The antonyms for the word "unbends" are words that mean the opposite of unbend or relax. These words include tense up, stiffen, strain, toughen, contract, solidify, and harden. When people are tense, they tend to stiffen up and strain their muscles. This can result in a contraction of the muscles making them tough and less flexible. Similarly, when materials harden or solidify, they become less flexible and less likely to bend. It is important to keep in mind that finding the right balance between bending and not bending is key to being flexible and resilient, both physically and mentally.