An attempt to run a marathon using SCIENCE - part II (Interval training)

Long run, week 1/13 of the countdown. A very decent start!

PART II: Interval training

On the first Friday after Christmas 2012, I drove out to a soggy field in north Bristol, parked my car and trudged across the grass to a pavilion in search of a bunch of wiry, lycra-clad people. I located them immediately, tried to look as if I knew what I was doing and went for quick bound around to assess the mud situation. It was a bog and I didn't have any spikes, but I couldn't possibly be seen to be backing out. I went back to the pavilion and watched in trepidation as Bristol & West AC coaches trudged back and forth positioning small red cones around the perimeter, blocking off areas where the ground had gone to mush. Ten minutes later I was sliding my way around the mile-long, makeshift running track in a pair of completely grip-less trainers, doing my best to hang onto the back of the "slow" group. This insanity was repeated three times, allowing only a couple of minutes for recovery between miles, at a rapidly deteriorating pace (on my part, anyway).

This particular brand of torture is called high intensity interval training or HIIT for short. Actually, most of the training sessions I've been to so far have taken place in far less slidy surroundings - at an athletics track - but all of them have been variations on the same theme: pain. I jest! Well, not really. Other variations include: sets of 400m and 800m separated by single slow laps; pyramids of 300m, 400m, 500m, 600m, 500m, 400m, 300m; and a 5k "steady" (actually quite fast) run followed by 200m repetitions. Oh, you get to enjoy it, honest.

I was lured into HIIT by the suggestion that it would improve my endurance running over longer distances and since, as discussed, I have 26 miles to cover in April, it seemed like a good idea. Well, I have to report that it seems to be working. Just since the start of December I've taken around a minute off my 5k time and yesterday I ran to half marathon distance a minute quicker than I ever have before... and carried on running for another 9k! (See pace graph above, more on data geekery to come in another post). Get in! But of course, plenty of other factors could be contributing to these gains. So I've been doing a bit of background research on HIIT to see what SCIENCE says about all this.

It turns out the benefits are actually fairly well documented. There are an awful lot of papers out there on this subject and I won't pretend to have read them all, but there are two things I've tried to find out. First, what changes is HIIT making to the way my body works when I run? And secondly, will HIIT actually help me run faster over longer distances?

I'll start by answering the second question, because it's fairly easy to say whether or not something is having an effect, whereas it can be a little bit more difficult to say why. Most of the papers I looked at focused on elite athletes and they showed that, yes, HIIT can help them improve their performance. One small study, for example, focused on endurance runners who were asked to swap their 45km a week training schedule for HIIT sessions involving repetitions of 30-second sprints. After four weeks, they had maintained their 10k times, without regularly running that far. The effect seems to extend to other endurance sports as well, including cycling - a couple of HIIT sessions involving 8 x 5min a week actually improved performance over 40km time trials. While many of these studies are small, there are scores of them, all using different HIIT schedules and trying to work out the optimal combination of high and lower intensity training for improving performance.

With most of these studies we're talking Olympic level athletes. One review suggested elite athletes could expect to see improvements of between 2-4% in intense exercise performance. I haven't found as many studies to tell me whether I, as a lowly recreational/club runner, can expect to make the same gains.  But I think it's fair to say that HIIT could help me run faster, with one possible caveat: I can't just do a few fast laps of a track two or three times a week. Although it may be possible to maintain performance over a few weeks by replacing all of my 5-30k runs with HIIT, the general feeling seems to be that to get the best result, I have to do both.

To deal with the first question and why this works, I found a paper entitled 'Endurance exercise performance: the physiology of champions'. So again we're looking at elite athletes, but assuming we're all built in a similar way, there are a few things you want to improve to get better at long distance running. I'll just look at a couple that seem to crop up constantly in the literature. The first is the amount of oxygen your body can use in a given time, known as VO2 max. This depends on processes in your mucles and (or including) your heart - most importantly, perhaps, how much blood your heart can pump with each beat, or what's known as stroke volume. The second thing you want to improve is your lactate threshold: the point at which your body stops operating under normal aerobic metabolism and turns to anaerobic metabolism. Essentially, it stops using oxygen to send energy or ATP to your muscles and starts makes ATP without it, producing hydrogen and lactic acid and causing you enough pain to stop you in your tracks. (Interestingly, it may actually be the hydrogen and not the lactic acid that causes the "burn").

So the crucial question is: does HIIT increase your body's ability to do these two things? Well, here's one study that suggests that it does. What's particularly encouraging is that the people involved in this study weren't elite athletes; they were "recreationally active" types, people who maybe jogged or cycled two or three times a week - normal people! (What's surprising is that as part of their study, the researchers seem to have taken muscle biospies from their victi... er, participants' legs and then asked them to cycle to exhaustion. Presumably this didn't all take place in as quick succession as the paper suggests?) The main result was that these people improved their metabolic capabilities over a six weeking training programme - their abilities to use sugar and fat as fuel. Another study does the crucial comparison between HIIT and moderate exercise and comes up in favour of HIIT for the first factor we looked at, VO2 max.

Again, these studies were small, but given the wider breadth of research in this field in general, I'm pretty confident I should be seeing some benefit. The other interesting aspect is it seems that experts are now starting to look at HIIT training for people with underlying health problems such as heart disease. These sessions are pretty hard going, so I'd be surprised if a doctor was to prescribe a course of HIIT with the local athletics club for someone with heart problems, but I can see why the idea appeals - it appears to be less work for greater benefit. For healthy, slightly more serious runners though, reviews on the subject seem to suggest that incorporating some HIIT into your training schedule can help you improve your times while cutting down on some of those long distances. But importantly, I wouldn't presume to go into a 26 mile race without having run at least 23-24 miles in training.

So that was part II. It gives me some idea why my times may have improved over 5-10k in the last few weeks. But I think my surprise half-marathon PB yesterday during a 30k run was down to something else: finally conquering 'The Wall'. It's taken me longer than it should have to realise that my body simply stops functioning after about two hours of hard exercise. So when I went for my Sunday long run yesterday, I took what was basically a utility belt full of fuel in the form of energy gels and beans, and carried a bottle full of sticky, sugary squash. Part III is going to be all about fuel.