Short intervals have long been a poorly hidden secret of many accomplished cyclists.
This includes the 30/15, 40/20 and 60/30 intervals, where the numbers refer to seconds of high intensive work and recovery, respectively.
Despite the strong pedigree, this highly intensive style of training was re-introduced to many a keen amateur back in 2015 by a research paper by Rønnestad and colleagues (1).
The study reported increased performance with the 30/15 interval when compared to traditional 4×5 minute intervals.
Not surprisingly, the debate that followed in social media in the wake of this publication sparked both enthusiasm as well as critical appraisal.
Some of the (warranted) questions being raised were:
- The riders in the study were well-trained amateur (only)
- This was a single study with 20 subjects (only)
- Were the riders simply less accustomed to 30/15 intervals than the 4×5 min format?
In light of the above, several questions pertaining to the 30/15 interval remains unanswered.
As such, a recent publication from the same lead author sheds more light on the matter (2).
Superior performance improvements in elite cyclists following short‐interval vs effort‐matched long‐interval training
In this study, the authors once again compared the effects of 30/15 training with 4×5 minute intervals.
Of particular interest to the authors (and us) was whether or not a similar result would occur in more highly trained cyclists.
Who were the riders?
This experiment enrolled 18 male riders from national-level road and cross-country cycling. Riders were 18-30 years of age with a VO2 max at baseline ranging 68-77 ml/min/kg.
According to the authors, this places the riders within the category of elite cyclists.
How did they train?
The interventional period started after a period focusing on high volume training.
The short interval group performed three weeks of three weekly 30/15 interval sessions.
These sessions consisted of 13 repetitions of 30 seconds of high intensity, interspersed by 15 seconds of recovery at 50% of interval power. A total of 3 x 13 repetitions were undertaken each session, with a 3 min recovery between each 13th repetition.
The long interval group performed three weekly intervals of 4 x 5 minutes at high intensity. Each interval was separated by 2.5 minutes of recovery.
Riders in both groups were instructed to perform their intervals at their maximal sustainable intensity.
– Rønnestad and colleagues, Scand J Med Sci Sports 2020
This resulted in similar effort during each interval formats as evident by comparable rate of perceived exertion (RPE) scores.
The accumulated interval duration per session were 19.5 minutes and 20 minutes for the 30/15 and 4×5 session, respectively.
How did they perform?
Upon re-testing at the completion of the intervention period, the short interval group achieved a greater improvement in power outputs during a 20 minute maximal effort test.
This group achieved a 4.7% improvement in 20 minute power, which was significantly more than the long interval group, who displayed a 1.7% reduction in mean power.
Adjusting for heart rate and RPE scores did not change this results. This suggests that the effort invested during testing was comparable between the two groups.
The short interval group achieved a greater percent-wise change in power at 4 mmol/L lactate (often considered an approximation of anaerobic threshold). However, the within group change was not statistically significant (2.0% in short interval group vs. -2.8% in long interval group).
Furthermore, the short interval group displayed a greater improvement in watt max (mean power during final 60 seconds of VO2 max testing). This parameter increased by 3.7% in the short interval group, as compared to a decline of 0.3% in the long interval group.
Finally, the fractional utilization of VO2 max at 4 mmol/L lactate tested 3% higher in the short interval group following the experimental period. This, as opposed to a reduction of 3.5% in the long interval group. However, the within group change of of the short interval group did not achieve statistical significance.
Notably, VO2 max did not change in either of the groups. That being said, there was an increase of 2.6% in the short interval group and 0.9% in the long interval group that did not achieve statistical significance.
How does the 30/15 interval differ to longer intervals?
A few possible mechanisms have already been discussed in this regard.
It has previously been observed that reducing interval effort and recovery time from 1:1 to 2:1 induces larger time spent at above 90% of VO2 max (3). Which is often proposed to be a success criteria during high intensive interval training..
As such, it may that the 2:1 ratio of work and recovery applied during the 30/15 interval allows for increased training time to occur at above 90% of VO2 max (2).
