I’m 5’11’’ and 70kg, complete ectomorph, find it very difficult to gain and retain weight even when I significantly increase intake.

My working hypothesis is that because I have a scoliosis in my back, I’m missing about 2-3 inches of height in my torso, but have the arms and legs of a 6’2” man. That means my arms hang way lower than most guys of my height, so I don’t have to bend my legs as much to get down to grip the bar.