Objective: Improving of muscle flexibility is an important issue in physiotherapy and sport sciences. There are many methods for increasing muscle length and decreasing muscle stiffness. In research findings, PNF method has been found to be better than static and ballistic methods. There is another method named Harmonic technique (introduced by E. Lederman 1997) that has been claimed to be more effective, but there is not enough documentation about this claim. Aim of this study was to compare effects of stretching by PNF and harmonic techniques on hamstring flexibility.

Materials & Methods: This research is a RCT study in that 45 colledge students aged 18-35 years were arranged in three groups (Harmonic, P.N.F, and control). Subjects haven’t had any painful pathology in low-back and lower extremities for last six months. Subjects had limited hamstring length (20 degrees deficiency in Active-Knee-Extension test) and hadn’t professional sport activities. Dependent variablies were muscle stiffness and hamstring length which popliteal angle in AKE test was its indirect index. In pilot study, reliability of measurement of these variables were approved. Then hamstring muscle of subjects in harmonic and PNF groups were stretched by harmonic and PNF methods for six weeks, 5 minute per day and 3d/wks, whereas control group hadn’t any exercise.

Results: Findings of this study showed that in both used techniques, changes of hamstring length were significant (P=0.000), but in control group there wasn’t significant change. There wasn’t significant differences between changes of hamstring length in PNF and Harmonic groups. Only in harmonic group, muscle stiffness had significant changes (P<0.03).

Conclusion: According to findings of this research, both harmonic and PNF methods equally increased length of hamstring, and harmonic technique can be used as an alternative stretching method for other techniques. Maybe harmonic technique is better than PNF, because the significant changes of stiffness observed only in harmonic group ie. not only length of muscle increased in this group, but also stiffness decreased significantly which can be an indicator of considerable biomechanical changes in muscle and possibly increase of muscle length in PNF group is not real improvement in flexibility, and indeed, tolerance of subjects to stretching in this group has increased.

Objective: Patellofemoral pain syndrome is the most prevalent problem involving25 percent of all knee disorders. Such problems might be lead to functional disabilities. The goal of this study was to evaluate the relationship between functional tests and Isokinetic parameters of knee muscles and subjective assessment of knee function in patellofemoral pain syndrome and to compare between patient and control group.

Materials & Methods: In this analytical and case – control research fifteen normal subjects and 15 patients with patellofemoral pain syndrome were selected with purposive sampling method in performing two main levels of this study:

1- Functional tests (bilateral squat and step down test) which performed randomly with considering of repetitions per 30 seconds, within 3 minutes rest between them applied and followed by subjective assessment of knee function with Kujala questionnaire.

2- Isokinetic tests performed with Biodex dynamometer device, during 10 to 90 degree of knee flexion with two distinct speeds, 60 and 120 degree per second.

Results: No relationship was found between functional tests and Isokinetic parameters in patient group, but we observed a low significant relationship between functional tests and subjective assessment in this group (r=0/47 for Squat test and 0/37 for Step down test). Moderate significant relationship was found between subjective assessment of knee function and functional Hamstring: Quadriceps ratio for knee flexion at 60 degree per second (r = - 0/58). All of the Isokinetic parameters of quadriceps muscle in patient group were lower than control group.

Conclusion: As there were low correlation between Isokinetic strength measurement and functional tests and subjective assessment of knee function, it is not recommended using these methods of assessment interchangeable in patients with patellofemoral pain syndrome.

Objective: To investigate the intra-tester reliability of electromyographic (EMG) activity of lumbo-pelvic muscles during prone hip extension in subjects with chronic hamstring strain.

Materials & Methods: A convenience sample of 10 athletes with history of hamstring strain injury was studied. EMG signal amplitude of the right and left erector spinae, gluteus maximus, biceps femoris and semitendinosus was measured during prone hip extension three times a day. The peak amplitude of the muscles was normalized to maximum voluntary exertion of each muscle. Intraclass Correlation Coefficient (ICC) and Standard Error of Measurement were used to assess the reliability.

Results: The ICC values were greater than 0.90 for all tested muscles. The results indicate high reliability for EMG activity of the lumbo-pelvic muscles during prone hip extension in subjects with chronic hamstring strain.

Conclusion: The prone hip extension test can be used as a reliable method to assess the activity pattern of the lumbo-pelvic muscles in subjects with history of hamstring strain injury.