Why Your Butterfly Kick Is Killing Your 50 Free

The Misconception: Butterfly Is Only for Butterflyers

If you're a freestyle sprinter, you've probably dismissed butterfly as that exhausting stroke you avoid at all costs. I'm here to tell you that's a mistake. The dolphin kick—the undulating, simultaneous leg motion that powers butterfly—is not a niche skill. It's the secret weapon hiding in plain sight for anyone who races the 50 or 100 free. And if you're not training it, you're leaving speed on the table.

I'm not saying you should enter a butterfly race tomorrow. I'm saying that the technique you avoid is the same technique that can transform your underwaters, your turns, and your finish. And here's the kicker: the rules of competitive swimming—the ones you probably think of as restrictions—actually give you a legal window to use this kick to your advantage in every single race you swim.

Imagine You're a 50 Free Sprinter: Your Underwater Is Everything

Picture this: you're standing on the blocks for the 50-meter freestyle at a local meet. The pool is 50 meters long, and you've got one length to make it count. The gun goes off, and you dive in. What happens in the next few seconds determines the race. The fastest swimmers don't just swim fast—they swim *underwater* fast. They use a powerful dolphin kick off the start and off the turn, and they do it legally, because the rules allow you to stay fully submerged for up to 15 meters after each start and turn (World Aquatics). That's a third of the race if you're smart about it.

Now, here's the part that most swimmers get wrong: they think the dolphin kick is just for butterfly. But in freestyle, you're allowed to use any stroke except in medley events, and that includes the dolphin kick. The rules for freestyle simply require that some part of your body touches the wall at each turn and finish, and that you don't use backstroke, breaststroke, or butterfly in the freestyle leg of a medley (World Aquatics Swimming Rules Reference Card 2023-2025). Wait—does that mean you can't use a butterfly kick in freestyle? No, it means you can't use the *butterfly stroke*—the arm recovery. The kick is fair game. In fact, the dolphin kick is so integral to underwater swimming that it's used by elite freestylers in every race.

So, if you're a 50 free sprinter, your underwater dolphin kick is not optional. It's your fastest segment. And the best way to improve it? Train butterfly. Not because you're going to race it, but because butterfly forces you to develop the rhythm, the flexibility, and the power of that kick. The second fastest stroke after freestyle, butterfly is often considered the most difficult to master, but its kick is a transferable skill (Britannica: Butterfly swimming).

The 15-Meter Rule: Your Legal Speed Zone

Here's where the rules get interesting. You're allowed to stay underwater for no more than 15 meters after the start and each turn, in all strokes (World Aquatics). That's a rule that many swimmers see as a limit, but I see it as a gift. It means you have a defined zone—15 meters—where you can legally be fully submerged, using your dolphin kick, and not worry about coming up for air. The fastest way to swim that 15 meters is underwater, because water resistance is lower when you're streamlined beneath the surface, and the dolphin kick generates propulsion without the drag of your body breaking the surface.

Let's put some numbers on this. Pan Zhanle of China set the men's 100-meter freestyle world record of 46.40 seconds at the Paris 2024 Olympics on 31 July 2024 (Reuters). That's an average of about 2.16 seconds per 10 meters. If you can shave even a tenth of a second off each of your underwater segments by mastering the dolphin kick, that's a meaningful gain. And in a 50 free, where the difference between gold and fourth can be hundredths of a second, that underwater is where races are won.

But it's not just about speed. The dolphin kick also helps you transition into your stroke. When you surface at the 15-meter mark, you want to be moving at full speed, not decelerating. A strong underwater kick sets you up for a smooth breakout. If you're kicking weakly, you'll pop up and have to accelerate from a near stop—that's a killer.

Butterfly Rules: The Detailed Technique That Makes It Work

Now, if you're going to train butterfly to improve your dolphin kick, you need to understand the stroke's rules, because they define the technique. Butterfly requires both arms to be brought forward simultaneously over the water and a simultaneous two-hand touch at turns and the finish (World Aquatics). The body must be kept on the breast, and the legs kick together in an up-and-down (dolphin) motion. Alternating leg movements or breaststroke kicking movements are not permitted (World Aquatics Swimming Rules Reference Card 2023-2025). This is the stroke's discipline: it forces you to use your core, not just your legs.

