Rectus femoris knee muscle moment arms measured in vivo during dynamic motion with real-time magnetic resonance imaging

Niccolo M. Fiorentino, Jonathan S. Lin, Kathryn B. Ridder, Michael A. Guttman, R. McVeigh Elliot, Silvia S. Blemker

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Moment arms represent a muscle's ability to generate a moment about a joint for a given muscle force. The goal of this study was to develop a method to measure muscle moment arms in vivo over a large range of motion using real-time magnetic resonance (MR) imaging. Rectus femoris muscle-tendon lengths and knee joint angles of healthy subjects (N = 4) were measured during dynamic knee joint flexion and extension in a large-bore magnetic resonance imaging (MRI) scanner. Muscle-tendon moment arms were determined at the knee using the tendon-excursion method by differentiating measured muscle-tendon length with respect to joint angle. Rectus femoris moment arms were averaged across a group of healthy subjects and were found to vary similarly during knee joint flexion (mean: 3.0 (SD 0.5) cm, maximum: 3.5 cm) and extension (mean: 2.8 (SD 0.4) cm, maximum: 3.6 cm). These moment arms compare favorably with previously published dynamic tendon-excursion measurements in cadaveric specimens but were relatively smaller than moment arms from center-of-rotation studies. The method presented here provides a new approach to measure muscle-tendon moment arms in vivo and has the potential to be a powerful resource for characterizing musculoskeletal geometry during dynamic joint motion.

Original languageEnglish (US)
Article number44501
JournalJournal of Biomechanical Engineering
Issue number4
StatePublished - 2013
Externally publishedYes


  • joint motion
  • magnetic resonance imaging
  • musculoskeletal geometry
  • quadriceps
  • real-time measurement

ASJC Scopus subject areas

  • Biomedical Engineering
  • Physiology (medical)


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