CYCLING PERFORMANCE TIPS
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.
This reference focuses on nerve cells, but there is almost certainly a similar SIRT3 based process in mitochondria throughout the body. To quote: "Researchers ....discovered that an enzyme called SIRT3 that is located inside mitochondria may protect mice brains from loss of their energy supply (Cell Metabolism, November 19, 2015). Normal mice who ran on a spinning wheel increased their levels of SIRT3 in nerve cells, maintained brain function with aging ..... A special group of mice that were genetically engineered to be unable to produce SIRT3 gained no benefit from running on a spinning wheel..... This implies that SIRT3 strengthens brains and that blocking SIRT3 prevents exercise from benefiting brain function."
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:
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.