In and Out Abs Exercise: Form, Muscles Worked & Workouts

The in and out abs exercise is a seated bodyweight movement where you extend your legs out and pull them back in while balancing on your glutes.

It requires zero equipment, scales from beginner to advanced, and trains your abs through a range of motion that most floor exercises miss.

This guide breaks down proper form with specific breathing cues, which muscles actually fire, the most common mistakes we see, a clear progression ladder from beginner to advanced.

What Is the In and Out Abs Exercise

The in and out abs exercise (also called the seated tuck or in and outs) is a bodyweight core movement performed on the floor or a bench edge.

You lean back slightly, extend both legs out in front of you, then pull your knees toward your chest. That’s one rep.

What makes this exercise effective is the starting position. In a seated position, your hip joint begins at roughly 90 degrees of flexion.

This exercise bypasses the 0-to-90-degree range where hip flexors do most of the work. Your rectus abdominis engages immediately and intensely from the first rep.

The in and out core exercise works for all fitness levels. Beginners keep their hands on the floor behind them for support.

Intermediate and advanced lifters can remove hand support, add weight, or progress to full V-ups.

Whether you’re chasing a visible six-pack or building bracing strength for heavy lifts, this movement delivers.

Muscles Worked During In and Outs

The in and out abs exercise recruits more muscle than it appears to at first glance.

Primary movers:

• Rectus abdominis drives the trunk flexion when you pull your knees in and resists spinal extension during the “out” phase.
• Hip flexors (iliopsoas) assist with leg movement, though their role is reduced compared to lying leg raises because of the seated starting position.

Secondary stabilizers:

• Transverse abdominis acts like an internal belt, bracing the spine and generating intra-abdominal pressure throughout each rep.
• Obliques (internal and external) resist rotational drift and keep your torso centered as you extend and tuck.
• Erector spinae (lower back) fires isometrically to maintain your balance on the glutes.
• Quadriceps hold your legs extended during the “out” phase. Quad cramping is common for beginners and fades with practice.

Your core is more than just your abs. It includes your deep abdominals, obliques, pelvic floor, lower back, and even the glutes. The in and out trains most of these in a single movement.

Benefits of In and Out Abs

Your abs activate from rep one

The seated position skips the hip-flexor-dominant range. This makes every rep more abs-intensive compared to lying leg raises where the first 90 degrees of motion is primarily hip flexor work.

Train anti-extension strength

The in and outs train core strength and position control simultaneously. The “out” phase forces your abs to resist spinal extension. This transfers directly to heavier squats, deadlifts, and better posture.

Zero equipment required

Floor only. You can do in and outs at home, in a hotel room, or in a park, and the exercise scales from rehab-level regressions to weighted advanced variations.

Supports the movement pattern

The in and out shares the same seated hip-flexion mechanic. While in and outs were not directly tested, the biomechanical similarity suggests comparable activation levels.

Dynamic core work builds functional strength

A 2009 U.S. Army study found that soldiers who replaced sit-ups with dynamic core exercises performed better on physical assessments.

A deceptive move but highly effective. It targets multiple areas of the core at once.

How to Do the In and Out Abs Exercise (Step-by-Step)

You can learn this movement in under two minutes. The real skill is maintaining quality reps once fatigue sets in.

Setup

1. Sit on the floor with your legs extended in front of you.
2. Place your hands slightly behind your hips with fingertips pointing forward. Beginners keep hands here for support. Intermediate and advanced lifters can lift their hands off the floor.
3. Lean your torso back about 30 to 45 degrees, engage your core, and lift your feet 2 to 3 inches off the ground.

Execution

1. Inhale. Slowly extend your legs out straight while leaning your torso back slightly further. Take a full 2 seconds for this phase.
2. Exhale. Pull your knees toward your chest while bringing your torso slightly forward. Another 2 seconds.
3. Squeeze your abs briefly at the tucked position.
4. Repeat for your target reps without letting your feet touch the floor between reps.

The ideal tempo is 2-0-2: two seconds out, no pause, two seconds in. Exhale on the contraction (knees in), inhale on the extension (legs out).

Common Mistakes and How to Fix ThemAvoid

Even simple exercises go wrong when fatigue builds. These are the four mistakes we see most often with the in and out core exercise.

Mistake 1: Lower back arching

This happens when your TVA cannot hold a neutral spine, or when you extend your legs too far. Your lower back hyperextends, and you feel it in your spine instead of your abs.

Fix it by shortening your range of motion. Do not extend your legs fully until you can maintain a posterior pelvic tilt the entire time. Tuck your tailbone under before each rep.

Mistake 2: Hip flexors doing all the work

If you feel the burn deep in the front of your hips instead of your abs, you are initiating the movement with your legs instead of your core.

Fix it by cueing “ribs to hips before knees to chest.” Start the crunch with your upper body first, then let the knee drive follow. This sequence forces your rectus abdominis to fire before your hip flexors take over.

Mistake 3: Using momentum and swinging

Moving too fast turns this into a rocking chair exercise. You lose the eccentric loading that builds real strength. Fix it by using a 2-1-2 tempo: two seconds out, one second pause, two seconds in. If you cannot maintain this tempo, reduce the reps.

Mistake 4: Holding your breath

Breath-holding spikes blood pressure and limits core activation. Follow the breathing pattern from the form section: inhale out, exhale in. Pair each breath with the movement until it becomes automatic.

These mistakes compound under fatigue. Learn at lower rep counts first and only increase volume once your form is locked in.

