I have done nearly ever test to show which rebounders are jarring and which are not. The slinky test was also a good test that demonstrated jarring and even bounce. The rebounders that have too much ballistic impact are not comfortable on my knees. Jarring can be just as painful as a very soft rebounder that inverts my ankle. Both are bad but I find that inversion still hurts my knees worse than jarring. The bungees have the least jarring while the single tiered short spring rebounders have the most jarring. The rebounders that are for the Health Bounce take about 7/8ths of the ballistic impact out and the taper springs the person up only after all the ballistic impact has been dampened. If a person is 200 pounds then about 175 pounds of the person's weight is gently decelerated while 25 pounds after the belly of the spring is fully stretched then the tier gives the impact. That impact ONLY is at the bottom of the bounce after the speed of deceleration is stopped by the belly of the spring. With a bungee there is no tier and it throws the person up after the spring extends till the weight stops it. A bad or used bungee cord that has lost its elasticity can feel jarring. The Bellicon uses Latex and not rubber so it is the most elastic. The cheap import bungees are the ones I usually have problems with.
As far as jarring, as long as 7/8ths of the ballistic impact is absorbed by the spring before the taper it is easy on my joints and I have no jarring complaints. The Needak, Lympholine, and Cellerciser are the 3 least jarring rebounders that I use for the Health Bounce. The Cellerciser is the least jarring. Once about 80 to 90% of the ballistic impact is taken off the weight of the body is when a bounce is most comfortable on the body. The 106 Gram Cellerciser spring takes the most ballistic impact out. The Needak has a bigger belly in the spring and is the softest when jumping high. If a person is too heavy they need a stiffer spring like the Hard Bounce type springs. When bouncing on the rebounder people quickly know if it is jarring.
Notice to those with knee and hip problems: If getting too soft of a rebounder, it usually won't be jarring but the inversion of the ankle will put stress on the ankles to avoid pronation and if jumping with the legs not shoulder width it can also put pressure on the hips and knees even though the jarring is not what is causing the problem.
As far as lightweight people bouncing and jarring there is usually not a jarring problem with 90 grams or heavier springs but lightweight people often complain they don't get enough bounce and to get 3 G forces doing the Health Bounce their weight is not heavy enough to stretch out the spring. This is when lightweight people tend to jump higher out of the mat to get enough G force for the lymphatic flush. The Lymphaciser is better for lightweight people or the Cellerciser if doing cardio and toning along with the Health Bounce. The Reboundair rebounder has the lowest yield least yield for its spring size due to its low coil count.
If buying a rebounder for the first time that you haven't tried before, MAKE SURE YOU GET A 30 DAY RETURN POLICY. So many people get rebounders and they end up returning them because they were not the right fit and end up paying a 20% restocking fee plus shipping both ways. You really can't tell just by the first session if it is going to hurt your knees. After several weeks of jumping a rebounder that inverts or has too much jarring is the time it usually takes to see if it is hurting. The types that most people get and don't realize are the bungees that are too soft that invert and people call and say their knees are hurting. The bungees are great but just not for the Health Bounce.