Chain growth and pedal-kickback – as bikes utilize chains in their drive train, and it is in connection with the engine (the rider), any changes regarding to the chain feeds back to the rider. Compressing the suspension usually causes the wheel to get farther from the bottom bracket, thus the chain is required to “get longer”. This is caused by the geometry of the suspension linkage, and taken up by some chain-tensioning device (or the rear derailleur). Since most bike have a rear hub with a clutch mechanism, which not allows for free forward rotation, the chain lengthening will cause the hub to turn forward (if it can). So the chain length change can be balanced either by wheel rotation forwards, or the cranks turning backwards or the suspension not moving. In real life, if a rider rides over a bump and the suspension is compressing, he might feel his pedals turning backwards to some extents. Or if he’s strong enough to withstand this, either the wheel will have an “extra” rotation forwards or the suspension will not compress that much, as it would without the chain (or drive train). All of these effects work at the same time in different amounts, degrading suspension performance and rider comfort.
Wheel rotation caused by suspension compression – there is another effect affecting wheel rotation besides chain lengthening. For most designs, suspension compression also makes the wheel contact point with the ground getting more rearwards from the main frame, thus if the wheel is not sliding, the rear wheel will turn backwards. Also, as the suspension is compressed and the wheel's ground contact point remains the same (imagine a stationery position), it is turning backwards compared to the main frame. These wheel rotations cause pedal-kickback by the clutch mechanism and the tensioned chain – at the ratio of the rear and front cogwheels. Thus you will feel less pedal-kickback in larger gears.
You can check these previous effects (chain growth, pedal kickback, wheel backwards rotation) on your bike as well. Just pull the front brake and compress the rear of your bike. The wheel and the cranks will turn backwards. Of course, this also happens when you ride over bumps, just you can't separate this feeling this sharply from other effects.
The pedal-kickback values are shown positive counter-clockwise, since this what you really feel as "kickback". Wheel rotation values are shown positive clockwise, thus a positive value means "forward" rotation.
As an example (using Linkage and a model for a 2005 Intense 6.6), the chain growth when both front and rear suspension are compressed 100mm is roughly 13mm, this translates in a pedal rotation of 13.7 degrees in 32/32, 19.8 degrees in 26/32, 25.7 degrees in 22/32.
found this on mtbr