What is a Horst Link?
The "Horst Link" is a term for a four-bar rear suspension which attaches the rear axle to the seatstay instead of the swingarm. Horst Leitner, the link's namesake, discovered that this design separates braking and pedaling forces from the rear suspension. Instead of chain tension and braking, causing "brake jack" or pedal "kick back", the Horst link allows the wheel to move freely in a vertical path. In fact, the Horst link will cycle up and down with the rear tire locked nearly as well as it will when it is rolling, because the axle is on the seatstay and the seatstay is "decoupled" from the suspension. A Horst link design is often referred to as a "fully active" system, meaning it's free to compress and rebound at all times, both when the rider is in the saddle and standing up. Not only is the suspension independent from chain forces under pedaling loads, but it allows you to maintain an efficient pedal stroke since the suspension action has no effect on it.
What is VPP?
Take a look at the swingarm of a VPP frame like the Intense and note the dual pivot coupling at its main pivot point. This coupling allows the two adjoining pivots to rotate around each other as the suspension compresses, which causes the rear axle to follow a backwards S-path distinctly dissimilar to the vertical path taken by a traditional 4-bar linkage. This helps give a VPP bike the same level of "activeness" as a 4-bar, but it does so while causing pedaling forces to drive the rear wheel downward rather than up. On most full suspension designs, pedaling forces result in unwanted suspension compression. The VPP's link configuration and axle path counteract this tendency towards compression without limiting or deterring bump absorption. Provided that you take the time to calibrate your sag, a VPP bike provides truly active suspension, meaning the suspension compresses and extends with rises and dips in the trail. You'll ride in a suspended "pocket" with ample positive and negative travel available to maintain traction and momentum in all trail conditions, even while pedaling.