Do the hamstrings operate at increased muscle-tendon lengths and velocities after surgical lengthening?

Allison S. Arnold, May Q. Liu, Michael H. Schwartz, Sylvia Õunpuu, Luciano S. Dias, Scott L. Delp

Research output: Contribution to journalArticlepeer-review

68 Scopus citations


Children with crouch gait frequently walk with improved knee extension during the terminal swing and stance phases following hamstrings lengthening surgery; however, the mechanisms responsible for these improvements are unclear. This study tested the hypothesis that surgical lengthening enables the hamstrings of persons with cerebral palsy to operate at longer muscle-tendon lengths or lengthen at faster muscle-tendon velocities during walking. Sixty-nine subjects who had improved knee extension after surgery were retrospectively examined. The muscle-tendon lengths and velocities of the subjects' semimembranosus muscles were estimated by combining kinematic data from gait analysis with a three-dimensional computer model of the lower extremity. Log-linear analyses confirmed that the subjects who walked with abnormally short muscle-tendon lengths and/or slow muscle-tendon velocities preoperatively tended to walk with longer lengths (21 of 29 subjects, p < 0.01) or faster velocities (30 of 40 subjects, p < 0.01) postoperatively. In these cases, surgical lengthening may have slackened the subjects' tight hamstrings and/or diminished the hamstrings' spastic response to stretch. Other subjects walked with muscle-tendon lengths and velocities that were neither shorter nor slower than normal preoperatively (22 of 69 subjects), and the semimembranosus muscles of most of these subjects did not operate at increased lengths or velocities after surgery; in these cases, the subjects' postsurgical improvements in knee extension may have been unrelated to the hamstrings surgery. Analyses of muscle-tendon lengths and velocities may help to distinguish individuals who have "short" or "spastic" hamstrings from those who do not, and thus may augment conventional methods used to describe patients' neuromusculoskeletal impairments and gait abnormalities.

Original languageEnglish (US)
Pages (from-to)1498-1506
Number of pages9
JournalJournal of Biomechanics
Issue number8
StatePublished - 2006
Externally publishedYes

Bibliographical note

Funding Information:
The authors are grateful to Saryn Goldberg, Katherine Bell, Dennis Tyburski, Melany Westwell, and Jean Stout for assistance with data collection, to Silvia Blemker for contributions to the model, and to Jim Gage, Tom Novacheck, George Rab, Stephen Vankoski, Julie Witka, Roy Davis, and Kevin Granata for the many stimulating discussions we have had regarding muscle–tendon lengths and velocities. This work was supported by NIH RO1 HD33929, the Whitaker Foundation, and the United Cerebral Palsy Foundation.


  • Cerebral palsy
  • Gait
  • Hamstrings
  • Musculoskeletal model


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