Effects of flexibility and strength interventions on optimal lengths of hamstring muscle-tendon units

Shangxiao Li, William E. Garrett, Thomas M. Best, Hanjun Li, Xianglin Wan, Hui Liu, Bing Yu

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Objectives: The aim of the present study was to determine the effects of altering both hamstring flexibility and strength on hamstring optimal lengths. Design: Controlled laboratory study. Methods: A total of 20 male and 20 female college students (aged 18–24 years) participated in this study and were randomly assigned to either a flexibility intervention group or a strength intervention group. Passive straight leg raise and isokinetic strength test were performed before and after interventions. Paired T-tests were performed to determine hamstring flexibility or strength intervention effects on hamstring optimal lengths. Results: Male participants in the flexibility intervention group significantly increased range of hip joint flexion (P = 0.001) and optimal lengths of semimembranosus and biceps long head (P ≤ 0.026). Male participants in the strength intervention group significantly increased hamstring strength (P = 0.001), the range of hip joint flexion (P = 0.037), and optimal lengths of all three bi-articulated hamstring muscles (P ≤ 0.041). However, female participants did not significantly increase their hamstring optimal lengths in either intervention groups (P ≥ 0.097) although both groups significantly increased the range of hip joint flexion and strength (P ≤ 0.009). Conclusion: Hamstring optimal lengths can be modified through flexibility intervention as well as strength intervention for male participants, but not for female participants in this study. Hamstring optimal lengths should be considered as hamstring flexibility measures in future prospective studies to identify potentially modifiable risk factors for hamstring injury.

Original languageEnglish (US)
Pages (from-to)200-205
Number of pages6
JournalJournal of Science and Medicine in Sport
Issue number2
StatePublished - Feb 2020


  • Hamstring muscle strain injury
  • Injury mechanism
  • Injury prevention
  • Modifiable risk factors
  • Muscle biomechanics

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Physical Therapy, Sports Therapy and Rehabilitation


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