The importance of recognizing a closed-chain activity lies in the fact that the motions of multiple joints are coupled. Weakness at any one joint will consequently limit performance of the entire movement.
Personal trainersCoachesExercise ScienceProgram design
The exerciser with 8 to 12 months of training experience can begin to include exercise complexes that combine trunk movement patterns with multijoint movements. Single-plane and multiplane movements can be performed using both open- and closed-chain exercises.
This book excerpt from Developing Agility and Quickness describes the windows of opportunity in youth athletes to time progressions in speed and agility training with their biological and chronological development.