How muscle fiber lengths and velocities affect muscle force generation as humans walk and run at different speeds

Edith M. Arnold, Samuel R. Hamner, Ajay Seth, Matthew Millard, Scott L. Delp*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

182 Citations (Scopus)


The lengths and velocities of muscle fibers have a dramatic effect on muscle force generation. It is unknown, however, whether the lengths and velocities of lower limb muscle fibers substantially affect the ability of muscles to generate force during walking and running. We examined this issue by developing simulations of muscle-tendon dynamics to calculate the lengths and velocities of muscle fibers from electromyographic recordings of 11 lower limb muscles and kinematic measurements of the hip, knee and ankle made as five subjects walked at speeds of 1.0-1.75?m?s-1 and ran at speeds of 2.0-5.0 m s-1. We analyzed the simulated fiber lengths, fiber velocities and forces to evaluate the influence of force-length and force-velocity properties on force generation at different walking and running speeds. The simulations revealed that force generation ability (i.e. the force generated per unit of activation) of eight of the 11 muscles was significantly affected by walking or running speed. Soleus force generation ability decreased with increasing walking speed, but the transition from walking to running increased the force generation ability by reducing fiber velocities. Our results demonstrate the influence of soleus muscle architecture on the walk-to-run transition and the effects of muscle-tendon compliance on the plantarflexors' ability to generate ankle moment and power. The study presents data that permit lower limb muscles to be studied in unprecedented detail by relating muscle fiber dynamics and force generation to the mechanical demands of walking and running.

Original languageEnglish
Pages (from-to)2150-2160
JournalJournal of Experimental Biology
Issue number11
Publication statusPublished - 2013
Externally publishedYes


  • Biomechanics
  • Human gait
  • Muscle architecture
  • Musculoskeletal model
  • Plantarflexors
  • Simulation


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