Jared W. Papa and Dr. Brent Feland, Physical Education
Muscle flexibility is “the ability of a muscle to lengthen, allowing one joint (or more than one joint in a series) to move through a range of motion.”1. Various studies have been performed to determine the most reliable and valid means of measuring flexibility, which is important because of its ability to forewarn of the likelihood of injury.2,3 With an indication of the tightness of the muscle a therapist, trainer, or athlete can make necessary adjustments to avoid injury.
Three hamstring flexibility tests are the lying active knee extension test (LAKE), the sitting active knee extension test (SAKE), and the lying passive knee extension test (LPKE). Prior to this study, no published study has compared the reliability of active vs. passive measurements on hamstring flexibility testing using these three tests. This study, which used all three tests, helps to clarify which test is more reliable in measuring hamstring flexibility.
These tests have also been designed to limit pelvic and spinal movement, thereby producing more consistent measurements. This is important to know because if the pelvis tilts, a greater range of motion is available at the knee joint, thus producing an over-estimation of hamstring flexibility.3
To qualify, subjects had no recent past history (past 1 year) of neurologic or orthopedic disorders to the lower extremities, and demonstrated “tight” hamstrings; defined as an inability to touch toes in a stand and reach test. Twenty-one qualified male volunteer college subjects (mean age = 23.3, S.D. = 1.45) were randomly assigned to 1 of 3 groups (each group started with a different testing method). Randomization to limit the “order effect” was assigned using a Latin Square design.
Subjects were tested 3 times a week for 2 weeks with at least 1 day separating each day of measurement. Each subject completed 3 repetitions of one test with 5 minutes of rest between each repetition and each method of testing being performed on two different days.
Measurement for each test was performed with an inclinometer. Subjects wore gym shorts, and after being positioned for testing, the base of the tibial tuberostiy was marked with a permanent pen. This landmark served as a reference point for consistent placement of the inclinometer during measurement throughout the study.
When performing the LAKE the subjects laid supine on an examination table. While the left leg was held firmly to the table, the right leg, the limb measured in each test, was positioned at 90 degrees of hip flexion using a bar fastened above the subject’s pelvis to allow consistent positioning. The knee was then actively extended slowly by the subject to the point of the onset of muscle tremor, and the inclinometer measurement was recorded.
Sitting in an upright position on an examination table for the SAKE, the subjects maintained a straight back with the pelvic-femoral angle being 90 degrees. The knees dangled off the side of the table. The subject then extended the right knee to the point of feeling “tightness” and the measurement was recorded.
The LPKE was performed using the same cross bar as mentioned in the LAKE test. The subject laid supine while the right lower extremity was positioned at 90 degrees of hip flexion and the left lower extremity remained fully extended on the table. The examiner then passively moved the tibia into terminal knee extension, which is operationally defined as the point at which the subject begins to complain of “mild discomfort” in the hamstrings.
Analysis of the data was performed using a repeated measures ANOVA to determine if a difference existed between the methods of measurement and where the differences existed. Intraclass correlation coefficients (ICC 3,1) were calculated to determine intratester reliability using each method. After performing an r to z transformation and comparing each set of methods we found there to be no significant difference between LPKE and LAKE (p=0.0602), but there was a significant difference between LPKE and SAKE (p=0.0085). Also, using a Tukey post-hoc analysis of trials we discovered that there was a significant difference between the first trial performed and the third.
From these results we conclude that the LPKE method is most clinically consistent and the SAKE is the least reliable. Although our study indicated there is no significant difference between the LPKE and LAKE, it is important to note that, though the LPKE and LAKE tests may be assumed equally reliable the lack of difference between the two was actually due to a loss of statistical power because of too few subjects. Regardless of this, the LPKE is arguably better because it is easier to perform. When performing the LPKE the patient is able to consistently determine a discomfort end point of the stretch. In the active tests, subjects had difficulty determining the end point to the stretch.
Another interesting fact was that while there was not a significant difference between the 1st and 2nd measurements of the same day there did exist a significant change in the flexibility between the 1st and 3rd measurements. This may mean that taking measurements 5 minutes apart may be too close together or that it is OK to take the 1st and 2nd measurements only 5 minutes apart but not the 3rd. However, this discovery was secondary to the purpose of this study and further studies should be done before coming to a conclusion on this matter.
Using a reliable test to measure hamstring flexibility is essential for a clinician to obtain accurate results. This study is an indication that the LPKE is the most reliable test for measuring hamstring tightness. As a result, health care providers may be able to better document and measure hamstring flexibility and related changes. Overall, this study can be of great assistance to those making decisions on the proper hamstring test to use.
References
- Zachezewski JE: Improving flexibility. In: Scully RM, Barnes MR (eds), Physical Therapy, pp 698-699. Philadelphia, PA: J.B. Lippincott Company 1989.
- Gajdosik R., Lusin G. Hamstring Muscle Tightness. Reliability of an Active -Knee – Extension Test. Physical Therapy, 63:1086-1089, 1983.
- Brown A., Maxwell L., Salmond S. Assessment of Hamstring Flexibility. Which Test? NZ Journal of Physiotherapy Dec. 1993; pp 33-34