There’s a 3rd one…Specialized BG which was built around Dr. Pruitt’s research. Now a 4th one, Shimano PRO.
Selle Italia measures thigh circ. but never uses it in selecting a saddle, but it is important since for a given width saddle, the concave part that comes into contact with your inner leg varies greatly from saddle to saddle in a given S1,2,3, L1,2,3 size saddle so its up to the fitter to know the shapes of the saddles. Their system makes sense as the S is for small sit bone widths, the L for large. the 1, 2, 3 for how much loose your hamstrings are (which determines how far you can bend over to touch toes).
Selle Italia, Specialized and to some degree Fizik’s concept is that the more flexible you are, the more pressure will be applied to the nerves and blood supply to ‘man land’ area. That is where the cut out comes into play. If hardly any flexibility, then you will sit more upright and don’t need the cutout. Fizik has a slot which has been tested by Dr Pruitt not to work as effectively as an actual hole.
Sorry, but the Shimano guys actually have it backwards. The more flexible you are, the less you need a cutout. More ego than common sense and I have talked to the guy that in charge of the saddles and I don’t think he really understands the concepts - a pure marketing guy.
My greatest concerns are for the pro cyclists who use the wrong saddles and will suffer the consequences in about 10 more years.
Cycling can be a harsh sport to the body’s reproductive functions and one of our missions as fitters to have people be able to fully enjoy life off the bike.
You can quote me on that…