Furthermore, both 30/15 studies demonstrate a higher average power output when compared to the longer 4×5 minute intervals (1-2).
Additionally, in the most recent study the short interval group demonstrated significantly increased lactate levels at all 5 test points during the final 20 minute maximal effort test (2).
It is therefore reasonable to assume that the higher work intensity of the 30/15 interval might induce greater stimulus and adaptation of the anaerobic system. Greater ability to buffer lactate has indeed been correlated with improved time trial performance (4).
That being said, Rønnestad and colleagues emphasize that more research is needed in order to fully understand the mechanisms behind the 30/15 interval.
What is the practical implication of this study?
Does this new study mean you should skip all other intervals and go all in on 30/15s only?
As always, we need to take into consideration the context of the results.
In the recent Rønnestad et al study, riders came off of a period of high volume training.
The following reduction in volume during the intervention period, coupled with increased focus on shorter and more high intensive training includes several of the components of a traditional taper.
Some rather prominent authors have indeed put forward the notion that more than anything else, this demonstrates that the 30/15 seems to work well as a taper.
My comment: it should be noted that this intervention period lacks certain elements of traditional tapering, such as significant reductions in time at high intensity (shortened interval duration).
The authors points to the short intervention period (3 weeks) as a potential weakness in the study design. It could very well be that highly trained riders requires more time to achieve significant performance development.
Nevertheless, the short interval group did indeed achieve progress in the short time span of 3 weeks.
According to the authors, this may suggest a role for the 30/15 session in boosting high-end endurance capacity in the crammed period of season preparations.
…elite cyclists have a very long race season with a corresponding short preparatory period before entering a new race season. … The present study demonstrates that subsequent to a training period focusing on high training volume, a 3-week period with three weekly multiple short intervals can induce superior training adaptations compared to longer intervals.
– Rønnestad et al. Scand J Med Sci Sports 2020
One could also discuss potential upsides of using 30/15 intervals early on in base training.
If this style of short intervals does indeed improve buffering capacity, and the ability to tolerate higher levels of blood lactate…
…would such training allow you to later on perform your traditional long intervals (HIT & threshold) at a higher absolute intensity? And then in turn allow for greater adaptation and further enhanced performance?
The one thing that is certain is that the last word on this matter is yet to be written.
Want to try out this interval for yourself?
I have added the link to a PDF with instructions for how to perform different versions of this interval below.
Best of luck with your short intervals.
In summary, this study reports enhanced training adaptation of elite cyclists following three weeks of three weekly 30/15 interval sessions.
More specifically, the riders displayed enhanced 20 min power and power during the final minute of VO2 max testing (W max) 30/15 intervals when compared to 4×5 minute intervals.
Additionally, trends of greater improvement (without statistical significance) were seen in favor of 30/15 intervals for VO2 max, power at 4 mmol/L as well as fractional utilization of VO2 max at 4 mmol/L lactate.
This study is in agreement with previous results on the 30/15 interval format. As of today, there is an argument to be made that both well-trained amateurs and elite cyclists might benefit from including short intervals as a part of their training regime.
This post is one of many in a series of articles discussing recent research on interval training. You can get the complete series of articles to your inbox by signing up for my newsletter. Sign-up is free and you can unsubscribe at any time.
- Rønnestad BR et al. Short intervals induce superior training adaptations compared with long intervals in cyclists – An effort-matched approach. Scandinavian Journal of Medicine & Science in Sports, 2015;25:143-151
- Rønnestad BR et al. Superior performance improvements in elite cyclists following short intervals vs. effort-matched long intervals training. Scandinavian Journal of Medicine & Science in Sports, 2020. Jan 24 (Epub ahead of print)
- Rozenek R et al. Physiological responses to interval training sessions at velocities associated with VO2 max. Journal of Strength and Conditioning Research, 2007;21:188-192
- Weston AR et al. Skeletal muscle buffering capacity and endurance performance after high-intensity interval training by well-trained cyclists. European Journal of Applied Physiology and Occupational Physiology, 1997;75(1):7-13