The benefits of high-intensity interval training (HIIT) are profound. Research has well documented the benefits of HIIT for improving VO2 max, Functional Threshold Power (FTP), lactate buffering capacity, and many other adaptations.
While HIIT is an essential component of any athlete’s training program and should be incorporated regularly, more is not always better. For many athletes, the best way to continue improving is likely to increase training time at lower intensities. While it may not seem like it, low-intensity training (usually in Zone 2) has profound benefits, including improving your FTP and top-end performance.
Riding Harder Isn’t Always Better
It seems logical that to increase your FTP, you would need to train at high intensity, right? The line of thinking is that to get fast, you’ve got to go hard all the time — a common pitfall for many cyclists.
It’s important to understand that every workout has a cost-to-benefit ratio. The cost of a workout is the physiologic strain that it places on your body and the time it takes to recover. The benefit is the total fitness you can gain from the session. We want workouts that will give us the greatest benefit at the smallest cost.
Intervals have a huge benefit but also come at a great cost. If you do too many intervals, you may see rapid improvements for a short time; but over the long term, you may end up overtrained, stagnant in your progress, or at risk of injury. This is why intervals should be used with caution. As I like to say: “Intervals are like hot sauce, they give you a good kick, but more isn’t always better!”
Comparatively, Zone 2 training also has a huge benefit to your fitness, but at a much smaller cost. Training within Zone 2 can be repeated daily with little risk of overtraining, and regularly exposing yourself to this stimulus over time will yield great results. Let’s explore why.
The Link Between Zone 2 and FTP
How exactly does low-intensity training impact your performance? The answer can be found at a cellular level. Exercising at low intensity for prolonged periods of time instigates repeated muscle contraction, which increases calcium levels within the muscle. This activates a pathway for aerobic adaptations via a gene transcription factor called PGC-1α.
When PGC-1α is activated, many adaptations occur, including the creation of new mitochondria. Mitochondria are responsible for aerobic metabolism, and with more of them, your FTP can increase.
In my own studies, I have found a significant correlation between time spent training per week and FTP. Other studies have found a significant correlation between time spent training at low intensity and Ironman competition performance, thus indicating an increase in lactate threshold.
PGC-1α can be activated by both low-intensity and high-intensity training. Thus, it is important to include a combination of both modes of training in your program. However, since low-intensity training is much less taxing than high-intensity training, you can improve your fitness further by adding more low-intensity volume with smaller risk of overtraining.
Adding More Zone 2 to Your Training Plan
If you were to compare a professional cyclist’s training to that of an amateur cyclist, you’d find that many amateur cyclists do more total minutes at high intensity than the pros! Only 5-15% of a pro’s total training time is spent at higher intensities — the rest is spent almost entirely within the low-intensity zones. This might equate to an average of only one to two hours per week of total time at high intensity. Clearly, riding at low intensity is an effective way to train! But this doesn’t just apply to the pros — it applies to you, too.
Current evidence suggests that there is no added benefit in doing more than a couple of high-intensity sessions per week, as anything beyond that will not create any additional beneficial adaptations but can, in fact, increase the risk of overtraining and fatigue. This applies to pros and amateurs alike. Therefore, perhaps the best way to continue improving is by adding volume in Zone 2.
For example, consider two scenarios in which you do the same 3 x 15-minute FTP workout twice weekly for five weeks. In the first scenario, you add Zone 2 training time to your interval workouts to equate to six hours per week of training. In the second scenario, you do the same exact intervals, but add Zone 2 miles to your training to total 12 hours per week.
In which scenario do you think you will improve the most? Even with the same amount of intensity, you will clearly see much more improvement with additional time in Zone 2.
For the time-crunched athlete, this may not be what you want to hear, but there is no magic interval workout that can replace time on the bike. Every athlete should take a look at their training distribution to make sure they are training enough within Zone 2. Ideally, approximately 80% of your training sessions should be low-intensity Zone 2 sessions.
If you are looking to further your cycling fitness, one of the best ways to do so is by increasing your training volume by adding Zone 2 riding. This will allow you to make additional gains with little risk.
Combined with appropriately prescribed interval workouts, adding low-intensity volume to your training will yield beneficial results in every aspect of your cycling, including your top-end fitness. While it may seem contradictory, going slow can help you go fast!
References
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Esteve-Lanao, J. et al. (2005). How Do Endurance Runners Actually Train? Relationship with Competition Performance. Retrieved from https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.525.2658&rep=rep1&type=pdf
Hawley, J.A. & Bishop, D.J. (2021, May 4). High-intensity exercise training — too much of a good thing?. Retrieved from https://www.nature.com/articles/s41574-021-00500-6
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Laursen, P.B. & Jenkins, D.G. (2012, November 2). The Scientific Basis for High-Intensity Interval Training. Retrieved from https://link.springer.com/article/10.2165/00007256-200232010-00003
Muñoz, I. et al. (2014, March). Training-Intensity Distribution During an Ironman Season: Relationship With Competition Performance. Retrieved from https://journals.humankinetics.com/view/journals/ijspp/9/2/article-p332.xml
Rose, A.J. et al. (2007, August 30). Effect of endurance exercise training on Ca2+–calmodulin‐dependent protein kinase II expression and signalling in skeletal muscle of humans. Retrieved from https://physoc.onlinelibrary.wiley.com/doi/full/10.1113/jphysiol.2007.138529
Seiler, S. (2010, September). What is best practice for training intensity and duration distribution in endurance athletes?. Retrieved from https://pubmed.ncbi.nlm.nih.gov/20861519/
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