The “Birthday” Swim Workout

Challenge yourself with this endurance swim set.

Heading out the door? Read this article on the new Outside+ app available now on iOS devices for members! Download the app.

If you follow Ultraman world champion Hillary Biscay’s blog (, you know that she has an affinity for something known as the “birthday swim.” For Biscay—and for several of the athletes she coaches—the birthday swim session is an epic distance doozy: 100×100 (although it can be modified to a shorter set).

“The birthday set was something that Sutto [legendary coach Brett Sutton, with whom Biscay trained at the start of her career] would occasionally assign to commemorate someone’s birthday. I fell in love with the set, so thought I would share the joy with my athletes,” Biscay says. “For most of them this is a tough session—but what better birthday gift than to earn the sense of accomplishment that comes along with completing something like this?”

The mindset required for the birthday swim is perfect preparation for the mental challenge of an iron-distance race, says Biscay. “Unlike other swim workouts in which we often find ourselves counting down the remaining yardage, this workout requires a ‘swim all day’ mindset. It’s a workout to really embrace the process, being in the pool and being in the moment. Kind of like in an Ironman, it’s best not to think about the finish line till you get there!”

Sutton says he initiated the set as a “birthday swim” for a lucky athlete (and their lane mates), because “having a special occasion makes it more palatable.”

“It’s a mental drill,” he continues. “To swim this far takes a lot of mental strength. It’s longer in duration than an Olympic-distance triathlon as a whole. Triathletes are happy to do long rides or over-distance runs, but most don’t like the over-distance swim. It originated from my swim days. The distance lane back in my day was called the ‘animal lane.’ We used to do crazy things—100×100 on 1:15 was the bell ringer animal lane standard.”

Siri Lindley, also a former disciple of Sutton and now coach to Biscay and numerous other champion triathletes, says that over-distance swims are great for endurance and strength work. But she cautions against being overzealous. “You should at least be able to swim 6K before taking on a 100×100 set,” Lindley says. “Otherwise it could lead to injury.”

RELATED – Dispatch: This One Time, At Tri Camp…

The Workout: 100×100 Swim

– 10×100 super easy warm-up on 2:10
– 10×100 as 25 sprint / 75 easy on 2:10
Fuel break
– 30×100 swim on 2:00, steady pace
Fuel break
– 15×100 buoy/band on 2:00, steady pace
Fuel break
– 30×100 paddles/buoy/band on 1:45
– 5×100 easy cool-down as 50 kick/50 easy swim with 10 sec rest

Note: This is a beginner’s birthday set—designed for 10K swim first-timers who are comfortable swimming 100’s on a 2:00 interval. The workout remains the same for more advanced swimmers—simply adjust the interval accordingly, using the set of 30×100 as your base pace.

You’ll notice a lot of fuel breaks built in, maybe more than you think you need. But Biscay pushes her athletes to eat plenty. Better to err on the side of too many calories and risk a slightly bloated belly than to risk a spectacular bonk. “Going extra long—whether in swimming, cycling or running—the caloric burn can really catch up with you,” Biscay says. “Trust me—I speak from experience!”

RELATED: Swim Workouts From Sara McLarty

Trending on Triathlete

Jan Frodeno Reflects on His Final Ironman World Championship

Immediately after finishing 24th place at his final Ironman World Championships, the Olympic medalist (and three-time IMWC winner) explains what his race in Nice meant to him.