Interval Training

HIIT and sprints


There is something of a revolution currently unfolding within the exercise sciences. Physical activity guidelines for the general public stand at 2.5 hrs of moderate intensity activity per week, distributed amongst sessions of 10 min or more23. However, there is an overwhelming body of research now emerging that suggests similar, if not superior, benefits can be gleaned from low-volume, high-intensity interval training (HIIT). The majority of the research driving this movement has used sedentary/recreationally active subjects, which is of limited use to highly-trained athletes21. By comparison, studies with highly-trained individuals are lacking (as athletes are generally less willing to participate in research due to their own training demands)4. Nevertheless, from the paucity of studies that are available, there are some interesting findings.

While most would associate the term “HIIT” with short, maximal efforts (e.g. the Tabata protocol), it has actually been defined as “repeated bouts of short to moderate duration exercise (i.e. 10 seconds to 5 minutes) completed at an intensity that is greater than the anaerobic threshold…separated by brief periods of low-intensity work or inactivity”4. Therefore, athletes should appreciate that what researchers refer to as “HIIT” is not necessarily any different from what they know as ordinary “interval training”.

NB: There is a lack of consensus as to the definition of the “anaerobic threshold”.

The value of interval training is nothing new to athletes; it is an integral part of pre-competitive training (i.e. getting “race fit”). Fundamentally, the advantage of interval training is that it allows athletes to accumulate a greater amount of time at high intensities than could be tolerated in a single bout26. Indeed, it is well documented that solely increasing low-/moderate-intensity training volume will not in and of itself improve endurance performance in well-trained athletes11,12,16 (cue the outrage of cyclists everywhere…). While a high volume of submaximal training (“base miles”) is associated with improved movement economy13,22,25, and indeed performance itself31, highly-trained athletes will reach a point at which no further improvements can be gained from LSD training alone16,27. At this point, HIIT may be the only means of achieving additional performance gains4.

Short Intervals

The HIIT protocols of most endurance athletes’ centre around work intervals of >2 minutes, often at a “race-pace” intensity (personal experience). While the efficacy of such protocols is well supported as a means of improving aerobic performance9,15,19, it seems that long-distance athletes can also benefit from the inclusion of short, maximal intensity intervals within their programs. Under the doctrine of training specificity, most endurance athletes would see no value in repeated maximal/supramaximal efforts of less than a minute. However, such sessions can represent both an effective and time-efficient means of improving performance.


Laursen et al., 20055
  • 41 well-trained male cyclists and triathletes
  • 4 week intervention period
  • Three groups: 2 long interval groups + 1 short interval group
  • Short interval group: 12x 30 sec bouts at 175% of VO2max power (all-out!) with 4.5 min recovery, 2x a week
  • Long interval group (1): 8x 2–3 min intervals at VO2max power, with a 2:1 work:rest ratio, 2x a week
  • Long interval group (2): as above, only the rest period was dictated by the participant’s HR returning to 65% of maximum


  • All groups improved their 40km TT performance
  • Only the short interval group & long interval group (1) improved their VO2max
  • The short interval group increased their anaerobic capacity to a greater extent
  • The short-interval group showed significantly higher lactate values during the TT, suggesting a greater capacity for high-intensity work
Ronnestad et al., 20148
  • 16 male competitive cyclists
  • 4 week intervention period
  • Two groups: short interval + long interval
  • Short interval: 3x (13x [30 sec work, 15 sec active recovery], 3 min recovery between sets), 2x a week
  • Long interval: 4x 5 min work, 2.5 min active recovery, 2x week
  • Work intervals were prescribed as “best effort”


  • Superior training adaptations across all performance measures within the short interval group!

effect of long versus short training intervals on adaptation

Niklas et al., 20106
  • Ten male national elite level cyclists
  • 3 week intervention during the competitive season
  • Looking at markers of molecular markers of endurance adaptations (e.g. mitochondrial proliferation) in response to two training protocols:
    • Short interval: 7x 30 sec “all-out” efforts, with 4 min active recovery
    • Long interval: 3x 20 min max efforts, with 4 min active recovery


  • Markers of mitochondrial biogenesis (i.e. proliferation) were similar, if not higher, in the short interval group.


A suggested criterion to judge the effectiveness of an aerobic training stimulus is time spent above 90% of VO2max17. It has been shown that short, maximal intervals with even shorter recovery periods (e.g. 30 sec on / 15 sec active recovery) lead to a greater time spent above this 90% level18. In fact, it has been shown that VO2max can be maintained 3x longer with an intermittent protocol (30 sec on / 30 sec active recovery) compared to a single bout20.

The use of short intervals coupled with short recovery periods is perhaps not unfamiliar to most athletes. However, the use of single sprint efforts (e.g. 30 sec) with long recoveries (4 min) is perhaps more novel. How could this protocol improve endurance performance? Part of the answer comes from biochemistry, and the cell-signaling pathways associated with aerobic adaptations (interested readers are directed to Ref. 2). Improved neural functioning and efficiency can also account for the improvement seen in response to isolated, supramaximal efforts1 (akin to “giving your muscles a software upgrade”). It should also be noted that during a 30 sec “all-out” effort, athletes tend to utilise the metabolic system most relevant to their specialty3—e.g. a 30 sec sprint can be up to 45% aerobic (metabolically) when performed by an endurance athlete.

Practical Recommendations for Interval Training

When designing an interval session, there are 3 variables that you can manipulate: work period length/intensity, rest period length/intensity, and no. of repetitions/sets.

  • Intervals should probably not exceed 8 minutes, as this necessitates a lesser intensity and may compromise the training stimulus9.
  • Short, maximal-intensity intervals with shorter active recovery periods (e.g. Tabata intervals) will substantially tax both aerobic and anaerobic capacities4, so should regularly be included.
  • NB: due to the delay associated with aerobic metabolism, it may take several repetitions before VO2max is attained. For example, using a 30 sec work/30 sec recovery protocol (where intervals are completed at a wattage/speed equivalent to VO2max), VO2max may not be achieved until the 3rd or 4th interval20. Therefore, when using short intervals, include >6 repetitions within a set.
  • Active recovery is strongly advised during any interval session, as this will facilitate greater quality during the work periods24. While a higher intensity active recovery will elicit a higher overall session intensity (e.g. time at VO2max)27, this needs to be balanced against the output goal for the work interval. In most cases active recovery should be completed at a low intensity. It is interesting to note, however, that recovery may be accelerated when the intensity of the active recovery is relatively high30.
  • Fixed work-recovery ratios (e.g. 2:1, 1:1, 3:1) are often used, as well as HR recovery (e.g. 65% of max). In either case, recovery periods in excess of 2 minutes are likely unnecessary, regardless of work duration9. Most well-trained athletes will not see an increase in work intensity following a recovery period greater than 2 min26. However, sprint intervals are an exception. As these sessions (e.g. 30 sec “all-out”) require “supramaximal” efforts, this necessitates longer recovery periods8 (~4 min). Also note that the use of HR to prescribe recovery duration is, for physiological reasons, highly questionable26.
  • Do not underestimate the value of a strong anaerobic capacity. While this is perhaps a more obvious requirement in cycling (where the ability to “attack” etc. is essential1), all endurance athletes can benefit from having a substantial reserve above critical power/speed.
  • Variety is key. There are benefits to most interval training protocols, and it would be naïve to claim that any one is superior. However, the benefits of different protocols are not necessarily mutual. Thus, including a variety of sessions will ensure a greater variety of training stimuli.


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  2. Gibala, M. Molecular responses to high-intensity interval exercise Applied Physiology, Nutrition, and Metabolism 34(3): 428–432, 2009.
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