Can You Train for an Ironman Entirely Indoors? (Hint: Yes.)

There are pros and cons to training for an Ironman entirely indoors. Here's what you need to know, plus indoor swim, bike, run and strength workouts to get you rolling.


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For most people, training for an Ironman triathlon involves lots (and lots) of glorious outdoor rides and crisp morning runs. But imagine a training environment where that blue sky is gone, the sunlight hitting your face is rare, and the wind in your hair is from a fan. In other words, imagine training for Ironman entirely indoors. Can it be done? Should it be done?

Yes, it can. And, for some triathletes, indoor Ironman training is the only way. Their reasons vary: some do it because they need to train for a spring race when their neighborhood roads are covered in snow and ice. Others have family or work-from-home obligations that make it hard to get outside during the day. Still others may lack access to safe routes to ride and run, especially in this era of distracted driving.

Luckily, nearly every aspect of triathlon can be replicated indoors. You can swim in an indoor pool, set your bike up on a trainer, and make friends with the treadmill. Indoor training even has its benefits. But be warned: training for a 140.6 mile race entirely inside comes with its downsides, too. We’re here to help.

RELATED: Triathlete’s Guide to Indoor Training

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Indoor training can be great

Professional triathlete and coach Kelly Fillnow does a fair amount of her race prep indoors, and has even coached some of her athletes to Iron-distance success on an entirely indoor-focused training regimen.

“I have an athlete who lives in Minnesota and needed to prepare for Ironman Texas in April one year,” Fillnow said. “He trained entirely indoors throughout the whole winter and had a great race when it was time to do the big dance that April. I do believe it is fully possible to train for an iron-distance race entirely indoors, as long as you have a strong plan.”

On upside is that indoor training offers a controlled, focused environment that can allow an athlete to dig into a workout in ways they could not outdoors. For example, doing super high-intensity efforts on the bike is generally safe on a trainer, especially compared to doing such efforts on the road, where there’s a greater likelihood of distractions or accidents. Indoor training also means there are no cars on the road to contend with, so you can keep your focus on things like form and power.

Indoor training can also free up more time in your schedule. It can be heart-wrenching to show up late to your kid’s soccer game because your ride went too long, or to miss a friend’s night out because you have hill reps to do. When you train indoors, it becomes much easier to pick training times that work for your schedule, without worrying about variables such as temperature and daylight.

Kate Laing is a runner-turned-triathlete who recently trained for an Ironman nearly entirely indoors. “I signed up to race Ironman Boulder 2019, which was to be held in June,” she said. “I knew I’d have to train through the fall and winter in order to have a successful race, and was also focused on rehabbing some tendonitis in my foot, meaning I had to be very careful about the surfaces I ran on. Indoor training was a natural choice for my health and the icy, cold Colorado weather.” After months-on-end of trainer rides and treadmill runs, Laing was rewarded with a new personal best in her iron-distance race time.

Indoor training can also suck

Of course, it’s not all roses. Part of the reason many of us love triathlon is that it gets us outdoors. We get to ride up mountains that literally take our breath away, run in the middle of a pancake flat desert, and swim in the pristine waters of the Gulf of México. For example. Triathlon helps us break away from our four walls and live in awe of the environment that surrounds us. You know what doesn’t do that? Training indoors.

Even the most swagged-out pain caves are constant reminders that you are indeed doing a session that lacks fresh air and Vitamin D. Some people love to have a few bike and run sessions a week indoors (and for many of us, it’s necessary with work and family schedules), but day after day for months can be mentally taxing—and Ironman training is often already a mentally taxing endeavor.

Plus, the challenges of training for an Ironman entirely indoors go beyond simply being bored. Bike skills may begin to disintegrate after months of riding on a trainer. We often take for granted our ability to smoothly rip around a corner when riding outside in the middle of summer. But being able to do this without practice can be tough. It often takes repeated rides outside to feel confident in a variety of twists and turns on your ride.

There are also performance caveats when training indoors. Replicating hills on a treadmill or hard efforts on the bike are no match for the cruel beauty of a hilly course thrown at you by Mother Nature. Hills and descents in the real world are often much more dynamic than those generated by a treadmill or virtual reality program.

And then there’s the fact that you’re never really away from all those family and work obligations. Even though training indoors can open up more time in your schedule, it can also invite unwanted distractions such as kids bopping in and out of your trainer session asking for another juice box, significant others bugging you with a “quick question” that turns into an hour-long conversation, or pressure to check work email in between intervals or while moving from one workout to the next. Sometimes, quantity comes at the expense of quality.

There are pros and cons to the indoor Iron-distance training adventure. To succeed with carrying out an indoor training block for an Ironman, one must be focused, deliberate, and motivated.

Photo: Getty Images
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How to train for an Ironman indoors: The swim

This may be the easiest of the three to adapt to—except for that open water aspect. Most triathletes are familiar with the monotony of following the black line at the bottom of an indoor pool. Waking up to a wintry, dark morning to head to the chilly pool to complete a long Ironman-specific swim set however, takes it to another level. You not only need to cover big distances in the tiny pool, you also need to prepare for open water.

