Reframing Ground Force (In Rotational Sports): Direction Over Pressure
By Ken Cherryhomes ©2025
Preface
Most hitting instructors discussing “load” are actually talking about launch preparedness, creating muscle-fascial tension (lengthening), muscle recruitment and distribution of body weight to initiate force application¹. That distinction matters. So, when anyone suggests weighting the heels while loading, such as the claim that posterior chain activation comes from the “back half of the foot,” they overlook how the body actually recruits muscle groups and balances force. It is not the heel but the great toe that activates the glutes, a well-established principle in biomechanics. True, in gait mechanics, heel strike plays a role in glute activation, but in torque-driven movements like hitting, engagement comes from medial forefoot pressure, particularly through the great toe ².
Before we even get to rotation, we have to account for how posture and gravity interact. When a hitter bends at the knees to lower their center of gravity, a common element of pre-launch positioning, the body doesn’t drop straight down. It compensates. The pelvis tilts forward to stabilize the midline, and weight naturally shifts toward the forefoot. This happens reflexively. It’s basic postural physics³. And trying to force heel pressure in that configuration isn’t just unnatural. It introduces instability.
When we set the distribution of weight proportionally, back to front, if you bend one leg more than the other, the leg with greater bend will naturally store more weight. When the torso is centered between asymmetrically flexed legs, weight can reside in the rear leg while maintaining dynamic balance. If those bend angles remain unchanged from load through stride to foot strike, the weight proportions between the legs also remain stable⁴. The center of mass may move forward, and the base of support may widen, but the internal weight bias does not change. But if your knees are bent and you still feel heavy in your heels, regardless of the front-to-back distribution, you’re no longer balanced or centered. You’ve created artificial tension through the torso to hold your position. That’s not stability. That’s a braced delay⁵. It feels loaded, but it’s inert. And this is where most force plate interpretations go off the rails.
The idea that you can build high ground force simply by sitting into a bent-leg posture with the weight stacked over the heel is a misread. Yes, you can produce vertical force, and yes, the plates will light up. But the direction is wrong. You’re compressing⁶. You’re not priming rotation. You’re stalling it.
Efficient rotational athletes (hitters, in this case) don’t launch from their heels. They load into their hips through the rear leg medial forefoot, with the knee inside the foot (GFA) and the torso center-balanced to allow for directionality and stability⁷. That’s how ground force is translated into torque. It’s also why elite hitters like Pujols or Ohtani don’t require strides. They’re not shifting. They’re turning⁸. Weight distribution can be preset, back to forward. An effective load is actually a lengthening process, a coil or stretch that removes slack in the system and creates muscle-fascial tension. The stride serves as a timing mechanism, an initiation trigger, and sometimes a means of widening the base to support the forward rotation torque converted from those stored weight proportions⁹.
How weight is distributed along the rear foot isn’t just a matter of stylistic preference. It’s a mechanical constraint. If your heels are weighted while your knees are bent, the body is compensating. It’s bracing to stay back instead of priming to move forward. You’re not generating force. You’re storing tension. And the swing doesn’t launch from that tension, it has to escape it. Because no hitter actually launches from their heels. They all eventually shift to the ball of the foot when rotation begins¹⁰. Even heel loaders. So, if that’s where it ends up, why train from a position that fights it from the start?
Introduction
This analysis responds directly to a six-part video series produced by BERTEC featuring a presenter, current Director of Hitting for the Chicago Cubs. In these videos, he offers a set of claims about ground force production, loading mechanics, and weight distribution. But his model isn’t just flawed, it’s backwards. The data itself is neutral. Force plates measure pressure, not interpretation. But the presenter’s narrative misattributes causality.
This article isn’t intended to nitpick semantics or chase ideology. It’s meant to expose a pattern of misinterpretation that’s become endemic in modern hitting instruction. What BERTEC presents as scientifically validated truths often collapse under the weight of physics, physiology, and practical performance. And the consequences aren’t academic; they affect how hitters are trained, how coaches teach, and how teams interpret swing data.
