Reactivity is your body’s ability to respond quickly and effectively to unexpected movement, like catching yourself from tripping or adjusting your balance mid-step. It’s something most people take for granted until it’s gone.

Dr. Attia explains, “As we age, we don’t just lose our balance. We’re losing something else that people my age and certainly her age take for granted, which is called reactivity.”

He goes on to describe how this decline is connected to a specific type of muscle fiber:
“The type of muscle fiber that was necessary to do that, which if we want to get technical is called a Type 2A muscle fiber, is the type of muscle fiber that is responsible for explosive movement. Those muscle fibers start getting weaker and shrinking at about the age of 25. By the time someone’s your age, you’ve got threads of those things left.”

This loss of reactivity is one of the main reasons falls become so dangerous later in life. But here’s the good news: as Dr. Attia emphasizes, “You can train these muscle fibers, but the only way to train them is to move very heavy weights.”