fatigable

Fatigable is an adjective used to describe something that is capable of becoming fatigued or easily fatigued. In medical and biological contexts, it most often refers to tissues, cells, or systems that lose function or strength with sustained activity. The opposite term is fatigue-resistant or non-fatigable.

The word derives from the Latin fatigare, to tire, with the English suffix -able indicating capability. It is distinct from fatigue, which is the state of being tired, and from fatigability as a noun meaning the degree to which something fatigues.

In physiology, fatigability describes how quickly a tissue or organ loses its performance capacity during repeated or prolonged use. Skeletal muscles show varying fatigability linked to fiber type: fast-twitch fibers tend to fatigue quickly (fatigable), while slow-twitch fibers are more resistant to fatigue (fatigue-resistant). Fatigability can be influenced by energy supply, blood flow, temperature, and neural factors.

In clinical practice, fatigable weakness refers to weakness that worsens with activity and improves with rest, a hallmark of certain neuromuscular disorders such as myasthenia gravis and Lambert-Eaton myasthenic syndrome. Assessing fatigability helps distinguish neuromuscular etiologies from other causes of weakness.

Etymology: from Latin fatigare, to tire; the suffix -able denotes ability.

See also: fatigue, fatigability, fatigue-resistant, neuromuscular fatigue.