Belt Squat vs Squat Squat

Ok Rip, I've got a question:

I bought a SquatMAX belt squat to use while recovering from shoulder surgery. The first time I tried the thing, I had done no leg work in weeks. I loaded 180lbs and did three sets of ten. Barely made the last rep of each set. I expected my legs to be wrecked the next day.

Nothing. Not even the slightest twinge of DOMS.

Cut to last night. After using the belt squat 2-3x/week, adding weight each time, I finally managed to get barbell on my back and high-bar squatted 135x10x3. The weight was very light, but my grip was unstable so I didn't push it up. The next day, I could barely walk.

What the hell? The movements feel very similar, and the load was much more taxing on the belt squat. Any thoughts on why one would cause so much more soreness?

Makes no sense to be either. Belt squats used to make me sore.

When I tried the TSS version (with a cable) I definitely felt it. But, everyone in my gym reports the same thing with the SquatMax - zero soreness. Oh well, it remains a mystery.

If it has an eccentric component, should make you sore, at least a little.

SquatMax video linked to above shows handles for the lifter to hold onto while performing the squat whereas videos of other belt squat machines don’t show these. Could a different distribution of the load on the eccentric (i.e., including the tension in the arms) somehow account for the differences in DOMS? (I realize I may not be doing good force vector analysis, here, but it somehow *feels* like the handles could reduce the leg strain... then it should also be a cheat on the way up...).

The mystery abides.

I've done them on and off for years with the old school Ironmind rig and not had undue soreness as a result. Must be one of my character flaws.