Mitochondrial Dilution

Throughout my years training for races, I have tried to maintain my strength training routine in the gym. Achieving this balance has been very difficult as time spent in one area detracts from improving performance in the other. I used to run with people who avoided weight training stating that dense muscle would add speed-limiting weight to their body. Other running partners would engage in light weight training every morning to improve muscle strength. I am perpetually trying to find a balance between challenging the strength of my muscles and improve my endurance performance.

Below is an excerpt from Stephen Seiler's (PhD) website, the MAPP, dedicated to examining and explaining the physiology and training methods of the endurance athlete. In this excerpt, Seiler discussed strength training and endurance performance:

"When a bodybuilder trains, the goal is to make each muscle fiber as big as possible. Muscle fibers have contractile protein, mitochondrial protein, and other components. Increasing the relative proportion of one component (like more contractile protein) means that you have relatively less of everything else in the same fiber (like mitochondria). From an endurance standpoint this is not a good adaptation. We even give it a name in sports physiology circles, mitochondrial dilution. The bodybuilder's muscles may actually become more easily fatigued as they get bigger, because their mitochondrial density is not increasing at the same rate. The bodybuilder accepts that because the name of the game is size, not endurance.

It is possible for the endurance athlete to gain some muscle size and maintain mitochondrial density, but it requires that the volume of endurance training be maintained. If you are a runner and you decide to get stronger in the weight room by really doing a lot of strength training 3 days a week for an hour, you will probably drop some of your running volume to fit it in. After 6 months you have gained 5-10 pounds of muscle, you look really good, and you are running 2 minutes slower for 10k! Why? Well besides having to carry around 5-10 more pounds of muscle that you can't use when you are running, you have probably lost endurance capacity in those bigger stronger quads. So, you have a lower lactate threshold due to the detraining of your leg muscles, plus you are less efficient due to the increased bodyweight (and decreased training volume). The concept that just making muscles bigger and stronger will automatically translate to faster endurance performance is Wrong! "