The presenter concentrates his analysis on weight shift, an antiquated cue that mistakes transition for power. This framing, as opposed to weight conversion, drives much of the prevailing narrative and creates the illusion of how force is produced. When analysis begins with models that are mechanically framed around deliberate weight shift, the conclusions are already narrowed to that assumption. The presenter reinforces this framing by assuming that any active drive from the rear foot inevitably produces a forward weight shift, which then supports his comparison of heel load versus toe push as the only two viable options.
In contrast, another model exists that remains unexamined by BERTEC and the presenter, one that is both biomechanically valid and aligned with the physics of force generation. This model does not shift weight but instead converts stored weight into torque at the rear leg by actively directing ground reaction forces through the medial forefoot. Conversion here means generating rotational torque in the azimuth rather than transferring weight linearly, which allows hip counter-rotation to remain intact while adding ground-derived rotational force into the kinetic chain.
Both models will show high front foot spikes, but from entirely different causes. In the weight-shift model, the spike is the result of bracing linear transfer into the front side. In the conversion model, the spike reflects the front side catching rotational torque that was generated at the rear foot.
Misunderstanding the Posterior Chain
The first moments of the BERTEC video lay the groundwork for everything the presenter will go on to assert. And it’s here that the foundational misunderstanding begins. Before any data is shown, he describes a loading model that he claims is grounded in posterior chain activation and heel-based pressure. It sounds technical and anatomical. But it’s biomechanically flawed.
“First, we know that good back leg loading force comes from the posterior chain. That’s your hamstrings and your glutes. Well, this also comes from the back half of the foot.”
This statement reflects a basic misstatement of how the posterior chain is actually activated. In dynamic activities like hitting, the glutes are not engaged through heel pressure. They are triggered through pressure into the ground via the medial forefoot, particularly the great (big) toe. This is a known and well-established biomechanical pathway. The hip cannot externally rotate or drive torque with stability from heel loading. That platform does not allow for directional force. It locks the system.
“I’m trying to get players to get 100% of their body weight into their back leg load before the forward advance.”
But this isn’t load. It’s a misinterpreted displacement. Getting 100% of the mass into the back leg may look like stored energy on a heat map, but that weight isn’t going to be used. It has to be relieved before any rotational force can be applied. The presenter even draws a line here:
“Generally, when you’re doing this analysis, you’re gonna see players create anywhere from 90 to 100% in their back leg load… but there’s a drastic difference from a player that’s 92% body weight in their back leg load versus 100%.”
What he calls a difference in quality is actually a difference in function. At 100% (or 92%, for that matter), the system isn’t loaded. It’s stalled. That mass cannot drive the turn. It has to come off the backside first, passively, then redistribute into a manageable balance before any forward launch can begin. And by that point, the ground force vector is no longer the same. It’s not vertical. It’s been lost, reoriented, and delayed. The measurement he celebrates isn’t a precursor to force production through rotation. It’s an obstacle to it.
Bracing Is Not Loading
He conflates weight shift with applied force, mistaking vertical pressure for rotational readiness. But loading isn’t just stacking mass. It’s sequencing usable force. Whether the hitter starts at 92% or 100%, both must return to a launch-ready posture, something closer to 60/40, back to front, before rotation initiates. The real variable isn’t percentage. It’s posture, direction, and timing. The vertical drop he identifies isn’t stored energy. It’s passive recovery. And by then, the system isn’t prepared to launch.
This model reveals the deeper issue: the difference between falling into a position and driving into it. Efficient hitters like Albert Pujols don’t rely on a stacked posture and late rotation. They generate torque by engaging the rear medial forefoot and applying posterior ground force before the stride unfolds. The stride itself is minimal not because they’re conserving effort, but because the base was already widened to accommodate a shift and the rotation is already primed.
