How to Prevent Sinking Legs During Butterfly Swimming
Butterfly is widely regarded as the most physically demanding stroke in competitive swimming, and one of the most common technical flaws that plagues swimmers at every level — from beginners to national-level competitors — is the dreaded "sinking legs." If you've ever watched your own underwater footage and cringed at how your hips and legs drop deep beneath the surface during your fly, or if you constantly feel like you're dragging a parachute behind you, this article is for you.
Sinking legs during butterfly don't just look bad — they create enormous drag, waste energy, disrupt your rhythm, and can turn an otherwise powerful stroke into an exhausting slog. The good news is that this is a fixable problem. It comes down to understanding body position, kick mechanics, core engagement, timing, and a handful of targeted drills that retrain your body to stay balanced and streamlined through the water.
This article will walk through exactly why legs sink in butterfly, the biomechanics of a proper body position, and a complete set of drills, strength exercises, and coaching cues you can use to fix the problem for good.
Why Do Legs Sink in Butterfly?
Before fixing the problem, it's worth understanding what's actually happening. Butterfly relies on a whip-like, undulating motion that travels from the chest through the hips and down through the legs and feet. This wave-like body motion is what generates propulsion and keeps the body riding near the surface. When this undulation breaks down, the legs stop following the wave and instead hang below the body, creating a "sinking" effect.
There are several common root causes:
1. Weak or Late Core Engagement
The butterfly undulation starts at the chest and travels through the core. If your abdominal and lower back muscles aren't firing correctly, or if you rely purely on your legs to generate the kick, the wave motion breaks apart at the hips. This causes the lower body to drop instead of following through with the rest of the body.
2. Kicking From the Knees Instead of the Hips
Many swimmers, especially beginners, try to kick "harder" by bending their knees excessively and kicking from the knee joint, similar to a bicycle-style flutter kick. This disconnects the legs from the whip motion of the torso and causes the legs to sink independently, rather than moving as an extension of the body wave.
3. Poor Head and Chest Position
If the head lifts too high during the breath, or if the chest doesn't press down enough at the start of the underwater pull, the body loses its forward-rocking motion. This upsets the balance point of the body, and the hips and legs compensate by dropping.
4. Breathing Too Late or Too High
Butterfly breathing needs to be quick and low, with the chin skimming the surface. Swimmers who lift their head and shoulders too high to breathe create a "see-saw" effect: as the upper body rises, the lower body sinks even further to compensate.
5. Lack of Ankle Flexibility and Kick Snap
A stiff ankle or a kick that doesn't "whip" at the end of the downbeat reduces propulsive force from the legs. Without that propulsive snap, the legs lose the lift needed to stay near the surface.
6. Poor Timing Between Kicks and Arm Pull
Butterfly uses two kicks per arm cycle — one as the hands enter the water and one as the hands exit. If these kicks are mistimed, the body loses its rhythm and the legs can fall out of sync with the rest of the undulation, causing them to drag.
7. Insufficient Core and Hip Flexor Strength
Even with perfect technique, a swimmer without adequate core, glute, and hip flexor strength will struggle to maintain the body tension needed to keep the legs riding high through an entire length or race.
Understanding these root causes is the first step. Now let's break down the correct technique and the training tools to fix each of these issues.
The Biomechanics of Proper Butterfly Body Position
Butterfly is often described as a "dolphin" motion, and that's an apt description. Picture how a dolphin moves through water: a continuous wave that begins at the head, travels down through the spine, and finishes with a powerful whip at the tail. Your body should mimic this same fluid, connected motion.
The Wave Sequence
Head and chest press down as the arms enter the water in front of you.
The wave travels through the spine and hips, which rise slightly as the chest presses down.
The hips then drive downward, sending the wave into the upper legs.
The knees bend slightly as the wave passes through, storing energy.
The lower legs and feet snap downward and back, finishing the kick with a whip-like release.
This entire sequence should feel continuous — like a single ripple passing through your body — not a series of separate, disconnected movements. When any link in this chain breaks (usually at the hips or knees), the wave stops transferring energy efficiently, and the legs sink.
Two Kicks, Not One
Every arm cycle in butterfly is paired with two kicks:
The first kick (entry kick) happens as the hands enter the water and begin to press down and out. This kick helps drive the chest down and the hips up, setting up the propulsive pull.
