Do knee injuries have long-term consequences for isometric and dynamic muscle strength?

To ascertain whether decrements in knee extensor muscle strength persist ye ars after a traumatic ligamentous or meniscal knee injury, with reference t o (1) the type of muscle activity, (2) the dominance of injury, and (3) the time since injury, 36 subjects with previous unilateral knee injuries were assessed. Peak voluntary quadriceps muscle strength was measured using the KinCom 500H dynamometer during isometric, concentric (30 degrees .s(-1) an d 120 degrees .s(-1)) and eccentric contractions (30.s(-1)), and the findin gs for each type of contraction were compared. Significant differences in q uadriceps muscle strength were seen between (1) the injured and uninjured l imbs during maximal voluntary isometric (P=0.0003), concentric (P<0.0001) a nd eccentric (P<0.0001) contractions, and (2) the isometric and concentric decrements (P = 0.004), and the isometric and eccentric decrements (P=0.012 ) within the same injured limb. The decrements in eccentric strength were s ignificantly greater if they affected the dominant rather than the non-domi nant limb (P=0.0186). No relationship was seen between the time since injur y and the degree of isometric or dynamic decrement. Deficits in quadriceps muscle strength remained for a long time after traumatic knee injury, with exercise levels rarely returning to the previously uninjured state. The deg ree of decrement in muscle strength was dependent upon the type of muscle a ctivity, with concentric and eccentric activity showing greater decrements than those seen with isometric activity. Deficits in the type of activity v aried widely in the same individual, and eccentric decrements were signific antly worse following dominant knee injuries. Possible explanations for the se findings and the implications for rehabilitation following knee injury a re discussed.