Research Studies the Effect of Intervals on Endurance Cyclists

Peter Glassford
by Peter Glassford
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Research Studies the Effect of Intervals on Endurance Cyclists

Athletes often want a coach to tell them what to do, which makes sense since that is part of the role of a cycling coach. Training shouldn’t be too complicated, whether you have a coach or not. It can be confusing and frustrating to find a training plan that is practical and scientifically supported.

A practical study done in 2016 by an esteemed group of researchers in Norway does just that. If you are looking for a simple training routine to build your fitness, this study compared three different intensity levels and how they affected endurance, which offers clues into a successful training plan that’s easy to implement.


The researchers, including Stephen Seiler, who has become well known for the concept of polarized training, which is basically working very hard for about 20% of sessions, but then at a low-intensity for the remaining 80%, while avoiding the moderate intensities that are often used by age-group cyclists.

They looked at how three different interval prescriptions would affect measures of endurance fitness in 63 experienced male cyclists. They divided the athletes into three different groups, through 12 weeks of training organized into three blocks of four weeks. Each group did 2–3 interval sessions a week for three weeks and then took a rest week with one higher-intensity effort for testing.


  • Increasing Intensity: This group started with four weeks of longer intervals (4 x 16 minutes), then 4 x 8 minutes in the second month, finishing with 4 x 4 minutes in the final month. Rest periods for all intervals were two minutes. Their interval intensity increased each block as the intervals got shorter.
  • Decreasing Intensity: This group did the same number of intervals in reverse order to the increasing group (4 x 4 minutes; 4 x 8 minutes; 4 x 16 minutes). Their intensity would decrease each block as the intervals got longer.
  • Mixed Intensity: This group rotated through the three interval workouts for the 12 weeks completing the same total number of each type of interval as the other groups.

Other periods of riding for warmup and cooldown were done at low intensity (~55–70% HR max), which is slower than many riders typically ride, but it’s an important balance to the high-intensity interval work this plan asks you to do.


Before and after the 12 weeks, each cyclist did a 40-minute all-out effort. All of the athletes improved without much difference between the groups. Each training plan showed moderate-to-large improvements in physiological and performance-based measures suggesting training consistently — and performing both low- and high-intensity sessions alone — can be very effective, but specific interval types may not be as important as we think.

Looking at an individual level there was some tendency for the athletes in the increasing group (the one that started with longer intervals) to improve more than 3%. This matches how many traditional training programs are laid out with shorter, higher-intensity efforts coming later in the training phase closer to events. On the flip side, it is worth noting the mixed group seemed to have a lower overall response, which may reflect how athletes get familiar with training and intervals and can better pace and motivate themselves as they practice.

By putting a focus on the ‘skill’ of training the athlete gets better at elements of the sport like warming up, pacing, motivating themselves through hard moments, and becoming familiar with race intensity and their performance improves. This study backs up this deliberate practice.


Seiler has suggested 4 x 4 was often over-paced and more likely to be a failed session due to the temptation to go too hard, while the 4 x 15 minutes tended to be at a slightly lower intensity but was also mentally demanding. Consequently, he generally uses the 4 x 8 interval set to maximize both the intensity and the duration spent at the correct intensity. Following this thinking, you could further simplify your training and do several blocks of the 4 x 8, perhaps mixing up the hill, terrain or bike you use to adjust your training slightly each block.

Since all groups improved, you should be confident whichever plan is most attractive to you will be a great choice. If you gravitate toward long intervals, start with those. If you prefer a variety of workouts, then the mixed interval structure may be best. If you have a great 4-minute hill or want to work on higher intensity, start with 4-minute intervals. Whichever progression you follow, you now know mixing a couple of high-intensity days with lots of lower intensity rides (lower than many riders would typically ride, like at 60–75% of max heart rate) is supported by evidence. Having a plan you are confident in that is simple enough to execute wherever you are helps you train consistently and gradually improve over many weeks.

About the Author

Peter Glassford
Peter Glassford

Peter is a cycling coach and registered kinesiologist from Ontario, Canada. He travels frequently to work with athletes at races, camps and clinics. He also races mountain bikes for Trek Canada and pursues adventure in all types of movement. Follow @peterglassford on Twitter, or check out his online and in-person coaching at


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