“Training in a pool and staring at a black line are completely different than the dynamics of the open water you’ll face in an Ironman,” Fillnow said. “With a pool, you don’t get to experience sun glare, waves, and the need to make it to the next buoy. But, this doesn’t mean you should ignore these skills entirely. There are definitely ways to work on open water specificity in an indoor pool.” However, an Ironman race day should not be the very first time an athlete ever swims in open water. Athletes who do not have previous open-water experience should get acquainted with the conditions and gear (such as a wetsuit) well before race day.

RELATED: Triathlon Swimming: An In-Depth Guide

While we can practice the skills in the pool or get in a few open water sessions just to fine-tune, the biggest obstacle to indoor swimming often isn’t the training itself—it’s motivation. It’s hardest to get to the pool (literally and figuratively) and force ourselves to jump into that cold water. Ironman finisher Kate Laing suggested making your hardest workout of the day your first one. As hard as it can be to wake up early enough to head to the natatorium, it’s even harder to coax yourself into cannonballing into the water after a tough day at work. Making a pact with a training partner to meet before work to swim is a great way to ensure that you actually go and get it done; you don’t want to leave your accountability buddy hanging.

How to practice for open water in an indoor pool

  • To practice sighting, plan to look up and forward every 6-10 strokes, even if you end up looking at the other end of the pool.
  • To practice getting comfortable swimming close to others, get a buddy and swim side-by-side in the same lane during a hard effort.
  • To get comfortable with the dizziness of moving from horizontal to vertical after the swim, add in “deck ups,” where you swim a hard couple of laps, get out of the pool quickly, hop back in and continue swimming hard.

RELATED: The Triathlete Guide to Going from Pool to Open Water

Indoor open water swim workout

Coach Fillnow suggested this type of workout to improve your sighting skills and your get-out speed (how fast you’ll sprint into the water at the start of a race):

Warm-up: 

10 minute choice, rest for 20 seconds

6-8 x 25 practicing different sighting methods, rest for 10 seconds

Main set:

6 x 50, 10 seconds rest

-3 descend stroke count (DPS)

-3 build (increase stroke rate)

200 easy pull recovery w/ buoy, rest: 15s

6 x 50 w/ paddles, rest: 10s

-25 FAST/25 easy

200 easy pull recovery w/ buoy, rest: 15s

12 x 150, rest: 20s

Descend in 3s from 75–80/85–90/95% sighting 3x per 50

Cool-down: 

5 minutes easy

Photo: Getty Images
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How to train for an Ironman indoors: The bike

Triathlete Reggie Waller completed all of his bike sessions indoors when training for Ironman Lake Placid 2016. “The bike was the hardest discipline to train indoors,” Waller said. “It was more mentally hard than physically, because you’re sitting on a saddle sweating away, yet not going anywhere.”

Waller put it perfectly: when you ride a bike indoors you spend a lot of time pedaling hard just to go nowhere. An iron-distance bike course is 112 miles long, and is known to bring with it emotional highs and incredibly moody lows. The bike is also where nutrition and hydration begin to take center stage, fueling you for the grueling ride and hopefully setting you up for a strong marathon off the bike. So how do you prepare for all of this without leaving your house?

To start, you’ll need a bike trainer. You can purchase a smart trainer, which have connectivity functions to make access to Zwift and other online platforms feasible, or you can look into a “dumb” trainer (i.e. no connectivity) where you manually adjust the resistance with a knob. Either can work, but many prefer a smart trainer because of the programs it can sync with, making an indoor ride feel more like a video game. Some trainers even come with steering blocks to make it seem like you’re actually navigating turns, but they’re no replacement for cornering, descending, and gauging stop-time in real life.

RELATED: The Top 9 Indoor Cycling Platforms

No matter what trainer you buy, though, even the most tricked-out ones come with a lot of monotony, especially on century rides (100+ miles). To combat this, Fillnow recommends each trainer session should have structure and a distinct purpose.

“Even if you’re doing a multi-hour indoor ride, make sure there’s a workout in there, too,” Fillnow said. “I would not recommend trying to hop on your bike with no plan and crank out 100 miles. Have a defined warm-up, a workout with some efforts, and a cool-down to help break up the time in the saddle.”

Ironman workouts for the indoor bike trainer

Workout 1:

Warm-up:

10 minute easy spin

Main set:

4x 60 sec lighter aerobic @ high cadence 105-115rpm w/ 90 sec at normal cadence

3x 2 min seated @ 70.3 effort at 60-65rpm, 2 min 100rpm lighter aerobic

3x 12 min @ 70.3 effort, 3 min ez

5 min ez aerobic

2x 7 min @ 40k TT effort, 3 min ez

2 x 30 sec right leg, 45 both, 30 sec left leg, 45 both

Cool-down:

10 minute easy spin

Workout 2:

Warm-up:

10 minute easy spin

Main set:

4x 60 sec lighter aerobic @ high cadence 105-115rpm w/ 90 sec at normal cadence

2 x 5 min big gear 60-65 RPM @ 40K effort, 5 min easy

2 x 15-20 min at IM effort, 5 min easy recovery

2 x 5 min big gear 60-65 RPM @ 40K effort, 5 min easy

2 x 30 sec right leg, 45 both, 30 sec left leg, 45 both

Cool-down:

10 minute easy spin

RELATED: 10 One-Hour Indoor Cycling Workouts

Replicating your race conditions on the trainer

During your Ironman prep trainer rides, it’s important to place an emphasis on using the nutrition and bathroom breaks you intend during the race.

