HIIT Workout Design

This HIIT Workout Design article is part of our ‘Technically Speaking’ series which is a deeper look at a particular topic. A video lecture is available. 

We’ve covered the benefits of High Intensity Interval Training and HIIT protocols.

In this HIIT Workout Design article we are going to pull together HIIT protocols and HIIT physiology to show you how you can shape different protocols for different purposes.

You might want to revise the physiology behind HIIT before diving in to this article.

HIIT protocols – quick revision

All HIIT protocols have a work and relief period

Those periods have a mode, intensity, and duration

There can be several repeats in a series, and more than one series

HIIT physiology – quick revision

Acute response to HIIT

Intensity drives glucose breakdown causing lactate and hydrogen ions to accummulate

Lactate and H⁺ ions spill into blood and oxygenated tissues around the body burn the lactate in mitochondria

If lactate production outstrips clearance eventually glucose breakdown is inhibited and force production (work) reduces

Longer term adaptations to HIIT

The body adapts to repeated HIIT workouts becoming more aerobically capable and anaerobically powerful

As fitness improves cells use fat more readily as fuel during training and at rest due to mitochondrial biogenesis (more mitochondria, better functioning mitochondria)

In this HIIT workout design article we are going to explore:

1. how different HIIT workouts target different adaptations
2. how to choose elements in a HIIT workout to target different needs

Prefer to watch a video?

HIIT workout intensity zones or phases

Looking at figure 4 we can see the lactate turning points and the associated training zones that a HIIT protocol might target.

Using Figure 4 we can summarise:

• HIIT work intensities target at least LT1 and sometimes LT2.
• For ease you can think of any HIIT protocol that is designed to elicit lactate responses between LT1 and LT2 as phase/zone 2 training.
• And, any HIIT protocol that is designed to elicit LT2 and above lactates as phase/zone 3 training.
• Training in phase/zone 1 isn’t HIIT training.

Research by Edward Fox et al in the 1970’s showed that high-intensity interval training (HIIT) improved VO2max in line with the oxygen demand (expressed as a % of VO2max) of the work period of the interval.

Intensity proved to be a key factor in the improvement of the body’s maximal aerobic power – intensity is critical.

But, what about the relief period?

The relief period intensity in HIIT training

So far we have seen that the intensity of the work period will drive the aerobic and anaerobic capacity of the working cells.

• If you target intensity above LT2 you’ll get more anaerobic adaptation in the cells – they’ll adapt to produce more ATP anaerobically
• By targeting intensity between LT1 and LT2 you’ll get more aerobic adaptation in the cells and circulation – adaptations favouring aerobic ATP production will occur

The relief period intensity should always be below LT1 (so that lactate can be cleared) including being entirely inactive.

As an example, the original Tabata protocol involves no activity during the relief period. The athlete simply stops pedaling.

The 4 x 4 protocol involves 60% maxHR activity during a 3 minute relief period.

Generally the intensities of the relief periods are not the focus of HIIT – they are simply there to aid recovery between work periods.

Now the big question…

How long should the work and relief period be in HIIT?

Let’s revisit what we’ve learnt so far we know;

• The work period intensity is key to the HIIT stimulus.
• At high intensity, lactate is produced in the cell, then spills into surrounding tissues, and then is carried in the blood to other tissues.
• The lactate production can be very rapid (as in all out efforts – like sprints) or can be slower when intensity is closer to OBLA (LT1).
• Blood lactate decreases across the whole body when we reduce exercise intensity below OBLA or stop moving entirely, as lactate production slows and lactate clearance continues.
• If we work short and really hard we tend to drive anaerobic adaptations a little more, although aerobic adaptations still occur as there is considerable aerobic demand to oxidise lactate after the work period stops.
• When we work around OBLA and sustain the work period we’ll drive aerobic adaptations a little more than anaerobic adaptations – we are at the aerobic threshold in the working cells.

