20 January 2013

An attempt to run a marathon using SCIENCE: part III (Fuel)

Hello lovelies. Well, the weather here in Bristol has thrown a spanner in the works as far as marathon training is concerned.

Friday - definitely a rest day
Perhaps fortunately, the snow has made time for resting a niggly knee/ankle/lower back and exploring "cross-training", which I now intend to cover in a future post. (Cross-training is not, apparently, using one of those boring, horrible machines in the gym - it involves doing OTHER THINGS besides running, an idea I hadn't given much thought to until this week...) I have refused to feel guilty at the sight of the odd runner bouncing down the road, mostly on account of the fact that they might easily slip over on the ice and DIE, a fate which, I think we've established, it would be best to avoid. Anyway, onwards with today's post, which is about fuel.

A couple of weeks ago, I headed out for my Sunday long run, intent on breaking the half-marathon barrier for the first time. I'm a fairly early riser and do most of my running in the mornings before breakfast, but for long runs I tend to wait until about 11am, so I can get some porridge at a reasonable hour and have time to digest it. Clearly, though, a bowl of porridge wasn't sufficient to fuel my 25km attempt, because suddenly, at just over half marathon distance - about 22km - my legs became so heavy that I couldn't carry on. I had heard about "hitting the wall" and "the bear on the back", and this felt very much like both of those things. At once.

Being about 3km from home at this point, it took me over half an hour to walk back on unsteady legs. My head was swimming and I was on the point of falling over by the time I stumbled up the stairs to our flat. It was my own stupid fault and in retrospect, I should have at least carried a phone and some extra water in case of emergency. But having run six half-marathons (more if you count those run in training) including two in the last three months, I must have got a bit complacent and thought 25km was an easily achievable target. I was also skeptical about whether "the wall" actually existed.

If I had really done my homework though, I probably could have avoided any of this happening by taking on extra fuel during my run. I spent my evenings the following week researching carbo-loading and doing cost comparisons between energy gels (I am THAT cool...). One of my prime concerns was finding something that I could take without feeling sick, which is what happened after I knocked back one of the energy gels being handed out by the stewards in the Bristol half-marathon last year. I finally plumped for SiS's GO Isotonic Gel (60ml) and, on the potentially spurious advice of a triathlete I met in Moti, some Jelly Belly sport beans.


Now, before we get into how all of this worked out the following Sunday, let me share some of the results of my research with you. I want to recommend one particular paper for those who, like me, are a) interested in the science of endurance running, and b) fans of pretty graphs. Because this one has a RAINBOW EFFECT graph in it that I really enjoyed...

The paper is published in PLOS Computational Biology and it's open access. Although it's theoretical, it provides a really decent and not-too-complicated background on metabolic needs, i.e. fuel, for endurance runners; the key thing being that it's focused on marathon running and in particular avoiding hitting the dreaded wall. While there seems to have been some debate about whether the wall exists or not, and whether it's necessary to take on carbohydrate in the form of energy gels etc, this paper takes a more nuanced approach, suggesting that the wall exists for some runners but not for others. Perhaps unsurprisingly, it depends on how fit you are and how fast you run. So while a highly trained, elite athlete may be able to maintain a quick pace for 26 miles and finish without taking on extra carbohydrate, mere mortals will have to hit the sports gels.

"Runners with large aerobic capacities and relatively large leg muscles can store enough liver and muscle glycogen to fuel marathon runs at elite-athlete paces (paces approaching those required to challenge the current world records of 2:03:59 for men and 2:15:25 for women) without exhausting physiologic carbohydrate stores; runners with smaller aerobic capacities or relatively small leg muscles must run at slower paces or refuel during the race in order to avoid ‘hitting the wall.’"
As the author indicates, it all boils down to how much fuel you can store in your liver and leg muscles, and how efficient you are at using oxygen to get energy out of it. (Tying nicely into our discussion of VO2 max in the last post). So Paula Radcliffe can presumably do both of these things pretty well. Me: not so much. I can "carbo-load" my muscles before a race by eating lots of pasta, but I won't be able to take on enough to see me to the end of a marathon - my body is just not well enough adapted. The upshot is that at some point between about 1.5 and 4.5 hours I am likely to hit "the wall" unless I consume extra carbohydrate. At least according to the rainbow coloured graph...


This basically shows that runners of varying abilities and fitness will hit the wall anywhere between 9-26 miles. So given that I hadn't made any particular effort to carbo-load that Sunday and was carrying dilute squash only, it's probably safe to say that about 13-14 miles, I hit the wall. Incidentally, if you're interested in carbo-loading, there are references in the paper to some further studies on optimal strategies.

What of the next Sunday's long run then? Well, I had myself pretty well prepped by then. I bought what I've since referred to as a "utlity belt" for the beans and strapped on a little-used arm band/pouch to carry the gel. (Actually the utility belt also has special elasticated gel holders for easy access, but on the first run out with it I was worried about the packets slipping through).

All fuelled up

Going on advice from t'internets and the packet instructions, I took the gel at about 1 hour 30 and carefully chewed on sports beans (to avoid choking... another unforeseen way to DIE during a marathon) throughout my run. Whaddya know? I got to 25km at a nice, steady 5:30/km pace and, still flying, I decided to see how far I could go - 30km (~19 miles) total! Which brings me to almost three quarter distance. I can't put this all down to the gel/beans, of course - perhaps I had eaten extra pasta the night before, I can't remember - but I'll wager they helped. I guess there were also some psychological aspects involved too - once I got to 25km I suddenly felt awesome!

But back to the science. It doesn't seem to matter too much when you take these things, as long as it's before your existing stores runs out.
"The timing and distribution of midrace fuelings evidently have little impact on their effectiveness, provided the required total amount of carbohydrate is consumed sufficiently far (typically approximately 30 minutes) in advance of the anticipated onset of fatigue."
I'm still skeptical about using these types of energy drinks and gels too frequently. I don't recognise half of the ingredients on the back of those Go gel packets, so who knows what mischief some of the them might be causing. Doug at Rock Creek Runner has experimented with natural alternatives to energy gels. Fine if you fancy chomping on almonds or thinly sliced, baked sweet potatoes during your run, but I'm not sure how well such dry foods will go down. And I'm worried about the choking... Still, if you're braver than me, you can also salt the sweet potatoes to account for the electrolytes in energy gels. (Disclaimer: I haven't done any in depth research on electrolytes, but they do include salts. Probably more useful in weather warmer than SNOW, when you're really sweating).

Whatever you use, I'd definitely recommend trying it out before a race. During the Bristol half, I was silly enough to take an energy gel I hadn't tried out beforehand, but I'll never do it again. Plenty of websites advise testing different brands to find something that works for you, especially as it seems gulping down pure carbohydrate can upset your stomach. I personally chose isotonic as opposed to hypertonic (concentrated, take with water) because I guessed that a lower concentration would be less likely to make me sick. However, this does mean having to carry a slightly larger gel packet. I also avoided those with caffeine in them - watch out as it's not always listed explicitly. There's a fairly succinct review of five of the most popular here.

That about wraps up this post. Do have a gander at that paper, and others, and let me know what you find. I might have a go at tackling muscle recovery next week, as I seem to have got it all wrong so far...

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