The second kick (exit kick) happens as the hands finish pushing through the water near the hips and start to recover. This kick helps lift the upper body up and forward for the breath and arm recovery.
If a swimmer only performs one strong kick per cycle (which is extremely common among self-taught or less experienced swimmers), the undulation becomes lopsided, and the legs will sink during the "missing" phase of the stroke.
Step-by-Step Fixes for Sinking Legs
Fix 1: Learn to Initiate Movement From the Chest, Not the Legs
A great mental cue is to think of your chest as the "engine" of the stroke. Every cycle should begin with a strong, deliberate press of the chest downward, almost like you're trying to dive under a low bar in front of you. This chest press initiates the wave that travels down your spine and into your legs.
Coaching cue: "Press your chest like you're squeezing a beach ball underwater."
When swimmers press the chest first, the hips naturally rise, creating the correct downward slope that lets the wave flow into the legs with power, rather than the legs trying to generate motion on their own.
Fix 2: Kick From the Hips, Not the Knees
To correct a knee-dominant kick, swimmers need to feel the kick originating from the hip flexors and core, with the knee bending only as a natural response to the wave passing through — not as an active, deliberate bend.
A useful visualization is to imagine your legs as a single unit, like a mermaid tail, rather than two independent limbs. This encourages the hips to drive the motion rather than isolated knee flexion.
Drill: Vertical Dolphin Kick
Practicing in the deep end without a wall to push off forces the body to generate all its propulsion from the core and hips.
Float vertically in deep water, arms crossed over the chest or extended overhead.
Perform continuous dolphin kicks, keeping the knees together and the motion originating from the hips.
Focus on keeping the upper body tall and the head steady while the lower body does all the work.
Start with 30-second intervals and build up to 60-90 seconds as strength improves.
This drill isolates the hip-driven kick and builds the core and hip flexor endurance needed to prevent the legs from dropping during full-stroke swimming.
Fix 3: Fix Your Head Position and Breathing Timing
The head should remain in a relatively neutral position for most of the stroke cycle, with the eyes looking down and slightly forward. When it's time to breathe, the chin should skim just above the surface — not lift high into the air.
Coaching cue: "Breathe like you're sneaking a peek over a fence, not popping your head up like a periscope."
Drill: Head-Lead Breathing Drill
Swim butterfly focusing exclusively on minimizing how high your head rises during the breath.
Try to complete a breath with the chin barely clearing the water's surface.
Pay attention to whether your hips drop when you breathe — if they do, you're lifting too high.
Reducing the height of the head lift keeps the "see-saw" effect from happening, which in turn keeps the hips and legs from compensating by sinking.
Fix 4: Build a Powerful, Snapping Kick
A kick that lacks a final "whip" or snap through the ankles won't generate enough lift to keep the legs riding high. Ankle flexibility plays a major role here — stiff, inflexible ankles can't transfer the energy of the kick efficiently into the water.
Drill: Fins-Assisted Dolphin Kick
Swimming with fins (specifically short-blade training fins) exaggerates the feeling of a proper whip kick and helps swimmers understand what a fully "snapped" kick should feel like.
Kick on your front, on your back, and on your side using fins.
Focus on feeling the propulsion come from the whip of the ankle at the end of the kick, not from muscling the movement with the thighs.
Gradually remove the fins and try to replicate the same snapping sensation without them.
Ankle Flexibility Exercises
Incorporate regular ankle mobility work outside the pool:
Seated ankle flexion and extension stretches
Kneeling ankle stretches (sitting back on your heels with toes pointed)
Resistance band ankle flexion exercises
Over time, improved ankle flexibility translates directly into a more effective, propulsive kick that helps keep the legs elevated.
Fix 5: Master the Timing of the Two Kicks
Many swimmers know intellectually that there are two kicks per cycle but don't actually execute them correctly under fatigue. This is where drilling becomes essential.
Drill: Count-Out-Loud Kick Timing
Swim slow, controlled butterfly and count out loud (or in your head) "kick, kick" with each arm cycle.
Exaggerate the timing at first: kick as the hands enter the water, then kick again as the hands exit near the hips.
Gradually increase speed while maintaining the same two-kick rhythm.
Drill: 3 Kicks + Pull
Perform three dolphin kicks on your front, then execute one full arm pull with a single kick.
This isolates the kick rhythm before integrating it back into the full stroke and helps swimmers feel the difference between a "resting" undulation and a "working" one tied to the arm pull.
