Frequency analysis of surface EMG on knee extensors with anterior cruciate ligament insufficiency

Abstract

The muscle strength of knees with an injured anterior cruciate ligament (ACL) is generally assessed by the peak of the isokinetic muscle contraction. However, assessment of the characteristics of muscle contraction, such as the contraction velocity and contraction endurance, has been largely ignored due to a lack of data. In this study, we have performed frequency analysis of the surface electromyograms during sustained isometric contraction of the quadriceps femoris muscle in 22 knees with ACL deficiency to evaluate the characteristics of muscle contraction. Concerning the time-related changes in the mean power frequency (MPF), the decrease with time was smaller than normal (reflecting a deficiency in the number of fast-twitch fibers) in the rectus femoris and vastus medialis muscles of the injured limb in many subjects. However, a slightly different pattern was observed in the vastus lateralis muscle, which showed little difference between the injured and intact limbs. Therefore the vastus lateralis muscle was considered to be less affected by an ACL deficiency than the other two muscles. The time-related changes in the MPF in the ACL deficient limb were clearly different from those in the intact limb and a deficiency in the fast-twitch fibers was suggested. Therefore a frequency analysis of the surface electromyograms was considered to allow detection of qualitative changes, such as of muscle fiber deficiency, as well as detection of changes in the simple muscle strength.