Darell has a home gym that his older brother set up. Nobody has used the gym for a few years but Darell has decided to give weight lifting a try. He talks to his gym teacher, who shows him proper form for the exercises and does performance testing. Together they design a starter program that includes a warm-up, stretching, and some basic weight-lifting exercises, followed by a time of stretching. On the first day of his routine, Darell is injured. What is the most likely cause of his injury?\