Knee Extension Angular Velocity… Your Landing Can Make Difference!

By Courtney Semkewyc (RPP Bio-mechanist Intern, PhD Candidate Biomedical Engineering at Rutgers University)

A pitcher’s foot position at foot strike can provide a solid foundation to facilitate both knee extension and efficient transfer of energy. Foot strike is the moment a pitcher’s front foot makes contact with the ground and is the starting point of energy transfer up the kinetic chain. This energy is ultimately transferred to the ball at release, with efficient energy transfer being aided by the pitcher releasing over a firm front side. A firm front side provides lower body stability for proper upper body positioning through release. This stability is achieved by extending the front knee from foot strike to release and is why knee extension angular velocity at release is correlated with pitching velocity and an important metric to examine in pitchers.

Knee extension angular velocity tells us how fast the lead knee is being extended, and as such is representative of a firm front side. In a study conducted by Matsuo et al. they divided pitchers into two groups based on ball velocity and determined that the knee extension angular velocity was significantly greater in the high velocity group (243º/s) than that of the low velocity group (124 º/s) (Matsuo et al., 2001). They also found that the high velocity group demonstrated knee extension approaching release, while the low velocity group typically showed more knee flexion and less extension approaching release (Matsuo et al., 2001). We decided to utilize these findings to examine pitcher knee extension angular velocities based on foot strike technique.

We gathered data from 33 pitchers with our Qualisys Motion Capture and 4-camera video systems and then grouped the metrics by foot strike in two categories:

    • Rearfoot strike – Pitchers who contacted the ground with their “heel” first
    • Forefoot strike – Pitchers who contacted the ground with the “ball” of their foot first

There was a third foot strike group known as midfoot strike, which is characterized by a pitcher contacting the ground with both their heel and ball of their foot simultaneously. The midfoot strike pitchers were grouped together with the forefoot strike pitchers as they have similar physiological mechanisms that drive energy up the kinetic chain.

We found that out of the 33 pitchers examined there were 23 pitchers that landed on their rearfoot, and 10 pitchers that land on either their midfoot or forefoot.

It was found that pitchers that land on their rearfoot had an average knee extension angular velocity at release of 228.9 º/s, while the forefoot group had an average of 394.1 º/s. This means that the forefoot group had a knee extension velocity 172% faster than the rearfoot group, which is statistically significantly greater than that of the rearfoot group (p=0.02, p<0.05). This demonstrates that the type of landing could have a significant impact on a pitcher’s ability to post up at release.

When examining motion capture data, we look for a knee extension angular velocity of at least 300 º/s at release based on data collected from pitchers who throw over 88mph. As a result, the rearfoot group of pitchers would be flagged for being below the minimum threshold and would be assigned workouts to help improve this metric (click here for 2 Great Exercises to Help you Post-Up).

The forefoot pitchers on the other hand have a velocity above this threshold, and as such would not require additional work. Also, of note, in the rearfoot group only 26.1% or 6 out of the 23 pitchers were above the 300 º/s threshold, whereas in the forefoot group 70% or 7 out of the 10 pitchers were above the 300 º/s threshold.

This data shows that positional differences at foot strike can have a significant impact on knee extension angular velocity. This increase in knee extension velocity could be due to the fact that forefoot landing has a better posterior drive back through the heel, which better promotes knee extension. Since forefoot pitchers land on the ball of their foot they are able to immediately dorsiflex their ankle at contact driving their heel into the ground. This dorsiflexion allows the tibia to drive backwards initiating the extension of the knee. Strength research into ankle positioning has supported this idea by showing that ankle dorsiflexion results in the most strength gains and could possibly facilitate knee extension more than other ankle positions (Cha, 2014). This helps to support the fact that forefoot pitchers because of their dorsiflexion have increased knee extension velocities.

The rearfoot landing on the other hand forces the ankle into plantarflexion. This forward movement of the ankle has an increased tendency to also continue the forward movement of the tibia, which can lead to increased knee flexion post contact. Knee flexion post contact not only gives the pitcher less time to extend the knee it also creates an “energy leak” by acting as a shock absorbing and removing energy from the kinetic chain resulting in both a slower knee extension angular velocity and ball velocity.

Knee extension angular velocity graphs of two different pitchers can be seen below. In the graphs the blue arrow indicates the 0 º/s line, and the transition from flexion to extension, where flexion velocity is positive and extension velocity is negative. The blue vertical line is foot strike, and the red vertical line is release. It can be seen in this graph that the rearfoot pitcher continues to flex after foot strike (signified by the peak directly after foot plant) before they begin to extend their knee. The velocity curve for this pitcher doesn’t transition into extension until almost halfway between foot plant and release. Thus, their deceleration suffers as too much time is spent stabilizing the front foot/leg. Instead, this time should be utilized by extending and accelerating the knee and transferring more energy up the chain through a greater increase in knee extension angular velocity.

The figure on the right is of a forefoot pitcher that is efficiently driving straight into extension after foot strike and is demonstrated by the fact that the line almost immediately slopes down under the 0 º/s line after foot strike. By beginning extension at foot strike this pitcher has more time to accelerate and accumulate speed, and as a result they have a velocity 409% faster at release than the rearfoot pitcher.

It should be noted that this forefoot pitcher also has a larger time difference between foot strike and release (0.11s vs 0.14s), which provides additional time to accumulate velocity. That being said the rearfoot pitcher has to be able to utilize their time more efficiently between foot strike and release by starting extension sooner if they want to achieve a knee extension angular velocity above 300 º/s by release.

Landing on the forefoot can provide a better mechanism for more efficient knee extension by driving earlier ankle dorsiflexion. Rearfoot landing on the other hand leads to increased ankle plantarflexion, and knee flexion post contact restricting both the time and peak velocity of knee extension as well as transfer of energy up the kinetic chain. While we understand that there are many hard throwers who land rearfoot and possess the athleticism to put up big numbers, this is generally not the norm in a younger, less athletic/experienced population who do not.

In rearfoot strike the farther the forefoot is from the ground at foot strike the more drastic the landing on the heel, and the harder it is to stop forward momentum and reverse direction into knee extension. This also holds true in forefoot strike as landing with the heel high in the air takes more time to drive back into that heel and stabilize the leg. As a result, the closer a pitcher can land to midfoot strike the quicker they will be able to dorsiflex, stabilize, and drive into knee extension. The forefoot strike pitchers because of their immediate dorsiflexion are able to start this cycle sooner than the rearfoot pitchers, and better facilitate knee extension. The data presented in this article backs the hypothesis that pitchers landing on their forefoot or midfoot helps to maximize efficiency, lead leg stability, energy transfer, and velocity.

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Citations

Cha, Y. (2014). Isokinetic Training Effect of Ankle Positions on Knee Extensor Strength. Journal of Physical Therapy Science, 26(9), 1465-1467. doi:10.1589/jpts.26.1465

Matsuo, T., Escamilla, R. F., Fleisig, G. S., Barrentine, S. W., & Andrews, J. R. (2001). Comparison of Kinematic and Temporal Parameters between Different Pitch Velocity Groups. Journal of Applied Biomechanics, 17(1), 1-13. doi:10.1123/jab.17.1.1

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