core
Jackknife sit-up
Full-range ab crunch.
▶ Watch the full demo in the app3-second preview. The full demo with coach cues is in the FirstGym app.
How to do it
- Lie flat, arms overhead, legs straight.
- Lift your arms and legs to meet over your middle.
- Lower with control.
Beginner tips
- Move slowly, no flopping.
- Keep your core engaged.
- Bend your knees to scale.
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