Another day, another “study” in the news. Apparently they claim to have found significant evidence that (note: significant in science-land means “probably not due to chance”, it does not mean “really good” or “a large amount”) the hours a day we’re sedentary matters more than how active we are.
Consider a web developer who bikes to work and does aerobics a couple times a week. She’s easily getting 5 or more hours of activity a week; which is fantastic. But she’s also sedentary, sitting mostly still in front of one screen or another (work computer, living room display, car, smartphone), easily over 100 hours a week. Less than a couple hours of exercise a week is probably more typical. I don’t think it’s unreasonable to claim that 1 hour of activity for every 50 hours of being sedentary is just not going to be sufficient to avoid a loss of mobility over time.
But strength training dramatically changes the context. 2 hours of effective progressive-overload weight-training a week delivers a potent signal to the body to grow stronger. Growing stronger is not only about muscle. The central nervous system and cardiovascular system must adapt to support your skeleton & muscle moving heavier and heavier weight around. Of course running 5-10km a day will do this as well, but ain’t nobody got time for that!
It doesn’t matter if you’re 80 years old or 8 years old. If you don’t have a medical condition that prevents you from heavy weight training, and you have control of your arms and legs, you should be lifting weights. Not for muscle now, but to give yourself the best possible chance to remain fully mobile as you age, with the shortest possible weekly time requirement.