Both beginners and advanced lifters alike try to pull too far and too high on vertical pulling motions such as pull-ups and lat pulldowns. Rather than trying to touch the bar to your chest or reaching your chin over the bar (both of which can produce dysfunctional mechanics), the goal should be to achieve proper upper back and lat activation. This requires several components.
1. Create ample t-spine extension.
This is particularly true in the contracted position. This helps centrate the glenohumeral joint. Lack of t-spine extension facilitates a very unstable shoulder joint and allows excessive range of motion and faulty mechanics to take place. This is largely why many lifters touch the bar to their chest when performing pull-ups and pulldowns. This in no way indicates strong levels of mobility or strength, but instead indicates faulty activation patterns and dysfunctional movement.
2. Pull to the sternum.
Another important cue that promotes ideal vertical pulling mechanics is pulling to the sternum rather than to the clavicle. Pulling to the clavicle minimizes activation in the lats, particularly the lower lats, as the shoulders and scapula can't fully depress and medially rotate towards the spine. Pulling to the sternum, however, not only places the shoulders in the most biomechanically sound position, it requires an incredible amount of lat activation, regardless of the load. One cue that can be helpful is to think about pulling your body away from the bar rather than towards it.
3. Point the elbows straight ahead.
Screwing the elbows forward is another critical mistake when doing pull-ups and pulldowns. Regardless of the grip (pronated, supinated, or neutral) or hand placement (wide, medium, or close), the elbows need to point straight ahead throughout, rather than out to the sides. This helps to engage the entire musculature of the lats rather than just the upper portion. It also ensures you're not pulling from the upper traps and shoulders.
4. The bar should NOT touch the chest.
By incorporating these cues, the pulldown or pull-up range of motion will actually be more compact than what most lifters assume. In fact, proper vertical pulling mechanics during the concentric phase ends with the bar stopping one to several inches above chest height rather than touching the chest.