The term 'ADD SOME MUSCLE TO' can be solved by the seven-letter word 'TOUGHEN'. To 'TOUGHEN' something means to make it stronger, more resilient, and more durable. It is often used in the context of physical strength, but can also be used to describe mental or emotional strength. In this case, the phrase 'ADD SOME MUSCLE TO' suggests that the person or thing being referred to needs to become stronger in some way.