Q:

Physiological changes necessary to scale an insect's size up while maintaining a catapult jumping mechanism and jump/body ratio?

I understand that one does not simply scale up the smallest of creatures to the size of megafauna without violating basic physiological constraints like the square/cube law, among others; so what would have to take place to take a grasshopper and enlarge it to the relative size of a grizzly bear (in terms of 3D space) and preserve its catapult jumping system?
The only thing that need remain in terms of 'grasshopper-ness, or cricket-ness' is the catapult jumping system, and preferably a frightening insectoid appearance. It need not look at all like our starting-creatures. 

Higher oxygen content in the air?
Sturdier body-plan (i.e. thicker carapace? Different materials? Wider joints/legs?)
Bird-bone-esque adaptation of weight to power? Or is this irrelevant with mostly slow-twitch muscle at the play in the catapult system? 

I'm trying to think through a creature that relies on jumping and mechanoreception to hunt prey, and is somewhat frightening to behold. 

A:

I'd go with:

a composite exoskeleton - layers of highly compressive-resistant materials between layers of elastic ones; or highly elastic on compression and high tensile will do the same - is something needed to be elastic and diffusive (spread the energy/tension over higher area) enough to mellow the take-off/landing shocks while still conserving/converting as much energy as possible (e.g landing recover some energy required for the next jump).
Two YouTube down-to-Earth-engineering clips that deal with composites for hardening and elasticity: fiber glass strengthening and core composites
elastic and tough "tendons" that allow storing mechanical energy to be used in the jump - and maybe replenished over a longer time. That is, it would be easier if the creature doesn't keep kangaroo-style hopping but taking some time to prepare for the jump (like grass-hoppers do)

