Training in Zone 5: raising race pace

Zone 5 is the area of exercise intensity occurring at approximately 85% of your maximum. Most athletes would associate this work level with race pace of events ~20 to 30 minutes in duration. When you see this type of training in your schedule, you know it’s all about getting ready to race!

What is happening in the body when exercising in zone 5?

Exercise in zone 5 is hard work – the body’s physiology is in fact, moving toward a point of fatigue as soon as you start exercising: heart rate cannot stay steady, blood lactic acid levels are increasing, and your breathing often takes oxygen uptake towards its maximum levels.


From a sport scientist’s perspective, the athlete is well above their ‘steady state’: the ‘maximal lactate steady state’ (MLSS) occurs in the middle of zone 4 and is the upper limit of your physiology remaining stable. In fact, zone 5 has its own physiological landmark – the ‘Critical Power’ (you can read about the CP in another one of our factsheets). Though the MLSS and CP are well related, it would appear the underpinning physiology of each differs, which is an important factor to consider when preparing yourself for race events which last one hour (MLSS determined) vs those of 20 to 30 mins (CP determined).

How will using zone 5 change my physiology?

As zone 5 training forces the athlete to work in non-steady state conditions, the body’s reaction will be to adapt bringing about changes which will allow steady state in the future. We’ve already mentioned that in zone 5, the athlete will be generating a great deal of lactic acid in the muscles. This brings challenges to the body in terms of clearing the lactic acid which flows from the muscle into the blood: without this adaptation, the athlete would be limited in their tolerance of exercise. It is worth mentioning that it is not the lactic acid per se that brings about fatigue, but rather the hydrogen ions that form when the lactic acid converts to lactate (as the acid hits the blood after leaving the muscle). In this type of exercise, it has been found that the acidity in the muscle bed increases, whilst the markers of ‘anaerobic’ metabolism become evident: namely a drop in phosphocreatine, and an increase in inorganic phosphate1.

In order to better clear the lactic acid and H+ produced, the body will build structures that facilitate the carriage of these metabolites away from the muscle:

  • Increased capillaries in the muscle bed
  • Increased ‘buffers’ within the muscle cells


Another effect of exercise in zone 5 (see table above) is the impact on the muscle stores of carbohydrate. Since we are above MLSS, glycogen in the muscle is the predominant source of energy supply. It has been shown that exercising to exhaustion at zone 5 intensity can deplete the glycogen stores to around 50% of their resting content2. Frequent lowering and restoration of muscle glycogen will, in the long term, lead to the body storing more of this valuable energy supply.


Let’s take a cyclist who wishes to improve their 10 mile time trial power by 10W this coming season. Last year, their best attempt over this distance was 290W. Aiming at 300W is a reasonable target if broken down into this two-step process. A 6 week training block for this rider might be structured like this:

1.   The first 3 weeks will focus on taking the rider to this new race power level

  • Starting with 1 minute reps at 300W: the rider would aim to complete 10 to 15 of these, with equal recovery. Two of these sessions could be performed per week.
  • By the end of week two, the rider might be able to do 20 of these 1 minute efforts – when they are able to do the amount of work equivalent to their 10 mile time, they can increase the length of the work interval (keeping recovery at 1 minute).
  • A progression might look like - 15 x 1 min, 22 x 1 min, 10 x 2min, 7 x 3 min.

2.   The second block of 3 weeks would shift the emphasis to sustaining this race power

  • The rider can already achieve 3 minute blocks, so 5 minutes would represent a good target
  • This rider needs to be able to sustain 300W for approximately 20 minutes, so by the end of week 3, they need to be completing 4 x 5 minutes (equal recovery to begin with).
  • The rider can start with 3 blocks of 5 minutes in session 1
  • If the rider makes a quick progression to 4 blocks, they are likely to need a bigger challenge: decreasing the recovery time (from 5 minutes down to a target of 1 minute) is a good place to start. Or, how about increasing the target power?

How do I use zone 5 training to raise my race pace?

Training in zone 5 should be thought about in two steps:

1.   Firstly, increase the absolute power you can reach at the top end of zone 5

2.   Next, work at sustaining this newly accessible power output

As will all training in a periodised plan, it is important to have done sufficient work in other zones in preparation. Normally, the coach would have suggested work around the VO2max (zone 6) before hitting race pace work: this will provide the athlete with an ability to endure ‘top end’ power outputs.

What does the research say about training in zone 5?

Research documenting the training responses to zone 5 are difficult to find, since most research groups are more interested in responses to training at and around MLSS (zone 4) or at VO2max (zone 6). However, if we consider the few papers discussing the critical power concept and endurance training, we do see some promising benefits to working at this intensity. For example, one study found that training at CP for 3 times a week led to improvements in CP of 30% over an 8-week period3. Interestingly, these researchers went on to examine high intensity interval training and its effect on CP4 – using intervals of repeated 60s of maximal exercise, they did not find an effect.

More recently, research work at the University of Brighton5 compared training at critical power with an equal volume of work at lactate threshold. Not only did training at CP improve the CP itself (by 19%), but it also lead to 12% increases in maximal minute power. This was better than the training effect using LT and would suggest that it is more time effective to use CP work than traditional endurance training alone.The research also examined intermittent training below and above CP – like previous research, the study confirmed that maximal work is less effective at improving CP. These research findings perhaps remind us that training needs to be specific: race pace is predominantly aerobic metabolism limited, so focus on training that system!


Other training sessions to boost race pace

Every athlete appreciates variety, so how about trying these sessions to achieve similar effects:

Bonderenko sessions

This session gets its name from the middle distance runner Olga Bondarenko, the former Soviet Olympian.

[Strictly not zone 5, as it takes you across the training intensities, from the top end of zone 4, through to zone 6. However, the majority of the efforts are zone 5]

The session runs like this:

  1. Start with 5 minutes at the pace you can hold for an hour (have 5 minutes recovery)
  2. Perform a 3 minute block at the pace you can hold for 20 minutes (again, equal recovery)
  3. Next, step the intensity up to 10 minute effort, hold for 2 minutes (2 minutes recovery)
  4. Finish with a 1 minute effort at your VO2max.

It sounds easy enough, but add to the challenge my completing more than one set.

Redline pyramid

  • Take your target race pace and work above and below that for 6 minutes
  • For example, our rider working towards 300W would perform a 2 minute effort at 290W, followed by 2 minutes at 310W and finish with another 2 minutes at 290W.

The challenge to this session is that you are only given 2 minutes of recovery before attempting another 6 minute block. Aim for 4 to 5 of these blocks per session.


Message to take home:

Training in zone 5 should become the main focus of training in the final build towards the race season. Ensure you have done sufficient work in the lower zones in order to cope with the training demands of zone 5. Also, give thought to how much you wish to add to your current race performance. Having a realistic target in mind, and the progression in overload planned, will allow consistent steps towards your goal. Be mindful of the recover you will need from these sessions too: the intense nature of zone 5 work, and its impact on physiology is a double edged sword: it’s very effectiveness comes from the disturbances in physiology it creates: so remember to fuel well during, and post session.



1.   Jones et al. Am J Physiol Regul Integr Comp Physiol 2008, 294, R585-593.

2.   Brickley et al. Int J Sports Med 2007, 28, 300-305.

3.   Jenkins & Quigley. Med Sci Sports Exerc 1992, 24, 1283-1289.

4.   Jenkins & Quigley. Med Sci Sports Exerc 1993, 25, 275-282.

5.  McGawley, K., Dekerle, J., Brickley, G and Carter, H (2009). Training at the Critical Power enhances endurance more effectively than traditional training intensities. PhD thesis.