Taper, why and how much

The basic question that was forward to myself and Coach Manzi on our message board, was why do we taper, and why does it seems the intensity goes up, during a taper. I have compiled a paraphrase our our combined answers:

As we all train, we break our bodies down. We are suppose to rest to allow the muscle to build back up and tiny injuries or soreness the opportunity to heal. We generally do not do this. When you sit to plan a season you should have an idea of what your "A" race, or races are so you can build in your Taper or rest and healing period. Many of us will train through a C race, and taper only a few days for B races. Remember that in Triathlon unlike say running each individual sport generally has a different taper, because of how long the body takes to heal. Generally for most people Running taper is the longest, then Biking, then swimming. So for an Ironman, you may start your run taper a month out and your swim taper only two weeks, but each person is different.For and IM generally a taper will begin 4-5 weeks out from the race.
Volume begins to drop in approximatley 20% or so a week, but intensity of the workouts remains high, and in some cases gets higher. For shorter races the durations will decrease exponentionally. 70.3 2-3 weeks, OLY 1-2 weeks, Sprint 1 week is generally enough.The key part of the taper is rest. It allows us to heal. Becareful of your diet, as your training will decrease and some put on weight, becuase they eating doesn't change.

The reduction in volume allows us to rest in taper periods( which we call late build period or peak period). The intensity keeps us both physically and mentally ready building to race day, Intensity levels are different for the race distance that we're building to. For a sprint or Olympic distance race, it's wise to use schedule , in the taper period, workouts that build to 4 to 5a zone, this is Anaerobic or Lactate Threshold Heart Rate. In those distances the athlete will experience lactate build up, so when getting close to race day it's good to expose the athlete to what they are going to experience on race-day. Also, good w/o's for these races are lactate tolerance w/o's , where the athlete will experience lactate build up during the work intervals, sure gets them ready for that pain they will feel on race day. When training for long course races, such as 1/2 IM and THE IRONMAN, the intensity of these taper workouts will build to 3 to 4 zone, which is the very top of our aerobic intensity range. When racing at this distance we don't want to see our HR above 3 zone, with only small durations of 4 zone during the race, so no need to use anaerobic intervals as intensity workouts, better to use muscular endurance workouts for these distances (zones 3-4).
So, the intensity is kept high for a number of reasons, first it keeps mind and muscles fresh and focused. It also allows us to get our muscle memory for what race pace is. More importantly is what happens inside the body, in that the rest coupled with shorter higher intensity, allows glycoogen to store and improves blood volume and aerobic enzymes. So in effect this is like carb loading for our body. Its giving it rest, while allowing it to store and rebuild what we need to be successful.
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