We've often been told the benefits of exercise are enormous
Case in point: I recently saw the MRI thigh scans below on Alex Hutchinson's Sweat Science blog .
Pretty remarkable is all I can say.
The pictures speak for themselves. Use your muscles or you'll lose them. The actual study  is free if you want to read it.
Preserving Muscle Mass
But a word of caution. You'll only preserve muscles that you actually use. For example, if you simply run and never do any exercise for your arms, you'll still lose muscle mass in them as this study  showed.
So make sure you exercise your entire body. If you only run or bike, add some upper body exercises to your program. Or do some swimming.
Exercise Keeps You Young, Literally
To add even more evidence, if you need it, another study  concluded that 80-year-old people who've participated in lifelong aerobic or strength training were comparable to those aged 50 to 55 years old.
The same study stated that, "Exercise has vast beneficial effects on a multitude of organs and body systems and delays aging-associated losses in:
• cognitive function,
• insulin resistance,
• certain site-specific cancers,
• depression and
And the researchers also noted that there will never be a single drug that can counter the decline in all organ systems the way exercise can.
Now stop reading and get some exercise!