The Perfect Stride: Biomechanics of Invisible Movement

Hydrodynamic position, undulations, breakout timing: the complete biomechanics of the underwater dolphin kick in swimming. Progressive drills and strategy by distance.

Publié le March 25, 2026, par Théo WITTKE

Reading time: 7 minutes

Suggestion: Very clean underwater image, swimmer in streamline position, sensation of silent speed. The opening should establish the glide as an invisible, pure, and decisive moment.

The silence after the push-off

Push off the wall. Hard.

In the first second, the noise disappears. Conversations by the poolside, the lapping of the lane lines, the breathing of other swimmers. Everything fades away. All that remains is the glide. This seemingly effortless movement where your body slices through the water, propelled by the momentum of the push-off.

This is the glide.

It lasts two seconds, sometimes three. It's the fastest movement in your swim. Faster than any arm stroke. Faster than your most powerful kicks. The reason is purely physical: underwater, you only face one force, drag. On the surface, you face two: drag and wave resistance. Underwater, you have a mechanical advantage that you lose as soon as your head breaks the surface.

Each lap contains at least two glides. One at the start, one at the turn. In a 200-meter race in a 25-meter pool, that's eight glides. Eight opportunities to gain or lose tenths of a second without a single arm stroke. In competition, these tenths often decide the race.

The glide is not a dead time between two phases of swimming. It is a technical movement in its own right. One that demands the most rigor, and forgives the least.

Epigraph

The glide is not a dead time between two phases of swimming. It is a technical movement in its own right.

Anatomy of the position

Your goal underwater is simple to state, difficult to execute: present the smallest possible frontal surface while maintaining perfect alignment.

The arms. Stretched out in front of you, one over the other, biceps pressed against your ears. Hands stacked, palms facing the bottom. The space between your arms and your head should be zero. The slightest gap creates a resistance front that slows you down.

The head. In exact alignment with the spine. Gaze towards the bottom of the pool, slightly forward. Raising your eyes, even by a few degrees, is enough to break alignment and lift the hips. The neck remains a natural extension of the back, relaxed.

The torso. Engaged. Abs engaged, not locked. The difference matters. The pelvis remains neutral: neither arched towards the bottom nor lifted towards the surface. Your body forms a single continuous line, from fingertips to toes.

The legs. Together, active but not rigid. Ankles extended, feet pointed. They complete the hydrodynamic shape. Relaxed feet dragging in the wake measurably increase drag.

Common mistakes. The most common: sagging hips. Fatigue, lack of core strength, or simply habit cause a break at the hips. You don't always feel it. But it slows you down on every glide.

The other trap: opening your arms too early, before the momentum of the push-off has decelerated. You start your first arm stroke when you are still faster in pure glide. You brake to restart.

[PHOTO 2 — STREAMLINE POSITION / ALIGNMENT]

Suggestion: A very educational and clean visual of the hydrodynamic position. Ideally a swimmer underwater, perfectly aligned, to illustrate arms, head, torso, and legs as a single line.

Epigraph

Present the smallest possible frontal surface while maintaining perfect alignment.

The undulation: the invisible whip

The push-off speed quickly decreases. After one meter, sometimes two, propulsion must be re-initiated. This is the role of undulations, the dolphin kick performed in a streamline position.

The movement originates from the sternum. Not from the knees. Not from the hips. From the upper torso, like a wave propagating downwards. The shoulders initiate a slight oscillation. The torso transmits. The hips amplify. The legs whip. This is the final acceleration, the one that propels. The knees barely bend, just enough for the feet to powerfully kick.

The classic trap: bending the knees like a flutter kick. The undulation is not a kick. It's a continuous, fluid wave, without interruption. A whip, not a piston.

The frequency depends on the objective. In sprint, undulations are fast, powerful, short, two or three kicks at full intensity. In middle-distance, they slow down: three to four broad, controlled undulations that re-propel without exhausting. In long-distance, economy is key: one to two are enough, just enough to maintain speed before surfacing.

Initiation timing is critical. Starting too early, before the glide speed has decelerated, is like braking. Your body undulates when it would be faster gliding in a static position. Waiting too long allows speed to drop. The right moment is between the two: when you feel the momentum fading, but before it dies out.

When to surface

The rule is mechanical: as long as your underwater speed exceeds your surface swimming speed, stay underwater.

World Aquatics regulations require surfacing before 15 meters. But the technical question is not "how long can I stay?", it's "at what point do I lose the advantage?"

For most trained swimmers, the tipping point is between 5 and 10 meters. Elite swimmers push it to 12-15 meters thanks to an impeccable position and tremendously effective undulations.

