Part I: Don’t Dive Down—Fly Forward!

Welcome to my very first V.A.Log — short for Video Analysis Blog.
In this new series, we’re going to break down the Butterfly stroke piece by piece using real swimmer footage, real mistakes, and real coaching solutions.
And we’re starting with one of the MOST misunderstood elements of fly:

UNDULATION.

Get this right, and Butterfly starts to feel powerful and connected.
Get it wrong, and everything — your kick, your pull, your timing — falls apart.

Let’s dive in.

What Is Undulation in Butterfly (And Why It Matters)

If you’ve ever been coached in Butterfly, the word undulation shouldn’t be new.

Undulating simply means moving in a smooth, wave-like motion — not bouncing, not diving, not snapping — but flowing.

In Butterfly, undulation is what allows swimmers to:

• Maintain proper body alignment
• Create stronger fly kicks
• Set up a more effective catch and pull
• Reduce drag and move FORWARD, not up and down

In short-axis strokes like fly, undulation is non-negotiable.

No undulation = weaker pull + smaller kick + slower swim.

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Basically–if you do not undulate in fly, you won’t be able to pull or kick as much water!

How Undulation Creates Speed in the Fly Stroke

Undulation isn’t just about how the stroke looks — it directly affects propulsion.

When done correctly, undulation:

• Puts the swimmer in a stronger position to catch water
• Fires the hips and lower back to drive the kick
• Links the upper and lower body into ONE connected motion

Think of it like this:
Your body should move like a wave traveling forward, not like a dolphin bouncing in place.

If a swimmer doesn’t undulate properly, they physically cannot pull or kick as much water — no matter how strong they are.

To have a successful undulation motion during your fly stroke–there are few important concepts:

1.) A STRONG Core Starts the Wave

Undulation begins at the core, not the knees, not the head.

The motion should ripple:
Chest → Core → Hips → Legs

Without core control, the wave breaks — and body position suffers immediately.

Weak core = broken rhythm = sinking hips

2.) What Goes up–Must Come Down!

This is a BIG one — especially with younger swimmers.

Many swimmers use undulation to drive themselves up and down, instead of down the pool.
This turns Butterfly into a vertical movement pattern — which kills speed.

Remember:

• The goal is NOT to dive toward the bottom
• The goal is to travel forward efficiently

If your swimmer looks like they’re “butterfly diving,” they’re wasting energy.

3.) Body Alignment is Key!

If a swimmer leads undulation with the head instead of the chest, alignment falls apart.

What happens next?

• Hips drop
• Legs sink
• Frontal drag increases
• Stroke rhythm collapses

A misaligned body creates more resistance against forward motion, even if effort increases.

How can I identify if my swimmer is doing those concepts correctly?

Watch my analysis of fly undulation below!

As shown in the video, you can see how that swimmer struggled with the THREE main concepts behind a GREAT undulation. It is imperative (as a coach) that you understand these concepts and can identify these issues within your swimmer stroke’s. I hope–that is why I’m here  .

Coaching Takeaway: Why This Matters

A great Butterfly undulation doesn’t happen by accident. As a coach, it’s essential to truly understand what correct undulation looks like, identify breakdowns as they appear, and address the SOURCE of the problem rather than just the visible symptoms. That ability to see, diagnose, and correct movement patterns in real time is exactly why this V.A.Log series exists.

[CLICK HERE] for Part II—where we will discuss how important the kick is in Butterfly, along with timing issues, and the entire fly sequence!

Until Next Time

Abbie Fish

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