Learn how to Double Unders and watch the active muscles Jumping rope can increase the elasticity and resiliency of lower-leg muscles. The quick bounding action trains explosiveness since you need to jump about twice as high off the ground as you do with single-unders. Jumping rope regularly strengthens the calf muscles and improves the elasticity of the surrounding tendons and fascia. The gastrocnemius fibers contract almost isometrically while the fascial collagenous elements lengthen and short