2 KEY POINTERS
Push during the eccentric phase. Similar to any other movement, lock in the eccentric phase by recruiting the antagonist muscles as this creates eccentric-induced co-contraction. For the vertical pulling motion that means firing the shoulders, upper chest, and triceps, particularly towards the end phase of the stretched position. Simply put, it should feel as though you are pushing the bar away from you. This should occur almost automatically simply by achieving the proper position and allowing full elongation
Use eccentric isometrics to help dial in your form and body mechanics as these help the lifter have an enhanced sense of feel and improved ability to find the optimal positions including 90-degree joint angles. Read more in my book MOVEMENT REDEFINED.
Range Of Motion
A highly common training mistake I see in beginners and advanced lifters alike is trying to pull too far and too high on vertical pulling motions such as pullups and lat pull-downs. 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 by pulling to a position where the bar is approximately in-line with the mid face which will result in approximately 90-degree joint angles at the elbow. Read more about proper body mechanics here.
Using an excessive range of motion negatively affects all other components of the pulling mechanics. The natural tendency for many lifters is to achieve a maximal range of motion as a means of promoting mobility. Unfortunately, this is actually the very thing that impairs mobility! An exaggerated range of motion produces faulty mechanics and inflammation around the joints, which happen to be the factors that restrict mobility and ROM. Focus on producing optimal and therapeutic 90 degree joint angles and your mobility will actually improve including at end-range positions when needed in extreme situations. Read more about mobility and end range training here.
With that said aiming for 90-degree angles on most movements such as squats, presses, pulls, lunges, & hinges, represents the most effective & therapeutic stimulus not only for optimizing functional strength & hypertrophy but also for minimizing joint stress. Yes of course you can go farther but then it’s no longer producing the optimal training stimulus for the muscles and you’re also increasing the potential consequences. Additionally, 90 degrees represents a position where there’s optimal muscle activation, cross-bridge cycling, anatomical leverage, osteokinematics, the length-tension relationship of muscle fibers, elastic energy, proprioceptive feedback, muscle stiffness, co-contraction, motor control, stretch reflex response, reciprocal inhibition, force production, force absorption, and power output as well as transfer to athletic performance via principles of neuromuscular physiology.
Additionally, because the muscles are in the most biomechanically and neuromuscularly advantageous position to absorb force the 90-degree position is also the safest and most therapeutic for the joints and connective tissue. Simply put, when we examine and integrate principles of neuromuscular physiology, biomechanics, muscle physiology, osteokinematics, and functional anatomy we find strong support for the notion that the 90-degree position is optimal for most movements in the sagittal plane including, pullups, squats, presses, rows, lunges, hinges, and more.