If you're serious about shooting 4K action videos, the GoPro Hero3+ Black Edition just won't cut it with its 15 frames/second (fps) frame rate. You need at least least 30 fps for a smooth video and the first action camera able to do so at 4K is the Panasonic HX-A500H. The device is waterproof up to 3 m for 30 minutes and dust-proof and is divided into two parts: a camera with a built-in microphone and a recording unit, with a screen to see what you're shooting, connected via a cable. This division allows you to put the recording unit in your pocket and fasten the camera to your helmet, headpiece, backpack, shoulder, or others.
Bring down the resolution to 720p and you can shoot at 100fps or go to 200 fps at 800 x 480 resolution, which is a decent enough slow motion video for Youtube. Image stabilisation is built into the A500 and recording in 4K lets you tune out more camera shake by cropping into the frame and compensating for any movement. There's also a tilt compensation mode to make sure you're recording the way you want to.
The Panasonic A500 could be a good alternative for the GoPro with potentially more mounting possibilities and 4K video.
This product is outdated compared to what we have today and is no longer available.