The hip flexors are a group of muscles that help you bend your hips and knees. It’s fairly common for these muscles to get short and tight if you spend a lot of time sitting, running, or biking. To loosen your hip flexors, make sure to stand up and move frequently throughout the day. You can also incorporate hip opening stretches and yoga poses like Bridge Pose, Pigeon Pose, Butterfly Pose, Crescent Lunge, and Runner’s Lunge.