Sprinting for Endurance
Can sprinting improve your aerobic conditioning? Absolutely. Although not exactly common knowledge, in-the-know endurance athletes have been enjoying the benefits of sprint training as a substitute for some of their distance work. And you'll find that sprint work is part of the foundational training of a growing number of champion endurance athletes, especially those following the Crossfit Endurance program.
But is there any scientific foundation for the use of sprints to improve endurance? Again, absolutely. In 1993, scientists studied the percentage of energy pathway contributions during repeated maximal effort sprints. They theorized that although your phosphagen pathway might be responsible for a huge energy contribution on the first sprint, by the later sprints it would seem plausible that other pathways were making increasingly greater contributions. To briefly review: the phosphagen pathway is the responsible for quick, explosive strength over the first few seconds of a movement, while the glycolytic pathway contributes to the next couple of minutes worth of energy, and finally the oxidative pathway takes over for events lasting anywhere from several minutes to several hours.
But what about repeated sprint efforts? Would we see an increasingly greater contribution from the glycolytic pathway, even though the amount of work performed is a short sprint, firmly in the phosphagen's domain?
To test this theory, a group of subjects were tasked with six seconds of sprinting followed by 30 seconds of rest, for ten repeated efforts (a 1:5 work ratio). Any athlete who's run a set of suicides or repeated sprint intervals will attest to the fact that oxygen consumption clearly increases between the first and last sprint - which intuitively means that the body must be shifting from the use of one energy system (anaerobic) to another (aerobic). If we consider the types of conditioning work done at all levels of sport, we find that repeated sprints are a staple of every coach from Pee-wee Football to professional rugby, and every level and sport in between.
This effect can be seen with traditional weight training as well, when we use shorter rest periods between sets, leading to increased oxygen consumption (breathing heavier) and a stress on our oxidative (aerobic) system. So although it's uncommon to think of sprints as a form of aerobic conditioning, there are numerous practical examples of them being used as such.
So what happened between the first and tenth sprint?
What the researchers found was that there was a significantly reduced contribution from the anaerobic energy pathway on the final sprint as compared to the first one. Although they didn't measure the exact contributions of every energy pathway independently, they produced enough data to imply that as the sprinting session progressed, there was a trend towards a decrease in the phosphagen and glycolytic pathways, signifying a likely increase in the percentage of energy being derived from oxidative metabolism.
This data can't be interpreted as a good reason for endurance athletes to ditch all of their long efforts and focus on sprinting instead, but it does give those athletes a good reason to start working in some sprints to their routine.
You'll also note that these charts are given as percentages, not absolute values; although one may talk about "shifting" from one energy contributor to another, the analogy of shifting gears is not apt. We don't shift energy pathways like a car shifting from first (phosphagen) to second (glycolytic); either completely in one gear or another. Instead, the human body is constantly altering the ratio between one energy system to another, and sometimes back, in a fluid series of shifting contributions. So if you're looking to get some of the benefits of aerobic training without putting in endless miles on the road, maybe a set of 10 x 6s sprints is the workout you've been looking for. http://www.vpxsports.com/onlinearticles/default.aspx?unabletolocate=sprinting%20for%20endurance?ref=nf