Four years ago Zac Vawter was in a motorcycle collision that severely injured his right leg. He underwent an amputation at the knee, thereby becoming one of the more than one million amputees living in the U.S. Over half of the amputations in the U.S. are due to vascular disease – poor circulation caused by diabetes, smoking, and high cholesterol. Just under half are due to trauma. Modern leg prostheses that replace both the knee and ankle joint use motors that power each joint and multip...

Testosterone is one of the most over-prescribed and poorly understood medications. It is prescribed to millions of men for myriad indications, many of them unproven. Athletes believe it will improve their muscle mass and strength. Older men look to it as an anti-aging remedy. Men with flagging libido hope it will restore their sex drive. Testosterone has developed a mythology of masculinity. This is very similar to the notions we had a generation ago about estrogen being a fountain of femini...