This is an article series designed to help further educate my Performance Coaching clients. I am releasing it in this article series to help educate more people to create a life of health and adventure. If you are interested in getting fitter -- irrespective of whether you are a novice or regular athlete -- then please read through this series and learn more about the endurance training process. I welcome you onboard as your performance coach to help guide you to the summit of your athletic potential!
Training Science Series: Why We Focus on Capacity Training…to Eventually Go Really Fast
Part Eight - The Science of Endurance Training
A strong fat-adapted aerobic base is crucial to longevity in any endurance sport, and is done by performing a large volume of work beneath what is called the Aerobic Threshold. Athletes with a high aerobic capacity can maintain high speeds over long distances at a low metabolic cost. Highly enhanced aerobic metabolic pathways minimise lactate accumulation and use fat as the predominant fuel source, rather than sugar.
80-90% of yearly training load should be below the Aerobic Threshold according to the results arising from many decades of endurance sports science as discussed in the introduction. The low intensity training should not be going through the motions, but be as specific as possible to your goal event. Therefore, if you’re training for steep vertical racing, most of your low intensity training should be also performed on steep vertical terrain. Otherwise, some of the metabolic adaptations built will not match the demands of the event, thus an athlete will not be optimally conditioned for the event as they could be.
What is the Aerobic Threshold?
The Aerobic Threshold (AT) is the heart-rate intensity level where lactate in the blood first starts to rise, and where the body begins to switch over from primarily relying on fat oxidation for fuel, to greater reliance on carbohydrates (muscle glycogen). Constant fuelling with sugar becomes crucial above the AT, because our muscles only have a limited supply (approximately 2000 calories). This is a mixed fuelling zone where the body fuels itself on available fat and sugar. How fast muscle glycogen is used up depends on how efficient the body can use fat to assist in fuelling at increasing speeds and how large the developed aerobic capacity (base) is to suck up all the pyruvate created by the added glycolysis.
At heart-rates below the aerobic threshold, the body has enough oxygen to function without producing significant amounts of pyruvate/lactate and other associated by-products that build up from higher intensity. Athlete’s can perform for far longer at heart-rates below the AT without ingesting any form of fuel for support, getting by on fat stores alone. This is a relatively low level of intensity marked by light breathing and the feeling that you could maintain the effort for many hours. It occurs at about 60% of your aerobic capacity or at about 70-85% of max heart rate. However, the AT level can vary greatly between individuals based on aerobic conditioning, and is highly trainable.
Sustained low intensity training over a long-period of time, gradually increases muscle capillaries and develops fatty acid metabolism to improve your body's ability to increase training intensity without producing any lactate. This ultimately means you can keep going at a higher intensity for a longer time, raising the aerobic threshold to higher heart-rate value that soon approaches to within <10% of the lactate threshold.
Any athlete who can raise their aerobic threshold, can stave off their requirement for fuelling by muscle glycogen and this can only be achieved by training regularly beneath the aerobic threshold heart-rate.
What is the Anaerobic/Lactate Threshold?
The terms lactate threshold and anaerobic threshold are essentially synonymous, although to the sports scientists there are minor differences. For the sake of less complication, this article assumes they are identical. The Lactate Threshold (LT) is essentially your endurance limit. Any effort above it is often referred to as redlining, and is essentially the fastest pace you can sustain for anywhere between seconds to ~30-60 minutes, before you have to quickly slow down. As discussed earlier, this slow down occurs, because the aerobic system is overwhelmed by all the pyruvate it can no longer recycle back into ATP, forcing it to be converted into lactate for disposal. When lactate accumulates to higher levels, the body can no longer tap into its sugar stores for further fuelling, and without the fuel, muscles have to slow down. The point at which your body tips over this balance, is the LT.
This is why one athlete can run at 3:00min/km pace for 42km (Eluid Kipchoge), but even highly-trained athletes can only run one km at 3:00min/km before having to slow-down rapidly. This pace is beneath Kipchoge’s LT but above in the other athlete. The other athlete could rise to Kipchoge’s level (theoretically) if he can start to run 3:00km/km beneath his LT, which means training to increase his LT level.
It’s common for well-trained endurance athletes to be able to sustain an effort right at the LT for an hour at most. In events shorter than an hour, your performance is best predicted by running at your LT threshold heart-rate. That means it is a very useful pacing and predictive measure for events such as a 5K or 10K, or even a half marathon. With proper endurance training you can reduce the speed at which lactate accumulates, meaning that this threshold is the very adaptable and responsive to specific training designed to increase it.
Ultimately, when you exceed your aerobic systems capacity to produce energy, you are forced to rely on the anaerobic system, which is largely fuelled by muscle glycogen, to make up the deficit. Here you are on borrowed time until you will be forced to slow down.
A Quick Discussion on VO2 Max
VO2 max or maximal oxygen uptake is how much oxygen your body can utilise with each breath that you take. VO2 values can range anywhere from 30 in completely sedentary individuals, all the way up to around 90-95 in exceptional elite athletes. VO2 max can be increased through endurance training; however, the upper ceiling of VO2 max is largely determined by genetics.
Sedentary individuals will see modest increases in VO2 max by doing anything that makes them move. Regular athletes can improve it through increasing the duration and intensity of workouts through high-intensity interval training. Best improvements come from training at intensities as close to VO2 max as possible (in other words, as close to maximal heart rate as possible).
Because it is increased by utilization training, you will hear VO2 Max often being discussed as an important metric; however, VO2 max is given more credence than it probably deserves.
Well-trained athletes with modest VO2 max levels have been regularly noted to outperform athletes with superior values. Performance depends on a lot of other variables, such as red blood cell count, mitochondrial density, capillary density, aerobic base and so on. Sports scientists have determined that if you had two endurance athletes with identical VO2 max, the one with the higher lactate threshold is going to be the better performing athlete. Furthermore, if an athlete has a higher lactate threshold and a lower VO2 max than an athlete with a superior VO2 max, they'll probably still outperform the athlete. Ultimately, maximal lactate steady state performance appears to be the best indicator of endurance performance success, not VO2 Max.
Maximal lactate steady state is the point or the exercise intensity in which maximal lactate accumulation is equal to maximal lactate clearance. No matter how high your VO2 max is, if you accumulate too much lactate you will have to slow down.
Therefore, VO2 max is the least trainable component due to its genetic ceiling and has the poorest correlation to performance. It will naturally rise with fitness, but this casts doubt on focusing too much training on specifically improving VO2 max, but instead focus should be placed on increasing the aerobic and lactate thresholds. Increasing these thresholds eventually pushes an athlete to the ceiling of their genetic VO2 max capability by default, and thus the athlete will achieve their aerobic potential. Whatever that VO2 max number ends up being when that occurs, is what it is. Even Kilian Jornet’s VO2 max tests vary widely from 90 one year to 75 the next (see Figure 8) despite little to no reduction in his training and overall fitness levels and performance. Why this is so, remains to be understood, it could also just mean when he took those tests he may have been fatigued more than the other times he had higher readings. So, little credence should be placed on those tests and numbers that arise. Focusing training efforts on developing aerobic capacity and increasing the AT and LT thresholds is the best way to achieving optimal fitness performance for your genetic constitution.