A swimmer drops two seconds over three months. Great news — but what actually changed? Comparing swims over time only works if you break the race into laps, not just look at the clock at the wall.

Female swimmer racing with AIM Systems analysis in use

A single finishing time hides everything useful. It doesn’t tell you if the swimmer got faster off the start, held velocity better mid-race, or simply turned quicker. Without lap-by-lap data, coaches end up guessing which part of training actually paid off.

Why comparing swims over time needs lap data, not just final splits

Two swims of the same distance, months apart, can look identical on the scoreboard and still be completely different races underneath. Maybe stroke count dropped in the middle laps. Maybe breakout distance got longer off every turn. Maybe nothing improved except the start.

This is exactly why comparing swims over time works best lap-by-lap: turn time, breakout distance and time, stroke count, and lap time, measured the same way in both swims. AIM Systems captures this automatically for every session, so a coach can line up swim A against swim B and see precisely where seconds were won or lost — not estimate it from memory.

The part everyone assumes changed — and usually didn’t

Research from Gonjo and Olstad (2021), using the AIM race analysis system, compared elite and sub-elite breaststrokers across a full 100m time trial. The elite group was faster almost entirely because of clean-swimming velocity — 7 to 11% faster in every lap — and glide velocity off the wall, about 13% faster in laps two and three.

What didn’t separate the groups was the pull-out itself. Elite and sub-elite swimmers showed no real difference there, or in the very start of the swim-out that follows it. That’s counter to what most coaches would assume watching from the deck.

The same study modeled what would happen if a swimmer’s own best pull-out and transition segments replaced their weaker ones. Two swimmers with almost identical race times could both have gone under 60 seconds. The pull-out and transition are an underused area for gains, even in strong racers.

This matters for month-to-month comparison. A coach might see a swimmer’s overall time improve and assume the pull-out got stronger, when the real change was in clean-swimming velocity or glide off the wall. Without splitting the race into these segments, that distinction is invisible.

What to actually check when comparing two swims

  • Lap time and dropoff, lap by lap, not just the final split.
  • Stroke count and stroke rate — did the swimmer hold form longer before fatiguing?
  • Breakout distance and time after each turn.
  • Glide velocity right after wall push-off, separate from the pull-out itself.
  • Start entry distance and underwater speed off the block.

Run this against the swimmer’s own past top time, or a manually entered target, and the comparison becomes concrete instead of anecdotal. That’s the actual value of tracking swims over months: knowing which specific segment moved, and which one still needs work.

Bringing this into your own program

Every AIM Systems installation produces a stitched video with data overlaid, plus a full spreadsheet, for each timed swim. Because the same metrics get captured the same way every session, comparing swims over time doesn’t rely on someone’s memory of how the race looked in March.

If you’re curious how this would work with your own squad’s data, get in touch with AIM Systems — happy to walk through it.

Frequently asked questions

How do you compare two swims from different months fairly?
Break each swim into the same lap-by-lap metrics — turn time, breakout distance, stroke count, and lap time — so you’re comparing identical segments, not just final times.

Does a faster overall time mean the pull-out got better?
Not necessarily — research using the AIM system found elite and sub-elite breaststrokers showed no real difference in pull-out speed, with the gap coming from clean-swimming and glide velocity instead.

What part of the race is most often overlooked when tracking progress?
The pull-out and transition phase, which one study found could add several seconds of untapped gain even for swimmers with strong overall times.

Sources

  • Gonjo, T., & Olstad, B.H. (2021). Differences between elite and sub-elite swimmers in a 100 m breaststroke: a new race analysis approach with time-series velocity data. Sports Biomechanics. https://doi.org/10.1080/14763141.2021.1954238