I've seen double handled forks in all the gardening shops here, but hadn't seen one used until I watched a gardening programme last month. Looked like much easier work if you are simply loosening the soil for aeration and adding compost, rather than turning it over completely.
If you haven't seen one before, they are just as described- a fork with two handles. Usually they have two straight wooden ones without the hand grips at the top. Starting at around €80 I have concerns about the strain on your wrists so decided to take a gamble and buy a top-of-the-range version for digging our heavy and solid clay.
The use is quite simple. Grabbing it by the handles it is thrown downwards into the soil to set it vertical. Then you step onto it with both feet using your entire weight to push the prongs into the soil. This takes some balancing practice! Then step off and pull the fork back towards you to the lift the soil. As with a normal fork you work backwards along the bed.
I ordered an Agroforja (Spanish made) item. A very sturdy fork with two rotating hand grips, five very solid sharp prongs and a small platform to stand on. It is extremely easy to use and resulted in working a bed in a quarter of the time and with far less physical effort. The only downsides are it being difficult to carry and occupying more space in storage. I recommend giving this some consideration for anyone struggling with the amount of digging they need to do in their veggie plot each year.
A Google search isn't simple. Finding an 'Agroforja double handled fork' is straightforward (on Amazon), but finding the cheaper alternatives used here isn't. 'Fourche jardin double poingée' or 'fourche de jardin deux mains' did get some results, but I have seen a well known UK manufacturer (name escapes me at the moment) on a previous search, but couldn't find it again.