On my rest days between weight training I have added isometric exercise to my regime.
Grip pull: hook your hands and then hook them together and pull against them as hard as you can
Elbow pull: cup one hand and rest the opposite elbow into it... Push with your elbow pull with your hand.. Same with opposite.
Potato push: rest bottom of 1 fist on top of the other top fist pushes down bottom fist pushes up.. Then swap.
Chair grip: in the seated position grip sides of chair underneath the seat.. Try to stand up.. Thighs vs arms
Flamingo stance: stand behind a chair hold top with both hands, raise one foot up until knee is at a right angle hold for a while few seconds then swap legs.
Plank: go on hands and knees place arms on floor wrist to elbow, extend legs out until you have a straight line from head to ankles, hold your weight for as long as you can