In contrast, when the rear knee stacks over the foot and no early ground force is applied, the hitter shifts weight forward and braces it, creating what appears on the rear foot force plate as little to no change during the initial “hold.” This is not active torque generation but a static posture. The passive drift occurs after this hold, at which point the rear foot shows little or no meaningful ground force, vertical or shear, and the center of pressure migrates forward. In this model, the rear foot was never creating meaningful torque-driving ground force to begin with, and rotation is instead initiated off the front-foot spike rather than from sustained, weighted torque generated from the back side. The system rotates eventually but not as a result of efficient sequencing. It compensates. To the eye, this can resemble a clean rotational pattern, but the apparent efficiency masks a flawed sequence in which rotation is triggered reactively from the front side rather than proactively driven from the rear. The lack of early rear-foot torque is what causes the passive drift that remains hidden in plain sight.
Pujols (above) is in his pre-swing launch position with the rear leg braced at an optimal ground force angle. Pressure is driven through the medial forefoot, with the foot resisting backward against the ground to create torque. This resistance travels up through the ankle, knee, and hip, coiling the entire backside to prime rotation before the forward move begins.
In the GIF below, the hitter demonstrates true lower-body stability and efficient use of GRF. Rather than bracing or stacking into the heel, the pressure is grounded through the medial forefoot, with the ankle, knee, and hip coiling in unison. The body loads into a usable ground force angle without collapsing or requiring passive return. There is no stalled posture. No weight dump. Just anchored, directional force that readies the system to rotate. This is load, not lift. Rotation, not recovery.
Efficient posterior chain activation depends on a stabilized foot with pressure into the big toe and medial arch. That is what allows the glutes to contract and the hip to open. The heel remaining grounded during loading is not the initiator of the sequence. By tying posterior chain engagement to the back half of the foot, the presenter is confusing ground contact with ground force application. What he describes is not glute loading. It’s a braced position that resists movement and requires relief, a passive return to ground force in the azimuth (the horizontal angle or directional component of ground force application) in order to externally rotate.
The Illusion of Ground Force Mastery
This is where his interpretation finally unravels. By elevating heel pressure as a marker of efficiency, he confuses measurable intensity with mechanical utility. A heat map can show where force is applied, but it cannot tell you whether that force drives the turn. Heel dominance may create a visible pause, but it doesn’t direct energy toward rotation. That stall isn’t inherently wrong. The problem is where it happens. When weight lingers in the heel, it braces the system rather than loading it. Z-force spikes and vertical pressure readings may register high, but unless they’re redirected through the medial forefoot, they remain inert. Force is not function. Pressure is not power. And all the data in the world won’t fix a swing that’s pushing against itself.
In this GIF, the demonstration centers on driving straight down into the plate with the rear leg, showing a heavy heel-oriented press. This vertical force vector may register high Z-force readings, but it provides no rotational value. It disengages the medial chain (arch, inner ankle, hip rotators) which are critical for torque generation. It’s a false metric of loading quality; high force, poor direction.
Stacking Isn’t Steering
In this clip, the rear knee is vertically aligned over the back foot with a weighted heel during stride initiation. This stacked position signals that no directional force is being applied into the ground to initiate rotation. There is no visible posterior push, meaning force applied in the opposite direction of the intended linear move, the kind that drives into the ground toward the catcher, contributing to rotational torque toward the pitcher. In efficient hitters, this force vector originates with the knee positioned inside the foot with a ground force angle (GFA) of approximately 100°–115°, not stacked vertically. A stacked shin supports vertical motion, not horizontal drive, and is mechanically ill-suited to initiate rotation.
The False Link Between Vertical Force and Angular Speed
In another segment, the presenter claims:
“We want to hold that force as I work out into my positive move… holding that force for 1/3 of the way into the forward advance… This is what’s helping us in our adjustability as well as being able to take that force from the back leg and during rotation, transferring all of that energy into my front leg for greater angular speed.”
