Muscle rigidity is very common, and it can be uncomfortable. You can have stiff and tense muscles due to various causes—such as sitting or sleeping in the wrong position, or it can be the result of a ...

A busker, though, performs for tips: He sings and plays the guiro, a percussion instrument made from a hollowed-out gourd with a rigid surface. Kids sell candy and cigarettes to passersby.

Chronic stress impairs goal-directed decision-making, often leading to rigid, habitual behaviors that underpin several psychiatric conditions. Understanding the neuronal circuits involved could ...