Hanging Punchbag in Cabin - Structural
I would not.
That's a very lightly-constructed roof by modern standards. Those &quot;beams&quot; are little more than stiffeners--the roofing boards are carrying most of the load over their much shorter span. By themselves the beams are not up to the task of spanning that distance with any integrity.
In my judgement any load, even static, of 100 lbs. will result in sag or other effects, and the dynamic forces of a jiggling load of such weight could pull the beam loose from the deck boards. You're also likely to see spreading of the walls due to ridge sag since there are no rafter ties preventing such movement.