It is an unnatural position for the arms to be in and, even though properly applied, the cuffs are going to apply pressure to the wrist area as they restrain the movement of a subject. Improperly applied handcuffs can cause more pain and even injury.

Is it painful to wear handcuffs?

When the handcuffs are concealed by a handcuff cover and secured at the prisoner's waist by a belly chain, this combination will result in a rather more severe restraint and the restrained person may feel discomfort or even pain.

Do handcuffs cut off circulation?

When the suspect's wrists are too large and will not fit conventional handcuffs. ... If applied too tightly, flex cuffs can cut off blood circulation. The only way to adjust them is to cut them off.