In and Outs vs Other Ab Exercises

Choosing an ab exercise is not about finding the single “best” one. It is about understanding what each movement does well and stacking them together.

Exercise	Primary Target	Difficulty	Equipment	Best For
In and out abs	Rectus abdominis, hip flexors	Beginner to Advanced	None	Scalable all-level core training
V-ups	Rectus abdominis (full range)	Intermediate to Advanced	None	Peak contraction, athleticism
Bicycle crunches	Rectus abdominis + obliques	Beginner to Intermediate	None	Oblique emphasis
Flutter kicks	Lower abs, hip flexors	Beginner to Intermediate	None	Endurance, hip flexor conditioning
Hollow holds	Transverse abdominis, full core	Intermediate	None	Isometric stability, gymnastics
Dead bugs	Full core (anti-extension)	Beginner	None	Back-safe core training, rehab

In and outs vs. V-ups: V-ups are a direct progression requiring straight legs meeting straight arms at the top. Master in and outs first, then graduate to V-ups.

In and outs vs. bicycle crunches: Bicycles add rotation for oblique development. In and outs stay in the sagittal plane. Use both for complete coverage.

In and outs vs. hollow holds: Hollow holds are isometric (static). In and outs are isotonic (dynamic). Pair them for a routine that builds both strength and endurance.

In and outs vs. dead bugs: Dead bugs keep the spine neutral and work best for people with back issues. In and outs are more demanding on the spine but produce a stronger contraction.

Our recommendation: use in and outs as your primary sagittal-plane core exercise. Add bicycle crunches for rotation and hollow holds for isometric endurance.

Variations: From Beginner to Advanced

One of the best things about in and outs exercise variations is the clear progression path. Each level adds a new challenge, so you always have somewhere to grow.

Level 1: Hands on Floor (Beginner)

Keep your hands planted on the floor behind your hips. This gives you extra stability and lets you focus on learning the movement pattern. Use a shorter range of motion and do not fully extend your legs.

This variation is ideal for total beginners and anyone with lower back sensitivity. Master 3 sets of 15 reps before moving up.

Level 2: Hands Raised (Intermediate)

Remove the hand support entirely. Hold your arms out to the sides or in front of your chest. This forces your core to handle all the stabilization work that your arms were helping with.

Extend your legs fully as long as your lower back stays neutral. You will feel a significant jump in difficulty. Work up to 3 sets of 15 with full control before progressing.

Level 3: Bench In and Outs (Intermediate to Advanced)

Sit on the front edge of a flat bench. Perform the same “accordion” movement, but now your legs can dip below the bench level during extension.

This creates a greater range of motion and more stretch on the abs at the bottom. Work up to 4 sets of 15 before progressing.

Level 4: Hanging Leg Raises (Advanced)

Hang from a pull-up bar and raise your legs to parallel (or higher). The hanging leg raises produced significantly higher upper and lower ab activation compared to seated tucks. This is the end goal of the progression.

Move to this level when bench in-and-outs at 4 sets of 15 feel manageable. If you are working toward bodyweight training skills, hanging leg raises are a foundational movement.

10-Minute Core Routine Featuring In and Outs

This circuit hits your core from every angle in under 10 minutes. The order is intentional: warm up the deep core first, hit compound movements second, finish with isometric holds. Perform 2 rounds with 60 seconds of rest between rounds.

Order	Exercise	Reps/Duration	Why It Is Here
1	Dead Bugs	10 each side	Transverse Abdominis activation warm-up
2	Bicycle Crunches	15 each side	Obliques + rectus
3	In and Outs	15 reps	Rectus + hip flexor integration
4	Flutter Kicks	20 seconds	Lower abs + endurance
5	Plank Hold	30 seconds	Isometric stability, active recovery
6	Russian Twists	12 each side	Oblique rotation

How to Scale This Routine

• Beginners: Do 1 round only. Take 45 to 60 seconds of rest between exercises if needed. Use the hands-on-floor in-and-out variation.
• Intermediate: 2 rounds as written. Keep rest between rounds to 60 seconds. Use the hands-raised in-and-out variation.
• Advanced: 3 rounds. Add 2-5 lb ankle weights to in-and-outs and flutter kicks. Use a 10-25 lb weight plate for Russian twists. Extend the plank hold to 45 seconds.

This routine works best at the end of a workout when your core is already warm, or as a standalone session on rest days. Run it 2 to 3 times per week for consistent progress.

Do not skip the breathing cues on in-and-outs, especially when fatigue builds in the later rounds. Inhale out, exhale in. Every rep.

Frequently Asked Questions

Are in and out abs effective?

Yes. The seated position bypasses the hip-flexor-dominant range, forcing the rectus abdominis to engage from rep one. Add progressive overload and they build both strength and definition.

What muscles do in and outs work?

Primarily the rectus abdominis and hip flexors. Secondary: transverse abdominis, obliques, erector spinae, and quadriceps.

Are in and out abs exercises good for beginners?

Yes. The hands-on-floor variation gives you enough stability to learn the movement safely. Start with a shorter range of motion and 3 sets of 12 reps. Focus on the breathing pattern and controlling the eccentric before adding difficulty.

How many in and outs should I do?

Beginners: 2 to 3 sets of 6 to 10 reps. Intermediate: 3 to 4 sets of 10 to 15 reps. Advanced: 3 to 4 sets of 12 to 20 reps. Train 2 to 3 times per week.

Are in and outs bad for your back?

Not inherently. Rounding the lower back under load compresses spinal discs. Keep your chest lifted, control the tempo, and stop if you feel pain. Substitute dead bugs or bird-dogs if you have disc issues.