Athletes reach anaerobic threshold (AT) due to their muscles inability to keep pace with the energy demands of activity. When our muscles can no longer meet these demands hydrogen ions begin to accumulate, increasing the acidity within the muscles, and impairing the muscles’ ability to perform, i.e. you get DROPPED. This can happen due to either a lack of available oxygen, or a lack of mitochondrial ability. Through increases in our ability to deliver oxygen and mitochondrial activity, we can increase the muscle’s ability to produce energy. This can be accomplished through the improvement of at least two different physiological variables—increased mitochondrial density and angiogenesis.

Increases in Mitochondrial Density

Our mitochondria, as you probably know from high school biology, are known as:

The powerhouse of the cell.

-Every biology teacher, EVER.

This means they’re responsible for producing a vast majority of the energy (ATP) we need. This is accomplished through our electron transport chain or ETC. The ETC is located along the walls of the mitochondria and uses hydrogen ions (H) to synthesize ATP. After creating ATP, the H ions need to be removed from the mitochondria—this is where oxygen comes into play. Oxygen combines with two hydrogen ions to form water.

Now these same hydrogen ions can also play a role in the buildup of lactate if the ETC gets “backed up”. The ETC gets backed up when oxygen isn’t present to accept hydrogen ions at the end of the process, i.e. your body enters anaerobic metabolism. When hydrogen ions can’t be moved through the ETC, they combine with pyruvate to form lactate. This lactate formation helps slow the increase of acidity in the muscles. The lactate is shipped off to other parts of the body to be re-purposed. To increase the capacity of a muscle, it must be able to process more hydrogen. This electron transport system respiratory state increases (by 25%) much more in response to HIIT training, whereas typical endurance training shows much less improvement, i.e. a non-significant 9% increase (2). So, if you struggle with repeated hard surges, or struggle with recovering quickly after a very hard effort, your ETC is becoming “backed up” too quickly… More HIIT training for you!

Promoting Angiogenesis

Angiogenesis is the formation of new vasculature due to hormonal and mechanical related signaling.

The mechanisms by which this process occurs are not entirely understood but have been observed after exercise training. As previously mentioned, oxygen delivery is a key component in mitochondrial functioning due to it’s role in the electron transport chain. Without oxygen the ETC can’t function. Oxygen is delivered to working muscle, and subsequently the ETC, through our vasculature. When we breathe, oxygen defuses from our lungs into our bloodstream and makes its way through the body. As it travels through the bloodstream oxygen diffuses into working muscle, allowing it to be used for hydrogen acceptance. Theoretically, if more oxygen can be delivered to the working muscles, then the ETC can function at a greater capacity, delaying the onset of anaerobic threshold. So if the capillary surface area interacting with muscles increases more oxygen will be able to enter the cells.

Research shows that exercise can induce angiogenesis in the capillary beds around skeletal muscles. An increased capillarization has been observed in training studies performed at 70–80% of VO2 Max whereas training at an intensity of 45% of VO2 max has been shown to have no effect on capillarization(1). This suggests that engaging in exercise at or just below threshold will promote angiogenesis. This is one of the many reasons we have our athletes utilize Sweet Spot focused training throughout the course of their season, but especially during their base phase.

Improving Anaerobic Threshold 

Based on the information above it seems as though 2 main specific types of training will promote the adaptations needed in order to improve anaerobic threshold.

1. Working CLOSE to threshold for extended periods of time, i.e. 2x20s.
2. Performing HIIT WELL OVER threshold with brief rests, i.e. 30/30s, Tabata sets, etc.

Research has demonstrated that training at higher intensities is more effective than low-moderate training at improving mitochondrial function and the formation of new vessels through angiogenesis. Try to incorporate the following training methods into your program in order to improve your aerobic capacity and delay the onset of anaerobic threshold. 

Working CLOSE to Threshold

One method of improving your anaerobic threshold will come from training at or near your threshold. This level of intensity is also referred to as maximum lactate steady state (MLSS), and should be CLOSE to your FTP.
At this intensity, you’re putting a significant amount of stress on the system without going over the lactate tipping point. Depending on your training status, you can estimate the heart rate range, or power output, right around your threshold. Typically, this is equivalent to 70-80% of your VO2 Max.

REMEMBER, a 20 minute FTP test is an ESTIMATE of your anaerobic threshold, and you may need to modulate the % FTP you’re working at to ensure you’re working close your MLSS. In my opinion, most FTP tests OVER-estimate anaerobic threshold, and the Sweet Spot range (88-95% FTP) is actually closer to MLSS.

If you want a more accurate method of establishing your anaerobic threshold, I recommend utilizing software like INSCYD, or getting a true lactate threshold test at a lab.

HIIT

Interval workouts comprise of alternating short, high-intensity bouts followed by periods of active recovery. Typically, the high-intensity portion of the workout is performed at levels above lactate threshold. For well-trained individuals, this level will be close to their max effort. For untrained people, intervals should typically be performed between 120-150% of your FTP. This method of training is well documented to improve the lactate thresholds of both trained and untrained individuals.

A word of caution though, if you are relatively untrained, err on the side of caution with HIIT training as the power output required can lead to injuries and burnout if overdone.

However, if you are VERY well trained, taking a polarized approach can help you get to that ‘next level’. This typically entails an ’80/20′ approach where 80% of your training is performed at very low intensities (Zone 1/2) and the remaining 20% is performed at an all out intensity (Zone 6+). You also need to have a ton of training time available to squeeze the most out of this approach.

Conclusion

Hopefully this helps to shed some light on what is happening at a physiological level when you’re training, and what a good training program should be composed of that is focused at improving FTP. However, just like anything, every athlete is different and will respond better or worse to training stimuli. It’s up to the athlete, and coach, to utilize historical data and make educated decision on what works best for them. The more individualized you can make your training, the further you’ll progress in less time.

References

1. Jensen, L et al. “Effect of high intensity training on capillarization and presence of angiogenic factors in human skeletal muscle” Journal of physiology vol. 557,Pt 2 (2004): 571-82.
2. Lundby, C et al. “Adaptations of skeletal muscle mitochondria to exercise training” Journal of Experimental Physiology 101.1 (2016) pp 17–22