Mixed
Eccentric resistance training primarily increases muscle fascicle length (serial sarcomere addition), whereas concentric resistance training primarily increases pennation angle (parallel sarcomere addition).
To optimize specific functional goals, consider the structural changes: eccentric training lengthens the muscle fibers (fascicles), which may improve range of motion and force at longer lengths. Concentric training packs fibers more densely (pennation), which may improve force production at shorter lengths. For general aesthetics, either works, but for sport-specific range of motion, eccentric emphasis might be beneficial.
ECC results in a markedly greater increase in fascicle length (Lf) while CON promotes greater changes in pennation angle (PA), likely reflecting the differential addition of sarcomeres either in series or in parallel, respectively.
Why this rating
Supported by multiple ultrasound studies cited in the review showing distinct architectural changes.
Source
Skeletal Muscle Remodeling in Response to Eccentric vs. Concentric Loading: Morphological, Molecular, and Metabolic Adaptations
Martino V. Franchi et al. · Frontiers in Physiology · 2017
DOI 10.3389/fphys.2017.00447
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