Extreme Cardio - What Builds Endurance? #TriageNews
Published: Sun, 10/15/23
Extreme Cardio - What Builds Endurance?
On October 8th 2023, we witnessed one of the most remarkable feats in the history of endurance training. The elusive Eliud Kipchoge was dethroned by a fellow Kenyan runner, Kelvin Kiptum. 02:00:35 was the time it took him to cover 42 kilometres.
That's a pace of 2 minutes and 51.5 seconds per kilometre. 42 times. To understand how absolutely ridiculous this is, try to run this fast for just ONE kilometre. It will blow your mind, and teach you that endurance running
is certainly not 'slow'.
With that in mind, I thought it would be an appropriate time to discuss a question that has fascinated sports scientists for decades: what contributes to extreme
endurance?
There are 3 primary determinants of performance in endurance events:
1.) VO2max - maximal oxygen consumption
2.) Lactate Threshold - point of accelerated lactate accumulation
3.) Efficiency - the oxygen cost of a given level of work / power output
Figure 1: Components of Endurance
As an analogy, VO2max determines the total size of the engine, lactate threshold determines the capacity for that engine to continue using fuel efficiently,
and these two components dictate the overall capacity for sustained oxygen consumption (with a high lactate threshold, an athlete can sustain a very high %VO2max). Then, the efficiency component can be thought of as how well that engine can power the peripheral components of the vehicle to create external power (e.g. chassis, suspension, steering, etc.). Think about a Bugatti engine in a Toyota Corolla - that's what happens when you have poor efficiency.
What this means is that endurance is not as simple as just one of these variables. For example, some people discuss VO2max as if this is the primary determinant, but we know that performance does not scale linearly with VO2max, and Kiptum
didn't dethrone Kipchoge because of his VO2max. It's the combination of all 3 components that make elite endurance physiology, along with other variables (e.g. psychology, external environment, nutrition, etc.).
In 1991, Michael Joyner used these physiological variables to predict that the marathon could be completed in less than 2 hours. At the time, this was extremely controversial (the record at the time was 02:06:50).
Figure 2: Joyner's 1991 Model
Joyner, M. J. (1991). Modeling: optimal marathon performance on
the basis of physiological factors. Journal of Applied Physiology, 70(2), 683–687.
An elite runner may have a VO2max of up to 75-85 ml/kg/min, and when this is combined with a
high lactate threshold, you have got a seriously powerful athlete. Elite runners can maintain a pace of up to 85% VO2max or more, so if you have an athlete with upper end VO2max (85ml/kg/min) AND elite lactate threshold (85% VO2max), you've now got an athlete that can sustain oxygen consumption (VO2) of up to 70+ ml/kg/min.
If we take an athlete that can sustain 71.4 ml/kg/min VO2, and we give this athlete low, average, or high running economy (speed maintained at a given VO2), we end up with the following marathon times, as per Joyner (1991):
Low RE: 02:12:45
Avg RE: 02:05:46
High RE: 01:57:48
Therefore, theoretically, based on data available in elite athletes as early as the 90s, the marathon record could still be beaten by
another couple of minutes by an athlete with all 3 dials maximised.
Figure 3: Joyner's 2008 Conceptual
Framework
Joyner, M. J., & Coyle, E. F. (2008). Endurance exercise performance: the physiology of champions. The Journal of physiology, 586(1), 35–44.
In Joyner's elaborated 2008 framework, you can see some of the additional components of the endurance matrix. Breaking endurance into 3 pillars is, of course, a simplification, and it doesn't take us down to the deeper levels that
contribute to maximal endurance.
We need dense capillarisation of muscle, increased mitochondrial size, content, and function, optimised cardiac function with a high stroke volume and maximal heart
rate, elevated haemoglobin content, glycogen availability, and so much more.
And you know what your best bet is for building your own endurance to a high level?
Time. Consistency. Repetition.
There are many debates in exercise science about optimal heart rate / metabolic zones, the role of HIIT training, hypoxic training, and more, but what always shines through is the role of high volumes of endurance training over time.
Some simple rules of thumb:
80% of your sessions should be more comfortable, sustainable, but long in duration (e.g. 90:00 @ 60-70% maximal heart rate, or a "conversational pace" where breathing is managed well).
20% of
your sessions should involve harder intervals or "HIIT" training, which is more fatiguing, but gives you great bang for your buck.
These ratios vary by athlete, sport, coach, and stage of training.
There are no specific magic numbers, but using this as a heuristic for a beginner-intermediate endurance / cardio trainee is a good start.
Further training specifics are beyond the scope of this
particular post, but the one point I want to emphasise is that endurance is not developed overnight. Just like you can't build 20kg muscle in a year, you also won't develop elite endurance in a year. Stick with it!
