Shoulders & resilience

What Stroke-Side Asymmetry Looks Like From the Deck

For head coaches and aquatics directors

Ask a swimmer to push, pull, or hold a position with both arms and she will give you a number that looks fine.

Ask her to do it one side at a time, then compare the two. That comparison is where the interesting information lives, and almost nobody looks at it.

The tension

Two-sided testing is reassuring by design. It lets the stronger side carry the weaker one.

A swimmer with a meaningful gap between sides can post a completely normal two-arm number, the same way she can post a completely normal time. The system compensates. That is what systems do. So two swimmers can touch the wall within a tenth of each other and be carrying completely different physical profiles underneath.

The time cannot tell them apart. That is the problem with the time.

Where it comes from

Swimming builds asymmetry structurally. It is not a flaw in how a program trains — it is what the sport is.

A swimmer who breathes to one side repeats that rotation pattern thousands of times per week, and the body organizes around it. Most swimmers have a dominant arm whose catch quietly does a little more work in every stroke cycle. Turns rotate the same direction off every wall. Backstrokers and breaststrokers each collect their own versions.

Add a growth spurt, where limb length changes faster than the control of it does, and the asymmetry has room to widen.

None of this is avoidable through better coaching. It is the cost of specialization, and it is the same reason pitchers develop shoulder asymmetry and volleyball hitters develop it in the legs.

What it looks like from the deck

Mostly, like nothing.

If you know what to watch for, there are tells. One shoulder that sits a little higher on the block. A swimmer who always breathes away from you no matter which side of the pool you stand on. A pull that looks fuller on one side than the other in the last hundred of practice, when fatigue takes the polish off. A streamline that drifts slightly to the same side off every wall.

These read as preferences. Coaches usually interpret them as style, or handedness, or just how that kid swims.

Sometimes that is exactly what they are. Sometimes they are the visible edge of a gap large enough to matter.

The problem is that watching cannot tell you which.

Why the number matters more than the eye

In the water, an asymmetry is a moving picture that only a trained eye can even partially read. On land, it becomes a measurement.

A single-side comparison — pressing, pulling, or holding a position one arm at a time — takes a few minutes per swimmer and produces two figures and a percentage difference. That is a different kind of information than an impression. It can be tracked. It can be compared to where the swimmer was in September. It can be sorted across a roster so a coach can see, in one view, which swimmers are carrying the largest gaps.

And critically, it separates the swimmers who simply have a preferred side from the swimmers who have a deficit. Those look identical from the deck and completely different on paper.

What closing a gap looks like

In the athletes I have measured across sports over twenty years, the pattern repeats.

When the limiting factor is strength rather than structure, the weaker side responds quickly once it is asked to work alone — sometimes quickly enough to pass the other side. That is a reminder that “weaker side” describes a moment, not a permanent property of the athlete.

Gaps built over years of one-sided patterning are slower. They narrow with consistent work; they rarely vanish in a season. Smaller is worth having. A gap that is shrinking and a gap that is widening can look identical in a single test — which is why the comparison over time matters more than any one number.

Either way, the change happens on land, one side at a time, without touching a single thing about how the swimmer moves through the water.

What a coach should take from this

Asymmetry is not a sign that a program is doing something wrong. It is a predictable byproduct of swimming seriously, and every specialized sport produces its own version.

What varies is whether anyone knows which swimmers have it and how large it has become.

That is a measurement question, not a coaching question. And it is answerable in an afternoon of dryland.

The takeaway

The time is the number everyone collects, and it is the one that hides the most.

The left-right comparison is harder to see, more predictive of where problems will show up, and takes very little time to measure on land. For a coach, the practical value is simple: knowing which swimmers on the roster are carrying the largest imbalances, before the season decides it for you.

Athlete Academy works with swim programs as the dryland performance arm — strength, start and turn power, and shoulder resilience — so coaches can stay focused on the water.

This article supports our deeper guide: Shoulders & resilience.