What is the flutter kicks?
Flutter kicks are a dynamic core drill borrowed from swim training and military PT. Lying on your back with legs extended and heels hovering above the floor, you kick your legs up and down in small, fast, alternating strokes. The real work is isometric: your abs brace hard to pin your lower back to the floor while the hip flexors drive the kicks, and the lower you keep your legs, the harder that fight gets. They build core endurance and hip flexor stamina, which is why they show up constantly in bootcamps, Hyrox prep and ab circuit finishers.
How to do the flutter kicks
- 1
Set your lower back first
Lie flat, hands by your hips or tucked under your glutes, ribs down. Press your lower back into the floor and commit to keeping it there for the whole set.
- 2
Hover the heels
Extend both legs and lift your heels 15-20 cm off the floor, toes pointed. Chin slightly tucked, neck relaxed, gaze at the ceiling.
- 3
Kick small and fast
Alternate small kicks of 20-30 cm, driving the movement from the hips, not the knees. Legs stay near-straight, like a freestyle swimmer's kick.
- 4
Breathe and hold the brace
Exhale steadily through the set instead of holding your breath. The moment your lower back starts peeling off the floor, the set is over.
Pro tip
Think small and low, not big and high. The hardest flutter kicks are tiny kicks a few centimetres off the floor. If the set feels easy, your legs are too high.
Common mistakes
Lower back arching off the floor.
Once the back arches, the abs stop working and the lumbar spine takes the load. Slide your hands under your glutes or raise your legs higher until you're stronger.
Kicking from the knees.
Bending and flicking the knees turns this into a quad twitch. Keep the legs long and move from the hips.
Holding your breath.
Breath-holding makes the brace collapse halfway through the set. A steady, rhythmic exhale keeps tension without the pressure spike.
Legs way too high.
At 45° and above there's barely any lever left and the abs coast. Keep the heels low enough that you feel your trunk working every second.
Variations and progressions
Easier
Bent-knee flutters
Bend the knees slightly and tuck your hands under your glutes. Shorter lever, same pattern, and your back stays safely pinned while you build strength.
Harder
Hollow-body flutter kicks
Lift your shoulder blades off the floor and reach your arms past your hips while kicking. The hollow position roughly doubles the ab demand.
Cranky lower back?
Dead bug
The dead bug trains the exact same anti-extension skill with one limb moving at a time, so your back stays pinned with far less risk of losing position.
How to program it
Three protocols by goal. Pick one per cycle and aim for progression on load or distance.
| Goal | Sets × distance | Load | Rest |
|---|---|---|---|
| Core endurance | 3 × 30-45 s | Bodyweight | 30 s |
| Strict strength | 4 × 20 s | Heels at 10-15 cm, slow kicks | 45-60 s |
| Finisher | 2 × max time | Stop when form breaks | 60 s |
Flutter Kicks FAQ
Why does my lower back hurt during flutter kicks?
Because the leg lever is longer than your abs can currently control, your pelvis tips forward and your lumbar extensors take over. Fix it today with hands under your glutes, slightly bent knees and higher heels. Fix it long term with dead bugs and short, strict sets. Pain-free low flutter kicks are earned, not forced.
Are flutter kicks working my abs or my hip flexors?
Both, by design. The hip flexors drive the kicks while the abs work isometrically to stop your pelvis and lower back from arching. That's not a flaw, it's the point. If you only feel your hip flexors and nothing in your trunk, your back has lifted off the floor and the abs have clocked out: reset your position.
How long should a set of flutter kicks last?
Sets of 20-45 seconds with perfect position beat minutes of sloppy kicking every time. Once you can hold 45 strict seconds with low heels, make the exercise harder (hollow body, slower kicks) instead of just longer. Two or three core sessions a week is plenty; this is a quality drill, not a daily punishment.
