Muscle loss with age is common, but much of that decline is driven by inactivity, not aging alone.
On average, we reach peak muscle mass somewhere between 20 and 30, then lose about 8% per decade after that. By the time many adults reach their 70s and 80s, they may have only 60–80% of the muscle mass they had at 30.
A big reason why is anabolic resistance. As we get older, muscle becomes less responsive to amino acids, one of the key signals for building and maintaining muscle.
This is where resistance training becomes non-negotiable. It's one of the main signals that tells muscle to grow. And just as importantly, it helps re-sensitize muscle to amino acids, so the body responds to protein more like it did when you were younger.