Picture a power outlet that gets loose over time: the plug still goes in, but the contact is poor, and the appliance works intermittently. The connection between a nerve and a muscle is built much the same way. It is the place where the nerve delivers the command to contract. With age this contact wears out, and the muscle weakens even if it hasn't shrunk. Until recently, the only way to check the state of these contacts was through a piece of muscle, which is difficult and unpleasant.
Now scientists have found a simpler way. When the nerve-muscle contact is remodeled, fragments of the protein that holds it together get into the blood. The more destruction, the more fragments. The study involved 136 men aged 20 to 92. Each had blood drawn and the level of these fragments measured, and their leg strength and walking speed were also tested.
It turned out that the older the man, the more fragments in the blood. Those who exercised regularly had fewer fragments, especially after age 70. And most importantly: the more fragments, the weaker the legs and the worse the person handled simple movements, such as getting up from a chair or walking fast. So a simple blood test can reveal how the nerve-muscle connection is aging. This will help doctors spot the problem in time and suggest exercises to support the muscles.
CAF levels in physically active 70-year-old men were comparable to those in inactive 50-year-old men, vividly demonstrating the "rejuvenating" effect of movement on neuromuscular synapses.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.