Age-uke, the rising block, is a simple way to redirect attacks by diverting them upward. Rising block can also defend against blows raining down from overhead. While age-uke is one of the least-used karate blocks, it is one of the most-used kobudō blocks.
To begin a rising block, cross your arms in front of your solar plexus, just like you would for a cross-body block. Then, using only your shoulder, raise your blocking arm up in an arc overhead, with a clenched fist, palm facing downward. Pull your other hand to its hip, to chamber a counterattack.
[video of age uke, from the front and from the side, fast and slow]
In many martial arts, rising blocks end with the palm facing outward, but Goshin-Jutsu rising blocks end with the palm facing downward. This trivial detail has a profound effect. The forearm is comprised of two bones; the radius, and the ulna. Palm-out rising blocks cause the ulna to absorb the entire blow. Turning your wrists shifts and twists these bones inside your forearm, so the palm-down position will evenly dissipate the impact of incoming attacks over both bones. A palm-down rising block can thus stop otherwise bone-crushing strikes.
The rising blocks of many other styles raise straight-up, allowing force to meet force head-on. The subtle rolling motion of the Goshin-Jutsu rising block dissipates the energy of an incoming attack. By rolling over a broader area, the attack never contacts any one single point, reducing a direct attack to a glancing blow as it is deflected away.
Please snugly nestled your head inside the crook of your elbow, to prevent hitting yourself with your own fist when the block makes contact. (This seems silly, but it will happen if you let it.)