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  Latest update:6/26/2022

The Physiology Behind Athletic Improvement.

The pages in this section detail the effects of training on specific organ systems. The practical effect of exercise stress (intervals) on performance (increase in VO2max). If we can understand the physiology behind changes from training stress, we might find clues to other more effective ways to the same end.

Apply a physical stress to a biologic system and it adapts and improves, that's the rationale for all athletic training. With interval training, pushing an athlete's aerobic limits leads to changes in the cardiovascular system and muscle cells that mean they can push even harder the next time out.

This is a dynamic process. Changes reverse if the physical stress is removed. Luckily maintaining improvement does not require as much "stress" as the development of the increased capability in the first place. But it is true that you need to "use it or lose it". So on that business trip, or family vacation, it is worth taking the time for a short (30 to 60 minute) brisk walk that will boost your heart rate.

Exercise induced changes can be seen at three levels.

At the cell level.

At the organ level.

The heart size increases which means the amount of blood pumped per beat (the stroke volume) increases with more blood pumped per beat to the lungs and then on to the muscles.

At the organ integration level.

There are body wide changes in the vscular system. The number of capillaries per muscle fiber increases, supporting an increased delivery of oxygen (from the increased cardiac output) to individual muscle cells (which now have the mitochondrial capacity to increase ATP production.)

What is behind these chnages. How are they coordinated i.e. how do the cells and physiologic systems improve in parallel? Two possibilites are:

  1. Neurologic signals. These signals might originate at the spinal cord level or a more central cerebral level. A central governor coordinating all the systems involved in meeting increased physiologic demands is an example.

  2. Molecular signals. The traditional teaching was aerobic training stress lead to individual, cell specific improvements. An anaerobic state developed in the muscle cell which in turn led to adaptive changes in that specific cell's mitochondria to improve performance. But we now know that thousands of potential molecular signals are distributed to every cell at the same time.

    This NYT article explains how exercise changes the Metabolome - the set of metabolites (organic molecules) in a cell, tissue, organ or organism, which are involved in cellular metabolism. 9,815 - or more than half - changed after exercise. The explanation of positive training effects is almost certainly buried in this collection of 9815 organic molecules.

    How can molecules that make up the metabolome travel in the bloodstream without being degraded? They are packaged in small protected packets (vesicles) as explained in this original investigation (more easily understood in this NYT article.

    There is also evidence that the microbiome is indirectly involved. Regular aerobic training changes the microbiome. These bacteria metabolize unabsorbed food material from our diet (generally fiber) and as a byproduct of their metabolism manufacture short chain fatty acids (SCFA). The SCFA (which are absorbed from the colon) impact mitochondrial development and body wide energy metabolism.

    This article puts forth a good argument for part some of the aerobic performance being indirectly via the microbiome. Exercise --> changes in bacteria --> production of molecules that will positively influence mitochondrial metabolism and growth.

(More details on the these comments can be found on Intervals and Aging and Physical Performance pages.

All questions and suggestions are appreciated and will be answered.

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