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Alternate Leg in and Twist

The alternate leg in-and-twist is a seated core drill: you lean back, pull one knee in, and rotate your torso toward it, then switch sides in rhythm. It hits the obliques with rotation while the deep core holds your leaning position — two jobs in one compact move. Coached by Maddy (NASM-CPT) — these are the exact form cues he gives on every client's first week.

Muscles worked

Obliques Abs · rectus abdominis Deep core · transverse abdominis

Sets & reps by goal

GoalSets × RepsRest
Strength3 × 3–6 per side (with 2 s pause)90 s
Muscle3 × 9–12 per side60 s
Endurance2–3 × 18–27 per side45 s

Rep ranges per Helms 2014 · Schoenfeld 2016.

Level — Beginner

Beginner-appropriate with heels touching down; the hovering-legs version is a solid step up.

Proper form — 5 cues

  1. Sit tall first, then lean back to roughly 45 degrees with a long, proud chest.
  2. Draw one knee toward you as you rotate your shoulders toward that same side.
  3. Lead the twist with your ribcage, not by flapping your arms across.
  4. Extend the other leg long and low without letting it crash to the floor.
  5. Keep the switch smooth and deliberate — one full second per side minimum.

Breathing: Exhale as you twist toward the knee, inhale as you switch sides.

The 3 mistakes Maddy corrects most

Collapsing into a rounded slump. A fully rounded back loads the spine passively instead of making the core hold the angle. Fix: Think tall through the crown of the head even while leaning back; shorten the lean if you cannot.
Twisting only the arms while the torso stays square. The obliques rotate the trunk — if the trunk does not turn, they are not working. Fix: Turn your chest until both shoulders point toward the incoming knee.
Racing through the switches. Speed replaces muscle tension with momentum and the neck starts craning. Fix: Halve your pace; if you can hold a 1-second pause each side, the rep is real.

Common questions

What muscles does the leg in-and-twist work?

The rotation is driven by your obliques — the muscles wrapping the sides of your waist — while the rectus abdominis and hip flexors hold the leaned-back position and pull each knee in. The extended-leg hover adds a surprising amount of lower-ab work, which is why the move feels bigger than it looks.

Can beginners do this exercise?

Yes, with two easy regressions: keep your heels lightly touching the floor between reps instead of hovering the extended leg, and reduce the lean so your torso is closer to upright. As your core strengthens, deepen the lean and lift the legs — same exercise, honest progression.

How does this compare to a Russian twist?

Close cousins, not twins. A Russian twist rotates the torso with both feet fixed or hovering; this version adds an alternating knee drive, so each rep combines rotation with a leg tuck. That makes it more dynamic and slightly more demanding on the hip flexors and lower abs.

Related exercises

Russian TwistObliques Boat Hold Side TwistObliques Side Plank Reach ThroughObliques · Deep lower back WindmillsObliques Bicycle KicksObliques

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