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We've put together the following article which explains the often misunderstood subject of Training Zones. We're firm believers that training to heart-rate, even if secondary to pace and/or power, enhances an athlete's training and therefore race performances.

We've included a discussion thread to the right so please feel free to question, argue, or berate our ideas!


There is lots of terminology used relating to training zones and thresholds but the terms are often misused or not fully understood. Understanding the zones, how they are formulated and how they benefit both training and racing is vitally important in terms of athlete progression. Heart Rate zones allow athletes to gauge, target and restrict efforts as required, resulting in significantly improved racing results and achievement of potential.

Energy Systems

The body is provided with energy from 3 energy systems, the Aerobic, the Lactate and the Creatine-Phosphate energy systems.

The term Aerobic means ‘with oxygen’ and is a term used to describe exercise where sufficient oxygen is available to support this exercise for long periods of time, generally sustained exercise over 2 minutes in duration.

The term Anaerobic means ‘without oxygen’ and is used to describe exercise where there is insufficient oxygen to sustain long periods of exercise (generally less than 2 minutes) and the body has to use energy systems other than the Aerobic System to fuel exercise: the Lactate and Creatine-Phosphate energy systems.

The Lactate System - lactate itself is an acid salt that forms in the blood and is associated with the burning feeling felt when exercising intensely. The Lactate System is an energy system that works without oxygen and provides energy that is able to sustain intense exercise for 1-3 minutes, ie running sprints up to 400m, 1km bike sprints or 100m pool sprints.

The Creatine-Phosphate System is an energy system that is immediate and can sustain intense exercise for only 5-10 seconds, ie the first part of a sprint or an explosive weight lifting action.

The Lactate System is the first system to be used when moving from Aerobic to Anaerobic; so when we refer to thresholds, the Anaerobic Threshold and the Lactate Threshold are one and the same.

The Lactate threshold (LT) or Anaerobic Threshold (AnT) is the point at which lactate builds faster in the bloodthan it can disperse; below this threshold, lactate disperses faster than it builds. An athlete could exercise below the threshold for several hours (ultra marathons as an example) yet typically above it for only 1-3 minutes before having to drop below the threshold again. The Lactate Threshold is a performance limiter as it imposes a ceiling on maximum sustainable output.

Aerobic Threshold (AeT) isn’t a physiological term but is often used to describe levels of effort where the Anaerobic System starts to be used but lactate is dispersed faster than it builds. In training terms, the Aerobic Threshold sits 10-20 BPM below the Lactate Threshold.

Max Heart Rate (MHR).. This is the maximum heart-rate that an athlete can safely achieve whilst exercising. This heart rate isn’t an indication of fitness, strength or aerobic capacity and isn’t a limiting factor in endurance racing so has little relevance to training zones. Training zones can be calculated using MHR but this may not be the best way of calculating training and racing zones.

Lactate Threshold Heart Rate. This is an athlete’s heart rate when working at the Lactate or Anaerobic Threshold. Because this heart-rate is linked to the Lactate threshold, which is a performance limiter, and changes with athlete progression/ recession, more significant training zones can be derived from this figure.

Aerobic training increases muscular efficiency: the ability to produce a higher output for a given oxygen requirement. Therefore, with increased muscular efficiency an athlete will be able to achieve a higher heart-rate, and increased output, before reach their Lactate Threshold. Additionally, targeted training at or above the Lactate Threshold improves the body’s ability to flush lactate and therefore again allows the athlete to have a higher output before being limited. Both circumstances enable the athlete to have an increased output, at a higher heart-rate, before being limited by their LTHR.

It can now be understood that as an athlete progresses, their LTHR will increase and with this their zones will increase too. By altering zones as the athlete develops, we ensure that there is continued progression and stagnation is avoided. Zones do not change when training to MHR which can result in stagnation as the athlete may be under-training and racing as they progress.

When training using LTHR, it’s important to understand that each individual may have a different LTHR for different disciplines; for example, one LTHR for cycling and another for running.

