Utilizing the vertical tibia position in level changes such as the squat and split squat have been a major interest of mine since my tenure with the Philadelphia 76ers. Utilizing such techniques as the true box squat and rack pull not only have the posterior chain focus, but also I believe there are meaningful changes to knee mechanics that may yield durability long-term compared to movements with an angled tibia. There is considerable attention afforded this topic on my upcoming DVD, Training = Rehab, Rehab = Training.
The question below came from a D1 Strength Coach looking to gain some more insight to the vertical tibia message.
I have one question on vertical tibia training that I was not able to find an answer for in my research.
When you maintain a vertical tibia in an exercise such as a split squat, there is more of a true roll and less glide of the femur. With this there has to be a greater tensile force in the quad/patellar tendon due to the greater horizontal distance compared to a gliding femur. Have you come across any research that quantifies this tensile force and the relationship is has with patellar compression?
I will do my best to answer your question, but please keep in mind that my application of methodology in regards to the tibia angle is what I would consider science-based. I believe there are trends and literature to believe what I can explain, but as far as research, there is very little that specifically addesses the same movement pattern within terms of a vertical or angled tibia.
In the vertical tibia, there is a posterior weight shift which leads to a DEloading of the anterior chain, the quad/patella tendon specifically. It is certainly not slacked, but stress is funnelled to the hip joint much more than the knee.
The arthokinematic position the femoral head is in a more stable position more posterior to the position it would be in an angled tibia technique. While the femur is still in contact with the posterior aspect of the patella, it is with a graded posterior pull via the posterior weight shift that I mentioned above.
If there were greater anterior chain forces, which I have not read whether this is or isn’t, the translation of those forces through bony stability channels would be much more in the angled tibia position than vertical based on the arthokinematics that you recognize.
Fry et al’s fairly known “Biomechanics of the Squat” yields the trends that I am reporting on here.
There is another study that powers this presentation demonstrated the natural pattern for a pain-free ACL was with vertical while the non-surgical side descended into angled. I found this literature after I had actually seen this myself in an athlete, and it looks as bizarre as it seems if you are visualizing it. The trend that I am reporting on is the natural neuromuscular control that these subjects demonstrated to “get away” for a knee that the brian thought could not buttress any more bony contact(s). The nociception “memory” was enough to garner the posterior weight shift.
So basically I am not prepared to suggest there is any less patella compression from the anterior chain or from the anterior aspect of the patella. I am suggesting there is a more stable and posteriorly mediated environment on the other side of the patella. There may be a strong punch in, but there is less of a punch back, and the retro-patella is spared as is further caudal “grind” of any meniscal wear.
Always to keep in mind in considering my thoughts with the vertical vs. angled tibia is that the angled tibia is real-life. We operate in ADLs and athletic movement with an angled tibia. Fundamental movement and most power training utilize the positions. They can not be avoided. Strength training is where the vertical positions can be maximized in bringing up the weak link of the posterior chain.