Should is a form of Shall. Shall is similar to Will. Will is a type of Desire. 
Gym is related to Workout. Workout is related to Stretch. Stretch is related to Force. 
Should --FormOf--> Shall <--SimilarTo--> Will --IsA--> Desire 
Gym <--RelatedTo--> Workout <--RelatedTo--> Stretch <--RelatedTo--> Force 