But this logic collapses under even basic scrutiny. He’s confusing sustained vertical pressure with usable force. Ground force doesn’t accumulate like pressure in a valve, held and then released into torque. It must be applied early and directionally to create rotational momentum. Holding weight in the rear heel while drifting forward does not generate torque. It delays it.
More critically, the idea that a hitter can hold 100 percent of their weight on the back leg and then “transfer” that force into rotation is not just incorrect. It’s physically incoherent. You can’t rotate from a static, fully rear-weighted posture. Rotation requires a torque-ready axis, with weight re-centered or shifted forward to enable rotation around the body’s midline. A 100 percent rear-loaded system has no leverage point.
The claim that this posture improves adjustability is also misguided. If the system is braced in the heel, it limits the body’s ability to adjust posture, shift direction, or initiate rotation with timing precision. True adjustability depends on ground contact that allows for subtle shifts in force vectors, not locked vertical pressure with no directional intent.
And angular speed? That doesn’t come from dumping vertical force into the front side. It comes from early coil and efficient sequencing. Posterior ground force redirected through the medial forefoot, primed to initiate rotation before the front foot ever lands. What he describes isn’t energy transfer is just late compensation for missed engagement.
Why the BERTEC Demo Shows Upper-Body Bat Speed, Not Ground-Driven Power
In the BERTEC example, the hitter begins with 100% rear weight, shifts passively forward, and applies little or no horizontal ground force from the back side before front-foot strike. The front leg braces vertical load, but because torque was never generated from the ground up, the lower body contributes minimally to bat acceleration.
This sequence forces the swing to be powered largely by upper-body rotation after the brace. The high vertical ground force readings are support forces, not torque-producing forces. Isolating these force directions would show whether bat speed is built from efficient lower-body sequencing or compensated through late upper-body effort.
Transforming Data into Noise
What he presents as biomechanical insight is, in practice, an over-interpretation of surface-level data. Force plates and pressure mats measure contact, not contribution. They can tell you where pressure exists, but not whether it’s mechanically useful. Vertical spikes and heel dominance may look impressive in a heat map, but if that pressure isn’t redirected through the medial forefoot, and timed with posterior ground force, it doesn’t drive the swing.
Every claim of increased angular speed or adjustability hinges on flawed assumptions: that pressure equals power, that drift equals intent, and that load equals torque. But efficient hitters don’t wait to prime their rotation. They engage early, apply directional force before the stride completes, and rotate from a base that’s already prepared to move.
This isn’t just a misreading of force plate data. It’s a misunderstanding of how the swing works. And no amount of vertical pressure will change that.
The data was never unclear. It measured what it was supposed to measure. But the moment it was wrapped in a story that confused pressure for propulsion, heel loading for torque, and delayed drift for sequencing, it became noise.
Not because the sensors were flawed, but because the marketing outpaced the science.
This wasn’t just a matter of interpretation gone wrong. It was interpretation shaped to fit a narrative. It looked authoritative, sounded convincing, and packaged clean visuals as biomechanics. But the conclusions were never in the numbers. They were applied afterward.
The force plates don’t endorse any of it, they just report. And when you strip away the story, what remains is this: vertical force isn’t torque, pauses aren’t coiling, and magnitude isn’t the same as meaningful.
What matters isn’t where the pressure was. It’s when, where, and how the ground was engaged to generate rotation. That’s what the data could have shown if it had been allowed to speak for itself.
