Flutter Kicks: How to Do Them, Muscles Worked and Variations

Flutter kicks are the exercise where you lie on your back and alternate your straight legs up and down in small, quick scissoring movements. Military PT sessions love them, swimming coaches use them, and roughly half the internet insists they are an ab exercise. They are, sort of. The truth is more interesting: your hip flexors do the moving, and your abs earn their keep by stopping your lower back arching off the floor while that happens. Get that distinction and you will do them far better.

How to do flutter kicks

No kit needed. A mat helps if your floor is hard.

1. Lie flat on your back. Legs straight, arms by your sides. Slide your hands palm-down under your glutes if your lower back tends to arch; it props the pelvis into a friendlier position.
2. Set the brace. Exhale and press your lower back firmly into the floor. There should be no gap you could slide a hand into. Hold that pressure for the whole set, because the moment it goes, the exercise starts working your spine instead of your abs.
3. Lift both legs. Raise them to around 45 degrees with a soft, almost straight knee. Point the toes lightly.
4. Kick. Lower one leg a few inches while raising the other the same amount, then swap. The movement is small and quick, roughly 15 to 25cm of travel per leg, not a huge sweep.
5. Keep the head neutral. Either rest it on the floor or lift it slightly with the chin off the chest. Do not yank on your neck.

Muscles worked

The honest breakdown, in order of how much work each does:

• Hip flexors. Iliopsoas and rectus femoris drive the leg movement itself. If your hip flexors are the thing that burns first, nothing has gone wrong; that is the exercise doing its job.
• Rectus abdominis. Works isometrically to keep the ribcage down and the pelvis tucked. Whether flutter kicks preferentially hit the "lower abs" is genuinely contested. One 2023 ultrasound study found the lowest segment of the rectus thickened most during leg raises while the top segment thickened most during crunches (International Journal of Exercise Science). An older EMG study in the Journal of Athletic Training found no significant difference in activity between the four quadrants across four common abdominal exercises (EMG analysis of four abdominal exercises). Take the "lower ab" marketing with a pinch of salt.
• Transverse abdominis. The deep corset muscle that holds intra-abdominal pressure and stops the belly bulging outward as the legs get low.
• Obliques. They resist the small rotational pull created by moving one leg at a time.
• Quadriceps and adductors. They keep the knees straight and the legs tracking on their own line.

Benefits, and what they are not

Flutter kicks build endurance in the exact chain that fails when you sprint, swim, kick or carry something heavy in front of you. They need no equipment, they scale precisely by leg height, and they fit into any circuit without changing station. For swimmers, they mirror the front crawl kick closely enough to be worth doing on dry land.

What they do not do is burn fat off your stomach. There is no exercise that removes fat from one region on demand, and any programme selling that idea is selling something else. Building the muscle and losing the fat are separate jobs, and the second one is mostly diet plus overall activity, which is why the NHS pairs 150 minutes of moderate activity a week with strength work on two or more days rather than recommending any single move.

They are also not a complete core programme. Flutter kicks train anti-extension in one plane. Rotation, lateral stability and loaded bracing need other movements, which is why a side plank and a hanging leg raise belong alongside them.

Common mistakes

The arching lower back. The single most common fault and the reason people finish a set with a sore back rather than sore abs. Your legs went too low, your pelvis tipped, and your lumbar spine took over. Legs higher, back pressed down, no exceptions.

Kicking too big and too fast. Wide, thrashing kicks turn it into a cardio flail. Keep the travel short and the tempo steady. You should be able to hold a conversation, badly.

Holding your breath. People clamp down and go red. Breathe shallowly and continuously through the set; the brace comes from the abs staying tight, not from trapped air.

Bent knees creeping in. As fatigue arrives, the knees fold and the lever shortens, which is a sneaky way of making the exercise easier without noticing. Keep a fixed, soft knee angle from the first rep to the last.

Chin tucked hard to the chest. Straining the neck to look at your feet does nothing for the abs and leaves you with a stiff neck. Head down or gently lifted, eyes at the ceiling.

Variations

• Hands under glutes, legs high. The starter version. Almost anyone can hold 20 seconds here.
• Flutter kicks with a crunch hold. Lift the shoulder blades off the floor and hold that position through the set. Much harder on the rectus abdominis and worth trying only once the basic version is solid.
• Scissor kicks. Cross one leg over the other rather than moving vertically. Shifts more work onto the adductors and inner thigh.
• Weighted flutter kicks. Light ankle weights add load without needing a lower leg position. Start at 0.5kg per ankle; 2kg is a lot here.
• Hanging flutter kicks. Do them hanging from a pull up bar. Brutal, and the grip usually gives out before the abs do.
• Flutter kicks on a bench. Lie on a weight bench with your hips at the edge so the legs can drop below horizontal. Only for people who can already hold the brace at low angles.

Sets and reps

• Beginner: 3 sets of 20 seconds, legs at 60 degrees, hands under glutes. Rest 45 seconds.
• Intermediate: 3 to 4 sets of 30 seconds, legs at 45 degrees, hands by your sides.
• Advanced: 4 sets of 30 to 40 seconds at 30 degrees, or add ankle weights and keep the higher angle.

Two or three core sessions a week is enough. Progress by lowering the legs a few centimetres or adding a small ankle weight, not by grinding out longer and longer sets, because past about 45 seconds form nearly always slips before the muscle does. A cheap yoga mat makes floor work considerably less unpleasant on the tailbone.

Recommended reads

1. Hanging leg raise: technique and progressions
2. How to do a side plank
3. Reverse crunch technique
4. The best ankle weights in the UK
5. The best yoga mats in the UK