Why Does My Swimmer Slow Down in the Back Half of the Race?

This article walks through one real 14-year-old's 100m freestyle, splits and all, to show how to tell the difference and what changes if you read the race right.

What a "Split" Is, in 30 Seconds

A swimming race is timed in pieces. In a 100m race, you get two pieces: the first 50 (off the blocks to the turn) and the second 50 (the turn to the finish). Each piece is called a split, or parcial in Portuguese. Most timed competitions sanctioned by national federations capture splits automatically through electronic touchpads, per the World Aquatics Competition Regulations.

When parents watch a 100 freestyle, they see only the final time on the scoreboard, say 1:01.46. They feel the swimmer "go fast" and "come back slow" but rarely see the actual two numbers. The swimmer feels both. The coach, with a stopwatch, captures both. And the data exists in the official meet results.

A "split" is just one of those two pieces. Nothing fancier.

What Pacing Pattern Actually Means

Coaches and analysts classify how a swimmer divided up the race into one of three patterns:

• Positive split. First half faster than second half. The most common pattern at any level.
• Even split. Both halves roughly equal.
• Negative split. Second half faster than first half. Rare. Usually a sign of either great pacing discipline or a slow first 50.

Parents almost always see positive splits and read them as fading. Sometimes that read is right. Often it is not.

A Real 14-Year-Old, a 1:01.46, and the Trap

Consider a 14-year-old female club swimmer in Canada. Her personal best in the 100m free (short course meters, swum in a 25-metre pool) is 1:01.46. The splits behind that time:

• First 50: 29.88 seconds
• Second 50: 31.58 seconds

Difference: 1.70 seconds slower on the back half. Classic positive split.

The parent watches the race and concludes, reasonably, that she went out too fast and could not hold pace. The kitchen-table conversation that night is some version of "we need to work on the second 50" or "she needs more endurance work."

That conclusion would be wrong. The actual diagnosis sits somewhere else, and you can find it the same way the app does.

The Peer-Benchmark Reveal

Here is the move. Instead of comparing this swimmer to herself or to a generic chart, compare her splits to other swimmers her exact age who swim in her exact time range.

In the Gophin database, there are about 1,500 swimmers between the ages of 14 and 16 who have swum the 100m free SCM in a range from roughly 58 to 64 seconds in the last 24 months. That is her peer cohort. Not elite Olympians. Not slow beginners. Kids racing at her level.

Their average first 50 in a 1:01-range 100 free is 28.05 seconds.

She is going out in 29.88. That is 1.83 seconds slower than other kids her age finishing in her time range.

Her second 50, by contrast, is 31.58 against a benchmark of about 30.43. That gap is only 1.15 seconds.

So which half is the real problem? The half where the gap is bigger. That is the first 50, not the second.

She is not fading more than her peers. She is starting slower.

For broader context on what "fast for her age" looks like across the standards system (B, BB, A, AA, AAA), see Swimming Standards by Age Explained. The peer cohort approach is a sharper version of the same idea, narrowed to swimmers in the exact same finish-time range.

Why "Fade" Is the Wrong Diagnosis (and It Matters)

This distinction is not academic. The two diagnoses lead to two different practice plans:

If she actually faded (her second 50 was the problem), the right work is aerobic conditioning, lactate threshold sets, race-pace 75s, longer holds at goal speed. Build the engine that delivers the back half.

If she actually started slow (her first 50 was the problem), the right work is reaction time off the blocks, underwater dolphin kick distance, breakout speed, sprint starts, the first turn approach. Sharpen the front of the race.

Same swimmer, same race, same time. Two completely different practice focuses. And the wrong focus burns weeks or months of training without moving the time.

The peer comparison is what unlocks the right call. Without it, parents and coaches default to whichever half "looked worse" from the deck. And what looks worse from the deck is almost always the second half, because that is where the swimmer is visibly struggling. The first 50 happens fast and looks "fine" by comparison, even when it is the slow one.

What Changes in Practice (and at Home)

For our 14-year-old: the coach conversation is no longer "she needs to hold the second 50." It is "her first 50 is 1.8 behind her age cohort. We need to attack the start and the first turn."

At home, the parent stops asking "how was your endurance?" after a race and starts asking "how did the start feel?" That second question is more useful because it is about the part of the race where the actual seconds live.

For her own self-talk, instead of "I died in the back," she gets to say "I left seconds at the front." Same race, accurate language, different emotional load. Coaches who deal with anxious swimmers know that the diagnosis you carry into the next race shapes how you swim it.

The personal best the swimmer is chasing may stay the same, but what counts as progress shifts. Dropping 0.3 seconds on the first 50 is now meaningful in a way that dropping 0.3 on the second 50 used to feel like the only "real" improvement. For more on which "best" matters when, see Season Best vs Personal Best: What Actually Counts.

How to Run This Check on Your Own Swimmer

You can do this analysis manually, but it is faster inside the Gophin app's Splits Analytics tool. The path: open the app, pick your swimmer, choose a 100m race that has timed splits, and tap the Goal Engine tab. Enter the time the swimmer is chasing. The tool returns the peer-cohort splits at that target, calls out the weakest split versus the benchmark, and lets you drag a slider on any split to simulate the projected new total time.

