Boosting Cardio Fitness through Triathlon

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by Danny Robdrup

Which of the three disciplines (swim, bike, run) enhances your cardiovascular fitness the most?

Short answer: The discipline you can do most often without injury, consistency is key. Also, nutrition plays a huge role in building endurance along with proper recovery including sleep.

Long answer:

Looking at VO2max as an indicator of aerobic endurance is limiting, but I will use it as an indicator of cardiovascular fitness.

VO2max is the total amount of oxygen that your muscles can utilize before uptake ceases, even with an increase in work/effort. It is measured as millilitres per kilogram per min or ##ml/kg/min.

Working at VO2max will force the body to adapt in these ways: Increased blood plasma, increased muscle capillarization, and increased stroke volume of the heart. All this combines for more blood volume, more blood getting to the muscles, and a heart that pumps more blood per beat = better oxygen utilization. This effort level is sustainable for 3 to 8 minutes.

(But, you’ll notice, if you have a Garmin or other watch that estimates your VO2max, it is different for running and cycling, YOU haven’t changed, but there are different values. This is a result of the amount of muscles used that are utilizing that oxygen, and we use more during running activities than cycling.)

How high can you go? Let’s look at the professionals:

  • Cycling – 70-80 with the upper limits in the 90s (Greg LeMond)
  • Running – 85 for Males, 77 for Females
  • Swimming – 66-80

Based on the pro numbers, the higher values are all in the 80s for men and 70s for females. Looking at this info, they are all the same. Back to the short answer, which discipline can you consistently complete with the greatest frequency while avoiding injury/illness?

One caveat with VO2max is this: it doesn’t account for efficiency/economy. If you are running with your arms flailing around or cycling using more than just your leg and core muscles (with some arms to hold the bike), your VO2max goes up because you are delivering more oxygen to more muscles. Those muscles though are not aiding in your progress towards your goal to be faster or more efficient.

Also, people with more muscle will have an increased VO2 and will make those metrics useless for comparison’s sake.

In Jack Daniels’ (yes, his real name) book Daniels Running Formula (PHD), he also points to vVO2max or Velocity at VO2max, which is relatively more important.

Two runners with the same VO2max should be the same speed… but they aren’t. A comparison between 3 elite female runners whose VO2max are different but still post similar times:

  • Best 3k time: 9:07 | 9:06 | 9:06
  • VO2max (ml/kg/min): 60.4 | 73.3 | 69.6
  • vVO2max (metres per min): 328 | 335 | 336


In my opinion, I would mix all of the disciplines. This reduces the risk for impact-related injury and will provide you with an incredibly versatile base to work from. Work in the VO2max zone two times (total, not for each discipline) per week to reap the benefits.


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