The Hidden Speed in Swimming Turns and Starts: Why the Underwater Dolphin Kick Is the Fastest Phase of the Race

The Fastest Place in the Pool Is Underwater

The fastest moment for an elite swimmer in a race isn’t any stroke pull—it’s the underwater dolphin kick after the start and turns. The reason is physical: swimming on the surface creates wave drag, while at a certain depth underwater, there is almost no wave drag. Mastering this “fifth stroke” is like getting free speed on every turn; ignoring it is like throwing money at the wall on every lap.

Why Underwater Is So Fast

Key point: The initial speed after the start/turn push-off is usually higher than swimming speed. Maintaining that speed underwater with a tight streamline is faster than surfacing immediately to stroke—provided the streamline is good and the dolphin kick is effective.

Three Technical Pillars

1. Ultra-tight streamline: Hands stacked and squeezing the head, arms pressed against the ears, core braced, toes pointed. The moment the streamline loosens, the initial speed is gone.
2. Dolphin kick driven by the core: The wave travels from the chest/core to the legs, small and fast, with power on both directions (the up-kick counts too)—not just a knee-driven flick of the lower legs.
3. Correct timing for surfacing: When your speed decays to near or slightly above your swimming speed, it’s time to surface and start stroking—staying under too long actually slows you down, while surfacing too early wastes the underwater advantage.

The Tactical Meaning of the 15-Meter Rule

Competition rules require the head to break the surface before the 15-meter mark after the start and turns (freestyle, backstroke, butterfly). This rule essentially says: underwater is too fast, so it must be limited—which, in turn, tells you how valuable the underwater phase is. Even if you don’t race, understanding this shows you that “how long to stay underwater” is an optimization problem with an upper limit.

Should Open-Water Swimmers Train It Too?

There’s no wall to push off in open water, but this training still has value:

• Start: The underwater streamline and dolphin kick after diving in from a dock/beach start help you break away from the pack quickly.
• Core linkage: The core wave strengthened by dolphin kick training transfers directly to more efficient freestyle.
• Turn ability: If you also do pool training, a good turn makes your interval sets higher quality and keeps your rhythm unbroken.

Training Menu

• Streamline test: Push off the wall and glide in a pure streamline (no kicking), measuring how far you travel—the better the streamline, the farther you go. This is the foundation.
• Underwater dolphin kick: Push off and do 6–8 dolphin kicks before surfacing, 8×25 meters, gradually increasing the kick count while maintaining speed.
• Vertical dolphin kick: In deep water, do dolphin kicks upright to keep your head above water, training the core-driven two-way kick.
• Integration: Force a fixed number of dolphin kicks on every turn, making it automatic.

Coach’s note: Most amateur swimmers put all their attention on the pull during practice, yet throw away free speed on every turn. First, get the streamline ultra-tight—just that alone may improve your per-lap times painlessly.

The fastest swimming is sometimes those few seconds when you’re not stroking at all.

Related Reading

• Underwater Dolphin Kick: Don’t Waste the Fastest Position
• Underwater Dolphin Kick: Speed Advantage Within the 15m Rule
• Underwater Dolphin Kick Distance After the Start: Rule Limits and Optimization Strategies
• Open-Water Exit Technique: Timing the Walk, Run, and Dolphin Dive