XTC Explained

Physiology and Philosophy

While Zone 3 has become maligned by the recreational bandwagon in recent years, they call it "Zone X" to attach some negative stigma to it, running at roughly marathon pace, lactate 2.0, Sub-Tempo pace -all which translate to Zone X- has been historically one of the best ways to advance VO2, Lactate Threshold, and Running Economy. Studies from the 1970s used to predict running success by the most miles spent in this zone or an average training pace closest to this zone. Recently, elite, college, and high school coaches have moved away from voluminous anaerobic work and increased Zone X training. The ever increasingly popular "Norwegian Method" focuses on morning Zone X runs before afternoon workouts. In the base phase, these afternoon workouts are usually in Tempo "Zone T" and Zone 5 "Zone C." While this specific method was pioneered by Marius Bakken, I have used a similar format for over thirty years. While the terms Sub Lactate, Sub Threshold, and Sub Tempo have fairly recently come into vogue with elite programs to describe Zone X, the first record of it that I know of is from my own training log from December 1995. Zone X training is potentially more beneficial for non elite runners because they are more at risk of injury with HIGH intensity intervals and with generally lower mileage and fewer sessions per week, they don't need as many slow miles as runners logging over 100 miles per week in often over ten sessions per week.

The XTC Formula

The XTC Formula does not work with percentages like "80/20" which have no basis in science. XTC works because it uses the philosophy of progressive overload in distributing time spent in the three most valuable zones (3, 4, 5 - Sub tempo, Tempo, and the lightest anaerobic zone respectively) in total minutes per week. The rest of the week's mileage is easy runs and strides.
Level I for XTC is 60 total minutes a week in XTC, broken down as 40 X, 10T, 10C. For a TOP runner this will be about 10 miles a week although a top runner will probably not be at Level I. A more realistic runner will spend more like 6-8 miles in XTC, spread over 3-4 days. If someone runs only 4 days a week, all of their runs will include an XTC component. (Although not all their mileage will be XTC after warmups and warmdowns are figured in. XTC progresses to Level III for very experienced runners whose exact numbers will vary depending on the emphasis of the week but will get up to over two hours per week in XTC. This will be divided up into around 60 Minutes X, 40 Minutes T, and 20 Minutes C on a peak intensity week. Again, this is a rare example used for upper echelon runners with years of experience and who run at least 50 miles per week in 6+ sessions.

Heart Rate and Pa

XTC Zones

1 - Slow/Recovery 55-65% VO2 Max/Heart Rate Reserve/ Pace at VO2 Max
2- Easy/Comfortable 65-75% Max/Heart Rate Reserve/ Pace at VO2 Max
3 - X/Sub-Tempo 75-84% Max/Heart Rate Reserve/ Pace at VO2 Max
4 - T/Threshold 84-88% Max/Heart Rate Reserve/ Pace at VO2 Max
5- C/ Critical Pace 88-95% Max/Heart Rate Reserve/ Pace at VO2 Max

Lactate Levels and Associated Exhaustion Times

1 - Slow/Recovery 55-65% VO2 Max/Heart Rate Reserve/ Pace at VO2 Max
2- Easy/Comfortable 65-75% Max/Heart Rate Reserve/ Pace at VO2 Max
Lactate 2.0 (4 Hour Race Pace) (Start Zone X)
Lactate 2.5 (3 Hour Race Pace) (Mid Zone X)
Lactate 3.0 (2 Hour Race Pace) (Mid Zone X)
Lactate 3.5 (1 Hour Race Pace) (Start Zone T)
Lactate 4.0 (30 Minute Race Pace) (Start Zone C)

XTC Volume Per Week

X T C Total
30 20 10 60 - Level I
40 25 15 80 - Level II
50 30 20 100 - Level III
60 40 20 120 - Level IV

This is the highest level the vast majority of runners will see although there are times when very experienced runners will go higher. Also, in race specific weeks - like a marathon pace longer run, or even races, these numbers can vary. But this is the week in week out structure of XTC training. Only once Level I has achieved maximum adaptation does Level II commence in an ideal situation.