Came across this idea the other week. What is a tense grip? What is a tight grip? This is where the muscles that work opposite to each other are contracted. Therefore the joint still move but the opposing muscles are still working and wasting energy. What is a relaxed grip? It is a grip where on a swing, those muscles pulling the racquet in the intended direction are contracting but those muscles which have the opposite action are relaxed. The offshot is, the swing can be faster and use less energy.