Manipulating HIIT work and relief periods

So, the work and relief period can be programmed on a continuum.

• You can keep relief periods short, which will cause lactate accumulation over time.
• Or, you can lengthen relief periods to allow more lactate to be cleared from the blood.
• If you have short relief periods, you will decrease the intensity possible during the work period as acidity (caused by hydrogen ions) restricts glycolysis*.
• When you have long relief periods, you will be able to repeat the work intensity at almost the same level.

*Negative Feedback Loops in Biology

A negative feedback loop is where a product of a reaction will eventually rate limit that reaction.  So, a product of ‘fast’ glycolysis is H⁺ . Increased acidity inhibits glycolysis, so less glucose is broken down.  This is a safety mechanism so you can’t become too acidic.

Comparing two HIIT workouts

Our runner (from figure 8 below) has the following results from a staged exercise test;

We can see the runner;

• Achieves LT1 (OBLA) at 12 km/h
• Reaches LT2 at 14 km/h

From these results we know our HIIT work period must be 12 km/h or over to be HIIT.

What HIIT work intensity do I choose?

If we prescribed the work period as running at 120% LT2 pace (16.8km/h) for 1 minute we know the following;

1. Our runner can achieve this pace for the 1 min duration as they were running for 2 mins at 16 km/h during the test which was their peakVO2 pace.

2. The work period is long enough to create a lot of lactate due to the intensity and we can expect lactate to accumulate in the blood over the 1 min work duration.

3. The runner will be at a pace which is loading their musculoskeletal system beyond their current maximal sustained pace so we can expect improvements in running stiffness and running economy at high speed, and further development of the muscles involved with breathing.

4. The rate of energy production in the working tissues is maximal which will cause significant anaerobic adaptations as well as aerobic stimulus across the whole body during relief periods (as oxygenated tissues work to clear accumulated lactate).

What else might I consider for my HIIT prescription?

The work period intensity you choose is dependent on a lot of things – this is the nature of prescription.  To name just  items a fitness professional or coach might consider;

• The person’s injury and health status (current and previous).
• Next competitive or recreational goal and phase of training.
• Volume of training days and durations available and previous trainability.
• Runner’s mentality and preferences for maintaining training.
• Other training being completed and strengths/weaknesses needing development.

etc etc etc.

What if I’d chosen a different intensity of HIIT for my runner?

My example above, where I’ve chosen 120% over LT2 is for illustrative purposes.

Equally, this runner could have a 4 x 4 protocol prescribed at 110% LT1 (13.2 km/h) and many of the adaptations would still be achieved.

What the runner would lose with 4 x 4 is the stimulus of the maximal running pace and some of the anaerobic adaptations and musculoskeletal loading caused by that pace.

But, the runner would gain more aerobic adaptations from the sustained elevation in lactates when using 4 x 4.

Without dwelling on the plethora of options available, let’s get back to my example.

Now we need to choose the relief period duration and intensity.

HIIT workout example with different relief periods

Because I’ve chosen a running pace for work over VO2max, I’m going to use walking as the relief period intensity and mode.

Remember, the relief period must be below OBLA (LT1) so the lactate is being cleared by the body during recovery.  This allows the work period intensity in the next repeat to be achieved.

For the runner, a very gentle walk is 5 km/h.

For a relief period duration we could select either;

1. 30 secs relief or
2. 2 minutes relief

Let’s have a look at the lactate profiles our HIIT workouts would cause, based on the same work (period 1 min, intensity 16.8 km/h) but different relief periods.