Underwater, there's no reliable stopwatch, no clear visual markers. You must learn to read your sensations. The increasing resistance against your face. The propulsion losing efficiency. The rising need for oxygen. These signals converge at the same moment, the one when you must surface, initiate the transition, and start the first arm stroke without breaking the acquired speed.

[PHOTO 3 — UNDULATION / TRANSITION / SURFACING]

Suggestion: Underwater image with a real sense of undulatory movement or controlled surfacing. It can illustrate both the invisible whip and the timing of emergence.

Epigraph

The undulation is not a kick. It's a continuous, fluid wave, without interruption. A whip, not a piston.

Building your glide: 4 levels

Level 1: The line

Objective: To feel and memorize the hydrodynamic position.

Push off the wall, arms in streamline position, no undulation
Glide as far as possible while maintaining strict alignment
Mentally note the distance reached
Repeat 5 times, aiming to gain 10 to 20 cm with each attempt

What you're working on: Static core strength, hand placement, body line awareness. This is the foundation. Without it, nothing else holds.

Level 2: Controlled undulation

Objective: To add propulsion without losing alignment.

Same push off the wall, same position
Add 3 slow, wide undulations
Focus on initiating from the sternum; the hips should not break
Repeat 8 times

What you're working on: Torso-leg coordination, wave fluidity, amplitude control. If the movement is jerky, slow down further.

Level 3: The transition

Objective: To surface without losing speed.

Push-off + 3 to 5 undulations
Transition to your first swimming stroke
The arm exits the water in exact continuity with the glide, no abrupt pulling, a fluid ascent
Repeat 10 times

What you're working on: Surfacing timing. Speed retention. The glide-to-swim sequence, which is often the weak link.

Level 4: Gliding under fatigue

Objective: Maintain rigor when the body gives out.

After an intensive set (e.g., 8x50m at high intensity), immediately follow with 6 full glides with transition
Your body is tired, your abs are relaxing, your position is deteriorating
Maintain strict alignment despite everything

What you're working on: Discipline in competition. In a 200-meter race, the last glides are the ones that degrade the most, and where time is lost or gained.

Strategy by distance

Sprint (50m). Maximum push-off. Two to three full-power undulations. Fast surfacing, around 7-8 meters. The objective: reach maximum surface speed as quickly as possible, without wasting initial propulsion.

Middle-distance (100-200m). Powerful but controlled push-off. Four to five sustained undulations. Surfacing around 10-12 meters. The turn becomes strategic; it's often where gaps widen, because fatigue encourages sloppy glides.

Long-distance (400m and more). Controlled push-off, energy economy. Two to three undulations are enough. Surface at 6-8 meters to limit oxygen debt. Consistency trumps distance: it's better to have consistent glides over thirty-two lengths than one spectacular glide followed by fifteen mediocre ones.

The invisible movement

The glide is not seen from the stands. It plays out beneath the surface, in silence. Perhaps that's why it's so often neglected in training, and so crucial in a race.

Swimmers who perform share a common trait: their glides are identical from the first to the last lap. Same position. Same amplitude. Same rigor. The discipline of the invisible gesture separates those who swim well from those who perform.

It's also the moment when your equipment matters most, or rather, the moment when it should matter least. Underwater, in a streamline position, the slightest fold, the slightest excess thickness, the slightest resistance added by the fabric comes at the cost of drag. At 0.4 mm thick, woven warp and weft for a smooth and uniform surface, the DROP fabric was selected for this precise moment: when the suit must cease to exist. Assembled seamlessly, by high-frequency welding and bonding, laser-cut raw edges. Nothing snags. Nothing creates turbulence.

You should not feel your suit. You should feel the water.

It is in this underwater silence, in this fraction of a second where you effortlessly glide, that the glide finds its meaning. The position. The undulation. The timing. And that unique sensation: pure glide, without friction, without obstruction. That of shaping the water.

Final Epigraph

You should not feel your suit. You should feel the water.

SHAPE THE WATER.

[PHOTO 4 — CLOSING / PURE GLIDE]

Suggestion: Final image of a perfect glide, very smooth, very silent, almost abstract. A closing that gives the sensation of pure glide and invisible movement.

Key takeaways

The glide is the fastest movement in swimming, provided it is executed rigorously
Streamline position: a single continuous line, from fingertips to toes
The undulation originates from the sternum, not the knees; it's a wave, not a kick
Surface when your underwater speed drops below your surface swimming speed
In competition, the consistency of glides matters more than their length