Ground Reaction Forces

Written By Tim McCormick

Ground reaction forces in the golf swing act across three distinct directional axes: Horizontal (Lateral), Rotational (Torque), and Vertical.

In high-speed swings, these forces execute in a precise temporal sequence—lateral first, rotational second, vertical last—each contributing uniquely to kinetic chain velocity.

The Three Ground Reaction Force Vectors

1. Horizontal (Lateral) Force — The Initiator

  • Direction: Side-to-side force along the target line (X-axis).

  • Peak Timing: Very early in the transition (before the club completes the backswing).

  • Role in Speed: Creates the initial mass shift toward the target. By pushing off the inside of the trail foot, it establishes the lead-side pivot dynamic and creates spatial room for the arms to drop into the slot.

  • Speed Contribution: Low direct clubhead speed generation (~10–15%), but acts as the essential positioning phase for the secondary forces.

2. Rotational Force (Horizontal Torque) — The Engine

  • Direction: Equal and opposite shear forces between the feet (Y-axis)—pushing forward toward the ball line with the lead foot while pulling backward with the trail foot.

  • Peak Timing: Midway through the downswing (when the lead arm is parallel to the ground).

  • Role in Speed: Drives pelvic rotation. This twisting force against the ground converts linear momentum into angular velocity, uncoiling the hips and torso relative to the lower body.

  • Speed Contribution: Moderate-to-high direct contribution (~25–35%), primary driver of body rotation rate.

3. Vertical Force — The Multiplier

  • Direction: Upward push straight out of the ground (Z-axis).

  • Peak Timing: Late downswing, just before impact (shaft parallel to the ground).

  • Role in Speed: Converts downward body pressure into vertical elevation (lead knee extension). Because the lead hip is offset from the center of rotation, pulling the lead hip upward accelerates the lead shoulder up and back, rapidly snapping the handle upward and whipping the clubhead through impact.

  • Speed Contribution: Highest magnitude driver (~50%+ of overall ground-generated speed in long hitters).

Comparison & Kinematic Sequence

Force Vector. Primary Mechanical Goal. Peak Force Timing. Peak Magnitude (% Body Weight)

Horizontal (Lateral) Weight transition to lead foot. Late backswing / early transition. ~25–30% BW

Rotational (Torque) Torso uncoiling / pelvic rotation. Lead arm parallel downswing. ~100–120% BW

Vertical Lead side extension ("posting"). Shaft parallel downswing. 150–200%+ BW

Tim McCormick
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