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[New performance series] Train fast, race fast!

[New performance series] Train fast, race fast!

Triathlons are usually long events. Sure, the mixed relay, super league, and other forms of super sprint triathlons have been changing the picture a bit. Nevertheless, it might still take you at least 20-plus minutes to finish these shorter events. And that is nothing compared to the Olympic distance or the Ironman, where the race will last for several hours. So, how can short intervals, lasting from 30 seconds to a few minutes improve your performance? And most importantly, why are these a key part of your training?

High-intensity Interval training (HIIT) has exploded in popularity in recent years. While it (most often) lives up to the hype created, the marketing around it has helped as well. The 1-minute workout, the 30-second revolution, and many other headlines have caught the public’s attention and brought HIIT to the spotlight. But the truth is, we have known it’s an effective training intervention for quite some time. References to interval training are found in training programs in the early 1900s, with many further mentions throughout the years, culminating with some ground-breaking research in the 1960s that showed how manipulating exercise intensity and duration could have a massive impact on physiological responses to intermittent exercise. History lesson aside, interval training is today one of the most popular and efficient forms of exercise. It’s been proven to induce similar or superior adaptations in aerobic fitness, body composition, insulin and triglycerides levels, to name a few, when compared to traditional endurance exercise, but with a much lower time commitment. But what about endurance performance?

Well, there is plenty of research here too. And the results are promising. In 2007, one study showed that aerobic intervals (performed as 4-minute intervals or a series of 15-second ones) were more effective in improving maximal oxygen consumption (VO2max) when compared to programs focused on long-slow distance or threshold training (Helgerud et al., 2007). And that’s just one of many, many papers. The evidence for HIIT keeps pilling up and we know that if the goal is to improve VO2max, then interval training is the tool for the job.

Just in a brief recap, remember that your body’s maximal oxygen consumption (VO2max) represents its ability to intake, distribute, and effectively use oxygen to maintain your exercise needs. Its importance to performance has been established back in the 1920s, when a direct relation between medal winners and VO2max was found among elite athletes. In the years since, our understanding of endurance performance has grown to acknowledge the importance of the lactate threshold and movement economy, but a high VO2max is still of the key factors for an endurance athlete. And along the way, research has discovered that to maximally stimulate the adaptations needed for VO2max improvements, training at the intensity that elicits the maximal VO2max response, or very close to it, is necessary. In fact, many studies have shown that increasing training volume has no additional effects on VO2max, and that intensity is king for improvements to occur.

So, if intense training is key in improving VO2max, why not perform all our sessions at high intensities?

In theory, that seems like a good idea. However, there is only so much intense training our bodies can tolerate. Performing exercise above a certain intensity threshold delays recovery, and too much intense training has been linked to a higher injury risk, negative health outcomes (such as illnesses), and a reduction in performance. A recent study has highlighted the idea that two to three hard interval sessions a week seems to be a tolerable limit for most recreational and well-trained athletes. Indeed, research on training intensity distribution has shown that a polarized approach, where most of the training sessions are performed at low intensities is the best approach for improvements in performance, as long as there is a contribution of intense training sessions in the process. This was popularized as the 80/20 rule, where 20% of the training should be performed as high-intensity sessions. And while increasing the training volume of low intensity sessions might not lead to improvements in VO2max, lower and higher intensity sessions can lead to physiological adaptations related to performance.

Not to get too science-y, but both long, slow sessions and intense, interval sessions seem to activate the same “master switch”, which is directly linked to the adaptations that can make us better endurance athletes (see image below). Thus, since there is only so much intense training that can be performed, supplementing your interval sessions with long, slow sessions is important to enhance your performance.

Figure 1. Both interval training and slow, long distance training can trigger the same “master switch”. (Laursen, 2010)

Figure 1. Both interval training and slow, long distance training can trigger the same “master switch”. (Laursen, 2010)

But, let’s stick to the intervals. What is the best way to perform them to get the most improvements in your VO2max?


