You clip the buoy between your thighs and your 100s drop by seconds. It feels like fitness. Often it’s just flotation, and your real swim is the one you do without it.
That’s pull buoy reliance: building your swim pace, your zones and your confidence on a tool that lifts your legs for you. The risk shows up on race day, when the wetsuit rules are different or the water is rough.
Here’s how to measure your own gap, and how to stop it from distorting your training.
What a Pull Buoy Changes
A buoy raises your hips and legs. In towing trials with 14 swimmers over 20 m, higher legs and a flatter trunk meant less passive drag (Cortesi et al., 2014). In short: the buoy does the job your core and kick are supposed to do.
It also changes your arms. A small 2024 study of seven swimmers suggests hand force and trunk angle were higher without the buoy at slower speeds (Sports Biomechanics, 2024). We couldn’t read the full paper, so treat this as a hint, not a rule. Translation: you probably don’t pull the same way with a buoy as you do in a race.
Think of a phone with a battery pack taped to it. It runs longer, but you haven’t improved the battery. The buoy is the pack. Your own body position is the battery.
A buoy set isn’t useless. It isolates the arms and cleans up a messy stroke. But it can’t tell you how fast you swim.
Buoy times measure the buoy.
How Much Does the Kick Really Add?
Researchers don’t agree, because they measure different things. A 2011 paper by Sortwell in the International Journal of Exercise Science collects the figures for Hollander (1988) and Nakashima (2007). Here’s the spread.
One 25 m sprint study found that adding the kick raised top speed about 10% (Deschodt et al., 1999). The authors think the legs mostly help the arms work better. A buoy removes that link.
In short: the kick may not push you far, but it keeps your whole stroke tuned. Take it away and you hide the problem.
Why a Wetsuit Hides the Same Weakness
A wetsuit works like a built-in buoy. It cut drag by about 14% at 1.25 m/s and about 12% at 1.50 m/s in 12 swimmers (Toussaint et al., 1989). Most of that comes from extra buoyancy.
The real speed gain is smaller. It’s about 6% over 400 m in a study of 95 swimmers, and nearer 3.7% at 1,500 m per one secondary summary we couldn’t verify. Translation: the suit helps, but less than the drag number sounds like, and less over long swims.
So a swimmer with sinking legs can look fine in a wetsuit. Then the water hits 78 degrees, the swim is non-wetsuit, and the legs drop. If you’ve also trained with a buoy for years, you never felt the problem.
Here’s how the three conditions compare.
| Condition | Measured effect | What it hides |
|---|---|---|
| Pull buoy | Higher legs, flatter trunk, less passive drag | Weak core, weak kick, sinking hips |
| Wetsuit | About 14% less drag at 1.25 m/s, 12% at 1.50 m/s | Poor body position, until a non-wetsuit swim |
| Kick added to arms-only sprint | About 10% faster top speed over 25 m | How much your legs help your arm stroke |
If you’re fast in the pool and slow in open water, your buoy habits are a place to look. We found no verified number for the pool-versus-open-water gap, so measure yours. Poor breathing and rhythm in open water can add to the loss, too.
Measure Your Own Pull Buoy Reliance
Don’t trust anyone’s “buoy is X seconds faster” claim. We found no peer-reviewed number, and forum posts report mixed results. Run this test instead.
| Step | Do this |
|---|---|
| 1 | Warm up 400 m easy. |
| 2 | Swim 400 m full stroke, steady hard. Record the time. |
| 3 | Rest 5 minutes. |
| 4 | Swim 400 m with buoy, same effort. Record the time. |
| 5 | Divide the difference by 4 for seconds per 100 m. |
Then read the result with these rough bands. They’re coaching rules of thumb, not research.
| Gap per 100 m | What it may mean |
|---|---|
| Under 4 sec | Good body position. Buoy use is a choice. |
| 4-8 sec | Normal. Add kick and core work. |
| Over 8 sec | Legs sink. Fix body position before you chase more pace. |
Repeat it every 6 to 8 weeks. A shrinking gap means your body position is improving, even if the clock barely moves.
If your gap is over 8 seconds, change your week. Add two short kick sets, such as 6 x 50 m kick with no fins. Add body-line drills, like kicking on your side with one arm extended. As coaching practice, not research, cap the buoy at about one set in five. Then retest.
How to Test Critical Swim Speed Properly
Your critical swim speed (CSS) is the pace you can hold for a long, steady swim. Your swim zones come from it.
The original method comes from Wakayoshi and colleagues in 1992. You swim several distances, plot distance against time, and draw a line through the points. The slope of that line is your CSS. In short: the steeper the line, the faster your steady pace.
Most coaches use a two-point shortcut with a 200 m and a 400 m time trial:
CSS (m/s) = (400 - 200) / (T400 - T200)
Here, times are in seconds. Say you swim the 200 m in 3:32 (212 s) and the 400 m in 7:20 (440 s). That’s 200 / 228 = 0.877 m/s, or about 1:54 per 100 m.
Even a clean test has limits. A 2024 reliability study of 32 national-level swimmers found the 200/400 m pairing repeats well but gives higher CSS values than protocols with longer trials (Scott, Burden & Dekerle). The authors suggest adding trials of 800 m or more. Translation: the quick test flatters you a bit, so don’t add a buoy on top. For the full protocol, see our guide to critical swim speed.
What a Buoy Does to Your Zones
If either trial uses a buoy, your CSS comes out too fast, and every zone is too fast with it.
Take Dana, a 41-year-old training for her first 70.3. This is an example, not a study. She did her 200 and 400 with a buoy: 3:20 and 6:48. Her CSS came out at 1:44 per 100 m. A month later she retested full stroke: 3:32 and 7:20. Her CSS was 1:54.
Her zones had been 10 seconds per 100 m too fast. Her “threshold” sets were really all-out swims, and she faded in every one. After she reset her zones, the sets felt hard but repeatable.
The buoy didn’t make Dana faster. It made her zones wrong.
A Practical Buoy Split
| Use the buoy for | Skip it for |
|---|---|
| Isolating your pull | CSS and pace tests |
| Cleaning up a crossover | Race-pace sets |
| Short warm-up or cool-down drills | Most of your weekly yardage |
Pair buoy-free sets with kick work and body-line drills. If you lean on a buoy for most of your yardage, you’re training the part you don’t need to train. Our post on building an aerobic base applies in the water too: easy volume only helps if it’s the swim you’ll actually race.
Once the pool work is honest, practice sighting without losing pace in open water.
Where AthleteOS Fits
AthleteOS builds your swim zones and CSS from your logged sessions, and it bases them on your full-stroke efforts. When you log your equipment, you can compare buoy and no-buoy paces side by side. Start a 14-day trial and run the 400 m test as your first swim.
Run the test once. Then you’ll know what the buoy is really doing for you.