Primarily, risk of injury can be reduced with nutrition - fueling your body with the right vitamins, minerals and other such essential elements will strengthen the immune system as well as both internal / external organs.

However, along with good nutrition, good exercise will also improve your circulation, strengthen the muscles, and build bone density / strength. All of these factors will reduce the possibility of contracting coronary heart disease, stop (or slow down) the onset of osteoarthritis - a condition caused by wear and tear that causes inflamation of the joint.

Stronger muscles help to support the skeleton in good postural positions which in turn reduces wear and tear on parts not designed to support loads. It can also reduce postural issues that can occur later in life where posture has been poor for long periods of time.

Another benefit to stronger muscles is that injuries tend to be less severe with stronger muscles than with weaker ones - stronger muscles are able to take a greater level of impact than weaker ones before they tear or break.