Impact of Foot Position on Supine Active Knee Extension Assessment

Two common validated assessments of hamstring extensibility include the straight leg raise test (SLR) and the supine active knee extension (AKE) test. Both tests indirectly measure hamstring flexibility. A plantar (PF) or dorsiflexed (DF) foot position may influence either assessment, particularly if the two-joint gastrocnemius is taut. Dorsiflexion decreases hamstring extensibility in the SLR test (Gajdosik, 1985), but the affect of dorsiflexion on supine AKE test results remains undocumented. PURPOSE: The purpose of this study was to quantify the impact of foot position on the supine assessment of AKE. Decreased knee extensibility was expected in the DF position. METHODS: Forty-seven (22 men; 25 women; 21.5 ± 2.4 years of age) recreationally active students, free of lower extremity and back injuries, voluntered to participate and provided informed consent. Subjects avoided strenous exercise 12 hours before testing. The first AKE assessment, in the PF position, determined eligibility. Eligible legs showed at least a 20 o deficit in knee extension. All 94 legs tested were included. The second test, in the DF position, occurred approximately 48 hours from the first test. For all tests, subjects were supine on a table top with the non-test leg securely strapped to the table. To insure 90 o of hip flexion on the test leg, a long arm goniometer was located over the hip joint axis. One arm was attached to the thigh and the other held parallel to the pelvis and table surface by the investigator. Subjects were positioned with the anterior surface of the thigh in contact with a cross-wire device to facilitate maintainence of 90 o of hip flexion, Subjects slowly extended the knee with the ankle relaxed (PF tests) or held in neutral by a specially designed splint (DF tests). The investigator stopped the test when the hip angle was no longer 90 o . An inclinometer, placed on the anterior tibia, measured knee angle in reference to the horizontal. Ninety degrees were added to each measurement to express hamstring extensibility as the posterior intersegmental angle at the knee. RESULTS: A paired samples t-test (p < .0001) indicated a significant difference between the PF (102.95 ± 12.67) and DF (96.97 ± 11.53) positions. CONCLUSION: Clinicians should be aware that foot position influences hamstring extensibility as determined by AKE and reminded that gastrocnemius tautness influences knee extensibility. I nterventions addressing knee pathology should consider the influence of gastrocnemius tautness.

2006, Russell PJ, Decoster LC: The impact of ankle position on a common measure of hamstring flexibility.  MSSE, Vol 38 Suppl.