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I have never fully understood how this exactly works. These questions pertain to the long term effects of strength training only.

Basic Physiology of Hypertrophy (what is understood)

  • During muscle hypertrophy you’re tearing myofibrils, which are composed of stacked sarcomere’s.

  • This tearing causes the immune system to repair the damage. Proteins called cytokines are released to the damaged area.

  • The repair occurs as satellite cells differentiate into myocytes (muscle cells) which then fuse the torn myofibrils together which increases the diameter of the myofibril.


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Sources:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2785020/

The Physiological Effects of Detraining (what I DO NOT understand)

Detraining (as related to long term strength training) obviously leads to loss of muscular strength and power.

  1. At a basic physiological level, how is this occurring?

  2. Are the sarcomeres (containing myosin and actin) used as fuel by your body and expelled?

  3. After myofibrils decrease in diameter since they now contain less
    contractile proteins?

Full and Partial answers are both great -- ideally with supporting research. Thanks!

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  • I totally want to sit down with a cup of coffee and answer this! Great question, and if someone beats me to it so much the better!
    – Eric
    Oct 16, 2017 at 17:41
  • 2
    @EricKaufman would definitely appreciate it!
    – Mike-DHSc
    Oct 16, 2017 at 17:43
  • I've also been looking at this, and most of what I am finding relates to #1, and fiber type conversions + attendant muscle changes. (Such as the reduction in neovascularization, etc). I am not finding anything at the moment on the sarcomeres and myofibril effects. Interestingly, I did find some suggestions that fiber angles change which could also account for some of the attendant loss of strength.
    – JohnP ♦
    Oct 16, 2017 at 19:35
  • "Detraining (as related to long term strength training) obviously leads to loss of muscular strength and power." Yes it does. Your body adapts to what you need. Assume you deadlift 500lb and then stopped training for 3 months. Since your muscles and nervous system have not been forced to do a work, their performance deteriorates. But keep in mind that when you return training, after a few months you would be able to lift 500 lb again thanks to muscle memory.
    – PIC16F84A
    Oct 17, 2017 at 21:51
  • 3
    @Eric 'bout time for that cup of coffee, wouldn't you say? I'm very interested in reading an answer to this!
    – Cullub
    Jul 26, 2019 at 18:11

1 Answer 1

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At a basic physiological level, how is this occurring?

Every day, your body builds up and breaks down muscle. Under homeostasis, this breakdown evens out the buildup and there is no net-muscle gain. Training hard and eating properly provides the stimulus to gain more muscle than you initially had.

Once you take away the training stimulus, your body will still be building and breaking down muscle, however the breakdown will exceed the buildup, and you'll have a net-loss of muscle. This loss is faster the more nutrient-deprived you are. The loss of muscle mass seems to be mediated by an increase in protein breakdown. To cite1:

The majority of studies have inferred an increase in protein degradation through the measurement of genes associated with specific protein degradation pathways.

Note that the above discussed muscle loss is known as disuse-induced muscle atrophy1. Another form of atrophy, known as sarcopenia, which is associated with aging, is thought to have different pathophysiological aspects3:

... loss of individual muscle fibres associated with the loss of motor units, and a concomitant reduction in muscle ‘quality’ due to the infiltration of fat and other non-contractile material

Are the sarcomeres (containing myosin and actin) used as fuel by your body and expelled?

Some of it likely is, to cite2:

Skeletal muscle proteolysis can provide amino acid substrates for glucose and glycogen formation, notably glutamine and alanine. Alanine is released into circulation and reaches the liver, where it serves as an excellent substrate for gluconeogenesis.

Besides turning amino acids into glucose, the body can, among other things, reuse amino acids to build other proteins.

[1] https://pubmed.ncbi.nlm.nih.gov/23800384/
[2] https://pubmed.ncbi.nlm.nih.gov/27324808/
[3] https://link.springer.com/article/10.1007/s10522-008-9131-0

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