Cardio Training is dead – at least, it should be if your goal is to improve your ability to ride faster and with more endurance on the trail. Much like bodybuilding workouts that try to isolate different muscle groups from each other, traditional Cardio Training tries to improve your ability to ride as fast and as long as you want by isolating your different Energy Systems. Just like those outdated bodybuilding workouts won't prepare your muscles for the real world demands of working together to create movement on the trail, traditional Cardio Training doesn't prepare your cardiovascular and metabolic systems for the real world demands of integrating everything together to fuel your efforts on the trail either.
In other words, it is one thing to have a high level of fitness with the different energy systems but it is another thing entirely to be able to easily transition from one to the next. Metabolic Flexibility is a relatively new term that refers specifically to the ability to easily and efficiently switch back and forth between different energy systems as well as how effectively they support each other. Based on some of the things that have been found out so far I think that you will be hearing a lot more about Metabolic Flexibility in the future.
What has been found so far is that the fittest athletes have a higher level of Metabolic Flexibility, not just specific measurements of different kinds of cardio like VO2Max and Lactate Threshold. This explains why there isn't a direct relationship between lab tests for cardio fitness and actual performance on the trail. This also means that training to improve your cardio as traditionally thought of isn't the real goal; it is to improve your Metabolic Flexibility relative to your sport.
This news is especially important for mountain bikers because trail riding requires a higher degree of Metabolic Flexibility than almost any other sport. In my experience of working with and hearing from hundreds of riders around the world tells me that most riders suffer from a lack of metabolic flexibility, not just a specific type of cardio.
Without being able to quickly transition back and forth between your different energy systems you don't recover as efficiently from your Higher Tension/ Anaerobic efforts, which causes you to build up residual fatigue much faster. This residual fatigue causes the cardio system to work even harder, leading to more labored breathing and severe muscle fatigue. It is the little bit of fatigue that you can't feel at first adding up slowly over the course of a ride that results in you "blowing up" towards the end of a ride, not a lack of a fitness with a specific Energy System.
1 – Directly fueling a low level effort like a long steady state ride on a trainer or relatively flat course.
2 – Fueling the recovery from a High Tension/ Anaerobic effort like between stages of an Enduro race, heats in a Dual Slalom/ 4X race or the rest period between intervals.
3 – Fueling both an effort and recovery from a previous High Tension/ Anaerobic effort like when you crest a section of a climb and have 15-45 seconds before the next part of the climb forces you back into High Tension/ Anaerobic mode. During those 15-45 seconds you can sit down and "rest" so your direct effort level is no longer high enough to warrant the anaerobic energy system taking over. However, your heart rate stays high because your aerobic energy system is also working hard to repay the oxygen debt from the previous anaerobic effort.
It is this last job of the aerobic energy system that I think is lacking for most riders and is the pinnacle of Metabolic Flexibility – when your aerobic energy system can multi-task and both fuel an effort and support recovery from a previous effort you know you can more easily handle a lot. Unless you train this very specific type of Metabolic Flexibility you will always struggle with it on the trail and continue to think that your "cardio" is what is holding you back.
What I really like about the Metabolic Flexibility concept is that it ties together a lot of ideas I've had about better ways to approach "cardio" training. In fact, it explains why things like Combo Drill and Kettlebell Countdown Drills work so well for mountain bikers since those workouts build a lot of residual fatigue and force the body to better deal with it, leading to improved Metabolic Flexibility on the trail.
I'll be writing a lot more on this subject in the coming months as I find out even better ways to apply this new training concept. In the meantime hopefully this article has helped you see that there is a lot more to the Cardio Training story than what we thought and given you some ideas on ways you can work to improve it through your training.
James, you are on to something here, I've trained for the last 3 years under a Tactical Athlete program that includes an Energy System Development (ESD) component, I've seen huge returns on my MTB as a result of training (=increasing) my metabolic flexibility, I look forward to future info on this, keep up the good work.