High-intensity intervals for endurance: Just do them!

In recent years, a growing body of evidence has accumulated showing that performing regular bouts of high-intensity interval training is an extremely effective training tool for endurance athletes seeking to maximise performance. Put simply, short sessions of high-intensity intervals are a great way of producing gains in aerobic power, which then enables you to sustain a faster pace for longer.

What’s less clear however is the precise recipe of any high-intensity interval programme for maximising gains. Determining exactly what the optimum interval length and intensity is, the number of intervals needed, and the number of sessions per week is tricky. That’s because so many different studies have been conducted on different athletes of varying fitness levels using a wide array of interval protocols (different interval lengths, numbers of intervals, rest lengths, number of session per week etc). But research by Norwegian sports scientists suggests that the way you implement high-intensity interval training might be rather less important than actually making sure you do it [Med Sci Sports Exerc. 2016 Nov;48(11):2165-2174]!

The research

In the study, researchers set out to compare the effects of three different high intensity training (HIT) protocols, which were balanced for total load but differed in training plan progression and implementation. Sixty-three well-trained cyclists were allocated to three training groups and instructed to follow a 12-week training program consisting of 24 interval sessions, a high volume of low intensity training (LIT), and laboratory testing. These groups were as follows:

  • Increasing HIT group, which performed interval training as 4×16 minutes in weeks 1-4, 4×8 minutes weeks 5-8 and 4×4 minutes in weeks 9-12 (ie intervals became shorter and more intense as time elapsed.
  • Decreasing HIT group, which performed the same weekly block of interval sessions but in the opposite mesocycle order as above (ie started with the shorter, intense intervals then progressed to longer, less-intense intervals).
  • Mixed HIT group, which performed the interval prescriptions in a mixed distribution throughout the 12 weeks.

In terms of interval intensity, all the sessions were prescribed as ‘maximal-effort’ sessions. This meant that the cyclists averaged 4.7, 9.2 and 12.7mmol/L of blood lactate in the 16, 8 and 4-minute sessions respectively. Before and after the 12-week intervention, all the cyclists were tested for average sustained power during a 40-minute all-out ride, their peak power output during incremental testing to exhaustion, and also how much oxygen they were able to use while riding with a blood lactate concentration of 4mmol/L (often referred to as lactate or anaerobic threshold).

The findings

The key finding was that regardless of the way they implemented the high-intensity programmes, all three groups improved equally across the board. The gains in average sustained power during the 40-minute ride, their peak power output during incremental testing, and also how much oxygen use at 4mmol/L lactate were between 5 and 10% in all the groups, with no differences between the groups.

PP verdict

The key finding in this study is that the way you execute a high-intensity interval training programme in terms of training progression and interval lengths might be less important that previously assumed. This of course comes with one caveat – that the total training load in any interval programme is constant. In other words, two differently structured interval programmes where the total load (over a period of several weeks) is the same are likely to produce similar gains; two programmes where the total loads are different probably won’t – a the higher volume programme might produce better results but only it it doesn’t result in the athlete become over-fatigued and/or overtrained.

Practical suggestions

  • If you’re not already doing so, add some high-intensity training such as intervals to your programme for maximising performance gains. Start with a just a few, shorter intervals performed no more than once a week, and build up gradually.
  • When adding or increasing high-intensity interval sessions to your programme, remember to back off a little on your steady-state training in order to avoid becoming tired and possibly overtrained.
  • Providing you stick to your desired training load in the longer term, structuring an interval programme around your own needs and commitments is likely to work as well as a rigid, pre-prescribed programme.

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