This is from my weekly email newsletter but I republish it here for sharing and referencing. If you're not already a subscriber you can join below:
Happy Tuesday!
If you're the type that exercises to maintain your weight and stay healthy then you've probably integrated some kind of cardio exercise into your routine. We all know that combining cardio with a strength training program is optimal for health and longevity but doing hard cardio sessions can really suck ...
High intensity interval training (HIIT) has been in vogue for quite awhile and a lot of fitness classes tend to practice this style of training. If you're anything like me than you don't feel like you're getting your money's worth unless you get your ass kicked a little bit. The whole point is that you're forcing yourself to your limit, at least for short periods of time.
But ...
Improvements from pushing yourself to your limit through HIIT training only gets you half of the benefits of cardio of training. If that's all you do then you're missing out on a critical pillar of health.
If improving cardiovascular strength is one half then improving aerobic efficiency is the other.
At this point I can feel your eyes glazing over. As soon as scientific terms come up I too want to stop reading and just skip to the end. I challenge you to stick with me, I'll use helpful analogies of normal things we all understand ... like cars!
Using a car as an analogy, your cardiovascular strength is like the size of your engine. A big strong engine equates to a high VO2 max, a strong heart, diaphragm, and similar respiratory organs. Just like a bigger engine can use more gas more quickly, a higher VO2 max, for example, can pull oxygen into your body more quickly.
Lots of HIIT training will increase the size of your engine.
Your aerobic efficiency is a measure of how efficiently your engine can run. Even if you have a large engine and lots of gas, you're still limited by how well you can turn that gas into mechanical speed. In biological terms, what we're talking about is the ability of your body to efficiently make use of all the energy sources available to it.
Efficiency is critical for both performance and long term health.
In order to perform any kind of exercise your body requires energy. Depending on how much energy your body needs it will escalate through a series of energy phases, almost like gears in a car.
Endurance athletes will know these gears as "zones". In each zone a different combination of chemical energy is used.
Fat is the primary energy source used at the lowest levels of exertion. Fat is the most efficient energy source and is the kind of chemical energy your body prefers to use most of the time.
Unfortunately, it also takes your cells longer to convert fat into energy (ATP) and therefore as the demand for energy increase your body starts to switch over to faster burning forms of chemical energy like carbohydrates.
While burning carbohydrates for energy is faster, it's also less efficient.
The level of your body's aerobic efficiency determines when you'll switch from burning the most efficient energy sources i.e. fat to the less efficient energy sources i.e. carbs.
The graph above depicts a healthy, efficient aerobic system which continues to burn fat well into higher ranges of oxygen consumption. Depending on the person, fat utilization will stop at anywhere between 55% and 75% of VO2 max.
So how do you improve your ability to keep burning fat well into the higher ranges of effort? It's not through HIIT training.
The most effective technique to increase aerobic efficiency is through longer periods of zone 2 training.
Depending on your fitness, you want to train at a level that optimizes fat burning (aerobic / oxidative phosphorylation) without tapping into the energy systems that use carbs (anaerobic / substrate phosphorylation).
For most people this means trying to do more 30-40 minute sessions of lower intensity running / cycling / elliptical where you're still able to have a conversation but you're breaking a sweat.
And that's it!
It may not seem as hardcore and you won't feel dead at the end but prioritizing zone 2 training is an easy way to improve your aerobic efficiency and therefore your metabolic health.
Plus you'll become a fat burning machine and who doesn't want that 🙂
Cheers,
Nick
P.S. For the real hardos out there, the best way to know whether or not you're staying in zone 2 is to measure your lactate levels in realtime. Lactate is a byproduct of burning carbs so measuring the concentration of lactate in your blood is the best proxy. You'll need a finger stick for this though.