What does 'impair' mean in relation to physical condition?

'Impair' in the context of physical condition refers to the act of diminishing, reducing, or injuring the effectiveness, quality, or strength of something. Therefore, the term signifies a weakening or deterioration of physical function or ability. When a physical condition is impaired, it means that it is not operating at its full capacity, often leading to limitations or challenges in performance or endurance.

Understanding the term in this way clarifies why 'weaken' is the most fitting answer. The other options convey concepts that are contrary to the notion of impairment. 'Fortify' and 'reinforce' imply strengthening or adding support, while 'stabilize' suggests bringing something to a state of balance or maintaining its current condition, neither of which aligns with the concept of impairment.