Nowadays, true posterior chain strength work seems to be disappearing? It seems that many strength coaches are abandoning some great posterior chain exercises in favor of rehabilitation type exercises. Glute bridging, single-leg glute gridges (Cook Hip Lift), slideboard leg curls, quadruped hip extension exercises, and single-leg RDL's seem to be the flavor these days.
My question is what happened with bilateral RDL's/stiff-leg deadlifts, deadlifts, glute-ham raises, cleans and snatches from the floor, or even straight-leg hip extensions (remember the "old school" roman chairs)? Did these exercises become obsolete? Were the coaches who used these exercises with great success, for years upon years, wrong when it came to working the posterior chain?
The key is critically looking at any exercise in both a biomechanical and physiological sense. Questions that need to be answered: does the exercise recruit high-threshold motor units and does the movement put the specific muscles in an optimal mechanical position to function? Not many sports, especially team sports, involve low-threshold motor units (slow-twitch fibers) and limited hip flexion and extension. What is the adaptation from low load, low velocity exercises and their carryover to high load, high velocity activities? (principle of specificity)
For example, does a glute-bridge (any version; single-leg or double leg) or slideboard leg-curl recruit most or all of the possible motor units? Do these exercises take the hip through a full range of motion to get maximal activity out of the hip extensors? My answer would be, no they do not. Could they be loaded to increase motor unit recruitment... maybe, but I haven't found a very effective way to do so, and again you can't or don't get a pre-stretch of the hip extensors into hip flexion.
How about a standard 2-leg RDL or the glute-ham raise? Do they or can they recruit high-threshold motor units? Most definitely. When done correctly do they biomechanically stretch and contract the hip extensors? The glute-ham raise, depending on how it is done, may or may not, but it certainly gets work out of the hamstrings, and the RDL absolutely does.
Also one of the main functions of the glute complex is to control forward lean of the torso, some of the above exercises negate this very important function.
Now I must be clear on everything here, I most definitely have and/or do use some of the previously mentioned exercises. Some of the glute bridging and other exercises can be great for pedagogical purposes. And I am aware that a single-leg RDL can be loaded relatively heavy and of the research behind bilateral deficit, but the load on the system in any bilateral exercise, I would argue, does quite a bit for the development of the athlete.
Single-leg training is important for balance of musculature, reducing the bilateral deficit, and recruiting stabilizing muscles. I do think single-leg/limb training is a necessity, however...
... areas of question that I have: the stability component of high speed movement is much different than weightroom stability. Running actions are cyclical and the effect is more like a gyroscope with the actions of the arms and legs; the need for single-leg stability is minimal. Multi-directional movement is different and does require a tremendous amount of single-leg stability, but the force vectors required in multi-directional movements require more horizontal stability than the force application and vectors in the weightroom which are more vertical in nature. Also, upper body mechanics play a larger role in lower body stability during dynamic movements than one might think...
The key is to train and strengthen posterior chain/hip complex, not just stimulate it.
Front Squat vs. Back Squat
There has also been an increased favor towards the front squat as opposed to the back squats when it comes to knee dominant exercises or lower body pushing, if you will. The thought is that the back squat places too great of a load on the low back and that the front squat reduces this load. Research shows a slight difference, and looking at moment arm lengths when watching a squat this can be visually seen to be true with the increased forward lean and hip flexion in the back squat as opposed to the front squat. But this increased hip flexion leads to increased activity out of the hip extensors which in a anterior/quad dominated society can be a very good thing. So, could it be said... the back squat is a posterior chain exercise?
Plus, the increased hip flexion in a back squat lengthens the proximal hamstrings pulling on each muscles (semi-membranosus,-tendinosus, and biceps femoris) insertion at the tibia, which reduces the anterior sheer at the knee caused by the quadriceps (anterior displacement of the tibia on the femur). (Also why hip flexion upon landing is so important for females... the increased "tug" from the hamstrings reduces ACL stress)
Another positive of the back squat is the necessity of increased dorsiflexion at the ankle. This stretches the soleus/gastrocnemius complex creating an extension moment at the knee, again reducing and/or neutralizing anterior sheer on the knee.
Another overlooked aspect when it comes to the front squat vs. back squat is the necessity of thoracic extension to maintain good technique. Yes, I am aware, that those with shit for posture (myself included) can make up for this with abduction and increased external rotation at the glenohumeral joint, but with good coaching this can be worked on and improved. The front squat does require upper back extension but is limited with the reduction of an anterior sheer force and abduction of the scapula.
These qualities to the back squat and a whole lot more...
There are many more benefits to the back squat than the few I listed here and I think it is safe to say that the back squat IS an effective exercise. I believe both the front and back squat have a place in a program, but I don't believe that because "so and so" only uses the front squat, that the back squat needs to be banished for eternity.
In a program lacking high load, hip flexion to extension posterior chain/hip dominant work and utilizing only front squats, there is a missing gap. Single-leg exercises may help, but most are anterior/knee dominated movements. An anterior dominant program is great for acceleration out of blocks or a three-point stance in running the 40 yard dash, but limited in "upright" acceleration (which most sports involve) and top-end sprinting and most importantly in injury prevention.
To wrap things up...
-The posterior chain needs to be trained in a way that induces high threshold motor unit recruitment and effectively targets hip extension from a pre-stretched position of hip flexion.
-Back squats are a great exercise.