The 100m of every stroke is free for every Gophin user. No card required. The other distances (50, 200, 400, 800, 1500) and the side-by-side comparison against up to three other swimmers are included too, free for everyone.

Open Splits Analytics, free for everyone.

If you prefer the pen-and-paper version, here is the manual workflow:

1. Find the swimmer's 100m time and the two splits. Most meet results sheets list them.
2. Find three or four other swimmers the same age who finished in roughly the same time at recent meets. The USA Swimming SWIMS database and the Swimming Canada results portal both let you filter by age, event, and time range.
3. Compare the first 50 average across those swimmers to your swimmer's first 50.
4. Compare the second 50 average to your swimmer's second 50.
5. Whichever gap is bigger is the real weak point.

For a broader look at how to read race results beyond just splits, our guide on tracking swimming times covers the metrics worth following over a season.

What This Approach Does Not Tell You

Be honest about the limits. The peer-benchmark approach answers "where in the race is the gap?" It does not answer "why?" The why might be:

• A short underwater dolphin kick on the start
• A weak turn into the second 50
• A breath pattern that costs speed early
• A stroke mechanics issue in the first or second half specifically
• Anxiety at the start that smooths out by the second length

Those are coach-eye and video questions, not data-only questions. The split data tells you where to look. The coach tells you what is happening there.

Quick Decision Guide

Use this when you walk off the pool deck and want to know what to actually do with the splits you just saw.

• "Did she go out too fast or come back too slow?" Compare both gaps to a peer cohort. The bigger gap is the answer.
• "What practice focus should I bring up with the coach?" Front-of-race work if first 50 has the bigger gap. Back-of-race work if second 50 has the bigger gap.
• "What do I ask after the race?" Skip "how was your endurance?" Ask "how did the start feel?" first. Pivot based on the answer.
• "Where do I find peer cohort data fast?" Goal Engine inside Splits Analytics in Gophin. Free for everyone.
• "What if there are no peers at her exact time and age?" Widen the band slightly (one year older or younger, time range plus or minus 1 second). The relative comparison still works.

Frequently Asked Questions

What is a "split" in swimming?

A split is one piece of a race that is timed separately. A 100m race has two splits: the first 50 and the second 50. A 200m race has four splits of 50m each. Most timed competitions sanctioned by national federations capture all the splits automatically.

What does "positive split" mean?

Positive split means the swimmer's first half was faster than the second half. It is the most common pacing pattern in age-group swimming and does not automatically mean the swimmer faded. The size of the gap and the comparison to peer swimmers are what determine whether it is a problem.

Is a positive split bad?

Not necessarily. A small positive split (under 1 second on a 100m) is normal. A larger one might mean the swimmer went out too fast, or that the swimmer simply went out slow and the second half looks worse by comparison. The peer-benchmark approach in this article distinguishes the two cases.

Why does the first 50 of a 100m race usually look "fine" from the bleachers even when it is the weak split?

Because parents see a swimmer dive in, sprint, and look fast. The back half is where struggle is visible (slower turnover, late breath, body position changing). The eye reads the back half as the problem because it is the visible part of the problem. The data reads the actual gap, which often sits in the front.

Where can I find peer-cohort split data for my swimmer?

Inside the Gophin app, the Goal Engine inside Splits Analytics does this comparison automatically using its database of swimmers age 14 to 16 (or other age brackets) who have swum the target time in the last 24 months. Manually, you can build a peer cohort from official age-group results portals by filtering to age, gender, and time range, and then averaging the splits of three to five comparable swimmers.

Does this work for distances other than the 100m?

Yes. The same logic applies to the 200, 400, 800, and 1500, although the number of splits to compare grows and the "where is the gap" question becomes more nuanced (early, middle, or finish). In the Gophin app, splits analysis is free for every distance, including the 100 of every stroke.

How often should I check my swimmer's splits?

Once per competition cycle is usually enough. After a key meet, look at the splits from the top one or two events, compare to peer cohort, and bring the finding to the next coach conversation. Doing it every practice is overkill. Doing it once a year is too rare.

What if my swimmer has a negative split? Is that always good?

A negative split (second half faster than first half) usually signals one of two things: excellent pacing discipline, or a slow first 50. The peer-benchmark check tells you which. If both halves are within range of the cohort and the second is faster, it is pacing discipline (a strength). If the first 50 has a big gap and the second 50 is close to benchmark, the negative split is just the math working out, the front of the race is still the weak point.

One Last Thing

If your swimmer is "fading" in the second half, the right next question is not "how do we build endurance?" It is "how does her first half compare to other kids her age in this time range?" Often, the answer is that she has more time to find at the front of the race than at the back. The split data makes that visible, and the practice plan flips accordingly.

The race you watched from the bleachers is not the same race the swimmer swam. The splits are how you close the gap.

Open Gophin and check your swimmer's splits, free.

Sources

1. World Aquatics. Competition Regulations and timing equipment standards (automatic split capture at federation-sanctioned events). worldaquatics.com/rules/competition-regulations
2. USA Swimming. SWIMS database for individual times, splits, and age-group filtering. usaswimming.org/times
3. Swimming Canada. Results portal with filterable age, event, and time-range queries. swimming.ca/en/results-rankings