Fast Start Intervals for Fast Times


TOOLBOX: For shorter time trial efforts like the track kilometre, pacing with a fast start results in the fastest overall times. What about intervals? Should you pace them evenly or are there greater training benefits by pacing them with a fast start?

Interval training for Wout

xpedo cxr pedalbanner with Brian McCullough

Most cyclists understand the concept of high intensity interval training (HIIT), which involves repeated bouts of high intensity efforts separated by periods of recovery. Some very common examples of these include 2×20, 4×8, or 5×5 intervals. The idea behind interval training is that you can increase the training stimulus on the body in a shorter duration than a prolonged, continuous bout of exercise.

In today’s Toolbox article, we are going to look at another way of further increasing the effectiveness of your intervals with a fast start! You can also check out a relevant article on variable vs constant intervals by Stephen Cheung.

Fast Start Intervals!

Although the study we are looking at today was performed using high-performance skiers, it is not unreasonable to assume that a similar response would be observed in another aerobically intensive sport such as cycling.

This study recruited 11 well-trained skiers (~23 years old) with high VO2max values (~70.6 mL/kg/min).

Participants came to the lab 5 times. The first visit consisted of a battery of tests to determine their Maximal Aerobic Speed (MAS; analogous to Maximal Aerobic Power in cycling) and VO2max. On the four following visits, the athletes performed 2 different 5×5 minute HIIT sessions twice.

Each HIIT session consisted of a standardized warmup followed by 5 repetitions of either a decreasing workload (DEC) or a traditional, constant power workload (TRAD). It is very important to note that HIIT conditions were work-matched – by doing so, any differences that the researchers find in the physiological responses are not from the amount of work done, but rather how the work is done.

  • The DEC protocol had each 5-minute work interval start with 1.5 minutes at 100% of MAS, followed by 3.5 minutes at 85% of MAS.
  • The TRAD protocol was performed with a constant speed at 90% of MAS for the entirety of the 5 minutes.

Researchers monitored VO2 consumption, heart rate, blood lactate concentration, and rate of perceived exertion during the trials.

Study Results

The primary finding of the study was that the DEC interval strategy resulted in higher maximum & average VO2 values, as well as a lower rate of perceived exertion. Also, the DEC interval strategy resulted in 10% increase in time spent > 90% VO2peak. In plain terms, not only was the DEC session more stimulating on the body, but athletes also found it easier to complete!

Considering that the two HIIT sessions were equal in terms of total work performed, it seems that the modifying the specifics of how an interval is performed can further fine-tune workouts.

Emerging Field

There seems to be growing interest on the idea of non-constant power intervals and their efficacy for training.

From a theoretical standpoint, it would make sense that manipulations to traditional, constant power interval sessions should result in greater training stimuli when performed over a longer period (say 6-10 weeks or more), but both studies highlight that there is more data needed before that theory can be confirmed. Until then, you can always experiment for yourself!

How do I personally use this information?

The Xert platform that I use for my training features a unique type of interval (called an Xert Strain Score Rate, or XSSR interval), which features an overall design very similar to those mentioned by the research study. For example, here is a Xert analysis of a 5×5 min interval session that I performed using XSSR intervals.

The Pink line on top represents my Maximal Power Available. The Multi-colored line indicates my power output, and the solid red line indicates my Heart Rate.

As you can see, each interval starts quite high (around my 5 min power), but gradually decreases and approaches my Threshold Power near the end of the interval. Despite a fairly large change in the power output over the course of the interval (380 W down to 270 W), you can see that my HR stayed elevated in a relatively narrow range (172bpm – 167 bpm).

Group intervals for the Deceuninck boys


This novel decreasing intensity interval might be a good alternative to traditional constant-power intervals if the aim of the session is to increase the time spent at a high percentage of VO2peak/max HR. However, the long-term efficiency of this interval strategy is yet to be determined. For now, try experimenting yourself and see how the two types of intervals compare!

That’s all for this month – stay safe and ride fast!


Bossi AH, Mesquida C, Passfield L, et al Optimizing Interval Training Through Power-Output Variation Within the Work Intervals. Int J Sports Physiol Perform 15:982–989, 2020.

Rønnestad et al. Increasing oxygen uptake in well-trained cross-country skiers during work intervals with a fast start. Int J Sports Physiol Perform, 15:383-389, 2020.

Billat LV. Interval training for performance: a scientific and empirical practice. Special recommendations for middle- and long-distance running. Part I: aerobic interval training. Sports Med. 2001;31(1):13–31. PubMed ID: 11219499 doi:10.2165/00007256-200131010-00002

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