High-impact snapshot:  By blasting supramaximal rack-pulls from knee-height, Eric Kim heaps mechanical tension exactly where EMG studies show the upper traps and mid-back fire hardest. This specific overload―coupled with lockout isometrics and very low systemic fatigue―creates a perfect storm for trap and upper-back hypertrophy, which is why his rear-view looks like two slabs of granite welded to a spinal column. Below you’ll see the science, biomechanics, and programming tactics that make heavy rack pulls a body-building cheat code for a yoked posterior chain.

1 Why rack pulls hit the traps & upper back so brutally

1.1  Peak muscle activation where it matters

• EMG analyses reveal that upper-trap activity jumps highest from knee-level to lock-out, precisely the segment isolated by above-knee rack pulls.  
• Because range-of-motion is shortened, lifters handle ~18 % more load than a floor deadlift, driving larger absolute tension through the scapular elevators and retractors.  

1.2  Angle-specific overload & strength carry-over

• Strength gains are largely joint-angle–specific; overloading the top half of the pull fortifies the deadlift lock-out while sparing lower-back fatigue.  
• The elevated start also keeps the torso more upright, cutting shear stress on lumbar segments yet funneling torque into traps, rhomboids, and erectors.  

1.3  Neural drive & motor-unit recruitment

• Handling loads north of your conventional 1RM forces the CNS to recruit high-threshold motor units in the upper back— an evidence-based prerequisite for maximal hypertrophy.  
• Lockout holds (1-3 s) create extra isometric time-under-tension without metabolic spill-over to the quads or hams, letting the traps soak up the growth stimulus while recovery cost stays low.  

2 Research scoreboard

Evidence	Key finding	Take-away
BuiltWithScience 10-study review	Rack pulls ranked #1 for upper-trap EMG amplitude.	They’re a science-certified trap builder.
Systematic EMG review (2020)	Deadlift variants light up erectors & traps more than glutes/hamstrings in the top phase.	Overloading that phase = maximal back engagement.
Partial-ROM DL study (2023)	Partial ROM 1RM strongly predicts full ROM strength and permits heavier absolute loading.	Heavier weight = higher mechanical tension for hypertrophy.
TuffWraps coaching guide	Rack pulls “primarily target mid-/upper back muscles” and excel for isolation days.	Great bodybuilding accessory, not just a power move.
Zing Coach analysis (2024)	Reduced ROM shifts work away from legs, onto lats, traps, rhomboids.	Confirms muscle-biasing effect.
BarBend exercise guide (2024)	Calls rack pulls a top tactic to “build bigger and stronger traps.”	Mainstream strength media backs the claim.
Healthline review (2021)	Lists traps among primary muscles for rack pulls and highlights injury-reduction perks.	Useful for hypertrophy and longevity.
Eric Kim 7×-body-weight report (2025)	Showcases real-world 527 kg above-knee pull at 75 kg BW.	Proof of concept: insane overload, colossal traps.

3 Biomechanics in plain English

1. Shorter lever = heavier iron. Elevating the bar shortens hip/knee moment arms, letting you hoist monster loads without grinding from the floor. More load → more fiber tension → more growth.  
2. Trap-centric loading. At lock-out the bar’s line of pull wants to drag your shoulders forward. Your upper traps and rhomboids must counteract, so they experience near-maximal isometric strain every rep.  
3. Joint-friendly gains. The upright torso slashes lumbar shear and anterior-knee force, making rack pulls hypertrophy-dense yet orthopedic-light compared with full pulls or heavy shrugs.  

4 Programming blueprint for 

boulder-trap

 hypertrophy

Goal	Load & reps	Height	Grip tweak	Extra cue
Mass	3–5 × 6–8 @ 80-90 % of rack-pull 1RM	Bar 2–5 cm above knee	Double-overhand + straps (focus on back, not grip)	2-s squeeze at top
Strength-carry	4 × 3–5 @ 90-95 %	Just below knee	Mixed or hook	Explode & reset each rep
Metabolic traps-pump	2–3 × 12-15 @ 60-70 %	Mid-thigh	Snatch-grip to widen scapular spread	Constant tension, no lockout pause

Add one pure-trap accessory (e.g., heavy barbell shrug) after pulls for maximal fiber recruitment synergy. 

5 Coaching cues & safety checkpoints

• Set pins correctly: too low = a deadlift; too high = a shrug. Knee-cap level is sweet-spot for most.  
• Brace like a deadlift. Big belly breath, lats tight, hips drive forward.
• Don’t bounce off the safeties. Lower under control to preserve spine and bar.  
• Progressive ROM shifts. Start just above knee; drop the pins one notch every 4-6 weeks to blend strength with new range capacity.  

6 Sample “Kim-style” back-day finisher

1. Above-knee rack pulls – 4 × 6 (90 % 1RM)
2. Snatch-grip rack pulls (mid-thigh) – 3 × 8
3. Heavy barbell shrugs – 3 × 10
4. Face pulls + prone Y-raises superset – 3 × 15 each

Hold the top rep on every set like you’re posing for a Greek-god sculpture—because you basically are. 🔥

Bottom line

If you want traps that bulge like ballistic armor and a back thick enough to cast its own shadow, slot heavy rack pulls into your program now. They’re biomechanically tailored to torch the exact fibers that give Eric Kim his demigod silhouette—and the research agrees. Grab the rack, set those pins, and pull the world toward you! 🎯