I've read a few books about training zones over the last few months including Joe Frills, Guy Andrwes and John Metcalfe's. This is what i've learnt:
Zone 1 (50-60%)- Great for active recovery. These sessions (no more than 30mins long) get the blood pumping to your legs that which aids repair and recovery following hard training sessions. Target HR should be 55%. Can actually be more beneficial than complete rest.
Zone 2 (60-70%) - Good for building an endurance base. Encourages your body to use fat as primary fuel for energy. As you body get's more efficient you will find you ride faster for the same level of effort. The training impact of this zone is relatively low so you can do more of them. The efficiency gains also make you faster when training in the higher zones. Feels slow to train in this zone to begin with but you WILL get faster. In terms of hours spent training, the majority will be in this zone.
Zone 3 (70-80%) - No mans land. Some training in this zone is beneficial but you are riding too fast to build your aerobic base but too slow to develop your V02MAX and lactate threshold. The result of spending too much time in this zone is that you’ll get home feeling tired but not have really improved your fitness. You will deplete your glycogen stores making it much harder to train in harder zones on following days. Useful during periodisation in a macro training cycle.
Zone 4 (80-90%). Hard training zone where you will really start to push what you are capable of to realise training adaptions. It is here where you will be training at or about your Lactic Acid threshold. Training just above your LT will mean you can go harder to longer as your performance improves as your tolerance to the accumulation of LT will increase. Much of this will be achieved via use of intervals although this will be considered average race pace for many (but perhaps not for marathons where that level would be unsustainable). The training impact of this zone is very high and rest or active recovery is essential to avoid over-trainng.
Zone 5 (90-100%) Maximal effort. Can only be sustained for very short periods of time (for most of us). Perhaps up to 5 mins max. Good level to aim for when doing sprint intervals say 30seconds to one minute. Training at this level of intensity should be done infrequently or as part of a meso-cycler prior to racing season transition.
A word on Zones.
There does seem to be a lot of debate on the zones to train in. I've used those recommended by Polar but both the British Cycling (developed by Peter Keen) and Australian Cycling federation recommend slightly different zones (see below). Note these are all based on MaxHR and do not factor in your resting HR (e.g. Karvonen method).
British
Z1 60-65%
Z2 65-75%
Z3 75-62%
Z4 82-89%
Z5 89-94%
Z6 94-100%
Australian
Z1 60-65%
Z2 65-75%
Z3 75-84%
Z4 85-91%
Z5 91-100%
What they all seem to agree on is that training routinely between 75-85% is counter productive for the reasons given in the definition of Zone 3 above. The rule seems to be mix low (z1) moderate (Z2) and hard (z4/5) sessions per week. Making sure you get good rest and are eating and hydrating well. Every third or fourth week it essential to schedule an easy week to avoid long term accumulation of fatigue (aka overtraining). At best your performance will plateau but most likely diminish.
Also of benefit is using a system to rate your training load. More advanced Garmin and Sunto HR monitors do this with Training Effect score. Polar has training impact or you can calculate it yourself using the TRIMP methord (Google it). This objectively lets you see how hard your sessions were so you can schedule easier sessions or complete rest days.
I'd also highly recommend Sage Rounteee books, the Athletes guide to Recovery. Less is indeed more.
Just keep stepping up in each phase, rest move up.
