This is the most asked question be it Uganda or Rwanda. Its not easy to answer. So many factors are involved, and if they all go against you, you could be in for a genuinely exhausting outing . On the other hand, if everything works in your favor, the excursion will be little more demanding than the proverbial stroll in the park.
There are two types of trekking, one where you go find gorillas next to the beginning of the forest and it would just take about 30-60 minutes. the other is when you go deep into the forest to search for the gorillas but they would have been already followed by the rangers before you to easily locate them.
The first type of the trek is obvious because the surface if flat and not demanding may be if you are trekking Susa-A which begins with a steep surface. The next part is difficult to guess and will depend much on the location of the groups that day.
The other factors that will determine will be the thickness of the forest and the terrain if muddy or not.
You fitness and age are also key in which group will be easy for you. Those in the late 50s will find it hard to track groups like Susa-A because of the steep terrain.
The trek to susa-A is of course the most demanding but with a reward of over 40 gorillas while the sabyinyo family is the reliable one to reach. Kwitonda family and Hirwa family is also not that demanding.
Though people may say trekking is a bit easy, do not take this hiking for granted. If you have problems with altitude you also have something to worry about. The elevation is up to 3000m.
Its is important that you ask for a walking stick for the hike and also hire porters to help you with your luggage.
While tracking, take things easy and always ask for a stop if you feel you need it. Carry alot of water which you tour operator will provide for you and some snacks.