Ankling, does it matter?

Triathlon Forum
21

I’ve just thought of a much simpler way to address this exercise limiting problem…when exercising at, let’s say, an intensity of 60% of your maximum heart-rate…why do you think your performance drops off after a period of time?

It’s not due to inadequate cardiovascular function…your heart will beat at 60% of it’s maximum heart rate for a LONG, LONG time…I’m talking about days to weeks when I say a LONG, LONG time. And, your lungs will dutifully allow the exchange of respiratory gases for a LONG, LONG time at this heart rate. Even if you were to allow for some heart muscle fatigue or decrease in vascular volume resulting in a ventricular stroke volume that decreases somewhat, requiring a slightly higher heart rate (and the heart can beat at higher than 60% maximum for a LONG, LONG time) in order to maintain the original cardiac output (stroke volume times heart rate), your performance will still decrease over time.

It is the LOCAL muscle tissue conditions that are responsible for the decreased performance, not a decrease in cardiac output.

Remember, we are talking about trained athletes here. In untrained persons, without developed and conditioned cardiovascular systems, local muscle conditions are what shut performance down so quickly, because these people surely aren’t able to exercise at levels demanding high cardiac output.

If you still don’t believe this…do the following simple experiment. Take a 5 lb. weight, fix your arm in a manner that isolates your bicep muscle, and begin to lift that weight 40 times a minute. Your heartrate will increase somewhat. Surely you will realize that your cardiovascular system is equipped to operate at a level that provides all the energy needed to do this task for a LONG, LONG time. However, your biceps muscle WILL tire out fairly soon. WHY? Local muscle tissue conditions. Not because of an inadequate cardiovascular function.

22

Yaqui,

I thought your explanation of efficiency was wonderful. You are right. limitations on performance are always local (at least, in the healthy). And, the limitation is almost always capillary bed density. Your frog experiment shows this. Even pushing twice the blood through the same capillaries, all the nutrient transport from the capillaries to the cell/mitochondria is done by diffusion. The rate of delivery is determined by the gradient and the distance. The gradient can never be greater than the level of nutrients in the blood as the level of that nutrient in the cell cannot be lower than zero. Actually, it must be less than this because there must always be a level in the cell for the cell to function. The more the cell needs to function, the higher that level must be. So, under high stress the gradient is going to be lower. But, the distance is fixed, except when we train and cause more capillaries to devleop. a muscle with twice the capillary density should have about half the diffusion distance to the furthest cell and so be able to sustain about twice the level of activity. This is the reason we train.

If you were to do the frog experiment but compare frog muscles that had come from aerobically trained frogs from those who had lived a sedentary life (Kobe frogs?) one would find the active muscle performed better than the inactive one at similar blood flow.

Frank

23

“those who live sedentary life (Kobe Frogs?)”

Ha ha. I love it.