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Background and Purpose. The purpose of this study was to examine the effect of isometric training of the quadriceps femoris muscles, at different joint angles, on torque production and electromyograpbic (EMG) activity. Subjects. One hundred seven women were randomly assigned to one of four groups Three groups trained with isometric contractions three times per week at a knee flexion angle of 30, 60, or 90 degrees. The fourth group, which served as a control, did not exercise. Methods. Isometric torque was measured using a dynamometer, and EMG activity was measured using a multichannel EMG system. Measurements were obtained during maximal isometric contraction of the quadriceps femoris muscles at 15-degree increments from 15 to 105 degrees of knee flexion. Measurements were taken before and after 8 weeks of training. Results. Following isometric exercise, increased torque and EMG activity occurred not only at the angle at which subjects exercised, but also at angles in the range of motion at which exercise did occur. Further analyses indicated that exercising in the lengthened position for the quadriceps femoris muscles (90 [degrees] of knee flexion) produced increased torque across all angles measured and appeared to be the more effective position for transferring strength and EMG activity to adjacent angles following isometric training as compared with the shorter positions of the muscle (30 [degrees] and 60 [degrees] of knee flexion). Conclusion and Discussion. These findings suggest that an efficient method for increasing isometric knee extension torque and EMG activity throughout the entire range of motion is to exercise with the quadriceps femoris muscles in the lengthened position. [Bandy WD, Hanten WP. Changes in torque and electromyographic activity of the quadriceps femoris muscles following isometric training. Phys Ther. 1993;73:455-467.], Key Words: Electromyography; Exercise, general; Functional training and activities, Lower extremity, knee; Muscle performance, lower extremity. Isometric contractions are used for strengthening exercises in the rehabilitation of orthopedic and sports-related [...]

After axonal injury on postnatal day 14 (P14), but not P21, motoneurons in the spinal nucleus of the bulbocavernosus (SNB) do not display their normal response to circulating testosterone levels. This could result from a permanent disruption of communication between motoneurons and their testosterone‐sensitive target muscles. We assessed the extent of reinnervation of one of these target muscles, the levator ani (LA) muscle, 5 months after the pudendal nerve was cut either on P14 or P21. The number of motoneurons innervating the LA in control and nerve cut animals was determined using retrograde labeling procedures. Functional recovery of the LA muscle was determined via the testing of its in situ contractile properties. Compared to control muscles, reinnervated LA muscles were smaller, had fewer muscle fibers, generated a lower maximum tetanic tension, and were more fatigable. In spite of the fact that fewer motoneurons reinnervated the LA muscle after nerve cut on P14 than on P21, there were no differences in the weight or contractile properties of the LA muscle between these two groups. These data suggest that motoneurons that survived injury on P14 innervated more muscle fibers than normal and exhibited a similar ability to functionally reinnervate the target muscle as those motoneurons that survived injury on P21. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2005