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Almost all athletes and coaches agree that tapering - the reduction of training in a systematic way - is a good thing, because it ensures good recovery from heavy training(1) and is a key part of preparation for an important competition(2). Unfortunately, there is wide disagreement about how tapering periods should be constructed. These debates revolve around how long a tapering period should be, the extent to which training volume, intensity, and frequency should be reduced during a taper, and also - very importantly - the rate at which these variables should be reduced.

One dispute has centred on whether tapers should contain 'step reductions' in training or 'exponential decays'. In a step reduction, total training is reduced by a certain amount, and the new volume of training is sustained throughout the tapering period; in an exponential decay situation, the quantity of training decreases steadily over the course of the taper in a continuous slide, reaching bare-bones levels at the end of the tapering period. One popular step-down strategy is to clip training by 65-70%, then maintain the new, lower volume of work for 1-3 weeks. Traditionally, exponential decays have been linked with shorter durations of time, often just 4-8 days.



Until now, the relative merits of step reduction and exponential decay tapering have been poorly evaluated. Several years ago, the outstanding tapering theorist Joe Houmard asked 5k runners to cut training by 70% for three weeks (a step reduction). At the end of the 21-day period, the runners' 5k race times were not significantly better, nor did they exhibit greater muscular power(3). By contrast, a seven-day exponential decay in which training volume was reduced each day and overall weekly volume dropped by 85% produced dramatic improvements in 5k race times and muscular power(4).
These very different results have led some tapering theorists to argue that when training volume is reduced aggressively and progressively to an extremely low level, performance is improved to a greater extent than with a single step reduction - or even several such reductions - over a longer period. Some anti-step scientists even argue that step reductions usually maintain performance rather than enhancing it.
Such arguments are not completely fair, since step reduction tapering has been linked with fairly impressive gains in physical capacity. For example, in a classic study carried out by renowned exercise physiologist Dave Costill in his laboratory at Ball State University, collegiate swimmers reduced training volume from 10,000 to 3,200 yards per day over a 15-day period(5), after which their performance times improved by 3.6%, their arm strength and power increased by up to 25% and blood lactate levels were lower during 200-yard swimming 'sprints'. These impressive results led Costill to recommend (in his fine book Inside Running: Basics of Sports Physiology) tapering periods of approximately two-weeks' duration, with volume set at about one third of usual levels - a large step reduction.

Short step reduction tapers do work well - at least in some studies
In later work, Raymond Kenitzer and Catherine Jackson asked 15 female collegiate swimmers to pare training volume by about 60% over a four-week period(6). For the long-distance swimmers involved in the study, volume dropped from 8,000 yards per day to 3,500 yards. During this step reduction taper, blood lactate levels fell steadily for about two-and-a-half weeks, and performances increased progressively over the same time. After this period, however, lactate concentrations and performance times both began to worsen. Kenitzer and Jackson drew the obvious conclusion: 60% step-reduction tapers lasting up to 17-18 days are good things.
Step reductions can do more than maintain performance levels. However, the exponential cause was advanced pretty dramatically shortly after the publication of Kenitzer's work. Another scientist with a strong interest in tapering, Duncan MacDougall of McMaster University in Hamilton, Ontario, asked a group of well-conditioned runners, who were averaging 45-50 miles of running per week, to try out three different kinds of one-week tapering strategies, as follows:
(1) doing nothing at all during the week (a 100% step reduction)
(2) running about 18 miles during the week at a leisurely pace, with a complete rest day at the end of the week (a 64% step reduction)
(3) undertaking a drastic exponential decay in training over the week, with an emphasis on quality running. Using this strategy, the runners completed five hard 500m intervals on the first day, four 500m blasts on the second day, 3x500 on day three, 2x500 on day four, and a single 500m surge on day five. After a rest on day six, they were ready to be tested on day seven (along with the runners in the other two groups). Crucially, each 500m interval was performed at about one-mile race pace, and since the runners warmed up with 500m of slow jogging before the quality intervals, the total training volume for the week was about 10k, or just over six miles. Thus, this decay involved an overall 87-88% reduction in training(7).

