Monday, November 9, 2009

the limiting factor

Disclaimer: Parts of this post are well-supported by empirical evidence and other parts I'd call "reasonable conclusions". But I make no claims regarding the science behind any of it.

We got started shortly after Mayor Bloomberg's short speech in which he referred to the race as: The World's Greatest Sporting Event. I immediately thought of how the BAA has labeled Boston -- which is already close to filling up for 2010, by the way -- as the "most prestigious annual marathon" and the "premier distance race in the world". I suppose all three titles could be correct. It's a fun discussion anyway.

Mile one was a crawl (7:30) but I was okay with it for several reasons: First, well, it would've been terribly dumb to panic after mile one of a marathon. Second, it's the hardest part of the course -- up and over the Verrazano-Narrows. Third, as with any big field, we were packed tight and there was jostling and bottlenecks. Finally, I estimated that it had taken me 20-30 seconds to reach the starting line and that my split was closer to 7:00 flat (more on that later).

Assuming I did a 7:00, therefore, I figured I'd run the next six at a 6:25 pace to make up the time, and then I could settle into my 6:30 overall goal pace. This worked beautifully, and I felt great. There were several rather windy spots, and more concrete than I was comfortable with, but when are marathons ever ideal? Onward.

The next eight miles (8 - 15) were what has become my typical mid-marathon frustration: I feel strong and relaxed and the 6:30 pace feels sort of silly. All I want to do is pick up the pace and blow through the next five miles -- but I can't. Because it's a marathon. And I have to be "strategic" and "mentally tough" which simply means: Running considerably slower than how I like to run.

Mile 16: The Queensboro Bridge -- a decent climb, very windy, and lots of concrete, so I consciously dialed it down a little. I was also toying with the idea of stopping for a pee break but eventually decided against it. The course then turns right and heads downhill for a bit so I picked it up for 17 & 18 (roughly 6:20s) and then settled back to 6:30s for 19 & 20. As I ran past the clock at the end of mile 20, it read 2:10:30, and I thought: Perfect! If it took me 20-30 seconds to reach the starting line, then I was at most ten seconds below my target time of 2:10:00 for the first twenty.

In other words, after 20 miles I was well-positioned for a 2:50 finish. And the rest of this post is my explanation as to why I averaged 7:25 per mile over the final 6.2...

When muscles contract they do not use all of their fibers to actually do the work. In fact, many training guides and fitness studies claim that during sustained running, the percentage of activated motor units out of the total available pool is generally under 30%. Furthermore, the "active" pool continuously changes during extended activity. In other words, the motor units are sort of like hockey players coming in and out of the game as they cycle between tired and rested states.

At the same time, not all muscle fibers are created equal. One way of categorizing them is as "slow twitch" (good at sustained aerobic activity) and "fast twitch" (good at short, anaerobic bursts of power). It's actually more complicated than that but the slow and fast twitch categories are probably sufficient for this discussion.

The situation becomes more interesting as some motor units go beyond being just "tired"; during activities like the marathon, many of the muscle fibers suffer damage -- the cell membranes actually rupture. And these crippled motor units are no longer part of the total available pool. In the hockey metaphor, those players have been knocked out of the game. They aren't on the ice, and they aren't even resting on the bench. They are injured and the coach can't use them for a line change.

Now, running a 6:30 mile obviously places more of a demand on the fast twitch fibers than running a 7:25 mile does, although both require a blend of both types. Similarly, a 5:30 mile puts even more of a demand on fast twitch fibers than a 6:30 mile does. My theory is that during the race I basically discovered the weakest part of my lower body in terms of the fast twitch fiber pool: My calf muscles. Not my quads, glutes, hamstrings, tibialis anterior (near the shin), or hip flexors -- which are all important -- but my calves. In other words, I believe that through cellular damage, I reduced the total available pool of fast twitch motor units to the point where I no longer had the explosive power needed to run faster than a 7:25 mile.

This isn't a cramp in the traditional sense although that is what I originally called it. When I did try to accelerate into the 6:30 - 7:00 range, all of the muscles in my legs responded -- except for my calves. What they did was spasm uncontrollably and feel as if they were going to seize up permanently. As soon as I slowed down, the sensation rapidly went away. And it's not like my calves weren't able to do any work at all; I was able to finish the race at a 7:30 pace and even walk for 2+ miles afterwards (which requires at least a small contribution from the calf muscles). So I still had a decent pool of slow twitch motor units available and a minimal amount of fast twitch as well. But whenever I tried to accelerate towards 6:30 in the last six miles, I was effectively asking my calves to perform at an intensity that the remaining fast twitch motor unit pool could not support.

The sensation also isn't fatigue in the traditional sense. At least not how I think of it. I became very familiar with old-fashioned fatigue in the 2001 Toronto Marathon. In the last four miles of that race I was completely spent. I wasn't in pain, I didn't have cramps, and my leg muscles weren't refusing to work past any particular intensity. I was just thoroughly exhausted and wanted nothing more than to stop running. Every step was a chore. At no point during NYC did I feel an overwhelming urge to stop. In fact, I really really wanted to run faster and continually tried to do so.

How should I fix this? I have two basic ideas, both of which (of course) seem absurdly obvious in hindsight. First, lose as much weight as possible without adversely affecting my overall fitness. Let's say, for example, that I went into NYC weighing 143 lbs instead of my current 148. Carrying even five extra pounds over 26 miles surely represents a considerable amount of non-essential motor unit activation, a portion of which leads to cell rupture and therefore premature removal from the game. Without that weight my calves would have been able to sustain a 6:30 pace for a longer duration, all other things being equal. I can easily increase my training volume, but unfortunately losing 5 - 10 lbs probably entails eliminating some of the junk that I like to eat. That's sort of a bummer because, as a distance runner, I always viewed eating anything in sight as an irrevocable boon.

Second, increase the pool of fast-twitch motor units in my calves, and, if possible, reduce the amount of motor output required by my calves at any given speed. This means: Make my calves stronger and make my stride more efficient. My remedy here is to add short hill sprints and one-legged jumping to my training cycle. In the latter, you stand on one foot and continuously jump onto and down from a curb or a low step for 30 seconds, never letting your "up" foot touch the ground.

To summarize: Eat better, run more, and get stronger. Simple, right? Right. Anyway, thanks for reading!