Stiffest

adjective

1. (of an object) Rigid; hard to bend; inflexible.
2. (of policies and rules and their application and enforcement) Inflexible; rigid.
3. (of a person) Formal in behavior; unrelaxed.
4. Harsh, severe.

   "He was eventually caught, and given a stiff fine."

5. (of muscles or parts of the body) Painful as a result of excessive or unaccustomed exercise.

   "My legs are stiff after climbing that hill yesterday."