By Chris Carmichael Founder and Head Coach of CTS
Endurance athletes spend a tremendous amount of time training to increase aerobic endurance, maximize sustainable power at lactate threshold, and maximize aerobic capacity (VO2max). All of these efforts are aimed at improving the delivery and utilization of oxygen in working muscles, so you can produce more energy more quickly and subsequently do more work at a sustainable intensity. But some of the most important moments of a race or group ride or solo challenge demand a higher and unsustainable intensity level. This is where anaerobic capacity comes into play. The amount of energy you can produce through anaerobic glycolysis–and how you use it–is a major factor in whether you make the breakaway, stay with the pack over the summit of a short and steep hill, charge up a technical feature on the mountain bike, or sprint to victory in a criterium. Thankfully, even though the concept of anaerobic capacity may seem complicated, the workouts to improve it are simple (but not easy!).
How to Increase Anaerobic Capacity
Before designing workouts, we have to know a bit about glycolysis and how to create a training stimulus that will lead to positive adaptations. Glycolysis is an energy express lane that splits a molecule of glucose to quickly liberates some of its energy through a process creates. The lactate is then processed completely (but more slowly) through regular aerobic metabolism in mitochondria.
Your anaerobic capacity is the amount of work you can perform at an intensity above lactate threshold power output. The amount of work you can do stays the same, whether you perform a higher power but shorter effort, or a slightly longer effort at a lower power output. In other words, a cyclist with a lactate threshold of 300 watts and an anaerobic capacity of 20 Kilojoules (the work they can produce), could us their anaerobic capacity for a 1000-watt sprint that lasts just under 30 seconds or a 500-watt effort that lasts 1:45. In order to produce 1200 watts for that 30-second sprint, or to maintain that 500 watt effort for 2 minutes, you have to increase anaerobic capacity.
To increase anaerobic capacity, you have to perform efforts that burn through the maximum amount of energy you can currently produce through glycolysis. That means repeated short, hard efforts above lactate threshold that rely heavily on fast-twitch muscle fibers. Making the intervals too long is one of the mistakes athletes make when trying to develop anaerobic capacity. As intervals get longer, the energy contribution from the aerobic system increases. And as you empty the anaerobic tank, so to speak, power output decreases until you’re back to performing at a sustainable aerobic intensity.
Workouts for Developing Anaerobic Capacity
Efforts that target the development of anaerobic capacity include maximum power efforts of up to about 30-60 seconds. Once you get closer to the 2-minute duration you will be targeting VO2max more than anaerobic capacity.
A few of the best workouts for developing anaerobic capacity include:
Anaerobic Power Intervals
Power Intervals can be used for developing power at VO2max or anaerobic capacity, depending on how the workout is structured. For the purpose of developing anaerobic capacity, perform 6 intervals of 30-40 seconds each at the highest power output you can sustain for the duration of the interval. It should take everything you have to maintain your output at the end of the effort. Take 5-7 minutes of easy spinning recovery between intervals. These are purposely long recovery periods between intervals because each effort should deplete your anaerobic capacity (really empty the tank) and you need adequate time for it to replenish. This is why it’s kind of tricky to prescribe an intensity range for these intervals as a percentage of FTP. We generally prescribe it as 120%-150% of FTP, but it’s best to think of it as aiming to be as far above FTP as you can manage for the duration of the interval.
In contrast, when we prescribe short Power Intervals with short recoveries (like 10×30 seconds separated by 30 second recovery), the workout is more targeted toward lactate tolerance and repeatability.
Performing intervals uphill increases resistance and can help athletes achieve a higher power output, which is important for developing anaerobic capacity. Find a moderate to steep hill you can complete in 45-60 seconds. As with the Power Intervals above, aim for the highest power you can manage, and maintain that power over the top of the hill, rather than stopping the interval at or before the summit. Your actual power for these efforts will be slightly lower than the Anaerobic Power Intervals because the efforts are longer. Recovery periods between these efforts can also be a little shorter, but still on the order of 3-5 minutes.
Both of the workouts above can be scaled up for more advanced riders by increasing the number of intervals or creating two sets of intervals separated by a longer recovery period between sets. The interval durations, however, should not increase, because the duration is what is defining the physiological stress. As anaerobic capacity increases, you’ll produce higher power during 30-second Anerobic Power Intervals or 45-second Hilltop Sprints, and you’ll be able to repeat more of them before your power output drops. If power drops more than 10% compared to your second or third effort, you’re done for the session, no matter how many intervals you had planned.
Anaerobic capacity workouts are very taxing, despite total time-at-intensity being just 5-10 minutes. The intensity is very high, so these should only be completed when you are fresh and they are typically separated by at least one full day, if not two or three days. The good news, considering how hard these workouts are, is that you don’t need to complete many of them to see improvement. Incorporate them into your training plan once or twice a week over the course of 4-5 weeks and you’ll see improvement. Just remember to schedule them for days when you will be well rested. These are not workouts that will be effective if done on tired legs.