“As tempting as it can be to eat homemade cookies or jump off the bike for a bit to chat with family or use the bathroom, that can actually be detrimental to your race,” Fillnow noted—sicnce you won’t have that option on race day. “While it’s OK to have the occasional treat to get through a long indoor ride, you really do want to be incorporating race-day specificity into your trainer rides when it comes to food and bathroom breaks.”

While both Laing and Waller avoided any crashes during their races after their indoor training blocks, Laing did note that the absence of outdoor riding did make it harder to fend against the wind during her big day.

“The wind picked up toward the end of the first loop of the bike course and due to not having biked outside a lot, I struggled handling my bike,” Laing said. “However, biking inside with a cadence and power meter had made my cycling and pedal stroke much more efficient; my newfound strength on the bike outweighed my issues with the wind and I ended up hitting a new personal best for an Iron-distance bike course by 90 minutes.”

If there is a day that is even slightly warm (maybe in the 30s or higher) or you have the time to get outside, it is a very good idea to bundle up sufficiently and either take your bike for an easy ride on the roads or head to a parking lot with cones and do some cornering and bike handling drills. A few rides outside just to refresh your skills will do wonders for your handling on race day. Just be sure that whatever surface you’re riding on is ice- and snow-free.

Photo: Getty Images
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How to train for an Ironman indoors: The run

For those training indoors, the treadmill will probably be the go-to method. Some gyms also offer indoor tracks (generally shorter and smaller than typical 400m outdoor tracks) which can also be good for incorporating speedwork into your plan. No matter what, though, running entirely indoors can be a brain drain at times.

“Treadmill runs longer than 10 miles were not my favorite,” laughed Laing. “But when it’s dark and icy outside and you want to reach your goal, you convince yourself that it isn’t that bad.”

And treadmill runs truly don’t have to be that bad. Indoor training is largely about keeping the mind focused on the goal you’re working toward. Fillnow says removing the distractions of outdoor runs allow for a different kind of focus: “Indoor runs are great time to connect with your why—why did you sign up for this race in the first place? Why is running on the treadmill worth your time right now? Why are you doing any of this at all? Digging deep to answer those questions and remind yourself of the bigger picture is a great use of your mental energy during these sessions.”

If that doesn’t work, there’s always streaming. Incorporating music, documentaries, footage of past races, podcasts, and other media can be a great way to stay in the moment and keep your brain occupied while your body does the work. Both Laing and Waller leaned on music and TV to get them through some of their more mentally challenging long runs on the treadmill. Laing, who likes to bake, would spend her warm-ups scrolling through recipes on her phone to choose what she’d cook up as a treat after her time on the indoor grind was finished for the day. Waller noted that he pulled up past recordings of the Ironman World Championship in Kona on YouTube to motivate him to stick with the session.

Just as on the bike trainer, it’s important to use your actual race day nutrition and hydration when executing a long run indoors. Just because there are freshly made scones in the kitchen doesn’t mean they should become part of your workout fuel (but definitely have one after you’re done!). Try to train with the same fuel you’ll use on the race course, and if you’ll be relying on aid stations, time your intake to where fuel will be handed out along the way.

RELATED: 7 Treadmill Tips for a Better Indoor Run

Ironman workout for the treadmill

Warm-up:

10 minutes easy

Main set:

3-5 x

4 min @ 2% @ 10K effort

2 min @ 4% @ 5K effort

2 min @ 0% @ Easy recovery effort

Cool-down:

5 minutes easy

RELATED: Stuck On The Treadmill? Boost Speed With These 3 Workouts

Post-run strength workout for Ironman training

It’s key to incorporate strength workouts too throughout the winter to maintain a stable core and muscles that are resilient to things like hills and descents. “I’ll have my athletes doing some type of strength training one-to-two times a week,” Fillnow said. “Strength training throughout the winter will help your body become familiar with the demands an Ironman puts on your muscles and joints.”

Glute + core activation

2 x 60 seconds*:

Clam hold (for more of a challenge, perform clam in a side plank)

Straight leg hold (lie on side and lift top leg) (for more of a challenge, perform in a side plank)

Fire hydrant (for more of a challenge, perform standing)

*These are all isometric holds. Start out without a band, then progress band strength as you get stronger.

The bottom line

It’s entirely possible to train on an all-indoors schedule for your next iron-distance race; it might even leave you more prepared and mentally tough. It just takes some planning and preparation. Know your “why,” build a plan, keep your mind busy, and put in the work—and be ready to lay it all out there come race day.