While a common phrase, it is incorrect to call very flexible gymnasts double jointed especially if you want to appear knowledgeable.
For strength training, weight machines are the safe to use and progress is easily tracked and to train muscles to the point of momentary muscle failure
High intensity cardio is the the best type of strength-to-body-weight, calorie burning and explosive running power training for gymnasts.
Gymnasts and coaches could learn some things about toe and foot strength and flexibility training from ballerinas who take great care of their toes and feet
A good gymnastics conditioning program requires personalization, positive psychology, attention to detail, and discipline.
Correctly done plyometrics exercise program are far too rare in gymnastics. Learn what every gymnast needs to know about plyometric strength training.