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Arming Ratio

The Arming Ratio is the diagnostic test for detecting Arming in real time: does the racket head accelerate before the hips have cleared?

Specifically — does the hand pass the plane of the back hip before the navel faces the net?

If yes: the Stretch-Shortening Cycle has failed and the player is pulling with the shoulder rather than whipping from the core. This is the first fault to identify and correct.

The Test

The Arming Ratio is framed as a single binary question:

Does the racket head accelerate before the hips have cleared? If the hand passes the plane of the back hip before the navel faces the net → the SSC has failed → Arming is occurring.

This test can be applied by a coach watching live or from video at any frame rate that captures the hip clearance moment. It is the first check in the Technical Diagnostic Matrix (Chapter 6, section 6.10) before any other technical cue is introduced.

What It Detects

The Arming Ratio catches the precise moment the Kinetic Chain sequence breaks down. In correct sequencing:

  1. Legs drive → hips uncoil → navel turns to the net
  2. After the navel faces the net → torso accelerates
  3. After torso decelerates → shoulder transfers to the arm
  4. After shoulder decelerates → wrist/racket fires

When the hand passes the back hip before the navel has faced the net, steps 2–4 have been short-circuited. The arm is generating acceleration before the hip chain has delivered its momentum — pulling from the shoulder rather than receiving from the chain.

Why It's the First Fault

The handbook is explicit: the Arming Ratio is checked before any other diagnostic because:

  • It reveals whether the fault is biomechanical (chain sequencing) or technical (follow-through, grip, contact point)
  • A player who is Arming needs core sequencing work — not follow-through instruction, grip adjustment, or contact zone coaching
  • All downstream technical faults (flat shots, mistimed contact, inconsistent direction) may be caused by Arming; fixing them without fixing the sequence is futile

The Diagnostic Matrix Context

From the handbook:

When coaching your player's forehand, use the Technical Diagnostic Matrix in section 6.10 as your first-pass analysis tool before introducing any technical cue. A player showing contact compression needs footwork work, not arm instruction. A player showing Arming needs core sequencing work, not follow-through instruction.

The matrix maps symptoms to sources:

Symptom Source Intervention
Arming (hand before hip) SSC failure / chain sequence break Core sequencing work
Contact compression Footwork / court position Footwork work
Floated shot, no pace Leg drive absent Leg drive emphasis
Ball going long Wrist mechanics / grip Racket face / grip adjustment

Coaching Cue

The most common corrective cue: "Let the hips go first." A more specific cue: "Your navel must face the net before your hand passes your hip." Shadow swing drills with a hand on the hip to feel the sequence order are the primary training tool.

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