The Effect of Pelvic Tilt in the Frontal Plane on Front Knee Stability

Pelvis strength and stability is well documented as playing a crucial role in overall pitching mechanics. With numerous studies illustrating the importance of a strong stable lower half having an effect on accuracy, velocity, and overall mechanical integrity, a majority of these studies focus on the pelvis angle in the transverse axis 1-3. With pitching being primarily a rotational movement, the core of kinematic research around pitching will analyze joint angles and velocities in the transverse axis to analyze performance. While I firmly agree that the pelvis placement in the z axis (at foot plant) should be the highlighted variable when breaking down a pitcher's mechanics, it shouldn’t stop there.?

What about pelvis tilt occurring in the y axis??

To break this down further, how much tilt occurs from foot contact to ball release? Does the hip collapse to the contralateral side away from the pitching arm causing a similar effect to Trendelenburg gait seen in runners, or does it stay strong as the front leg braces and the pitcher rotates around a sturdy and steady base?

Trendelenburg gait is seen in people who lack strength in gluteal musculature, causing the pelvis to dip on the contralateral side when running or walking (Figure 1) 4. A similar movement pattern can be seen in pitchers as they plant their front leg and rotate into ball release. This effect is seen as the pelvis tilts down, or away from the throwing arm, suggesting this same lack of glute strength that occurs in runners. How does this movement of the pelvis affect the rest of the pitching motion? Does this movement create an unstable base with the front leg?

Figure 1

We examined relationships between kinematic and kinetic variables from over five hundred collegiate pitches, and found a correlation coefficient of -0.35 between the amount of pelvic tilt from foot plant to ball release and knee varus/valgus movement from foot plant to ball release. So as the pelvis tilts up towards the throwing arm from foot plant to ball release (positive on the graph) the knee has more varus movement occur (negative on graph), and vice versa.

Figure 2.

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This varus movement suggests a stronger gluteal muscle group, allowing the body to rotate around a stronger and more stable front leg.?

What is the practical significance of it? The simple answer is front leg stability. The more stable the front leg, the better the foundation. A simple comparison is throwing a baseball in the deep end of a swimming pool. Without that connection to the ground, the pitcher relies heavily on the upper body to create velocity in an inefficient and injury prone manner. This can be compared to a knee that is collapsing under a valgus stress as the body rotates into ball release. While a varus movement may be more advantageous than valgus, I would argue that excessive varus movement can also be problematic in a pitcher's mechanics and delivery. This may suggest that only a mild translation of pelvis tilt from foot plant to ball release (7 - 14 deg) would result in a knee that remains stable throughout the pitch, allowing for a stronger and more stable front leg.?

Figure 3.

Regardless of the relationship, one can infer that pelvic tilt in a pitcher may be caused by gluteal strength of the pitcher. With the glutes having such a pivotal role in lower half stability in a variety of movements, it is reasonable to assume that they would play a role here. Whether it is helping stabilize the pelvis, stabilize the front leg, extend the front leg, or help the pitcher ‘ride’ the slope with the back leg into foot contact, glute strength has many crucial roles in a pitcher's mechanics and delivery 5-7.?

This is just the beginning of our understanding on the relationship between the pelvis in the frontal plane and other pitching kinematics can relate to one another.?

As I always state, the correlation seen here at -0.35 is not anywhere close to a one to one correlation but when it comes to pitching and taking into account the amount of variability that occurs from one to the other, I would argue that any trend between two distinctly different variables is worth noting. However; every pitcher is unique in their mechanics and delivery and just because you observe the pelvis dip in one pitcher doesn’t mean it will have the same cause and effect in another. I do however think that the individuality of the knee to hip is a relationship to take note of.?

References

1. Stodden, D. F., Fleisig, G. S., McLean, S. P., Lyman, S. L., & Andrews, J. R. (2001). Relationship of Pelvis and Upper Torso Kinematics to Pitched Baseball Velocity. Journal of Applied Biomechanics, 17(2), 164-172. Retrieved Jun 10, 2024, from https://doi.org/10.1123/jab.17.2.164

1. Plummer, Hillary A.1,2; Oliver, Gretchen D.1. The Relationship Between Gluteal Muscle Activation and Throwing Kinematics in Baseball and Softball Catchers. Journal of Strength and Conditioning Research 28(1):p 87-96, January 2014. | DOI: 10.1519/JSC.0b013e318295d80f?

1. Oyama S, Yu B, Blackburn JT, Padua DA, Li L, Myers JB. Effect of Excessive Contralateral Trunk Tilt on Pitching Biomechanics and Performance in High School Baseball Pitchers. The American Journal of Sports Medicine. 2013;41(10):2430-2438. doi:10.1177/0363546513496547

1. Gandbhir VN, Lam JC, Lui F, et al. Trendelenburg Gait. [Updated 2024 Feb 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK541094/

1. Oliver, Gretchen D; Keeley, David W. Gluteal Muscle Group Activation and its Relationship With Pelvis and Torso Kinematics in High-School Baseball Pitchers. Journal of Strength and Conditioning Research 24(11):p 3015-3022, November 2010. | DOI: 10.1519/JSC.0b013e3181c865ce?

1. Plummer, Hillary A.1,2; Oliver, Gretchen D.1. The Relationship Between Gluteal Muscle Activation and Throwing Kinematics in Baseball and Softball Catchers. Journal of Strength and Conditioning Research 28(1):p 87-96, January 2014. | DOI: 10.1519/JSC.0b013e318295d80f?

1. Oliver, Gretchen D.; Weimar, Wendi H.; Plummer, Hillary A.. Gluteus Medius and Scapula Muscle Activations in Youth Baseball Pitchers. Journal of Strength and Conditioning Research 29(6):p 1494-1499, June 2015. | DOI: 10.1519/JSC.0000000000000797?