An athlete to you complaining of left anterior thigh pain after doing step back lunges during a weight training session. She states she did heavy squats that same day which was 2 days ago. You find increased muscle tone at mid-thigh with pain upon palpation. She has difficulty performing an air squat as well as a lunge. She cannot extend her knee against manual resistance because of pain. She has never felt this before. What is she suffering from?