When Kelly Anderson shed her arm cast two months after a wrist operation, her joints were so stiff she couldn’t turn a doorknob. She didn’t fully recover for another four months. Daniel Amante suffered similar post-cast complications after he injured his knee; Amanda Harton watched her soccer teammates struggle following various injuries; and Clara Tran saw even greater suffering among the frail patients in the nursing home where she volunteered. By the time the four met as undergrads at the University of Virginia, they all recognized a common medical dilemma: Long periods of immobilization he...