Flexibility
Flexibility is the trainable extensibility of muscles and other soft tissues around a joint. It is one factor that can permit or limit a range of motion; joint anatomy, balance, pain, and neural control can also affect the position someone reaches. In common training language, mobility often emphasizes whether you can reach and control that position actively.
Flexibility is specific to the joint and direction being tested. Flexible hamstrings do not imply equally flexible shoulders, and two people can reach different positions because of anatomical structure as well as soft-tissue extensibility. A 2026 review of training terminology therefore recommends treating flexibility as one modifiable component of range of motion rather than using the terms as synonyms. Tests such as a sit-and-reach can track one movement but should not be treated as a complete score for the whole body.
Stretching can increase flexibility immediately and with repeated training. A systematic review and meta-analysis of programs lasting at least two weeks found a moderate average improvement in range of motion. The response depends on the joint, method, dose, and person, so consistency and a task-specific test are more useful than chasing a universal stretching prescription.
Dedicated stretching is not the only option. A meta-analysis of resistance training and range of motion found that strength training with external loads can improve range of motion, with no significant average difference from stretch training in the available direct comparisons. Exercises performed through an appropriate, controlled range can therefore develop strength and flexibility together.
Greater flexibility does not by itself guarantee better form, performance, or fewer injuries. A lifter needs enough range for the chosen exercises and goals, plus strength and control within that range. Flexibility work should create manageable tension rather than sharp pain, and it should target a real limitation instead of an arbitrary ideal.