Tuesday, February 12, 2008

Constant Effort

Why should you hold a nearly constant effort when riding or running up and down hills? It is almost axiomatic among coaches that when racing you need to hold a nearly constant effort for the entire race, up or down hills. And why is that? Is there a justification? Couldn't you simply rest on the downhills and it will all average out? Well it kinda averages out but not really, let's talk about fatigue for a moment. In triathlons there are two types of fatigue we routinely face, there are other fatigue processes but these are the ones we hit routinely.
  1. Fatigue from lactate accumulation in the muscles. When needing energy quickly, your body breaks down glycogen without oxygen and produces lactate ions. The biochemistry of lactate ions is quite complex and the understanding of it gets better every year. But what we need to know is this, elevated lactate concentration is associated with a lack of contractility in muscle, during a race if your muscle fibers get higher lactate levels in them - those fibers won't want to fire for a while.

    Lactate as a cause of fatigue is actually controversial, but lactate as a marker of fatigue is not. Not only that, but once these fibers have decided they won't contract, they will stay that way for a "long time." You can consider them pretty much done for the course of the race. For reasons not entirely clear, those muscle cells will not fire again for a while. If you rest about half of those fibers will start firing again in 20ish minutes; but of course, you aren't resting - you are riding the rest of the race.

    One way to experience this is a gross pacing error, going out WAY too hard. Just really spanking it from the get go. It's almost silly to mention it but it does happen. Going out too fast on the swim is not entirely uncommon. Also hitting your favorite sport and trying to make up time. Say you're a strong cyclist and want to pick up some time on your competitors who swam faster than you. You can easily overdo it here. Same thing with running. The more common way to encounter this type of fatigue is in small bursts, over hills. You hit it too hard over one hill and you take a subset of muscle cells out of the action for the duration. On another hill another set of cells are down for the count, the next hill your body recruits another set of them and THEY go down for the count. Then you get to the last hill and everyone is down for the count! Your legs just won't go any faster!
  2. The second type of fatigue we encounter regularly is glycogen depletion. The way this works is that your liver supplies its glycogen reserves to your bloodstream as glucose. Keeping your blood sugar up as your muscles get part of their energy supply from your blood (not all of it). Running up against this type of fatigue is much more common. It represents an error in pacing and also nutrition.
Back to the lactic acid fatigue. You might think well, I can go hard up the hill and go easy down the hill and everything will even out. Unfortunately as I mentioned earlier once your muscle cell pH gets low enough that your muscles don't want to fire any longer, it takes a long time for those muscles to be ready to fire again. Long enough that you can consider them done for the race. So every time you dig deep to get up a hill you are taking part of your muscle cells down. Depending on the length of the race, this is fine. In a 5k, possibly a sprint tri for the faster people, you might do this for tactical reasons or just to make sure you fully expend everything you have. But when the race starts getting up over 2.5 hours and even more so with longer races, it will take everything you have to keep the glycogen depletion fatigue at bay. So adding this type of fatigue to the mix is a REALLY bad idea. You already have enough problems to deal with with. Those of us here in the Baltimore area have another reason to practice the skill of keeping an even power distribution. It's that the big races, Iron and half iron races will be in territory that is flatter than what we usually ride on. Even if there are hills, the hills are longer than the 2 minutes up and 1 minute down hills we routinely ride on. I know everyone talks about how riding in the hills is hard but don't lid yourself. At all but one Ironman North America Race and at most of the half iron races in the mid atlantic, you hop on the bike, get in your aerobars, get your hr to race pace and stay there. For an iron distance you'll stay there for the next 6 hours, half iron around 3. Cycling in hills is hard but it's a different type of stress than the race situation. So to get good at it, you need to replicate race conditions as much as you can. By the same token, on the run you need a different type of strength to keep running at the same pace with the same muscles than you do in the hills. Lots of it actually mental, but that doesn't mean we don't need to practice it. So how to do it? It's pretty easy actually? Just back off on the hills. With a bike power meter it is easy as the feedback is immediate. If all you have is your hr you need to remember that your hr reflects what you were doing about 30 seconds before. So your power expenditure will have already gone up substantially by the time you start to breathe harder and you heart rate goes up on your monitor. The way to practice if you are using a heart rate monitor only is that when you hit the hill or slightly before you hit the hill you need to back down. As you start up the hill watch your hrm, it needs to stay within 2 to 3 bpm of wherever you were before you hit the hill. By the same token on thew first part of the downhill, until your legs spin out on the bike, you need to keep your effort up and keep your power right where you want it or keep your hr right where you want it. On the bike when you spin out the gears just tuck in and ride. For running you can do the same thing if running on a clear path of road, I don't recommend legging it out on downhills when running trails. The risk of an ankle sprain is too high when running fast downhill on trails. So get your intensity either in the form of hr or power under control and you'll have all your motor units ready to fire the length of your next race. Kevin

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