Here's a common mistake: swimmers try to kick butterfly from the knees, but the power comes from the hips. The undulation starts in your chest, travels through your torso, and ends in your feet. If you're doing it right, your entire body is involved. And that's exactly the same motion you need for a powerful underwater dolphin kick in freestyle. So, when you practice butterfly, you're not just training a stroke—you're training a movement pattern that directly transfers to your freestyle underwaters.

But there's a catch: butterfly is unforgiving. It demands a precise rhythm. The two-hand touch at the wall, the timing of the breath, the recovery of the arms—it's easy to get it wrong. And if you get it wrong, you'll be disqualified. The rules are strict: in butterfly, you must keep your body on the breast, and you can't use a breaststroke kick. That's why many sprinters avoid it. But I say, embrace the difficulty. The struggle is the point.

Let me give you a concrete example. Imagine you're doing a set of 50-meter butterfly in practice. You're focusing on your underwater dolphin kick off the wall. You're allowed to stay underwater for 15 meters, but you're also required to break the surface before the 15-meter mark in backstroke—but in butterfly, the rule is that the head must break the surface before the 15-meter mark as well? Actually, the 15-meter rule applies to all strokes, but in butterfly, you must break the surface before the 15-meter mark (World Aquatics Swimming Rules Reference Card 2023-2025). The point is, you have a legal window to be underwater, and you should use it. By the time you surface, you're moving faster than you could ever swim on the surface.

The Specific Drills That Will Change Your Race

Okay, so you're convinced. How do you actually improve your dolphin kick? I recommend a few specific drills that I've seen work for swimmers at all levels.

• Vertical dolphin kick: In deep water, keep your arms crossed over your chest and kick dolphin vertically, staying in place. This isolates the core and forces you to use your hips, not your knees. Do 10 seconds on, 10 seconds off, for 2 minutes.
• Underwater dolphin kick on your side: Streamline on your side, kick dolphin, and rotate to your back and stomach every few kicks. This teaches you to control your body position and keep your kicks compact.
• Butterfly with a focus on the kick: Swim a 25-meter butterfly, but count your kicks per stroke. Aim for a 2-beat kick (two kicks per arm cycle) to feel the rhythm, then a 4-beat for power.

These drills aren't just for butterflyers. They're for anyone who wants to own the underwater part of their race. And here's a tip: when you do your underwater dolphin kick in freestyle, make sure you're not crossing your ankles. Keep them together, toes pointed, and kick from the hips. This is the exact same technique you use in butterfly, and it's what makes the difference between a powerful underwater and a wobbly one.

Now, I'm not saying that butterfly is the only technique you need. But I am saying that if you ignore it, you're ignoring one of the most valuable cross-training tools in the sport. The fact is, butterfly evolved from breaststroke in the mid-20th century, and FINA recognized it as a distinct stroke in 1953, adding it to the Olympics in 1956 (Britannica: Butterfly swimming). Since then, it's been a proving ground for world-class swimmers. Michael Phelps, who won a record eight gold medals at the 2008 Beijing Olympics, was a butterflyer first (World Aquatics: About World Aquatics). And Mark Spitz, who won seven golds in 1972, dominated in butterfly and freestyle (World Aquatics: About World Aquatics). These legends didn't separate their strokes—they used them to build each other.

Bottom Line

The single best move you can make to improve your freestyle sprint is to start training your butterfly kick—not as a casual afterthought, but as a dedicated part of your technique work. Master the dolphin kick, understand the 15-meter rule, and you'll turn your underwaters into a weapon. Butterfly isn't just for butterflyers. It's for anyone who wants to be faster.

Sources

• World Aquatics - https://www.worldaquatics.com
• World Aquatics Swimming Rules Reference Card (2023-2025) - https://eastswimming.org/wp-content/uploads/2024/04/WA-Swimming-Reference-Card_13072023-Large-Print-Bold.pdf
• Reuters: Pan Zhanle 100m freestyle world record - https://www.reuters.com/sports/olympics/swimming-chinas-pan-obliterates-100m-freestyle-world-record-gold-2024-07-31/
• Britannica: Butterfly (swimming) - https://www.britannica.com/sports/butterfly-swimming
• World Aquatics: About World Aquatics - https://www.worldaquatics.com/about