We’ve made several timelines on the adaptive-response that follows intense exercise ranging from: 2-3 months it takes to “get in shape” to the the 12 hours it takes to cement muscle-memory in the brain. One topic we have not discussed is the 1-week it takes to recover-and-rebuild from an intense bout of exercise.
Interesting, it is the immune-system (not stem cells) that manage the whole repair and rebuilding process. To use a building analogy, the immune system: (1) demolishes the old building (damaged muscle) and (2) erects the steel-sub-structure (extracellular matrix). Only then do the stem-cells install plumbing, electricity and internet (new muscle). On other words, the immune-cells “build the building” while the stem-cells “make it functional.”
OVERVIEW HEALING PROCESS:
- DAYS 1-2: “soreness” = “cleaning”
During this period, damage-signals from the the muscle activate stems cells to start growing and attract immune cells to “cleanup the mess” Neutrophils and M1-macrophages are the dominant immune cells during this period and their main jobs are to (1) remove debris and damaged cells (2) help stem-cells proliferate and (3) prevent stem-cells from turning into muscle cells just yet.
- DAYS 3-5: “achy-ness” = “rebuilding” During this period M1-macrophages change into M2-macrophages which specialize in laying the foundation for new muscle. In collaboration with regulatory T-cells (Tregs) and fibroblasts, these immune-cells lay down the extracellular matrix (which new muscle will rely on for structural support) and helps all the new stem cells turn into new muscle cells.
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- Arpaia, N; et al. A Distinct Function of Regulatory T Cells in Tissue Protection Cell 2015,162, 1078.
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This work by Eugene Douglass and Chad Miller is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.