"improve flexibility" is correct and usable in written English.
Here is an example of how it could be used in a sentence: "Developing a regular stretching routine will help to improve flexibility."
Or if you are flexible or want to improve flexibility join a gymnastics club.
The additives may be so-called plasticizers that improve flexibility or fillers that strengthen the matter.
Muscles and tendons can be stretched to improve flexibility (the range of motion at a joint).
Exercises that improve flexibility help keep your feet limber and may reduce your risk for injury.
Stretch and do other activities that improve flexibility and balance every day.
The basic components of the exercise prescription are activities that improve flexibility, muscle strength, and endurance.
Kirsty explains that the classes can help to improve flexibility, posture, strength and core stability, and to lengthen muscles.
Hersey resorts to sitting on her ankles to improve flexibility and stands like Charlie Chaplin with her feet pointed out.
Without efforts to improve flexibility and balance, she said, people can put themselves at greater risk of falls.
Students will learn how to increase their cardiorespiratory fitness level, boost muscular strength and endurance, and improve flexibility.
Aiming towards more autonomous robot systems, we want to improve flexibility.
