If 1 can break, so can the other 3. You see this when too much [more than 1 drop of thin CA] is applied to each side.
Regular hinges rarely fail, but they can pull out if not pinned in place with round toothpicks.
As a "stop-gap" measure you can sew about 3 pairs of stitches with carpet thread in the spot that has the broken hinge...do a complete round trip with the stitches and tie the loose ends off.
Since it's a trainer I wouldn't take it any further than making it functional.