There are three main physical attributes which are crucial to keep our bodies 
youthful, energetic, and strong. 

Flexibility - In order for our bodies to maintain a youthful appearance, it is necessary to maintain our ability 
to bend and flex our torso and limbs. Many of the injuries suffered in old age stem from the inability to flex 
the body through large ranges of motion. As our body becomes rigid and tight, 
our muscles begin to exert a frictional force on our joints and connective tissues.
We begin to move our limbs through smaller and smaller ranges of motion, which 
continues to exacerbate the problem. When our muscles become tight, they 
begin to lose their ability to recover from stress and strain, leading them to 
weaken and deteriorate like the fraying of an old rope.
R.O.M. (Range of Motion) -  Our ability to move our joints through their full 
range of motion is another critical factor in maintaining a youthful demeanor. As 
we age, we tend to be less involved in physical activity and therefore move our 
bodies less. As we move our joints through smaller ranges of motion, the joints
themselves begin to stiffen and lose their capacity to function to their fullest.  As the joint itself becomes stiff the body begins to look at the stiffness as injury or weakness. In an attempt to stabilize the weakened joint, the body creates tiny bits of connective tissue scaffolding, called cross-bridges. Unfortunately, those cross-bridges are not very flexible and tend to decrease the range of motion around the joint even further.
Muscular Stability - Finally, it is necessary for us to maintain
the strength and stabilizing characteristics of our muscles in
order to stay youthful energetic and strong. By stressing our
muscles they become larger and stronger as well as increasing
the stability of our joints. Through our muscular strength we
maintain the postural or structural stability of our entire body.