“变僵硬”的英语可以翻译为：[医]stiffen，anchylose ...

人一紧张，身体就会变僵硬。When we are under stress our bodies tend to tense up.人一上年纪,关节就变僵硬了.Joints stiffen with advancing years.我们谈到他的欠款时,他的表情变僵硬.He froze up when we mentioned his debts....