Back to research we go. In 2007, a study from Norwegian researchers found out that 4-min intervals separated by 3 minutes of rest were effective in eliciting large improvements in performance. Over 8 weeks, the 4-min interval group improved VO2max by 7.2% (initial VO2max of the participants ranged from 55-60, so a group of decent endurance athletes, but definitely not world class). Still, a few years later, another group of Scandinavian researchers found out that there is an important interaction between intensity and duration, and that time spent at higher intensities is linked to the changes in VO2max. In this study, 8-min intervals separate by 2-min of rest were more effective in improving endurance performance than 4-minute intervals separate by 2-min of rest. According to the authors, there is an important interaction between duration and intensity, and more time at higher intensities seems to be beneficial.


In fact, research has shown that time spent at the intensity associated with your VO2max (or close to it) is key in the process. So, what is the best strategy to spend a lot of time at higher intensities? Well, it would seen that longer intervals would be the best option considering the results of this study. But not quite.


A recent study compared short and long intervals and discovered that short intervals were more effective in improving VO2max and performance. The short interval group would perform 30 seconds of intense work, separated by 15 seconds of rest, continuously for 9.5min (I guess you could consider it one long interval) while the long interval group performed 5 minutes of intervals separated by 2.5 minutes of rest. Total work time per session was similar between both groups (1170 vs 1200 seconds for the short and long interval groups, respectively), but the short interval group was able to generate a higher power output during the work intervals, which could have been the difference in the study.


So, short or long? Well, while the above research indicates that short intervals are more beneficial, there is much more to interval training. Take a quick look at the figure below and you will see that interval training can have up to 6 different applications depending on the adaptations that are desired. And endurance performance relies on many different things, with research evidence suggesting that anaerobic capacity, stimulated by short intervals, is a key determinant in ultra-endurance racing performance. Thus, it is possible that a combination of short and long intervals could be the best approach.

High-intensity interval training and the many factors that go into deciding which one to use based on expected physiological responses (Buchheit & Laursen, 2013). .

High-intensity interval training and the many factors that go into deciding which one to use based on expected physiological responses (Buchheit & Laursen, 2013). .

How? Well, let’s look at some interval protocols that have been shown to be effective in improving VO2max and endurance performance.


1. Ronnestad et al. (2015)


This one has been mentioned before. The study employed male competitive cyclists who maintained an average of 10 training hours per week during the 7 weeks of the study. The researchers employed 2 protocols:


Short protocol: 3 x 9.5 minutes (alternating between 30 seconds of work and 15 seconds of rest) and 3 minutes or rest between each set.

Long protocol: 4 x 5min (2.5 min of rest between each set).


Both groups were instructed to perform the intervals at the maximal work intensity they could sustain, aiming to achieve the highest average power output during each session, and the rest periods were performed with 50% of the load of the work intervals.  


The short protocol significantly improved their mean power during the intervals (9% ± 5%), VO2max (8.7% ± 5%), and maximal power (8.5% ± 5.2%), while no significant changes were seen in the long interval group.


2. Helgerud et al (2007)


This one is simple, yet quite effective. It was done with your regular university students that you could consider decent, but not high-level endurance athletes, given their baseline characteristics.  


Protocol: 4 x 4 minutes of work (at 90 – 95% HRmax) with 3 minutes of rest between each interval (performed at 70% HRmax).


The authors showed that this interval approach resulted in an average improvement of 7.2% in participants VO2max (from 60.5 to 64.4


3. Seiler et al. (2013)


This study evaluated recreational cyclists, who had a training volume of 4-10 hours per week, and a goal of competing in regional or national cycling competitions (average VO2max values at baseline ranged between 50 – 55 Once again, decent recreational athletes, but far from elites.


Protocol: 4 x 8 min, separated by 2 min of rest. Like the first protocol, the authors asked participants to perform each interval with their maximum sustainable intensity.


Over the 7 weeks of training, the group that performed these intervals had the largest improvements when compared to groups performing 4- and 16-minute intervals. Positive changes in VO2max ranged from 5 to 12%, average power at the intensity that elicits VO2max went up by 5 to 10% and time to exhaustion at an intensity of 80% of their VO2max intensity went up by 50 to 125%! This improvement in time to exhaustion is remarkable but remember that a time to exhaustion test is different than a time trial, when we try to complete a set distance in the shortest time possible (as in races). These improvements in time to exhaustion do not necessarily transfer to improvements in time trial performance.


