? That's what this latest TikTok challenge is all about. DeepEndFitness has posted videos of people attempting underwater backflips while holding onto hand weights, all without coming up for air. We could do this too! You know, if it was above water, while we sat on the couch and this was actually a video game.