Hamstrings contractile timing in anterior cruciate deficient subjects
Poling, Michael Peter
Master of Science
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Anterior cruciate injuries are extremely debilitating injuries for active individuals. It is estimated that 60 to 70% of all serious knee injuries involve damage to the anterior cruciate ligament (ACL) (Brant. 1989). One of the functional roles of the hamstrings is to prevent the anterior translation of the tibia, absorbing a portion of the anterior shear forces on the ACL (Brant. 1989; Nordin & Frankel, 1989). Timing of the hamstrings contraction during gait provides an important counter force to stabilize the knee. However, if the force occurs too early or too late, stabilization is compromised. Electromyographical (EMG) research analyses demonstrates that the hamstrings increase in actuation just before heelstrike (GaufBn & Tropp, 1992; Gronley & Perry, 1984; Phyllis, 1993; Johnstone, 1993). This response may be due to training of the muscle to respond to spatial and temporal cues, causing a compensator) contraction of the hamstrings (Schm idt 1988; Vlagill, 1989).