Assumptions for this runner’s HIIT workout

• The baseline blood lactate of our runner is 1 mmol
• That LT2+20% pace (16 .8 km/h) has been selected for 1 minute (this is from the runner example in figure 7)
• The runner produces 4 mmol/L lactate per minute at this pace – so after 1 min of work they’d be at 5 mmol/L (1 at rest + 4 from 1 min of work = 5)
• The runner clears lactate at 2 mmol per minute when walking

Phase/Zone 3 HIIT Workout

Looking at figure 7 we can see;

• At end of the first work period 5 mmol blood lactate is achieved
• The 30 secs relief results in 1 mmol clearance
• The second work period would start at 4 mmol
• Each subsequent work period would start with a higher lactate
• The work to rest ratio is 2:1
• The runner would likely stop around 10 mmol lactate which would be about repeat 3
• This is a lactate stack (increasing lactate as the series continues) for a very fit runner

Now, let’s take a look at another option, with a different relief duration.

Phase/Zone 2 HIIT Workout

Looking at figure 8 we can see;

• 2 mins relief results in 4 mmol clearance (at a rate of 2mmol per min)
• Therefore, each work period would start at 1 mmol (resting lactate)
• The work to rest ratio is 1:2
• The runner could likely repeat the interval 6 times or to mechanical fatigue (that is where the muscles/joints/tendons are becoming uncomfortable due to the intensity of the work period)

It’s fair to say, with HIIT you have options!

Designing HIIT there is a lot of freedom – but with freedom comes responsibility.

You need to understand how much work you are actually prescribing.

This allows you to start at the right level, and progress the workouts as fitness improves.

How much work is in your HIIT workout?

You can calculate how much work is in a HIIT workout in a number of ways.

Some research [ref 4] suggests that it is the ‘mean workload’ achieved through the HIIT workout that relates to the aerobic adaptations.

As an example, all of the workouts in figure 9 have been normalised for the amount of work completed in the workout time – that is the ‘mean work’.

How the work and relief is shaped changes HIIT adaptations

However, you can see in figure 10 that the emphasis of the adaptations, because of the shape of the work and relief periods (intensity and durations) are different.

Some protocols emphasise muscular adaptations (sometimes called local or peripheral adaptations).  And, some emphasise systemic adaptations (sometimes called central adaptations).

Thinking again about the runner, I can choose from these HIIT protocols which to fit their needs.

I can also vary protocols to round out the training stimulus.  If they were doing long training on weekend days, and had less time during the week, I could focus on fast paced HIIT during the week to compliment some of the phase 1 training they were already doing.

Ultimately I can give the runner HIIT choices, so they can know they are doing a HIIT workout, but can choose their preference on the day.

HIIT Workout Design Summary

1. Work period intensity must be over LT1 to be considered HIIT.
2. You can use a combination of work period duration and intensity, and relief period intensity and duration to emphasise more aerobic or anaerobic adaptations.
3. Because there are so many options, HIIT can be manipulated to suit almost anyone – from beginner to advanced.
4. Your mean work output over a workout can give you a reasonable measure of the total value of the HIIT protocol.

Want some further reading on HIIT training? 

1. HIIT training benefits and protocols
2. HIIT physiology

These are references listed or used for this high intensity interval training (HIIT) workout design article

[ref.1] Journal of Obesity Volume 2011, Article ID 868305, doi:10.1155/2011/868305

[ref.2] Tabata I, Nishimura K, Kouzaki M, Hirai Y, Ogita F, Miyachi M, Yamamoto K (1996) Effects of moderate intensity-endurance and high intensity-intermittent training on anaerobic capacity and VO2max. Med Sci Sports Exercise 28:1327–1330

[ref.3] E. G. Trapp, D. J. Chisholm, J. Freund, and S. H. Boutcher, “The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women,” International Journal of Obesity, vol. 32, no. 4, pp. 684—691, 2008

[ref.4] Tschakert, G., & Hofmann, P. (2013). High-intensity intermittent exercise: methodological and physiological aspects. International journal of sports physiology and performance, 8(6), 600-610.

[ref.5] D. Wen, T. Utesch, J. Wu, et al.. Effects of different protocols of high intensity inter-val training for VO2 max improvements in adults: A meta-analysis of randomised controlled trials. J Sci Med Sport (2019), https://doi.org/10.1016/j.jsams.2019.01.013