Let's face it: Most of us define the limits of endurance running performance in terms of the ability to transport and utilize oxygen.

We speak of expanding the heart as a result of endurance training-so that it can send more oxygen to the leg muscles. We talk about enriching capillary beds around muscle fibers-so that muscle cells can greedily devour more oxygen. We note that one goal of training is to build up higher concentrations of "aerobic enzymes" in our muscles- and higher densities of mitochondroa, the little structures which permit oxygen-dependent energy creation to proceed. And we orate about VO2max (the maximal-possible rate of oxygen consumption), vVO2max (the minimal running velocity which elicits VO2max), TlimvVO2max (the duration of time that vVO2max can actually be sustained), and even running economy (the oxygen "cost" of running at a specific speed), saying that these oxygen-related variables are critical predictors of running success.

This kind of thinking dates all the way back to 1923, when noted physiologists A.V. Hill and H. Lupton published a paper which contended that "hypoxia" (low oxygen levels) in muscles during strenuous exertion produced fatigue and therefore limited exercise performance (1). This "oxygen-limitation paradigm" for explaining fatigue and endurance performance seemed to be verified in later research. For example, a variety of studies completely in the 1970s suggested that VO2max was responsible for setting the upper limit for endurance performance (2, 3, & 4).

One small problem for the paradigm popped up when researchers noted that athletes with identical values for VO2max could have quite-different performances! These variations in competitive times were postulated to result from differences in economy between runners (5 & 6). Here's how that kind of situation might work: Let's say that VO2max is 70 ml.kg-1.min-1 for both Runner A and Runner B, but when A cruises along at 4:40 per mile pace he is using all 70 of those mls (per kilogram per minute), while at 4:40 Runner B is utilizing just 63 ml.kg-1.min-1 (he is more economical). You can see that B would win any race conducted at 4:40 tempo (the speed is easier for him-it is a smaller fraction of VO2max). The same could be said for any race involving a pace slower than 4:40 (it would be significantly easier for Runner B). At faster-than-4:40 velocity, A would immediately be above VO2max and would begin to really struggle, while B would still have "room to maneuver" before VO2max was actually attained. A would be a decent runner, but B would be taking home the cash prizes.

Of course, no one bothered to examine closely the performance differences which still existed between runners with the same running economy and VO2max values, but the bottom line was that it seemed fully possible to explain performance differences in terms of oxygen utilization, even in cases when there were no differences in VO2max between runners. If VO2max was not the performance determinant, then oxygen utilization (economy) would fill the bill. Ultimately, a "consensus" emerged that VO2max and running economy were the major variables which determined endurance racing ability (7 & 8). To find out more information about training, BUY NOW To start a subscription to Running Research News.

At this time of year, marathon runners are looking for the perfect "tune-up" workouts for their marathons - sessions which spike fitness and increase the likelihood that an up-coming marathon can be completed at goal speed. 5-K runners, on the other hand, are searching for sessions which will produce one last 5-K PR before the season ends.

Strangely enough, both groups of runners can employ the same kind of training - in the form of VP workouts. Performed properly, VP (variable-pace) sessions produce major up-swings in aerobic capacity, vVo2max, and lactate threshold, all of which are important for 5-K and marathon success. VP training also enhances running economy at both 5-K and marathon speeds, making goal pace for either race more sustainable.

VP running is very similar to traditional interval training, but it differs from classic interval work in a fundamental way: When you conduct intervals, you ordinarily alternate between a high-quality velocity (your work-interval speed) and a rather-low-quality pace (your recovery, jogging speed). In VP training, you interchange two very important, high-quality running speeds during the course of your workout.

How is a VP workout actually constructed? Here's a perfect example of this unique form of training:

Carry out a thorough warm-up which fires up your cardiovascular and neuromuscular systems. Then, run 400 meters at your current (or reasonable-goal) 5-K pace and - without stopping for recovery - run 400 meters at your current, goal, or estimated marathon pace. Once you have completed the marathon - pace 400, return - without a break - to 5-K pace for another 400 meters. Finally, scamper through a fourth 400 - back at marathon tempo again. To summarize, you will have run four 400s in succession (1600 meters total) no recovery at all; the first and third 400s will have been at 5-K speed and the second and fourth at marathon pace. Jog lightly for three to four minutes to recover.

To learn more about VP training (the full article can be read by purchasing Vol.21 Issue 5) and many more running/marathon related topics.

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