Despite being a core group of muscles used when running, the hip flexors—a cluster of muscles in the front part of the hip—are a part of the body many people neglect to stretch. “Hip flexors refer to a group of muscles around the hip joint that are responsible for lifting the leg or ‘flexing’ the hip,” says Duke Hasson, MD, an orthopedic surgeon at DISC Sports & Spine Center in Newport Beach, CA. Whether you want to prevent tight hip flexors or already have them, regularly doing hip flexor exercises can help.