Getting to the start line fresh rather than exhausted
For this article we'll consider the need for Tapering. Let's define what we mean first. During your training, your workouts will have given you a training load or stress that helps you to become fitter through a process of adaptation and super-compensation.
If you have followed a training plan, the training load will have progressively increased through a combination of greater intensity or longer duration workouts to help you maintain progress and prevent plateauing.
We calculate this training load on intensity and duration, the combination of which in relation to your power and/or heart rate thresholds is called the the Training Stress Score (TSS). A workout at threshold for 1 hour would yield a TSS of 100, whereas if it was 30 minutes the TSS would be 50. You get the idea.
Using the principle of TSS, sport scientists worked out that we could use the accumulation of TSS to judge your ability to perform according to the demands of the event. The first element is the chronic training load (CTL) which equates to your relative fitness, calculated as an average of workouts over the last 42 days (obviously there is more to it in that the algorithm takes into account that workouts done three weeks ago have less impact than those done this week for example). The second is the acute training load (ATL), the algorithm takes into account the training load over 7 days and equates this to your relative fatigue.
However it isn’t a great idea to arrive at the start line in a state of exhaustion, so your fitness and fatigue needs to be managed.At a single point in time we can calculate your relative freshness (or form) by subtracting ATL from CTL. During training is is expected that your levels of fatigue (ATL) will be greater than your fitness (CTL). This is healthy and is required to stress the body to make those adaptations. For the event we want CTL to be larger than ATL, ie your fitness is greater than fatigue, and hence you are judged to be fresh or "in form".
To do this we introduce the concept of Tapering, thereby delivering you on the day of the event as fresh as possible. This is achieved (generally) one or two weeks ahead of the event by reducing the training load so that you scrub off the 7 days accumulation of fatigue while still retaining the residual 42 days of fitness.
As you can see in the image, this athlete increased their CTL (blue shaded area) while accumulating fatigue (purple line). As their event approached we cut back the training such that fatigue (purple) dropped in relation to fitness and we delivered the athlete to their event (the Donegal 555) in positive form (the purple spike is the 555km event, staged over 24 hours).
What this means that you should look to avoid any massive training workout in the final week or so ahead of the ride as you are simply adding to the accumulation of fatigue without getting the benefits of improved fitness.
If you use platforms such as TrainingPeaks, etc then these will give you clear graphs of fitness, fatigue and form. You can also get an indication from Strava's Training > Fitness & Freshness graphs. A note of warning though, this is only accurate if you have set and kept unto date your power and heart rate thresholds, as the TSS is relative to that. Furthermore, the CTL score is relative and hence cannot be compared across two people, it is not an indicator of performance. .