Daiya Seto Chasing Michael Phelps’s 400 IM WR: An Analysis

Earlier this month, Japanese swimmer Daiya Seto indicated his goal of breaking Michael Phelps world record in the 400 IM at this summer’s Tokyo Olympics. Phelps’s record of 4:03.84 was set at the 2008 Beijing Olympics. Approaching 13 years since that swim, it is the oldest men’s individual swimming record.

Seto, like Phelps, is a great all-around swimmer. His 1:52.53 in the 200 butterfly makes him the third fastest person of all time in the event. Two years ago he put a 59.79 in the 100 breaststroke. In 2016 he swam 1:59.50 in the 200 backstroke. And while he’s not known as a freestyle specialist, his best time of 1:47.71 was back in 2015. Seto definitely has the pedigree and strength in the individual strokes to make a run at the record. 

In light of his stated goals, I decided to take a look to see what it would actually take for Seto to break this record. We don’t want to just look at Phelps’s splits and say that Seto has to be faster than that. No, we want to take a look at how Seto swims his races and use that as a base for the splits he needs to target.

As a refresher, Phelps’s world record splits were the following:

Seto’s best time of 4:06.09 was swum in January 2020 and ranks him as the fifth fastest swimmer all-time in the event. His splits of that swim break-down as follows:

A quick comparison shows us that Seto’s splits on the fly and breaststroke were actually faster than Phelps’s WR splits. The breaststroke split isn’t surprising as that was Phelps’s slowest stroke relative to his other four. What is surprising is that Seto’s fly split is faster than Phelps considering at one point Phelps was the WR holder in both the 100 and 200 fly. 

Rather than just look at Phelps’s raw splits from his WR and say “that’s where Seto needs to be”, we can dig a bit more into the splits. We can take each stroke and look at it as a percentage of the overall time. For example, using Phelps’s fly split, 54.92 seconds/243.84 seconds = 22.52%. 

We can do the same thing with Seto’s 4:06 from last year:

We can also do the same for other swims from Seto, particularly those within the past two years:

We can confirm the trend where Seto is regularly faster on fly and breast than Phelps but Phelps is faster on back and free. With Phelps’s freestyle split being significantly faster than Seto’s, he will need to be well ahead of WR pace after the breaststroke.

Using the races and splits percentages, we can calculate the splits Seto would need based on the four races above:

The numbers above show how truly impressive Phelps’s record is. There is a reason that the record has lasted almost 13 years — a swimmer needs to have a great combination of speed and endurance in all four strokes. Will Seto break Phelps’s last standing individual record? It will take a lot of work but at the Olympics in his home country, we’re saying there’s a chance.