These are only a few of the many combinations of duration and intensity that can be achieved with high-intensity interval training (as you can see in the figure above). If you are trying to develop your own approach to it, aim to spend a large amount of time at higher intensities. This can be achieved by having a higher work to rest ratio (exercise more than you rest). For example, 8 minutes of work and 2 minutes of rest leads to a ratio of 4:1, and your 30-second intervals separated by 15-seconds of rest leads to a 2:1 work to rest ratio.


But what if you really want to take it to the next level?

Well, let me tell you about this interesting concept. Have you ever heard about blocked periodization of HIIT sessions? In short, instead of performing 2 HIIT sessions per week, a study had participants perform 5 HIIT sessions in the first week of the study, and then only perform 1 HIIT session per week over the next 3 weeks. A control group maintained their regular schedule of 2 HIIT sessions per week, throughout the 4 weeks. Sessions were performed as 5- or 6-minute intervals and were performed in zone 3 (88 – 100% HRmax). The blocked periodization group improved their VO2max (4.6%) and peak power output (2.1%), changes that were considered moderate to large. However, it must be noted that the blocked periodization group had more complaints about “heavy legs” and only felt their legs being back to “normal” on week 3.

To sum it up, intervals are a great way to improve your VO2max, which is a key determinant of your performance. Short and long intervals are beneficial, and you should aim to spend a large amount of time at higher intensities. And while an intense block can lead to better results, keep in mind that it might not be for everyone as it will take a temporary toll in your body.


To put it in practice, do intervals 2-3 times per week (often separated by 48 hours), in combination with another 2-3 low intensity sessions, aiming to hit the 80/20 polarized approach. And if you ever need to take some time off training, remember that in one of the mentioned studies participants reduced their training volume by 54%, and still improved their performance by replacing the sessions with shorter, intense interval training.


So, hit the track, the treadmill, the park…push the pace, sprint as hard as you can, work hard. Because as the saying goes, if you want to be fast, you have to train fast!


Interested in knowing more? Check some of the papers below. And if you are interested in any particular topic or have a specific question, let us know @

Gibala, M. J., Bostad, W., & McCarthy, D. G. (2019). Physiological adaptations to interval training to promote endurance. doi://

Gunnarsson, T. P., & Bangsbo, J. (2012). The 10-20-30 training concept improves performance and health profile in moderately trained runners. Journal of Applied Physiology (1985), (1), 16. Retrieved from

Helgerud, J., Hoydal, K., Hoff, J., Wang, E., Karlsen, T., Berg, P., . . . Bach, R. (2007). Aerobic high-intensity intervals improve VO2max more than moderate training. Medicine and Science in Sports and Exercise, (4), 665. Retrieved from

Laursen, P. B. (2010). Training for intense exercise performance: High-intensity or high-volume training? Scandinavian Journal of Medicine & Science in Sports, 20, 1-10. Retrieved from

MacInnis, M. J., & Gibala, M. J. (2017). Physiological adaptations to interval training and the role of exercise intensity. The Journal of Physiology, 595(9), 2915-2930. doi:10.1113/JP273196

Martin, B., & Paul B., L. (2013). High-intensity interval training, solutions to the programming puzzle. Sports Medicine, (10), 927. doi:10.1007/s40279-013-0066-5

Ronnestad, B. R., Hansen, J., & Ellefsen, S. (2014). Block periodization of high-intensity aerobic intervals provides superior training effects in trained cyclists. Scandinavian Journal of Medicine & Science in Sports, 24(1), 34-42. doi:10.1111/j.1600-0838.2012.01485.x [doi]

Rønnestad, B. R., Hansen, J., Vegge, G., Tønnessen, E., & Slettaløkken, G. (2015). Short intervals induce superior training adaptations compared with long intervals in cyclists - an effort-matched approach. Scandinavian Journal of Medicine & Science in Sports, 25(2), 143-151. Retrieved from

Seiler, S., Jøranson, K., Olesen, B. V., & Hetlelid, K. J. (2013). Adaptations to aerobic interval training: Interactive effects of exercise intensity and total work duration. Scandinavian Journal of Medicine & Science in Sports, 23(1), 74-83. Retrieved from




[New performance series] Lift weights, sprint to the podium?

[New performance series] Lift weights, sprint to the podium?