You have probably seen the lizard and snake scene a few months ago, it was so dramatic and really looked like something out of an action movie and not a documentary. The Vox team did a great behind the scenes look at how the tech evolved from the first 16mm cameras used in the very first film the BBC did many decades ago.
The gimbal rig they used is something that is holded with both hands and was probably filmed over the last two years. Since then, we got a couple of handheld gimbals like the DJI Osmo Mobile and the IKAN MS1, both below 500$ and usable with a single hand. I’m looking forward to the next Planet Earth with small 4K (or 8K) cameras that can be handled with one hand.