How did Walt Whitman and Gerard Manley Hopkins challenge traditional English prosody?

Walt Whitman and Gerard Manley Hopkins challenged traditional English prosody by mounting an assault on the conventional syllable-stress metric, effectively paving the way for modern poetic techniques.1

Walt Whitman

Whitman broke from tradition through his development of free verse, which abandoned the practice of counting syllables, stresses, or feet. Instead of relying on regular metrical schemes, his prosody was largely rhetorical, deriving rhythm from:2
* Parallelism and Anaphora: Utilizing repetition of syntactical units and phrases, often inspired by biblical verse.2
* Thematic and Sound Patterns: Creating rhythm through alliteration, thematic repetition, and the visual shape of lines on the page.2

Gerard Manley Hopkins

Hopkins introduced sprung rhythm, an irregular system designed to imitate the natural cadence of common English speech. His approach challenged traditional metrics by:31
* Variable Foot Structure: Allowing each foot to contain one stressed syllable and an indeterminate number of unstressed syllables, rather than the fixed two or three syllables found in traditional metre.34
* Counterpointed Verse: Incorporating trochees, spondees, and pyrrhics against a ground rhythm to create a more intense, muscular, and organic verse.42