High-intensity Intervals: Hurts so Good

High-intensity intervals will improve your aerobic capacity and sustained power even if you're already fit.

Turning up the speed

With the arrival of spring, many of us in northern climates are optimistically looking forward to getting off the trainer and out onto the road on a more consistent basis.

It also marks the arrival of more regular group rides and the start of training races, such that the intensity of our training generally increases.

The urge to get outdoors and hammer is almost irresistible after months indoors. However, this is also the phase where over-eager cyclists can push themselves too far by going too hard too soon. One approach to building through this phase is the common "train by racing," where natural competition during group rides and races takes care of any intensity training.

While group rides are invaluable and fun for both training and motivation, the random nature of group rides makes it difficult to truly use them as a training tool. Therefore, especially with the goal of improving and building up to a bigger goal later in the season, it's also good to incorporate some controlled interval training either solo or in small dedicated groups with a common purpose.

High-intensity intervals

At the end of the day, road cycling is primarily an endurance sport, and the defining characteristics of strong cyclists remain maximizing aerobic capacity and the power output that can be sustained. What kind of interval gives you the biggest bang for the buck?

A 2002 study by scientists at the University of Queensland in Australia focused on intervals done at maximal and supra-maximal intensities as defined by power output.

Thirty-eight trained cyclists and triathletes participated, ranging from top-level to lower-level amateur road cyclists (VO2max 64.5 ml/kg/min, training volume 285 km/wk). They were then split into four groups (matched for experience, fitness) as follows for four weeks of training:

  • HIT1: Two sessions/wk of eight intervals at 100% of maximal power (or Pmax, the power output at which oxygen uptake begins to plateau during the initial VO2max test), with each interval lasting 60% of time at which Pmax could be sustained during initial test. Recovery was for 120% of the time at Pmax.
  • HIT2: Same as above, but recovery was until heart rate returned to 65% of maximum.
  • HIT3: Two sessions/wk of 12x30s intervals at 175% of Peak Power Output (or PPO, the peak power subjects could pedal during the initial VO2max test -- this is higher than the Pmax value, so these intervals are HARD!). Recovery of four and a half minutes.
  • CON: subjects maintained endurance training and didn't perform interval work.
Subjects were tested for VO2max, PPO, Pmax at two and four weeks, with the intensity of the intervals adjusted as needed following two weeks. Subjects also performed a 40k time trial at the start, second and fourth weeks.

Watt's up, doc?

So what did the study find? Probably not surprisingly, all three HIT programs significantly improved every performance measure compared to steady endurance, low-intensity training, with improvements ranging from three to eight percent in these measures.

Considering that the subjects were already fit to begin with (40k time trials of about 42k/hr before the study demonstrates that the subjects were not slouches!), this definitely highlights the efficacy of all three styles of high-intensity training in improving performance in even already trained individuals.

Secondly, these intervals are TOUGH! Subjects were pretty much knackered after each interval training session, and actually only 64 percent of the planned intervals were completed. Lesson here is that there's no substitute for hard work!

Also, the important thing with interval training is NOT to drop the intensity later on when things start to hurt and get hard in order to complete the planned number of intervals. Rather, it's much better to keep the original workload and stop when you can truly no longer keep the pace.

Which interval plan is best?

The interesting part, of course, comes in comparing across the three HIT programs. Was one significantly better than the other? The short answer is no, probably due to the limitations in the number of subjects and also in comparing across individuals. There's not much that can be done about this, because monitoring and training almost 40 subjects over four weeks is an incredible feat of logistics as it is!

However, some trends do seem to emerge:

  • HIT2 seemed to have a little bit better improvement than the other groups. This was the group with recovery defined by a return to 65-percent heart rate rather than a standardized recovery time. Remember that HIT2 was identical to HIT1 except for HIT1 having a set recovery time.
  • This suggests that it's more important to "maximize" the training load by individualizing the recovery time, and to begin the intervals again as soon as the body is ready rather than allowing the body to recover too much between intervals.

  • HIT3 was just as effective as HIT1 and HIT2, and significantly improved performance compared to control training. HIT3 was the group with the very high-intensity but short bursts, consisting of 175 percent PPO for 30s.
  • The total workload was MUCH lower than either HIT1 or HIT2. This suggests that, given limited training time, it might be a good strategy to increase the intensity of the intervals rather than do a fewer number of lower-intensity intervals. This also fits in well with my previous advocacy of high-intensity training improving aerobic fitness.


    Controlled studies like this clearly demonstrate that intervals WILL improve your aerobic capacity and your sustained power even if you're already fit and well-trained. Keep in mind though that it's important to have a base of aerobic fitness before jumping into this type of high-intensity interval training, as the body needs to have the foundations for adapting to this high stress in place first.

    Another important point to conclude from this study is the wide spectrum of training possibilities. While all three interval programs were roughly similarly effective, it remains clear that interval training still must be tailored to individual needs.

    For example, while HIT3 was effective, the supra-maximal sprint efforts may not be as relevant to the steady sustained effort of triathlons and duathlons.


    Stephen Cheung is an Associate Professor of Kinesiology and a Canada Research Chair in Environmental Ergonomics at Brock University, with a research specialization in the effects of thermal stress on human physiology and performance. He can be reached for comments at thermal.doc@gmail.com.

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