Sandbag Lunge · Trunk Rise (Stripper Lunge)

Why this matters

This is a two-frame measurement — it captures a relationship, not a static angle. As the athlete drives up out of the lunge, the hips and shoulders should rise at the same rate, so the trunk angle holds.

If the chest dips toward the floor while the hips shoot up, the core brace has failed — the athlete is levering the sandbag up with their lower back. Coaches call it the "stripper lunge."

Under a high axial load and 100 m of fatigue, this is both inefficient (the small erectors do the legs' job) and a genuine injury risk.

How the tool works

You draw the trunk twice:

1. At the bottom of the lunge (line 1).
2. A few frames into the ascent, after the hips have left the ground (line 2).

The reported Δ is how much the trunk's forward lean changed between those two frames. A near-zero Δ means the torso stayed rigid; a large positive Δ means the chest dipped as the hips rose.

What good looks like

• Trunk angle barely changes from bottom to mid-rise (Δ ≤ 8°).
• Hips and chest travel upward together, as one rigid unit.

Common faults

Core Failure (Δ > 20°)

The "stripper lunge." Hips shoot up, chest drops. The lower back levers the bag up.

Causes: weak trunk endurance, fatigue, too heavy a bag, or never grooving a braced ascent.

Effect: lumbar strain, wasted energy, accelerating fatigue.

Minor Leak (Δ 8–20°)

A small forward dip — the brace is starting to give. Catch it before it becomes a full failure.

Coaching cues

• "Hips and chest rise together" — names the correct relationship.
• "Chest up as you stand" — keeps the torso from dipping.
• Tempo lunges holding a fixed trunk angle build the braced-ascent pattern; drop the load until the brace holds.

How to mark

1. Line 1: at the bottom, draw greater trochanter → acromion.
2. Scrub a few frames into the rise (after the hips leave the ground).
3. Line 2: draw greater trochanter → acromion again.
4. The reported Δ is the change in forward lean.

Related measurements

• Trunk Angle at Depth — the starting trunk angle this measures the change from.
• Hip Lockout at Extension — the top of the rise this ascent leads into.