HIT vs ET: A Scientific Review

Sometime late last week, my partner-in-running-crime Frayed Laces, asked me to review her latest running science report on the benefit of long endurance training vs short interval workouts in increasing aerobic capacity. Since I am a passionate runner, a medical scientist and somewhat of an Alberto Salazar to her Kara Goucher (okay the last one is a bit of a stretch, but work with me here people…) I will oblige her request and share with you all my scientific opinions on her piece.

For all who haven’t done so, please read my review on the physiologic differences of interval training, tempo workouts, and long runs because what is to follow will be somewhat of a continuation on that theme. First of all, let me start by saying that I agree with FL’s general assessment of the NY Time’s report. The physiologic benefit of HIT (high intensity training) vs ET (endurance training) is oversimplified in their review. On the protein level, the rise in PGC-1a seems rather short after HIT compared to ET. The peak levels (as she has shown) is indeed lower as well, even if the difference may not be statistically different. It is also impossible to extrapolate the changes in concentration of one protein level as the cause/effect of training as we know that it is sometimes not the quantitative effect but a qualitative effect on protein-protein interaction that affects muscle performance.

On the macroscopic level, I surmise that HIT/ET produces some qualitative differences on running economy that may be not measured in their simple rat/human experiments. As I explained in my initial review, I surmise that HIT is similar to going at max speed for a short time, while ET allows the oxygen delivery system to become more adapt at sustaining top efficiency for a much longer period. In the span of a 30-minute test or some other short-term measure, both parties can have similar benefits but if you extended the test and asked the subjects to bike/workout at equivalent time/effort to a marathon, I surmise that there would be a clear difference in their exercise physiology. (Maybe that’s why the study clearly state that they’ve never tested their hypotheses on runners…)

In the end, I think although there is clearly some crossover benefit, specificity training is clearly the best way to prepare for an event. Short distance runners should clearly concentrate their efforts on the track while marathon runners should stick to their consistent long runs. Clearly though, it helps for each to train in the other’s shoes every once in a while.

Thanks to F.L. for bringing forth this interesting topic for discussion!

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I spent the entire weekend packing and completely missed my long run. So instead of amassing 36 or 38 miles for the week, I got stuck at a pitiful 28 miles. Total suckiness. But at least I'm almost all packed up! Moving day is just 2 days away! Will provide some pictures of my new crib once it's a bit more presentable. Hope everyone had a great weekend!