Appendix A: Supporting Research
- Load as Launch Preparedness
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1.2. McGill, Stuart M. Ultimate Back Fitness and Performance. 6th ed., Waterloo, ON: Backfitpro, 2017. - Great Toe Activation and Glute Engagement
1. Watanabe, Kazuki, et al. “Effect of toe grasping on the electromyographic activity of the lower extremity muscles during standing posture control.” Journal of Physical Therapy Science 27, no. 1 (2015): 37–40. doi:10.1589/jpts.27.37
2.2. McKeon, Patrick O., et al. “The foot core system: a new paradigm for understanding intrinsic foot muscle function.” British Journal of Sports Medicine 49, no. 5 (2015): 290. doi:10.1136/bjsports-2013-092690 - Knee Flexion, Pelvic Tilt, and Forefoot Bias
1. Neumann, Donald A. Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. 3rd ed., St. Louis: Elsevier, 2017.
3.2. Lees, Adrian. “Technique analysis in sports: a critical review.” Journal of Sports Sciences 20, no. 10 (2002): 813–828. doi:10.1080/026404102320675657 - Stable Weight Proportions with Constant Joint Angles
1. Winter, David A. Biomechanics and Motor Control of Human Movement. 4th ed., Hoboken, NJ: Wiley, 2009. - Heel Bias and Artificial Tension in a Bent-Knee Stance
1. Zajac, Felix E. “Muscle and tendon: properties, models, scaling, and application to biomechanics and motor control.” Critical Reviews in Biomedical Engineering 17, no. 4 (1989): 359–411.
5.2. Chang, R., et al. “Postural responses to forefoot and rearfoot perturbations.” Gait & Posture 30, no. 3 (2009): 341–345. doi:10.1016/j.gaitpost.2009.06.009 - Vertical Force vs. Rotational Force Directionality
1. Szymanski, David J., et al. “The relationship between ground reaction force variables and bat swing velocity of high-school baseball players.” Journal of Strength and Conditioning Research 23, no. 6 (2009): 1608–1615. doi:10.1519/JSC.0b013e3181a3c6a4
6.2. Nesbit, Steven M., and Kerry M. Serrano. “Work and power analysis of the golf swing.” Journal of Sports Science & Medicine 4, no. 4 (2005): 520–533. - Medial Forefoot Loading and Ground Force Angle (GFA)
1. Kwon, Young-Hoo, et al. “Role of lateral-to-medial ground reaction force in generating torque and speed in baseball hitting.” Sports Biomechanics 12, no. 2 (2013): 127–135. doi:10.1080/14763141.2012.660799
7.2. Ball, Kevin A., and John W. Best. “Different centre of pressure patterns within the golf stance and their effect on swing mechanics.” Sports Biomechanics 6, no. 3 (2007): 285–301. doi:10.1080/14763140701491558 - Preset Weight Distribution and Rotation in Elite Hitters
1. Welch, Christopher M., et al. “Hitting a baseball: A biomechanical description.” Journal of Sports Science & Medicine 7, no. 4 (2008): 542–550.
8.2. Fleisig, Glenn S., et al. “Kinematic and kinetic comparison between baseball batting and golf swinging.” Journal of Applied Biomechanics 18, no. 4 (2002): 367–376. doi:10.1123/jab.18.4.367 - Load as Lengthening; Stride as Timing
1. Escamilla, Rafael F., et al. “A three-dimensional biomechanical analysis of the baseball swing.” Journal of Applied Biomechanics 25, no. 2 (2009): 116–123. doi:10.1123/jab.25.2.116
9.2. Szymanski, David J., et al. “Effect of strength training on bat speed in high school baseball players.” Journal of Strength and Conditioning Research 24, no. 1 (2010): 1–10. doi:10.1519/JSC.0b013e3181c6a0c3 - Heel Rise at Rotation Initiation
1. Kageyama, Masahiro, et al. “Kinematic and kinetic profiles of baseball batting.” Journal of Applied Biomechanics 30, no. 6 (2014): 1187–1197. doi:10.1123/jab.2013-0247
10.2. Inkster, B., et al. “Ground reaction forces and center of pressure patterns in the golf swing: A review.” Sports Biomechanics 11, no. 2 (2012): 159–175. doi:10.1080/14763141.2012.671354