As the name states, hikers who set off on these tours generally want to move along quite quickly. This means that the tours are usually more strenuous than, say, a classic hike is. For this reason, you really have to focus intensely on tour planning and then come up with the best possible approach to your outing.
Just like any hike, you should realistically assess your physical condition and avoid selecting a route that will require you to take on more than you can handle. Anyone who heads off to the mountains only every now and then should certainly not take on a multi-day speed hiking tour. The key aspect at this stage is to assess the distances as best as possible and to select shorter routes at the start.