Training in Zones

A fundamental aspect of any training programme is that you, the athlete, train at a variety of intensities. Anyone who does not train at a variety of intensities is merely exercising.

For any degree of interaction to take place between athletes and coaches a means of communicating intensity is required.

Communicating Intensity

For historical and practical reasons means of measuring, or describing, intensity vary from one sport to another. Some are very specific (lap times), some less so ("seven minute mileing"), and some are very vague ("hammering"). Many are also very specific to individual athletes – that seven minute mile pace is a dawdle for an elite runner but well over "race pace" (another frequent description of intensity) for many.

Describing intensity in terms of Heart Rate has the advantage of being both sport and output independent. A certain percentage of your maximum heart rate (MHR) is a certain percentage of your maximum heart rate however fast you can swim, cycle or run. Thanks to modern technology it is now cheap and easy for athletes to monitor and record their own heart rates under everyday training and racing conditions.

Percentages, Zones and Levels

As MHR varies hugely across the population (forget the 220 minus your age 'rule') coaches are rightly wary of handing out numbers and in many cases describe ‘zones’ relating to heart rate ranges. There are several different zone systems around: many cyclists use Peter Keen’s original four level system but I know of at least three others in use in cycling alone and British Triathlon uses yet another.

Whilst zones solve the problem of varying MHR they still don’t address the fact that individuals’ physiologies and fitness levels also have an impact on the training effect of working at different percentages of MHR.

In order to use zones effectively I believe that we have to relate them to the physiological changes that occur as the heart rate increases. These changes relate to the sources of energy that the body utilises and the level of lactate – a by-product of the energy conversion process – in the blood.

Physiological Changes

At low intensities the body tends to make the best use it can of its fat stores. At medium intensities it cannot metabolise the fat stores quickly enough and makes more use of glycogen stored in the muscles. However it needs large quantities of oxygen to metabolise muscle glycogen. As the demand for energy becomes higher again, and the heart and lungs are unable to keep up with the muscles' demand for oxygen, it metabolises glycogen without oxygen - but it cannot do that for long.

Training in each of these three bands conditions the body differently and the heart rates at which the body moves between them varies from one individual to another. They also change according to how an individuals condition themselves. For an endurance athlete, aiming to developing efficiency, it is an important objective to extend the top of the low and medium intensity bands.

Determining Zones

Simply calculating zones based on fixed percentages of MHR does not necessarily correspond to the values at which these physiological changes occur – with the result that training to calculated zones might well not have the desired effect.

A better method is to measure the amount of lactate in the blood across a range of intensities. Latcate is a product of the body's energy conversion process, so changes in lactate level give a good indication of where the changes in energy metabolism take place. There are two lactate 'turn points' where the concentration of lactate typically reaches 2 and 4mmol/l (the units are millimoles per litre of blood). Finding these turnpoints involves controlled testing and blood analysis under laboratory conditions.

For practical purposes you can feel where these changes take place. As you move out of the fat burning band and into the glycogen burning band (crossing the Lactate Threshold, LT, at 2mmol/l) your breathing becomes rhythmic and you can no longer chatter. I call this the chattering threshold. The move from aerobic to anaerobic, crossing the Anaerobic Threshold, AT (at 4mmol/l), corresponds with the onset of muscular ‘burn’ and the feeling that you cannot talk (because you are using absolutely all of the oxygen that you are breathing).

The graph below is a somewhat idealised representation showing how HR and lactate level vary as intensity (power output) increases. At AT the relationship between output and HR becomes non-linear which means that this point can be found without blood analysis equipment. Practical tests rarely result in outputs as deterministic as this and using your own perception and knowledge of your body can yield equally useful information.



Having found your turn points – either in the lab or by gauging them yourself – you can set out your training zones in a meaningful manner. I use the BCF six zone system which groups zones 1 & 2 as ‘basic’, zones 3 & 4 as ‘intensive’ and zones 5 & 6 as ‘maximal’. I have included the BTA zones in brackets and the old BCF levels in italic.





Type of Training


(Below 60-65% MHR)


Very relaxed

Promotes blood flow to the muscles.

Allows concentration on technique


Some drills & technique work


(Below LT)

Body is able to use fat stores for large proportion of fuel.

Relatively low demands on aerobic system.

Duration is practically unlimited and refuelling is fairly simple.

Zone 1

Level 1


Strengthens & enlarges heart muscle

Improves oxygen transfer

Reduces heart rate (for given output)

Improves ability to use fuel (food), especially fat

Develops motor muscles and muscular endurance

To gain the full cardiovascular benefit sessions need to be long (typically over 1h for running & swimming, 2h for cycling) & continuous.

Shorter sessions are useful for developing technique & muscular endurance

Zone 2


Low Level 2


Still able to hold a conversation


(Between LT & AT)

The main aerobic zones. Stored muscle glycogen is primary source of fuel so duration is limited.

Long sessions can be very fatiguing and require good recovery.

Zone 3


Upper Level 2


Still comfortable but the need to keep supplying oxygen means that breathing gets in the way of talking

Develops aerobic endurance. The ability to sustain high power output

Training is most effective at either end of the band – i.e low zone 3 & high zone 4. (See below)

Long efforts (sustainable for several hours) or long intervals (15mins to 1h) with short recovery.

Zone 4


‘Low’ Level 3


Hard work & breathing very heavily.

Sustained efforts of up to 1h or medium intervals (5 to 10 mins) with short recovery


(Above AT)

The anaerobic systems start to kick in resulting in lactate generation at a higher rate than it can be removed resulting in muscle pain ‘burn’.

Zone 5


‘High’ Level 3


Still largely aerobic so breathing very hard but struggling to get enough breath.

Power (sustainable speed). Lactate tolerance

Sustained efforts of up to 30 mins. Short efforts (up to 5 min) with equal length recovery.

Repeated short efforts with short recovery for developing lactate tolerance

Zone 6

Level 4

Flat out

Rapid fatiguing

Max Power (short distance speed)

Short efforts (up to 1min) with long recovery for power.

Short efforts with short recovery for lactate tolerance.




Training at close to AT, either in z4 or z5, is very much like hard work and very demanding on your body. Trying to train in these levels when tired is likely to result in working towards the middle of the Intensive band.

Training below LT, i.e. z1 and z2, feels easy to the point where you might feel that you are not really training. There is a strong urge to push harder and to end up working towards the middle of the Intensive band. Besides missing the benefits of Basic band training the upshot of this is glycogen depletion and too much fatigue to do any AT work.

Athletes falling in to this trap find themselves able to work hard for perhaps 1 to 2 hours but unable to go fast and very likely to blow up suddenly when their fuel supplies run out. Fit, perhaps, but not fit for purpose. Beware of merely exercising.


Tim Williams

Feb 2004


Locations of visitors to this page