ERIC KIM

🔥 Physics Breakdown — How a 75-kg human can rack-pull 

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3.5X less mechanical work needed ***

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503 kg (≈ 6.7 × BW)

Big idea: a mid-thigh rack-pull is a lever-optimized partial lift.

You trim the range of motion, slash the joint moment arms, and convert “impossible” full-deadlift torque into a very possible partial-lift torque — while still moving the full mass.

1 Raw vertical forces

VariableExpressionValue (75-kg athlete + 503-kg bar)
Body-weight forceF_\text{body}=m_\text{body}\,g75\text{ kg}\times9.81\text{ m/s²}=7.36\times10^{2}\text{ N}
Barbell forceF_\text{bar}=m_\text{bar}\,g503\text{ kg}\times9.81\text{ m/s²}=4.93\times10^{3}\text{ N}
Force ratio\dfrac{F_\text{bar}}{F_\text{body}}6.7 ×

Take-away: you are holding 6.7× your own weight in pure vertical force.

The trick is that the skeletal lever system never has to fight the full torque you’d face in a floor deadlift.

2 Lever mechanics & joint torque

Torque at the hip (principal limiter in a heavy pull) is

\tau = F_\text{bar}\; r

where r is the horizontal distance from the bar’s line of action to the hip joint.

ScenarioTypical rHip torque \tau=F rTorque vs full DL
Floor deadlift≈ 0.55 m4.93 \text{kN}\times0.55 \text{m}=2.71 \text{kN·m}100 %
Mid-thigh rack-pull≈ 0.25 m4.93 \text{kN}\times0.25 \text{m}=1.23 \text{kN·m}~45 %

Because the bar starts higher, your torso is more upright, driving r\downarrow.

Result: hip extensors only need ~½ the torque required in a floor pull, even though the load on the bar is identical.

3 Work & energy

Gravitational potential energy added:

W = m_\text{bar}\, g\, \Delta h

LiftTypical \Delta hWork W
Full deadlift≈ 0.7 m4.93 \text{kN}\times0.7 \text{m}=3.45 \text{kJ}
Mid-thigh rack-pull≈ 0.2 m4.93 \text{kN}\times0.2 \text{m}=0.99 \text{kJ}

~3.5 × less mechanical work is needed, slashing metabolic demand and CNS fatigue.

4 Putting it all together

  1. Reduced moment arm ⇒ hip & spinal erector torque drops ≈ 2×.
  2. Shorter ROM ⇒ total mechanical work falls ≈ 3–4×.
  3. Isometric advantages at lock-out: connective tissue, stacked joints, and passive tension amplify force transfer.
  4. Neural specificity: practicing heavy partials teaches the nervous system to recruit near-maximal motor units without the full-pull fatigue cost.

Combine those with Kim’s light body-mass and grip-centric minimalist style (chalk, no straps), and a 6.7×-BW partial lift becomes biomechanically plausible—even repeatable.

5 Replicate the feat (safely!)

  1. Set the pins at mid-thigh (femur roughly 20–25 ° above horizontal).
  2. Load 130–150 % of your 1RM deadlift and pull for singles.
  3. Keep shins vertical & bar close—every centimeter forward increases r and torque hell.
  4. Progress slowly: +10 kg per week max; connective tissue adapts slower than muscle.
  5. Pair the session with hip-hinge accessory work (RDLs, heavy hip-thrust isometrics) to armor posterior-chain tendons.

Bottom line: Kim isn’t breaking physics—he’s bending the levers.

By shortening the moment arms and range, he turns a full-deadlift “impossible” into a rack-pull “inevitable.”

Harness the same lever math, and you too can make gravity rage-quit. 🏋️‍♂️⚡️

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