*** many thanks to Neil Rooney for this blog post ***

Triathletes can be forgiven for getting confused by all the jargon relating to training zones.  Easy, hard, lactate threshold, aerobic training, VO2 max etc etc.  There are hundreds of ways of setting training zones, but I like a standard 5 zone breakdown.  I've been doing this for quite some time and I don't need a heart rate monitor anymore to know what zone I am in (I do however still use a Garmin on almost every run and on every cycle).

I thought it would be useful to set out what you can achieve in each training zone or what each training zone is for.

Zone 1 (aerobic zone, slow twitch muscle)

Recovery training zone. The purpose of this is to reuse lactic acid built up from a previous long session or high intensity session. The lactic acid is buffered to the liver converted to glycogen and reused as an energy source. This is an excellent was to stay fresh and limit or prevent injury. By training in zone 1 all your connective tissues get the chance to build up a responsiveness to the demands of training something they can't do at higher intensities when the demand on these structures is much higher.

Zone 2 (aerobic zone, predominantly slow twitch muscle)

Rich Roll (Ultraman) advocates Z2 training

This is the engine building zone. An endurance athlete should spend most of his/her training hours in this zone. It will promote the opening of new and dormant blood vessels, increasing blood flow to muscles which provides fuel faster and removes waste. It will also cause an increase in mitochondrial density. This is how the engine gets bigger allowing you to move faster for longer.

While training in this zone you can go for hours and hours without depleting fat stores. However you do need a small amount of carbohydrate replenishment to avoid the brain from bonking, this happens because the nervous system cannot use fat as a fuel source (see previous post)

Zone 3 (transition between aerobic and anaerobic zone, slow and fast twitch muscle)

Race pace zone. All those hours spent fluctuating between zone 2 and 4 will allow you to race at the high end of zone 3 without building up too much lactic acid or getting injured. If you are going long in zone 3 you need some carbohydrate fuel.

It is very important to do a few swims, bike sessions and runs in this zone on the weeks leading up to race day. This lets you get a feel for race pace and the task ahead.

During training this is known as the grey zone because you are not specifically relying on fats or carbohydrates as a fuel source but more a mix of the 2, if weight loss is you goal get out of this zone ASAP!

Anybody doing a marathon, ultra distance run, 70.3 IM or an ironman triathlon this is the zone you are going to race in. It requires a lot of refuelling while racing particularly on the bike during an ironman. If you get your nutrition wrong whilst racing in zone 3 you will bonk, hit the wall and your performance will deteriorate immensely.

Zone 4 (anaerobic zone, predominantly fast twitch muscle, lactic acid production)

The Brownlees and Gomez racing in Z4

Lactate threshold zone. Once you reach this coveted zone you are no longer relying on fats as a fuel source. This rapidly depletes carbohydrate stores, if you start a race in zone 4 due to excitement and nerves you will suffer the remainder of the race.

If you are a seasoned triathlete and you are fairly fit and fast you can probably get away with racing an Olympic triathlon at the low end of zone 4. Carbohydrate stores can last about 90mins and if you consider the swim will not be at zone 4 rather zone 3, then I think the real fit guys can race this in zone 4 with a small amount of fuel replacement.

Zone 5 (pure fast twitch muscle activity)

A very specific zone most notably know to build speed over a short distance by improving the neuromuscular junction message relay. Where the never tells the muscle what the brain wants it to do i.e. flex, extend, flex, extend very quickly so we can move fast and win this race.

Zone 5 is good place to be if you want to improve your sprint finish.