Boxing Punch Mechanics: Kinetic Chain Simulator

Stance

Throw a Punch

Weight transfer (kinetic-chain power) 70%

Impact Readouts

Fist velocity at impact0.0 m/s

Impact force (avg, 15 ms contact)0 N

Peak hip rotation0°

How it works

Punch power in boxing does not come from the arm alone -- it comes from the kinetic chain: the legs push off the ground, the hips rotate first, the torso follows a beat later, and the shoulder/arm extend last, each segment adding its rotational speed to the one before it, so the fist arrives moving faster than the arm could move on its own.

Kinetic chain (sequential summation):
  hips rotate  ->  torso rotates  ->  shoulder/arm extend
  v(fist) = sum of each segment's contribution, timed in sequence

Impulse-momentum theorem (impact force):
  J = m_eff * v_impact           (impulse, kg*m/s)
  F_avg = J / Δt                 (Δt ≈ 15 ms fist-bag contact)

Effective mass delivered:
  m_eff = m_arm + m_transfer * (power/100)
  m_arm ≈ 1 kg,  m_transfer ≈ 6 kg of body mass
  (well-sequenced weight transfer puts more of the body's
   mass, not just the arm's, behind the fist)

Struck pendulum (heavy bag):
  Δω = J * L / (M_bag * L^2) = J / (M_bag * L)
  θ'' = -(g/L) sinθ - c θ'   (damped pendulum after impact)

Weight transfer slider -- how completely hip rotation drives the punch, from an "arm-only" push to a fully sequenced, hip-and-shoulder-driven strike. It scales both the hip/torso rotation and how much body mass (m_transfer) is delivered into m_eff.
Jab / Cross -- straight punches from the lead / rear hand; the cross uses far more hip and torso rotation than the jab, which is why it hits harder.
Lead Hook / Rear Uppercut -- curved and vertical punch paths that route the same kinetic chain through a different joint trajectory.
The heavy bag is a real damped pendulum: the punch delivers an angular impulse Δω at the moment of contact, then gravity and damping bring it back to rest.

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Lead arm Rear arm Heavy bag

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