The performance test on day seven involved running as far as possible at one-mile race pace, and the 64% step reduction runners did fairly well, advancing endurance time at this speed by 6%. By contrast, the 100% reduction runners failed to improve at all. However, the exponential runners blew the roof off MacDougall's lab, raising endurance time at one-mile pace by a full 22%! The expo group also demonstrated enhanced leg muscle enzyme activity, augmented total blood volume, increased red blood cell density and greater muscle glycogen storage, by comparison with the step-reducing runners.
These results certainly made exponential decay tapering look better than step reduction plans, but a few comments are in order. First, note that MacDougall's decaying runners employed a relatively high quantity of quality running during their taper - about 7.5k out of a total volume of 10k (75%). It is possible that the 64% step reduction runners would have fared far better if they had been able to include quality work in their training as well.
In addition, the expo decay runners trained during their taper week at exactly the pace which was used for testing. Thus, their tapering period was highly 'neural', in that it 'tuned up' their nervous systems and prepared their neuromuscular systems for the exact intensities and most efficient patterns of coordination and overall movement which they would use in the test. So, as you can see, MacDougall's work did not really compare step reduction tapering with exponential decay cutbacks but instead merely contrasted two very different tapering plans.

Other studies offer support for the 'steep slide' course
None the less, MacDougall's unique exponential plan looked pretty good, and further work by Joe Houmard and his colleagues added weight to the idea that tapering should proceed along a 'steep slide' course. Inspired by MacDougall, and having used the Ontario taper to prepare very successfully for a marathon, Houmard asked eight experienced runners (six males and two females), who had been running about 43 miles per week, to abbreviate their weekly workout to 6.2 miles of interval training and seven miles of jogging(8). Almost all of the interval training consisted of high-intensity, 400m intervals at about 5k race pace, or slightly faster.
The exponential part of the plan was modelled along MacDougall lines, as follows:
1 Day 1, 8x400m intervals
1 Day 2, 5x400
1 Day 3, 4x400
1 Day 4, 3x400
1 Days 5 & 6, 2x400
1 Day 7, 1x400

During the workouts, recovery intervals (composed of walking or resting) lasted just long enough to let heart rates drop to 100-110 beats per minute, and an 800m easy jog served as both pre-workout warm-up and post-training cool-down, accounting for the seven miles of jogging for the week. A control group of eight runners maintained their usual training volume of 43 miles per week.
When a 5k race was held on the eighth day of the study (immediately following the one-week taper), the exponentially advantaged runners trimmed average 5k times by a statistically significant 29 seconds, from 17:16 to 16:47, with all eight runners able to improve their clockings. They also improved running economy by a rather dramatic 6%, while the control group improved neither economy nor 5k performance.

So, to settle the argument, what's the ideal tapering period?
Such investigations didn't settle the tapering controversy, however. For one thing, many athletes tried exponential decay tapers similar to those employed by MacDougall and Houmard, only to end up with very sore legs and quite modest performances. Furthermore, even if people accepted the idea that exponential decay tapers were best, questions remained about how long such tapers should last. Was one week really the optimum duration, or should the tapering period be longer - or even shorter?
Enter E W Banister, a kinesiologist at Simon Fraser University in British Columbia, Canada, who was known for his innovative, although sometimes eccentric, research on endurance training theory. Regular readers may recall Banister as the fellow who developed a unique system for determining how much 'training stimulus' an athlete gets from a particular workout.
To use the Banister system, you simply determine your average heart rate during a workout, then subtract your resting heart rate from that figure to obtain a number which we can call 'A'. You then take your maximum heart rate and subtract from it your resting heart rate to get a second number, 'B'. Finally, you simply divide A by B to determine the relative intensity of your workout and multiply the result by the length (in minutes) of your workout to obtain 'TRIMP', your 'training impulse' for the day.
For example, let's say that your max heart rate is 200 beats per minute and your resting heart rate is 50. On a particular day, you exercise for 30 minutes with an average heart rate of 150. Thus, A = (150-50) 100, and B = (200-50) 150. A/B = (100/150) 0.67, the relative intensity of the training session. Of course, TRIMP = 0.67x30 (the number of minutes in the workout) which comes to 20.
This is a logical way to determine the value of a workout: after all, the number A is simply a measure of how far you climb above your resting heart rate during a workout, while B is an assessment of how far above the resting rate you could go if your workout were truly maximal. That means that dividing A by B automatically calculates the intensity of your workout - how close you are to working maximally during your effort.
If A and B are identical, it means that you were at maximal heart rate throughout your session and have worked as hard as you possibly could. On the other hand, if you barely climb above resting heart rate during your training session, A will be a very small number, and the workout will have a low value (TRIMP) - unless, of course, you train for many hours. Multiplying A/B by the number of minutes in your workout simply allows you to reckon the overall impact of the session - and to compare one workout with another. For example, using the above figures (max heart rate of 200 and resting rate of 50) 23 minutes of exercise with a heart rate of 180 would have the same TRIMP as 30 minutes at a heart rate of 150.

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