The Engine & The Chassis

Fitness gains from running come in two types: cardiovascular and musculoskeletal.

You get fitter from a cardiovascular standpoint because running stimulates your body to make more red blood cells, capillaries, more & bigger mitochondria (the parts of your cells that actually produce usable energy from sugar & oxygen), pump your blood more forcefully, take in more oxygen more quickly, store more glycogen, etc. etc. etc.

From a musculoskeletal standpoint, running stimulates your body to grow more & tougher muscle fibers, tougher bones & connective tissue, stronger stabilizer muscles, etc.

The best analogy I ever heard for the development of these two systems in runners has to do with cars: Just like a vehicle, you have an engine (your cardiovascular system) and a chassis (your musculoskeletal system). To run your best, you need both in good working order.

A brand-new runner who has not been keeping strong & fit in other ways is (excuse the cruelty of the analogy, it's really not meant to be cruel) like an old, well-worn clunker -- neither the engine NOR the chassis are all that reliable. You can probably get around in it okay, but not very far, and not very fast. Unlike an old clunker, though, a not-very-fit new runner has the advantage that the more s/he drives that clunker around, the less clunky it gets. Both the engine and chassis will become better and better, and over time s/he can drive both farther and faster.

The trouble for many new runners is that the two don't develop at the same rate. It turns out that the cardiovascular system far, FAR outpaces the physical tissue in terms of how much it can handle how soon. This is a big part of why it's so common for new runners to end up overdoing it & getting hurt after a few months of steady improvement. The cardiovascular system feels great -- look how much farther s/he can run! And how much faster! And it felt AWESOME! Clearly s/he is ready for more of both.

This is kind of like putting a Ferrarri engine into a 20 year old station wagon & taking it to a racetrack. (Kind of an exaggeration, but you get the point.) It might be alright for a few laps, but sooner or later you know that something bad is probably going to happen.

I think even experienced runners are susceptible to this after some time off. The cardio gets back to reasonably okay after a few weeks, but the muscles/bones/tendons/etc. lag behind a little. I've done it. Lately I have gone to quite a lot of trouble to ensure that my chassis stays in good working order, so I wouldn't say I'm in that boat right now. But during my easy eight miles on Thursday I could definitely tell it was kind of tired--tired from yoga, from Pilates, from extra karate practice, from running ten days in a row (I usually top out at six, and the average is probably more like four).

Meanwhile, my cardio system was rocketing along & behaving kind of like that one friend we all have, bless her heart, that has to be the center of attention at every occasion and is forever abusing the caps lock. "Oh, this pace feels so EASY, don't YOU think it's easy?? I could keep going like this FOREVER OMG it feels soooOOooo GREAT!!!!!! I TOTALLY {heart} this run!!!! {heart} {heart} {heart}"

& the chassis's over there in the corner, making gagging motions & rolling her eyes & really just trying to enjoy a beer in peace. "Yeah, we got it, cupcake. You're freaking awesome."

But even rolling her eyes at the diva-esque engine a little, the chassis totally kept up, chugging up & down hills like they weren't there & keeping everything balanced & aligned & completely ache-and-pain free. I tried to rein the cardio system in somewhat, especially knowing I had a marathon pace run the next day, which was hard but got a breathless thank you from the musculoskeletal stuff.

So yeah. I think I probably should've taken this one a little slower, not because of my fitness level but just because I've been asking so much of my body lately. It takes a lot to wear out your cardiovascular system; it takes a lot less for the bones & muscles. On the other hand, it is a very good feeling to take an eight-mile easy run at only a minute slower than half marathon pace & believe that if my legs were fresh it would've been a complete and total cake walk.

For that reason, I'm starting to get really psyched about Hellyer 10K next Saturday. I'm not planning on tapering much, but I will probably skip my extra strength work in hopes of finding a *little* extra pep in the legs. I haven't run a short speedy race in nearly seven months so it is definitely time. Huzzah for racing!!