This is episode 39 of the Dunk Talk Podcast and the nerdiest episode we’ve ever recorded, in the best way. I’m Dylan Haugen, joined by Hunter Castona, and the guest is Sam Liu: 5’11”, self-described “dunk enjoyer,” Oxford engineering graduate, and a final-year biomechanics PhD candidate at Stevens Institute in New Jersey who has done something nobody else on earth has done: put 21 male and female athletes on force plates with motion-capture markers, with an adjustable hoop in the lab, to study the two-foot running dunk scientifically. Almost everything dunkers believe about jump technique comes from coaching folklore; Sam has actual data, and some of it will change how you train.
From the 2008 Olympics to a force-plate lab
Sam grew up playing basketball in China, where the 2008 Olympics (Yi Jianlian, Yao-era national frenzy) lit the dream that shrank in the usual stages: NBA, then D1, then any college ball. Schooling took him through Australia and then the UK, where high school basketball essentially doesn’t exist, so he trained alone, ran cross country, and grinded the OG Air Alert program (his review: nonstop plyos, did not help). At Oxford he studied engineering science, played basketball, and discovered biomechanics as a third-year elective during the 2016-2020 era when THP and the early jump-tech channels were first arguing about optimal technique online.
The detail that explains why dunk science doesn’t exist: when he asked about doing an Oxford PhD on jumping, his advisor told him good athletes would hit their heads on the gait lab’s ceiling. The field studies bone properties, tendon loading, walking. So he came to the US, found a professor gracious enough to allow a basketball hoop in the lab, spent four years on approvals and methodology, and built the dataset himself: two-foot running max-touch jumps and dribble dunks, force plates under each foot, full-body markers. He’s also a two-time Dunk Camp attendee; he got his first dunk at the 2021 camp, where John Evans told him he had no block foot, which, given what follows, is very funny.
Finding #1: the plant leg does almost everything
Sam’s first research question was beautifully simple: how much planting does the plant leg do, and how much blocking does the block leg do? The folklore assigns the roles cleanly. The force plates say otherwise: the plant leg does the majority of the deceleration AND the majority of the upward acceleration. It absorbs the horizontal momentum of your runup and redirects it vertical, under deeper joint angles, generating more force for longer. And this held for every single participant in the study, which almost never happens in movement analysis; when a behavior is universal, it’s a feature of the task itself, not a style choice.
The block leg’s role is different and arguably more elegant: by the time it touches the ground, your center of mass is already moving upward, which means every ounce of force the block leg produces translates directly into jump height. The plant leg is the engine and the brakes; the block leg is pure boost. Training implication: the plant leg deserves the majority of your strengthening and technical attention, and the block leg is where free inches hide.
The state of the field, for context: one peer reviewer on Sam’s paper, a former high jumper, could not envision how a person jumps off two feet. The right-left versus left-right question with different reach hands, the thing Hunter and I actually want answered, is a level of granularity the literature has never touched. Sam is essentially the entire field.
Finding #2: why you jump lower with a ball
The second study compares max-touch jumps against dribble dunks in the same athletes, and the punchline is that the difference is not one thing; it’s different for nearly every person, which is itself the finding. The mechanisms he’s documented:
- Attentional cost. Ball-in-hands sensation diverts focus from leg drive, especially in less-skilled jumpers.
- Arm-swing restriction. Everyone blames this first, and Sam thinks its effect is mostly indirect: you can’t lower your arms normally (the ball would hit your legs), so some people unconsciously cut their countermovement depth short.
- Approach contamination. The most interesting one: some athletes generated the exact same ground force with the ball but arrived at takeoff in a different body state because dribbling altered their runup, and jumped lower purely off worse initial conditions. The push didn’t change; the setup did.
His diagnostic prescription for anyone (like me) who jumps great off a lob and badly off the dribble: film two jumps as identically as possible, same start spot, same takeoff spot, camera fixed perpendicular to your plant, one with ball and one without, and compare frame by frame. If something visible differs (depth, posture, penultimate), fix that. If nothing visible differs, accept the residual: above a certain jump height there is essentially always some decrease with a ball, and that’s physics, not failure.
Finding #3: spin dunks are a block-foot trick
The 360 section is the best five minutes of the episode (Sam’s professor did her PhD on rotation in dance, so this is the lab’s home turf). The physics: whatever rotational momentum you have when you leave the ground is all you get; in the air you can only redistribute it (limbs in spins faster, limbs out slower, the figure-skater effect). So the entire 360 is decided at ground contact, and here’s the mechanism: in a normal jump, the rotation your plant foot creates is cancelled by your block foot. In a spin dunk, you deliberately don’t cancel it. Elite in-game spinners like Ja Morant and Donovan Mitchell visibly “kill the block foot” on 360 layups: instead of braking against the ground, the block foot steps over and pushes the opposite way, preserving and even boosting the rotation.
Practical takeaways for anyone grinding 360s: experiment with how your block foot meets the ground rather than just spinning harder; approach with a slight curve rather than dead straight to bring rotation in with you; and accept slowing your runup, because modifying the block foot genuinely reduces how much speed you can handle, and a spin dunk was never going to be your max-height jump anyway. (Hunter’s right-drift on fast 360 approaches, diagnosed live on the call: too much speed for a modified block foot to manage. He felt seen.)
On women’s dunking: the data says practice, not physiology
We brought Sam the women’s-vertical math from the growing-the-sport panel, and his answer carries real authority because his dataset includes female athletes: when you compare force output and generation patterns between an elite woman and a male athlete who jumps the same height, you cannot tell them apart. There’s no female-specific movement deficiency hiding in the data. Women’s dunking is nowhere near its physiological ceiling; the binding constraints are specific practice, coaching culture, and mindset, exactly the argument we’ve been making, now with force plates behind it.
What’s coming from Sam (and a spoiler about your ankles)
The pipeline: the ball-versus-no-ball paper explaining the mechanism for all 21 individuals, then a joint-loading paper quantifying what the hips, knees, and ankles of each leg actually endure, eccentric versus concentric, plant versus block. He dropped one preliminary spoiler that made Hunter and me sit up: the ankles aren’t doing nearly as much as everyone thinks. Watch for that one to upset some calf-raise evangelists.
Personally, Sam’s chasing a Windmill on his school’s 9’ hoop (front-rimming it, deload pending), enjoying jumping off every plant just for fun, and noting wryly that his jump technique improved over years in which his squat numbers went down and back up, a one-man case study in how messy the strength-to-jumping transfer actually is. His research life is the dream: write the paper, take a break, dunk in the lab.
Sam is “samlikesbiomechanics” on Instagram, with his published running-jump research linked in his bio. Go read the actual science; there is exactly one person doing it for our sport. Next episode is Daniel Castellani, one of the best dunkers in Australia. Comment with research questions you want Sam to tackle in a part two.