Trunk Flexion

Crunch

A practical movement guide for every Mission SOP that uses this exercise. Sets, reps, load, tempo, and purpose remain specific to each mission and phase.

Movement guide available

Anatomy map

Muscles involved

Primary musclesOrange · None
Secondary musclesGraphite gray · None

PrimaryAbs

Secondary

ShaOS custom anatomy illustration. Visual reference only; movement coaching and muscle classifications remain defined by the Exercise Library.

Description

A controlled floor exercise that trains the abs to flex the upper trunk while the pelvis and feet remain quiet.

Setup & Execution

Lie on your back with knees bent, feet flat, and hands placed lightly beside the head or across the chest.
Exhale and gently bring the ribs toward the pelvis without pulling on the neck.
Lift the shoulder blades only as far as the abs can control while the lower back and feet stay settled.
Pause briefly, then lower under control until the shoulders return to the floor.

Coaching Cues

Bring ribs toward pelvis.
Keep the neck relaxed.
Lift with your abs, not momentum.

Common Mistakes

Pulling the head forward with the hands.
Driving through the feet to create momentum.
Turning the movement into a full sit-up.

Movement media

See the movement

Reviewed short loop

Muscle highlight key

Primary musclesOrange · Abs
Secondary musclesGraphite gray · None

Published media: Short silent loop · 6 seconds
Reviewed: Sep 3, 2026
Video source: ShaOS production record

30–60 second tutorialplanned

Setup angleplanned

Side angleplanned

Key cue overlayplanned

Captionsplanned

Transcriptplanned

Accessible movement summary

Lie on your back with knees bent, feet flat, and hands placed lightly beside the head or across the chest. Exhale and gently bring the ribs toward the pelvis without pulling on the neck. Lift the shoulder blades only as far as the abs can control while the lower back and feet stay settled. Pause briefly, then lower under control until the shoulders return to the floor.

Key cue: Bring ribs toward pelvis.

The production indicators above are roadmap states, not claims that multi-angle footage, overlays, captions, or a narrated transcript are already available.

Adapt the movement

Regressions & alternatives

Preserve the movement pattern while matching current capacity, available equipment, and the mission environment.

Regression

Short-range crunch with hands reaching toward the knees

Progression

Slow-eccentric crunch with a top pause

Home gym

Controlled floor crunch

Commercial gym

Cable crunch with a light, controlled load

Used in