Training Zones

There are many HR training systems which all vary enormously: the number of zones, the names of zones, whether MHR based or LTHR based etc. These variations aren’t important – what is important is the intensity that the athlete is training too and what they are trying to achieve by doing so.

The following system we use has 5 zones and is based on the LTHR . Other similar systems split zone 5 into separate zones but this system works well as the zones are wide enough to allow for natural HR discrepancies such as chronic fatigue, caffeine, adrenalin, yet accurate enough to really target specific intensities.

Zone 1: 70-85% (run), 70-80% (bike) LTHR.

Recovery - this zone has many applications. It can be used for warm-up and/or cool-down. Zone 1 can also be used for an entire session in days following particularly long or intense sessions. This zone also works well for someone who is particularly unconditioned or for someone recovering from injury. Another use for zone 1 is for active recovery during interval sessions.

Race Application - ultra-distance bike or run .

Zone 2: 86-90% (run), 81-85% (bike) LTHR.

Extended Endurance - zone 2 training increases aerobic base fitness and endurance. Base training for endurance races normally focuses on Zone 2. Training in zone increases muscular endurance and also results in a shift of metabolism towards a greater use of fat rather than glycogen, which dramatically improves performance in endurance races.

Race Application - Iron distance bike and run, standalone marathon or ride over ~3 hours

Zone 3: 91-95% (run), 86-90% (bike) LTHR.

Intermediate Endurance - lactate production is significant in this zone but the body is able to flush the lactate faster than it builds. This zone can be held for relatively long periods but is punishing on the body. Zone 3 can be useful for increasing intensity of base building sessions and for introducing an increased intensity during the base phase training.

Race Application – Middle Distance triathlon bike and run or standalone ½ marathon and rides ~1-3 hours. In Zone 3 fast-twitch muscle fibres are employed alongside slow-twitch muscle fibres which can have a negative impact on performance in the latter stages of endurance races, particularly impacting the run of a long distance triathlon.

Zone 4: 96-99% (run), 91-99% (bike) LTHR.

Sub-threshold – this zone sits just below the lactate threshold with high levels of lactate but the body is just able to control – output is not limited, although sustained efforts can be uncomfortable. Depending on the amount of training in this zone, this intensity can be held between 20-60 mins, but this varies enormously between individuals. Training in this zone increases lactate tolerance and flushing efficiency which can increase an athlete LTHR. Although predominantly an anaerobic zone, aerobic efficiency is increased as the aerobic system is pushed to its limits. In a similar way, slow-twitch muscles benefit as they are equally pushed.

Race Application – varies enormously between athletes but zone 4 can be held between 20 and 60 minutes so can work well for sprint triathlon run and bike, potentially sustainable for long periods of a standard distance race. Stand alone 5km up to 10km runs or shorter rides or bursts during rides.

Zone 5: 100%+ (run,bike) LTHR.

Anaerobic - efforts where the lactate/ anaerobic threshold is crossed; performing at this intensity can normally only be maintained for up to 3 mins (varies between individuals). Zone 5 training is employed most frequently in interval training and has many benefits: time efficient, increases ability to disperse lactate, increases VO2 Max and benefits those who will need to work in Zone 4 for periods during their races. It’s important to utilise rest periods when working in Zone 4 at a ratio between 1 minute work to 2 minutes and 1 work to 4 minutes rest.

Race Application – short sharp efforts of less than 3 minutes, including sprint finishes or bursts to catch groups.

Training Programme Application

With knowledge of the various thresholds, percentage LTHRs, training zones and energy systems, we are able to train to increase our performance significantly. “Train smart, not hard” should be a phrase of the past in endurance sport. We need to train smart, but this includes training long, training hard and allowing for recovery. When formulating a training programme  we need to consider which zones are applicable to which periods of training, recovery periods and the applicability of each zone to chosen race distance/ phase.

We offer 7-Day free trials on our online endurance training, during which we schedule testing and allocate zones, so why not have a trial and see how zone training can enable you to reach your full potential.

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© Tiger Frog Ltd 2012     Hill Park, Dudleston Heath, Ellesmere, Shropshire, SY12 9LB

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