SkiErg · Drive Sequencing

Why this matters

SkiErg is a gravity-fed power tool. The power stroke is the body weight falling through the trunk hinge — the arms ride that motion and only contribute terminal wattage. The order in which the trunk and arms initiate the drive determines whether the stroke is body-weight-led or arm-led.

The trunk must drop before the elbows bend.

When the elbows bend first, the athlete has converted an indoor-rowing-style movement into a seated pull-down — biceps doing the work the hinge should be doing. Strokes become shorter, weaker, and far more fatiguing. This is the cardinal sequencing fault on a SkiErg.

What good looks like

• Trunk drops first — visible as a vertical descent at the acromion → trochanter line.
• Elbows stay straight until the trunk is well into its drop.
• The pull "rides" the body weight rather than initiating it.

Common faults

Elbow First (Δt < −50 ms)

Elbows bend before the trunk drops. The athlete is doing a standing lat pull-down instead of a hinge-led drive.

Causes: unfamiliarity with the rowing-style mechanic, dominant biceps recruitment, or anxiety about the body-weight commitment of the trunk drop.

Effect: every stroke is sub-optimal — shorter, weaker, and more taxing on the upper body. Race-pace drops the moment the biceps fatigue.

Simultaneous (−50 ms ≤ Δt ≤ +50 ms)

Trunk and arms initiate together. Not a clear fault but loses the timing advantage of body-weight-led mechanics. Often appears as fatigue accumulates and the rhythm tightens.

Causes: picking up the cadence without consciously protecting the hinge → pull order.

Effect: subtle wattage leak per stroke. Adds up over the 1000 m piece.

Coaching cues

• "Fall, then pull" — names the order explicitly.
• "Hands stay straight at the catch" — addresses the elbow-first fault directly.
• "Drop, drop, drop, pull" — a tempo cue analysts can use to drill the sequence.

How to mark

1. Start in the drive phase (handles at peak, just before they fall).
2. Step 1: scrub one frame at a time. Find the frame where the trunk first starts dropping — the acromion → trochanter line begins to angle downward.
3. Step 2: continue forward. Find the frame where the elbows first bend — the lateral epicondyle starts moving away from a straight line connecting shoulder and wrist.
4. The captured Δt = frame 2 − frame 1.

Why a two-click tool

Time-sequence faults are different from joint angles. There's no single static frame that captures them. The two-timestamp approach gives a precise, calibrated reading without the complexity of pose-tracking pipelines — and stays within the static-frame analytical paradigm coaches and analysts already trust.

Related measurements

• Global Extension at Catch — the start position the drive sequence flows out of.
• Hip Flexion at Finish — the result of a proper hinge-led drive (and the fault pattern when the hinge collapses).