sinewy

1. 1. Consisting of or resembling sinews.
   2. Having many sinews; stringy and tough: a sinewy cut of beef.
2. Lean and muscular. See synonyms at muscular.
3. Strong and vigorous: sinewy prose.

adjective

Characterized by marked muscular development; powerfully built: athletic, brawny, burly, husky², muscular, robust, sturdy. See strong/weak.

Definition: muscular
Antonyms: puny

The adjective has 3 meanings:

Meaning #1: (of meat) full of sinews; especially impossible to chew
  Synonyms: fibrous, stringy, unchewable

Meaning #2: consisting of tendons or resembling a tendon
  Synonym: tendinous
  Pertains to noun: sinew (meaning #1)

Meaning #3: (of a person) possessing physical strength and weight; rugged and powerful
  Synonyms: brawny, hefty, muscular, powerful