The best treadmill workouts for triathletes

These three hard-and-fast sessions are ideal for swim-bike-run competitors.

To many, triathlon saves the best for last. After making your way through the stress of the open-water swim, then cranking through the day's longest leg, the bike, you are left with just your running sneakers and the open road. No wetsuits to squeeze into, no anxiety over the possibility of a flat tire. Just running, pure and simple. And as the final third of the race, the run is your last chance to make a dent in your time, to pick off or be picked off.

Most importantly, athletes must prepare to break through the fatigue accumulated during first two legs to be able to finish strong. And to that end, Tier 4 trainer and resident triathlon expert Kai Karlstrom recommends hitting the treadmill for interval training. Karlstrom, who much prefers the Woodway treadmills, which have a rubberized slat surface that absorbs shock, uses treadmills to create hill workouts, which are lacking in his hometown of Chicago. Another advantage of indoor running: Accessible nutrition. "Nutrition is a big thing people forget about – so when people have a hard workout, they might not want or remember to carry their nutrition with them," he says. "It's much easier to do your workout when you have something sitting next to you."

Check out these three treadmill sessions, which will improve both your speed and endurance. "If you only do these three workouts each week, you would be a mean runner," says Karlstrom, who is competing for Team USA at the Sprint Distance Triathlon World Championships in London this September. "Just be sure to set the treadmill at a 1% incline—you should never have the treadmill flat."

Follow this guide to gauging your effort, the same as you would for a cycling workout, with your rate of perceived exertion falling on a scale of 1 to 10: Zone 1 (RPE of <2); Zone 2 (RPE 2-4); Zone 3 (RPE 4-5); Zone 4 (RPE 6-8); Zone 5 (RPE 8-10); Zone 6 (max).

Workout 1
Warm-up: 15 minutes with accelerations.
Main set: 5x(6 minutes Z4, 4 minutes Z1/2)
Cool-down: 20 minutes Z2

Workout 2
Warm-up: Dynamic warmup, such as the World's Greatest Stretch
Main set: 5x(5 minutes at 7% incline at long run pace, 5 minutes walking recovery)
Cool-down: Fill in the rest of the time in Z2

Workout 3
Warm-up: 10 minutes with accelerations
Main set: 15x(30 seconds all out, 30 seconds rest)
Cool-down: 15 minutes Z2

Get more of Karlstrom's triathlon training advice.