Monday, August 19, 2013

Building your Performance Pyramid II: Aerobic Fitness

Alan Couzens, MS (Sports Science)

In my last post, I outlined the importance of establishing a firm base of ‘metabolic fitness’ to both performance and general health.

When it comes to exercise for health, having a very good metabolic profile will take you a long way towards your goals of health & longevity. Considering that the most pervasive debilitating disorders of modern society are strongly linked to metabolic dysfunction (or the excessive inflammation that is related to this faulty metabolism), keeping your metabolic and stress hormones in an optimal balance will take you a long way towards optimal health. However, for the athlete intent on maximal performance, having a strong basal metabolism is only a part of the picture.

Once a strong basal metabolism is established, the serious athlete must address the limits of exercise metabolism, i.e. sugar burning. To put the relative importance of these 2 systems into perspective, check out the figure below which shows relative fat and carbohydrate contribution for a top age group Ironman athlete for each of his training zones.

While the breadth of the fat burning system is virtually limitless, its height, or power is not. Generating energy from fat is a rate limited process. Meaning there are inherent limits to exercise intensity if the athlete is intending to ‘run on fat’. Indeed, in this athlete’s Ironman power zone of 220-240W, for a 75kg, you can see that aerobic glycolysis (sugar burning) makes up more than 2/3 of the performance picture.

This fact has important implications with regard to the current push for “low carb, high fat” diets. When dealing with athletes, it’s important to recognize the difference between eating and training for optimal health vs eating and training for maximal performance. Make no mistake, the majority of athletes can greatly improve their ability to use energy for fat by making better choices in their daily nutrition. After such interventions, I’ve seen athletes double their fat oxidation rates in tests like the one above, i.e. go from the typical 3-5kcal/min up to an incredible 10kcal/min energy generation from fat! This adaptation greatly improves the athlete’s long term endurance. However, if we look at the 10kcal/min mark on the chart above you can see that it equates with a power output of less than 200W, a level that’s simply not going to cut it for an average sized athlete with competitive aspirations of a Kona slot or beyond.

The aim of the game, then, for the competitive athlete is to maintain a developmental balance between the fat burning and sugar burning systems over the long term.

In terms of nutritional and training periodization, this is a yin-yang concept. During the bulk of the year, when you are working on building your ‘health base’ and focusing your training on your ability to generate energy from fat, if you’re a competitive athlete, you should still include sufficient training (& sufficient carbohydrate in your diet) to maintain your glycolytic (i.e. ‘sugar burning’) power & capacity. On the flip side, when you are approaching your ‘A-Race’ & a good chunk of your training is metabolically similar to your event, i.e. focused on ‘sugar burning’, for the sake of your health and recovery, you should maintain your body’s ability to use fat for fuel.

In practice, for a high level AG male athlete of average size, this may look something like this….


General Prep (Base)



Specific Prep (Build)


90% Fat Burning/10% Sugar Burning ---------------------->

75% Fat Burning/25% Sugar Burning


40/30/30 diet -------------------------------------------------->

50/20/30 diet


Rather than give recommendation for all sizes and levels of athlete, the litmus test of ‘taking it too far’ is very simple. When an athlete is not including enough carbohydrate in the diet or enough ‘sugar burn’ training in the program, top end performance is noticeably compromised.

A great example of this comes from my experiences in the lab. When we schedule blood lactate or metabolic testing for an athlete, one of the pre-test instructions is to ‘come rested’, i.e. ideally tests take place towards the end of a recovery week. Invariably, though, over the course of a year an athlete will show up far from ‘rested’, sometimes without advising the tester of this (!) This may happen immediately after a big training camp or block of training, i.e. when the athlete’s glycogen stores are very low & their ability to generate energy from sugar is, consequently, compromised. The test unfolds as follows… The athlete looks spectacular in their ‘easy zone’ generating very high levels of energy from fat and showing a very slow rise in lactate & then they just… stop. When the body goes looking for sugar to fuel the increasing workloads, it comes up short. Therefore, the maximal lactate and maximal power that the athlete reaches are very low (often less than 7mmol/L LaMax)
This bring us to 2 practical recommendations for the athlete looking to improve their metabolic fitness without sacrificing performance…

1.       Periodically ‘check in’ on your glycolytic power via short, maximal tests to ensure that you’re not overdoing the low carb thing.

2.       As you get closer to your ‘A Race’ shift the emphasis to improving race pace endurance. Being able to roll 150W for 20hrs on water & chia seeds is a great test of your basic metabolic fitness but if your race requires 225W for 9hrs, you’re going to need to add a little something to your training (& your nutrition) to get ‘race ready’.

Train Smart,