Many people are used to train their chest muscles, but you definitly should pay the same attention to its counterpart - the upper back. If you have muscular imbalances at your upper body (chest much stronger than the upper back) you'll probably look like the "Hunchback of Notre Dame" one day. It also can cause pain at your back (especially for the girls because of the weight of the boobs at the front side). Not to mention that a strong upper back prevents injuries at this part of your body.
Pull ups, as a prime exercise for your upper back, have many benefits, including giving you a strong counterpart to the chest, giving you enormous power, are a really safe but challanging exercise for your upper back, shoulders, forearms and biceps, giving your body a nice shape and, last but not least, they are a feat of strengh and just look unmentionable cool ;)
Due to the fact, that most people aren't able to perform at least one slow and clean rep of full pull ups Paul developed a progression series to lead everyone to the full pull ups and beyond. And the first step of this progression is the Vertical Pulls. Vertical Pulls work your upper back and your biceps pretty slight but still enough so that your muscles get an impulse to grow and your tendons and joints (especially the ones in your elbows and shoulders) start to get used to this type of stress.
Let's come to the how-to-perform explanation:
Find a solid vertical base on which you can hold on safely (a doorframe or something similar). Stand close to that base (like me in the video) and grab it breast-high. In this position your arms will be well bent. Now allow your body to shift back by leaning slightly and extend your arms until they are almost straight in the same time. This should last 2 seconds. Hold for a count and pull yourself back in the start position by contracting your shoulder blades and bending your arms simultaneously (again 2 sec). Repeat the movement without a rest. If you can't manage to meet the target instantly, do as much reps as possible until you can do the requested amount.
Caution: To prevent your shoulders from injuries keep your shoulders tight (no relaxing) during any exercise when you hang somewhere. This advice is also valid for vertical pulls.
Target: 3 sets of 40 reps
With my physical ability it was easy to meet the target 3 times in a row so I moved on to the next step after I did verticall pulls 3 times. I guess some of you who are used to train before will meet the target as fast as I did, while others will need some more time.
Paul recommends to do the exercise only once a week but I prefer to do it twice (see "The Plan").