Wolf's Law states that when a healthy bone is under increased load, the bone will remodel itself to adapt to the increased load. This process makes the bone stronger.
This concept is important to remember for overall health, adapt to improve health. It is for this reason that you want to continuously change up your work-out. One day, do some cardio-vascular work such as walking, biking, jogging, something that gets your heart rate up. The next day, do strength work such as weightlifting. Things to do every day are work on balance and stretching. Also increase the challenge to get stronger.
Below is the definition & brief history of Wolff’s Law
Wolff's law, developed by the German anatomist and surgeon Julius Wolff (1836–1902) in the 19th century, states that bone in a healthy person or animal will adapt to the loads under which it is placed.[1] If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading.[2][3] The internal architecture of the trabeculae undergoes adaptive changes, followed by secondary changes to the external cortical portion of the bone,[4] perhaps becoming thicker as a result. The inverse is true as well: if the loading on a bone decreases, the bone will become less dense and weaker due to the lack of the stimulus required for continued remodeling.[5] This reduction in bone density (osteopenia) is known as stress shielding and can occur as a result of a hip replacement (or other prosthesis).[citation needed] The normal stress on a bone is shielded from that bone by being placed on a prosthetic implant.