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  7. Side And Front In Out

Exercise guide

Side And Front In Out

  • Intermediate
  • Compound
  • Rep-based
  • Lower legs
  • Upper legs
  • Waist

This dynamic core exercise targets the rectus abdominis and obliques by combining traditional leg tucks with lateral extensions, using a dumbbell to increase resistance and stability demands.

Reviewed by the Crucible team · Updated June 2026

Watch the Side And Front In Out demonstrationGuided video and your full workout live in the Crucible app.

Muscles worked

Primary

  • Abs
  • Obliques

Secondary

  • Erector spinae
  • Glutes
  • Quadriceps

Equipment

  • Dumbbell

Setup

  1. Sit on the floor with your knees bent and place a light-to-moderate dumbbell vertically between your feet, gripping it firmly with your arches.
  2. Place your hands on the floor slightly behind your hips for support, leaning your torso back at a 45-degree angle.
  3. Lift your feet off the floor, keeping a slight bend in your knees to engage your lower abdominals.
  4. Pull your shoulder blades back and down to maintain a proud chest and neutral spine.

How to do it

  1. Exhale and pull your knees toward your chest in a central 'In' movement, crunching your abs as the dumbbell moves toward your torso.
  2. Inhale and extend your legs straight out in front of you, hovering the dumbbell just above the floor without letting your lower back arch.
  3. Pull the knees back in, then exhale as you extend your legs diagonally to the right side to engage the obliques.
  4. Return to center and repeat the sequence, alternating between center, right, and left extensions in a controlled tempo.

Form checklist

  • Keep your lower back from arching excessively during the extension phase.
  • Maintain a firm grip on the dumbbell with your feet throughout the entire set.
  • Ensure the movement comes from the hips and core, not by swinging the upper body.
  • Keep your neck neutral by looking slightly forward rather than at your toes.
  • Move slowly and deliberately to maintain tension on the target muscles.

Pro tips

  • Focus on 'hollowing' your stomach by pulling your navel toward your spine as you extend your legs.
  • To maximize oblique recruitment, slightly rotate your knees toward the ceiling when extending to the sides.
  • Maintain a constant 'V' shape with your torso and thighs to keep the abs under tension even at the bottom of the movement.

Make it harder

  • Remove your hands from the floor and hold them across your chest or behind your head to eliminate the stability support.
  • Slow down the extension phase to a 3-second count to increase time under tension.

Frequently asked

What muscles does the side and front in out work?
The side and front in out primarily targets the abs and obliques, and also works the erector spinae, glutes, and quadriceps as secondary muscles.
What equipment do you need for the side and front in out?
The side and front in out uses dumbbell.
Is the side and front in out good for beginners?
The side and front in out is rated intermediate. Build a base with simpler variations first, then progress to it with light load and strict form.

Related exercises

  • 45 Degrees Arms PlankIntermediate · abs, deltoids, obliques, and pectorals
  • 90 To 90Beginner · abs, glutes, obliques, and quadriceps
  • 90 To 90 SwitchIntermediate · abs, glutes, obliques, and quadriceps
  • Air BikeIntermediate · abs and obliques

Train this with a plan, not guesswork

Crucible builds the side and front in out into a precise program around your body, equipment, location, and time.

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