Muscle-fiber pennation angles are greater in hypertrophied than in normal muscles

Y. Kawakami*, T. Abe, T. Fukunaga

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

395 Citations (Scopus)


Muscle-fiber pennation angles were measured in vivo with the use of ultrasonography to investigate the relationship between fiber pennation and muscle size for 32 male subjects (from untrained subjects to highly trained bodybuilders). From the image of a B-mode ultrasonogram, fiber pennation angles and thickness of triceps brachii were determined, the former as angles between echoes from the interspaces of fascicles and from the aponeurosis of long and medial heads of triceps and the latter as the distance between the fat-muscle and muscle-bone interfaces. The pennation angles were in the range of 15 and 53° for the long head and 9 to 26° for the medial head, which were similar to or greater than the published and the present data on human cadavers. Significant differences were observed between normal subjects and bodybuilders in muscle thickness and pennation angles (P < 0.01), and there were significant correlations between muscle thickness and pennation angles for both long (r = 0.884) and medial (r = 0.833) heads of triceps, suggesting that muscle hypertrophy involves an increase in fiber pennation angles.

Original languageEnglish
Pages (from-to)2740-2744
Number of pages5
JournalJournal of Applied Physiology
Issue number6
Publication statusPublished - 1993
Externally publishedYes


  • muscle thickness
  • pennate muscle
  • triceps brachii
  • ultrasound

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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