Flexibility

Flexibility refers to how much the soft tissues around a joint, such as muscles, tendons, and ligaments, can stretch. The key condition is that this happens 'passively.' It is about how far you can go when you let an external force, such as gravity, a partner, or a piece of equipment, move your body. Whether you can use your own muscles to move through that range is a separate ability covered by Joint mobility.

In terms of Range of motion (ROM), the angular range through which a joint moves, the value reached with an external force is passive ROM, while the value reached by moving on your own is active ROM. Greater flexibility means greater passive ROM.

Many people know from experience that regular stretching makes their bodies more flexible. It is easy to assume this happens "because the muscles get longer," but a widely accepted explanation today is somewhat different. According to Stretch tolerance theory, your sensory and nervous systems adapt so that the same stretch feels less uncomfortable.

When you stretch a muscle, sensory receptors such as muscle spindles and Golgi tendon organs send signals to the brain. The brain interprets these signals as a boundary saying 'go no further,' stopping the stretch at a certain point. Repeated stretching shifts this boundary to a greater angle, allowing the same body to stretch farther. Immediately after a stretching session, muscles and tendons also become temporarily less stiff, but they usually return to their previous stiffness within a few tens of minutes.

• Stretching — Static stretching, Dynamic stretching, and PNF stretching all increase ROM. Reports suggest that differences in the size of their effects are not large. You can choose a method you enjoy and can keep doing over time.
• Full-range-of-motion strength training — Exercises that load a joint while moving it through a wide range also help improve flexibility. Examples include deep squats and exercises that involve producing force in a lengthened position, such as Romanian deadlifts. These are a good choice when you want to build strength and flexibility together.
• Foam rolling — Studies consistently report that rolling muscles with a foam roller increases ROM in the short term. It is often used as part of preparation for exercise.

• Stretch when your body is warm. Stretching feels more comfortable after a shower or light exercise.
• Stop within a pain-free range. Hold for about 20–30 seconds at a point where you feel a stretch, and breathe comfortably.
• Try doing a little every day. Short, frequent sessions are better for building gradual changes than occasional long sessions.
• Finish with movement. Practicing using the increased range under your own control helps turn it into mobility. Strength and control need to keep pace with that increased range for comfortable movement in daily life and exercise.
• Use light movement before exercise. Immediately before exercise, Dynamic stretching is more suitable than slow, prolonged stretch holds.

Declining flexibility, which may feel like "I can't do movements that used to be easy" or "Even when I stretch, I can't go as far as I used to," refers to the tendency for both joint range of motion and the stretchability of soft tissues to decrease with age. It is not the name of a single disease, but the result of several overlapping changes, and its pace and extent vary greatly from person to person.

Commonly cited underlying factors include changes in collagen structure, reduced water content in tissues, and reduced elasticity in tendons and the capsules surrounding joints (Connective tissue aging). Reduced activity also plays a part. When there are fewer opportunities to move joints through a wide range, you use that range less, which makes your body feel stiffer.

However, the stretch tolerance perspective discussed earlier applies here as well. A reduced range of motion may not mean that the muscles have physically shortened. When stretching restores some of that range, sensory changes that make the same stretch feel less threatening also play a large role. This is why many people regain flexibility through regular movement and stretching even as they get older. Making a habit of using a wide range of movement in daily life helps. Being able to comfortably perform movements such as putting on socks, reaching for a high shelf, and getting up from the floor is a good goal.