Decoupling and Metabolic Efficiency

The 2010 race season is all but over, the holidays will soon find us neglecting our bike and diet, and the 2011 race season will be here before we know it (I can't believe my first race is less than 4 months away).  We have been blessed with some good weather and our rides have been more about hanging out with friends and enjoying the outdoors than they have been about "training".  But the truth is, every ride should have specific objectives.

In order to help you understand what those objectives should be I want to introduce you to two concepts for base training: decoupling and metabolic efficiency.

We have all been taught that base miles are LSD (long, slow/steady, distance) in Zone 2 heart rate designed to build aerobic endurance.  Joe Friel introduces us to the concept of Decoupling in this excellent post about the aerobic base ride.  To summarize the concept, imagine a chart where you graph a straight horizontal line that represents your hear rate in Zone 2 over time.  If you graphed power output on this same chart your power output would, over time, start to drop off while maintaining the same heart rate.  The goal of the aerobic base ride is to build your aerobic endurance or, more specifically, increase the amount of time/distance before your power output begins to "decouple" from your heart rate.

The second concept  I would like to introduce to you is Metabolic Efficiency.  We have all heard of the term "fat burning zone".  The idea is that you workout at a pace that burns more fat from our bodies.  We are burning calories all the time, but the amount of effort that we are exerting determines if our body consumes those calories from fat or from glycogen stores.  I will spare you some of the science behind this, but as intensity increases there become a crossover point when we go from using a higher percentage of fat than glycogen for these calories to getting a majority of these calories from glycogen.  The problem is that there is a limited amount of glycogen stored in our bodies and burning it also has some negative byproducts (lactic acid for instance).  This means that once our efforts exceed this crossover point, we have a limited amount of time before our bodies tell us to start slowing down.  One goal of base training is to help push that crossover point to higher levels of effort.  In other words, improving our Metabolic Efficiency.  This is done through a combination of proper training and, more importantly, proper nutrition.  If you want to learn more about this concept, I recommend this article on Metabolic Training for Athletes and this article by the same author.

Hopefully this will give you something to think about during those long, cold, dark, but fun training rides this winter.