TEMPORAL COMPARISON OF HAMSTRING CO-CONTRACTION LATENCY IN ANTERIOR CRUCIATE DEFICIENT KNEES - A PILOT STUDY

Abstract

Recently, anterior cruciate ligament (ACL) research has been focusing on strengthening the hamstring muscles, as previous studies have found there to be a significant stabilizing effect by the hamstrings in those subjects with anterior cruciate deficiencies. Research has primarily focused on whether differences existed between the strength (Moore & Wade, 1989; Seto, Wino, Morrissey, Medeiros & Mason, 1988), the electromyographical (EMG) output (Tibone & Antich, 1988), or the muscle activation patterns between the quadriceps and hamstrings. (Beard, Kyberd, Fergusson & Dodd, 1993; Jennings Seedhom, 1994). A key factor in hamstring co-contraction during gait is that of timing. Should hamstring cocontraction occur near to heelstrike, where the greatest anterior shear force is applied to the knee during a normal gait, or occur too far behind heelstrike, muscular strength is rendered useless. In such an event, stabilization cannot occur if the joint has already been displaced, or counteracting force has already been exhausted. This pilot study proposed to determine if latency exists between injured and uninjured knees, examining only temporal data relative to heelstrike. Similar studies involving static positions with an applied shear force have been performed and have had contradicting results. (Beard, Kyberd, Fergusson & Dodd, 1993; JeMings & Seedhom, 1994). To date, no temporal measures have been examined in dynamic movement. This may affect results as most joint receptors require motion for proprioception. Data collection procedures involved using a 3-channel EMG monitor to track the time heelstrike, hamstring contraction and quadriceps contraction during a 5-second period of normal walking/jogging on a treadmill. Speeds of 5 km/h and 7 km/h were used on incline, decline and flat surfaces. Data was collected at three randomly selected times for each condition and each leg. Differences found between injured and uninjured legs represent an area of concern for those in the field of rehabilitation. Research into variations in treatment methods to correct for latency in the hamstrings could provide a level of stability not before seen in non-surgical or even surgical patients. The next step to further this research will involve an eight-channel EMG monitor to track bilateral timing. A thorough patient history including Cincinnati and Lysholm scales of subjective functional ability will be included in the patient selection process.