Date of Award


Document Type


Degree Name

Master of Science (MS)


School of Kinesiology and Recreation

First Advisor

Rebecca L. Begalle


Introduction: Hamstring strains are among one of the most common acute injuries that occur in soccer players. Previous research has shown that reduced hamstring flexibility is a risk factor for injury, however this is modifiable through stretching. Some stretching techniques have contributed to decreased performance on measures important to success in sport. Proprioceptive neuromuscular facilitation (PNF) is one effective stretching technique to improve hamstring flexibility, but requires a trained partner or clinician to perform properly. It is unknown if the performance of PNF stretching without a clinician’s assistance could be as effective. It is also unknown if PNF stretching affects soccer related performance outcomes of force output and vertical jump height. Objective: To determine the effects of clinician assisted versus unassisted contract-relax PNF stretching on hamstring flexibility, maximum voluntary isometric contraction (MVIC) of the hamstring muscle group, and athletic performance via vertical jump height. Design: Controlled laboratory study. Participants: A sample of twenty-six physically active male and female college students with restricted hamstring flexibility, defined as limited passive hip flexion range of motion with the leg straight (<90 degrees), participated in this study. Procedures: Subjects were randomly allocated to one of three groups; the clinician assisted, unassisted, or control groups following confirmation of inclusion criteria. The control group completed pre- and post- test measures only. The intervention groups completed a 6-week stretching intervention (12 total sessions) either with the assistance of a clinician or utilizing a stretching strap. Pre- and Post- intervention measurements were recorded for all outcome variables. Main Outcome Measures: Hip flexion range of motion was measured passively with the knee extended. Hamstring MVIC was assessed using a handheld dynamometer and normalized to each participant’s body mass. Maximal vertical jump height was measured using a Vertec. Three trials were recorded for each measure and the arithmetic mean was used to calculate change scores (Post – Pre). Change scores were utilized for data analysis. Separate one-way ANOVA’s were performed to identify differences between groups in the magnitude of change. Results: The one-way ANOVA for hip flexion ROM change scores was significant (F (2, 25) = 9.853, p = 0.001), indicating there were significant differences in the amount of change in ROM when compared across groups. Post-hoc comparisons found both the Unassisted (10.26° ± 6.03, p = 0.002) and Assisted (10.27° ± 3.81, p = 0.004) PNF intervention groups had a greater improvement in ROM compared to the Control group (-0.41° ± 7.00). There were no differences between the amount of change in the Unassisted group compared to the Assisted group. The one-way ANOVA found no significant changes in MVIC (F (2, 25) = 2.542, p = 0.101), and vertical jump height (F (2, 25) = 0.133, p = 0.877). Conclusion: Both the Assisted and Unassisted PNF stretching techniques were successful in improving hamstring flexibility. Performance measures were not impacted by the stretching intervention. Teaching a patient to perform the contract-relax PNF stretching technique to target hamstring flexibility is as effective as the clinician providing the assistance. These results may provide time saving benefits to clinicians while promoting improved flexibility and independence in patients.


Imported from ProQuest Lockhart_ilstu_0092N_10989.pdf


Page Count


Included in

Biomechanics Commons