A follow-up study of muscle strength, muscle morphology, and enzymatic activity in 23 men, 73-83 years of age, was performed 7 years after the first investigation. With the exception of two men treated for congestive heart failure and four treated for hypertension, all were apparently clinically healthy and none had functional locomotor disturbances. Body weight was reduced by 2% and body cell mass by 6%, whereas the quadriceps muscle strength decreased 10%-22% over the 7-year period. Fiber composition in the vastus lateralis did not change significantly, and there was no significant difference between the biopsies from the biceps brachii and vastus lateralis. In the vastus lateralis, there was a reduction in fast-twitch fiber areas, which were smaller than in the biceps brachii (not studied at the previous investigation). There were also more histopathologic changes in the vastus lateralis than in the biceps brachii. The enzymatic activities of lactate dehydrogenase and myokinase, which were studied on both occasions in the vastus lateralis, did not change, and the activities of the other measured enzymes indicated a maintained metabolic capacity at high age. Oxidative enzymatic activities were higher in the vastus lateralis, and glycolytic enzymatic activities were higher in the biceps brachii, which could partly be explained by differences in relative fiber areas.

Nine men, 78-84 yr of age, participated in a dynamometer training program 2-3 times/wk, totaling 25 sessions, using voluntary maximal isometric, concentric, and eccentric right knee-extension actions (30 and 180 degrees/s). Measurements of muscle strength with a Kin-Com dynamometer and simultaneous electromyograms (EMG) were performed of both sides before and after the training period. Muscle biopsies were taken from the right vastus lateralis muscle. The total quadriceps cross-sectional area was measured with computerized tomography. Training led to an increase in maximal torque for concentric (10% at 30 degrees/s) and eccentric (13-19%) actions in the trained leg. The EMG activity increased at maximal eccentric activities. The total cross-sectional quadriceps area of the trained leg increased by 3%, but no changes were recorded in muscle fiber areas in these subjects, who already had large mean fiber areas (5.15 microns 2 x 10(3)). The fatigue index measured from 50 consecutive concentric contractions at 180 degrees/s decreased and the citrate synthase activity increased in all but one subject. The results demonstrate that increased neural activation accompanies an increase in muscle strength at least during eccentric action in already rather active elderly men and that muscle endurance may also be improved with training.

In 11 female patients with Fibromyalgia Syndrome (FS), biopsies from the m. vastus lateralis were analyzed, in order to reveal any possible changes which might explain muscular weakness and fatigue. Nineteen healthy subjects served as a control group. Light microscopy did not show any gross histopathological findings. Fiber composition and fiber areas did not differ between the two groups, except for a greater coefficient of variation of the area of type II A fibers and of the mean fiber area in the FS group. The number of capillaries per square millimeter and also the fiber area in relation to the capillaries, was lower in the FS patients. Analyses of enzymes showed decreased levels of 3-hydroxy-CoA-dehydrogenase and citrate synthase in the patient group. The reduced oxidative enzyme levels and capillarization indicate reduced physical activity, although this does not associate with muscle fiber hypotrophy.

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