Kroll PG, Spielholz NI, Bello BG, Bennie LJ, Millett K. Division of Physical Therapy, University of Miami, Miami, FL, [...], The hamstrings are thought to play an important role in supporting restraining efforts of the anterior cruciate ligament (ACL) in resisting anterior displacement of the tibia. Hamstring strengthening has been promoted to compensate for a decrease or loss in ACL function. PURPOSE: To compare electromyography activity of the quadriceps and hamstrings in normal subjects during two different squat exercise techniques at two different positions. SUBJECTS: This study was a single-group, repeated measures design which recruited 22 subjects with normal knee joints. METHODS AND MATERIALS: Electromyographic activity of the inner and outer hamstrings and the medial and lateral quadriceps of the right legs of each subject was recorded for a 5-second interval while performing two repetitions of squats to 45 ° and 90 °, both against the wall and in free standing. After a 5 minute rest, this protocol was repeated with the order of the squat types reversed. ANALYSIS AND RESULTS: Descriptive statistics and analysis of variance were used to examine the data. There was a significant effect on hamstring electromyography activity due to position and due to degree (p=.0002 position & p=.0021 degree), and quadriceps electromyography activity due to position and due to degree (p=.0132 for position & p=.0001 for degree); only the quadriceps data showed an interaction between position and degree (p=.0027). The greatest hamstring activity was elicited in the stand 90 ° position by the inner hamstrings. The greatest quadriceps activity was evident in the stand 90 ° position by the vastus lateralis. The hamstring-to-quadriceps mean ratio was significantly different when examining position and degree, although no interaction was found between the two variables. The highest ratio was present in the stand 45 ° position. CONCLUSION: If we presume that increased hamstring EMG activity, relative to quadriceps EMG activity, is indicative of more hamstring assistance to the ACL in preventing anterior displacement of the tibia, then data would suggest that the freestanding 45 ° squat elicits a more favorable hamstring to quadriceps ratio for preventing anterior displacement of the tibia. In order to develop safe and efficient protocols for the rehabilitation of patients, further research is necessary examining EMG activity relative to joint reaction forces produced under various loads and positions in patients with normal and ACL deficient knees. Kroll PG, Spielholz NI, Bello BG, Bennie LJ, Millett K. Division of Physical Therapy, University of Miami, Miami, FL, USA.