CBMP, Contra Body Movement Position

Yes, it's a strange name! It refers to the position of the moving foot at the end of a step.

Lets consider the Feather Step – Step 1 (Leader)

⚡ TL;DR – CBMP CBMP describes a foot position where the moving foot is placed in front of or behind the standing foot. It is a consequence of the previous two or more steps, and cannot be manufactured by “just putting your foot in front of the other.” Well... you can — it’s just really ugly and doesn’t feel good.

Please refer to the Feather Step for an explanation of how CBMP is a consequence of rotation.

Step Description

RF Forward, CBM during 1

✅ Clarified Technical Details

TermClarification
CBM on 1❌ Incorrect — implies a discrete moment
CBM *during* 1✅ Correct — rotation develops over the step
Arc of the figure❌ Misleading — Feather Step is a straight-line figure
Trajectory setup✅ The step sets internal frame rotation, not external path curvature

Key Insight

  • CBM is not a discrete action, but a rotational development during the previous 1 or two steps.
  • There is no arc in the floor path — the trajectory is linear.
  • However, the rotational gearing of the torso (Vf) shapes what will be required next.
  • Step 1 does not include CBMP. But it plants the biomechanical positioning that will make CBMP inevitable in Step 3.

Biomechanical Vectors

🔹 Vt - Travel Vector

  • Represents the motion of the stepping foot
  • Lies in the XZ plane
  • Directionally straight — the Feather Step is a linear figure
  • Magnitude reflects speed and drive \(V_t = (Δx, Δy, Δz)\)

🔹 Vf - Frame Vector

  • Represents rotational change of the upper body (which can give the appearance of CBM)
  • Originates from rotation around the Y-axis (spine) during the step
  • Varies over time: \(\dfrac{dθ}{dt}\) (rotational velocity)
  • Causes tangential alignment changes to set up for Outside Partner

\(\vec{V_f} = \dfrac{dθ}{dt} × r\)

Where:

  • \(\theta\) = torso yaw
  • \(r\) = lateral partner offset (approx. 1 unit)

\(\vec{V_f}\) must be a gradual progression to setup the Frame and Hip rotation to enable CBMP to occur without the dancer 'having to plop their foot there'.