In vivo measurement of dynamic rectus femoris function at postures representative of early swing phase

Antonio Hernández, Yasin Dhaher, Darryl G. Thelen

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Forward dynamic models suggest that muscle-induced joint motions depend on dynamic coupling between body segments. As a result, biarticular muscles may exhibit non-intuitive behavior in which the induced joint motion is opposite to that assumed based on anatomy. Empirical validation of such predictions is important for models to be relied upon to characterize muscle function. In this study, we measured, in vivo, the hip and knee accelerations induced by electrical stimulation of the rectus femoris (RF) and the vastus medialis (VM) at postures representatives of the toe-off and early swing phases of the gait cycle. Seven healthy young subjects were positioned side-lying with their lower limb supported on air bearings while a 90 ms pulse train stimulated each muscle separately or simultaneously. Lower limb kinematics were measured and compared to predictions from a similarly configured dynamic model of the lower limb. We found that both RF and VM, when stimulated independently, accelerated the hip and knee into extension at these postures, consistent with model predictions. Predicted ratios of hip acceleration to knee acceleration were generally within 1 s.d. of average values. In addition, measured responses to simultaneous RF and VM stimulation were within 13% of predictions based on the assumption that joint accelerations induced by activating two muscles simultaneously can be found by adding the joint accelerations induced by activating the same muscles independently. These results provide empirical evidence of the importance of considering dynamic effects when interpreting the role of muscles in generating movement.

Original languageEnglish (US)
Pages (from-to)137-144
Number of pages8
JournalJournal of Biomechanics
Issue number1
StatePublished - 2008
Externally publishedYes


  • Biarticular muscle
  • Electrical stimulation
  • Forward dynamic simulation
  • Induced acceleration
  • Musculoskeletal model

ASJC Scopus subject areas

  • Biophysics
  • Orthopedics and Sports Medicine
  • Biomedical Engineering
  • Rehabilitation


Dive into the research topics of 'In vivo measurement of dynamic rectus femoris function at postures representative of early swing phase'. Together they form a unique fingerprint.

Cite this