Sunday, February 12, 2012

What I learned from a VO2max Test

Using CardioPulmonary Exercise Testing as a training tool

I have been trying to increase my speed over the 5k-8k distances.  No matter how hard I think I can go or how hilly the course is, my pace over this distance didn’t seem to change much this season.  

I decided to look into why this could be.  After all, if I can do intervals faster than this pace, shouldn’t I be able to race at a faster pace?  This season I started doing threshold intervals that were slightly faster than my threshold intervals last season, but was unable to complete a full set of 6, usually getting tired by number 3.

I decided it was time to check if my heart, lungs and muscles were doing everything that they should be doing.

Using a ramp protocol (increasing speed by 1 mile/hr every 2 minutes), I ran on the treadmill while collecting the usual data (Heart rate, oxygen, carbon dioxide, breathing rate and volume).  While my VO2max was increased from 1.5 years ago, the real story is what happened on the way to my VO2max.

I topped out my slow twitch fibers at 8 mph.  I could theoretically keep this pace for ever, assuming I could continue fueling my body.  Beyond this point, the acid from lactic acid was affecting me.
My Anaerobic Threshold occurred at 9 mph (6:40 min/mile pace).  This is a pace I can sustain for about 5 minutes.
My VO2max occurred at 11mph and I was able to hold it for 90 seconds

What do these numbers mean?

My marathon pace would be 8mph, assuming I could remember to fuel during the marathon.
My 6:55 pace for my last few races is explained by my Anaerobic Threshold pace of 6:40.  For shorter distance races, I tend to use all of my slow twitch (type I) and some of my fast twitch fibers (type IIA) when I race.  

Starting the first two kilometers of an 8k at a 6:30 pace is definitely too fast.  I’d be much better off running just below my Anaerobic Threshold and kicking up the pace at the last half mile or so.  I now realize that my tendency is to start out too fast which leaves me struggling to recover during the middle part of a race.

To increase my Anaerobic Threshold pace, I plan on doing 6-8 intervals of 4 or 5 minutes at threshold with either 2 or 1 minutes of rest.  If I can’t maintain this pace for this time, I know that I will have to work harder on replacing my glycogen stores after a workout.

This also explains why I was failing during the second or third 4 minute interval at 11mph.  There’s no way I should be able to sustain my VO2max pace for that long, especially since I could only sustain it for 90 seconds during my test.  I had chalked it up to depleted glycogen and not eating enough during the day, however, now I know that I might actually be eating enough during the day to train after work.

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