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What I’ve Learned About Zone 2 Cardio and Ironman Training

As an Ironman Coach, I've witnessed firsthand the transformative impact of Zone 2 cardio on athletes' performance and overall training, especially in the last few months. I’ve done some deep diving into the world of Z2 Cardio, listened to a lot of podcasts, webinars, and read a lot of blog posts about this topic. While the allure of intense workouts in higher zones may seem tempting, dedicating time to Zone 2 training can be the secret weapon in unlocking your full potential as a triathlete. Yes, ME the coach who loves track workouts and hill repeats is actually saying this!

Zone 2 cardio, also known as aerobic endurance training, involves exercising at a moderate intensity where you can comfortably maintain a conversation. Here's why integrating Zone 2 workouts into your training regimen can take your Ironman journey to new heights:


Building Aerobic Base: Zone 2 training lays the foundation for endurance by strengthening your aerobic system. By consistently training in this zone, you enhance your body's ability to efficiently utilize oxygen, improving endurance and stamina essential for the long distances of an Ironman race. In Zone 2, the mitochondria -the powerhouse of our cells- are becoming more efficient, and when they multiply, we get better at removing lactic acid.  (You know you are accumulating lactic acid when you get that “hit the wall” feeling.) Stronger mitochondria help us recover faster.

Fat Adaptation: Zone 2 workouts primarily rely on fat metabolism for fuel, teaching your body to become more efficient at burning fat. (I don’t know any athlete that sees this as a negative!) This metabolic adaptation is invaluable during the grueling segments of the race, where preserving precious glycogen stores can make all the difference in maintaining performance.

Injury Prevention: In some cases, Zone 2 training offers a lower impact alternative to high-intensity workouts, reducing the risk of overuse injuries commonly associated with intense training. If I have an injured athlete, I will say that 90% of the time it is a running injury, often from an intense Z3/Z4 workout.  Let me use my athlete Rob as an example. Over the past few months, we have made the change from track workouts and hill repeats to more Z2 efforts. He has been keeping me posted on his musculoskeletal status since doing less speedwork and more Z2. So far, he has had far fewer injuries and reports that he feels less aches and pains since making the switch. The real test will be seeing how his times at upcoming Ironman Texas compare to times from last year. The evidence points to that staying in Z2 provides a valuable opportunity for recovery while still making significant fitness gains.

Enhanced Recovery: Engaging in Zone 2 workouts aids in active recovery, promoting circulation and flushing out metabolic waste products accumulated during intense training sessions. This accelerates recovery times, allowing you to bounce back faster and tackle subsequent workouts with renewed vigor. In this week’s TriDot podcast they said, “Your next interval is only as good as the recovery from the last one.” The benefits of Zone 2 training extend beyond its immediate impact. Integrating these workouts into your training regimen can also optimize performance in higher intensity zones:

Improved Thresholds: Strengthening your aerobic base through Zone 2 training enhances your lactate threshold, enabling you to sustain higher intensities for longer durations without succumbing to fatigue. Your next interval is as good as your recovery from the last one. (I think I already said that above.) Keeping it in Z2 for recovery is an investment in the next interval.

Efficient Energy Utilization: By maximizing your aerobic capacity, your body becomes more efficient at utilizing energy sources across all zones. Z2 helps you get faster but only to a degree so we still need other zones to get faster; This translates to improved performance during intense efforts, as you can sustain higher power outputs while conserving precious energy reserves.


So why don’t athletes like Z2?

They feel if they are not sweaty not out of breath, they didn’t work hard. And it doesn’t look good on Garmin or Strava. TriDot says that that is a misconception. Zone 2 is an investment in your tougher workout that happens tomorrow. Suffering often doesn’t make you faster. I used to think it did until I dove into all this data about Z2 Cardio.


How to Stay in Zone 2?

Start looking at Z2 as a benefit not a liability. Focus on how enjoyable it is as well as social in some cases. Let go of pace and power and let your heart rate be the only metric you are focused on. A good indicator of Z2 is being able to breath in and out of your nose for 2 min. Focus on good form, foot strike or efficient pedal stroke all while staying in Zone 2. See if you feel a runner’s high and picture in your mind how your mitochondria are becoming more efficient. You should finish the effort with gas in the tank at a pace you could keep for hours.


As an Ironman Coach, I encourage you to embrace more Zone 2 training. I’m not saying completely stop doing workouts in the other zones, but the focus should be Z2 across all three sports. By prioritizing endurance and aerobic development, you lay the groundwork for success in all facets of your training. I will admit, at first, I wasn’t sold on all of this, but the more I read the more it makes sense to me. I would love to hear your thoughts on this or if you have made the switch already how has it helped your training.


Have you thought about hiring a coach for your next iron distance event? Click the purple box below to set up a FREE 15-minute chat with me about your race goals.



Mary Timoney

Ironman University Certified Coach

USA Triathlon Certified Coach

TriDot Coach

ACSM Trainer

USA Cycling Coach


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