An interval session will regularly appear in a cyclist's training plan. Intervals come in all shapes and sizes, each serving a specific training purpose. High-intensity intervals are very popular but can also cause confusion among cyclists. Should an interval be short or long, and how much rest should a cyclist take after an interval? By optimising your intervals, you can improve your performance even further.
High-intensity interval training (HIIT) consists of repeated high-intensity efforts interspersed with recovery periods, making these sessions crucial for improving performance. Various types of high-intensity intervals can be performed. A HIIT session can include longer intervals of approximately 3-5 minutes at high intensity or shorter intervals of around 15 to 45 seconds, where the intensity is even higher. Recovery time between intervals can also vary. The amount of time spent training at or near your VO2max during HIIT determines your training outcome. The time an individual can sustain this intensity varies from person to person.
Shorter intervals appear more effective than longer intervals
Scientific research indicates that shorter intervals improve the performance of well-trained cyclists more than longer intervals1. However, little is known about the effects of these intervals on highly trained cyclists. Highly trained cyclists are theoretically closer to their genetic limit than recreational or well-trained cyclists. For highly trained cyclists, it is also more challenging to see relatively small improvements compared to the significant gains observed in cyclists who have just started training.
Nevertheless, a 2020 study by Rønnestad showed that even the training adaptations and performance of elite cyclists improved more after short intervals compared to longer intervals2. In this study, two groups were compared: the long-interval group performed four sets of 5 minutes with 2.5 minutes of recovery, while the short-interval group completed 3 sets of 13 x 30-second efforts with 15 seconds of recovery. However, some limitations exist in the study design, one of which is that the training volume of the participants was significantly reduced during the study.
Optimise your intervals with power variations
As mentioned earlier, the time an individual can sustain a certain intensity varies from person to person. Well-trained cyclists can maintain a high intensity for longer periods per session than those who have just started training. The effectiveness of an interval session appears to depend on the amount of time spent above 90% of VO2max. Shorter intervals are easier to sustain and can be performed at a higher intensity than longer intervals. Power variations during intervals can also increase the time spent above 90% of VO2max.
A 2020 study by Bossi compared steady-state intervals—where the intensity remains constant—with variable intervals. Two groups were compared: one performed six intervals of 5 minutes at a constant power output, while the other also did six intervals of 5 minutes but included three 30-second surges within each effort. Both groups showed no significant differences in average power, heart rate, lactate levels, or cadence. The perceived fatigue during both interval types was also fairly similar3.
The most significant difference between constant and variable intervals was the time spent above 90% of VO2max. In the group that performed steady-state intervals, this was 286 seconds ±162 seconds, while in the variable-interval group, it was 410 seconds ±207 seconds. Because variable intervals make it easier to sustain a high intensity for longer periods, this interval type can significantly enhance the quality of your training sessions3.
Start your intervals at high intensity
Research suggests that short intervals are more effective than long intervals1 2 and that variable intervals have advantages over constant intervals3. Another scientific study on cross-country skiers indicates that interval training can be even more beneficial if intervals begin at a high intensity4. It is reasonable to assume that a similar response would be observed in another endurance sport such as cycling.
In this study, two groups were compared. Both groups completed five high-intensity intervals of 5 minutes. The group performing constant intervals did so at 90% of VO2max, whereas the other group started each interval with 1.5 minutes at 100% of VO2max, followed by 3.5 minutes at 85% of VO2max.
This study also showed that the perceived fatigue was lower in the group that started intervals at high intensity compared to the group performing constant intervals. Additionally, the time spent above 90% of VO2max was greater in the group that began their intervals at a high intensity4.
What does this mean for my interval training?
It appears that the way intervals are executed can further optimise your training, although more research is needed to determine the long-term effects of these interval variations. Higher-intensity variable intervals have a greater impact on various physiological processes, which may not always align with the intended goal of a specific training session. Ultimately, a well-structured training plan ensures that your body receives the right stimuli at the right time. If you are unsure whether you are applying the correct training stimuli to improve your cycling performance, consider working with a coach.
1 Rønnestad BR, Hansen J, Vegge G, Tønnessen E, Slettaløkken G. Short intervals induce superior training adaptations compared with long intervals in cyclists - an effort-matched approach. Scand J Med Sci Sports. 2015;25(2):143-151. https://doi.org/10.1111/sms.12165
2 Rønnestad BR, Hansen J, Nygaard H, Lundby C. Superior performance improvements in elite cyclists following short-interval vs effort-matched long-interval training. Scand J Med Sci Sports. 2020;30(5):849-857. https://doi.org/10.1111/sms.13627
3 Bossi AH, Mesquida C, Passfield L, et al (2020) Optimizing Interval Training Through Power-Output Variation Within the Work Intervals. Int J Sports Physiol Perform 15:982–989. https://doi.org/10.1123/ijspp.2019-0260
4 Rønnestad BR, Rømer T, Hansen J. Increasing Oxygen Uptake in Well-Trained Cross-Country Skiers During Work Intervals With a Fast Start [published online ahead of print, 2019 Oct 15]. Int J Sports Physiol Perform. 2019;1-7. https://doi:10.org/1123/ijspp.2018-0360