Fix 6: Strengthen the Core, Glutes, and Hip Flexors
No amount of technique work will fully solve sinking legs if the swimmer lacks the muscular endurance to hold the correct body position for an entire race or long set. Dryland training should specifically target the muscles responsible for maintaining the undulating body line.
Recommended Dryland Exercises:
Hollow body holds: Builds the anterior core strength needed to maintain a tight, connected body line.
Superman holds and swims: Strengthens the posterior chain (lower back, glutes) that drives the downward phase of the kick.
Plank variations (front, side, with leg lifts): Improves overall core stability, which prevents the hips from collapsing mid-stroke.
Hip flexor raises (lying leg raises): Directly strengthens the muscles that initiate the upward phase of the kick.
Medicine ball rotational throws: Builds the rotational core strength that supports the whip-like transfer of energy through the torso.
Cable or band hip flexion exercises: Mimics the specific motion of driving the hips through the water.
A well-rounded dryland program, performed 2-3 times per week, will noticeably improve a swimmer's ability to hold correct body position deep into a set or race, when fatigue typically causes the legs to drop.
Putting It All Together: A Sample Training Progression
Here is a sample weekly progression a swimmer or coach could use to specifically target sinking legs over a 4-6 week period:
Weeks 1-2: Isolation and Awareness
Vertical dolphin kicking (3 x 30-45 seconds)
Head-lead breathing drill (4 x 25m)
Ankle mobility work (dryland, 3x/week)
Underwater video review to identify specific breakdown points
Weeks 3-4: Timing and Connection
3 kicks + pull drill (6 x 25m)
Count-out-loud kick timing drill (4 x 50m)
Fins-assisted dolphin kick (6 x 25m)
Hollow body holds and plank progressions (dryland, 3x/week)
Weeks 5-6: Integration Under Fatigue
Full-stroke butterfly with a focus on maintaining the two-kick rhythm (8 x 50m, descending effort)
Broken 100m fly with technique focus on each length
Sprint fly repeats to test whether the corrected position holds under speed and fatigue
Continued dryland strength work with increased volume
Progress should be checked regularly through underwater video analysis. Watching yourself from a side angle is the single most valuable diagnostic tool for identifying whether your legs are sinking, and if so, at which specific point in the stroke cycle the breakdown occurs.
Common Mistakes to Avoid While Fixing Sinking Legs
Overcorrecting by over-kicking: Trying to "kick harder" to compensate for sinking legs often makes the problem worse by encouraging a knee-dominant kick rather than a hip-driven one.
Rushing the tempo: Swimmers often speed up their stroke rate to avoid the feeling of sinking, but this frequently breaks the two-kick timing. Slowing down and rebuilding the correct rhythm is usually more effective than trying to swim through the problem at speed.
Ignoring dryland work: Technique drills alone won't fix sinking legs if the swimmer lacks the core and hip strength to sustain the position. Both must be addressed together.
Neglecting ankle flexibility: Even swimmers with excellent core strength and timing will struggle with sinking legs if their kick lacks a proper propulsive snap due to stiff ankles.
Skipping video review: It's very difficult to feel exactly what's happening with your legs underwater. Regular video check-ins (even from a phone at poolside) provide much clearer feedback than internal sensation alone.
Final Thoughts
Sinking legs in butterfly is one of the most common — and most fixable — technical issues in competitive swimming. The root cause almost always traces back to a breakdown in the body's natural undulation: either the core isn't initiating the wave properly, the kick timing is off, the breathing mechanics are disrupting balance, or the swimmer simply lacks the strength and ankle mobility to hold the position.
By systematically addressing each of these factors — starting with awareness drills, moving into timing and rhythm work, and finishing with strength training and fatigue-resistance — most swimmers can dramatically improve their body position within just a few weeks of focused work. The payoff is significant: a butterfly stroke with legs riding high and connected to the rest of the body isn't just more aesthetically pleasing, it's dramatically more efficient, less exhausting, and ultimately faster.
Like most technical fixes in swimming, patience and repetition are key. The undulating body wave that defines great butterfly technique takes time to internalize, but once it clicks, most swimmers describe the stroke feeling almost effortless compared to how it felt before — proof that the "sink" was never really about the legs at all, but about the connection of the whole body working together as one continuous, powerful wave.
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