No abstract

Muscle fatigue is the most disabling symptom in primary fibromyalgia (PF), which in addition is characterized by generalised pain and muscle stiffness. In order to assess whether the fatigue is of central and/or peripheral origin, skeletal muscle function was studied by measuring maximum voluntary hand grip strength, and by measuring various contraction characteristics in the adductor pollicis muscle after electrical stimulation of the ulnar nerve. The PF-patients were also studied after a regional sympathetic blockade of the forearm with guanethidine. A lower hand grip strength was found in the PF-patients compared to the controls, before as well as during the sympathetic blockade. The developed force, measured during electrical stimulation, did not differ between patients and controls. A lower muscle relaxation rate was found in the PF-patients. The relaxation rate increased in the PF-patients during the sympathetic blockade. The results indicate both a central and a peripheral cause of muscle dysfunction. Activity in the muscle sympathetic system may be one link in the chain of events that leads to muscular symptoms in PF.

Changes of the terminal innervation pattern in polymyositis were studied in nine patients using single fiber electromyography (SFEMG) and histochemical investigations of muscle biopsies. In all patients, and in 16 out of 18 muscles studied, reinnervation was found. The preceding denervation could be caused either by segmental necrosis of the muscle fiber that disconnects one part of the fiber from the end-plate region or by direct intramuscular nerve involvement.

Muscle fibre degeneration and regeneration, inflammation in intramuscular connective tissue and hypoxia in resting muscle are not necessarily associated with pain. However, when sustained or dynamic muscle contractions are performed in an ischaemic muscle, severe pain develops. In the chronic muscle pain syndrome called fibromyalgia (or fibrositis) the most likely cause of the pain is a combination of muscle tension and muscle hypoxia. This conclusion is supported by the finding of a pathological distribution of tissue oxygen tension in painful muscles and a subjective feeling of muscle tension and muscle stiffness in the majority of patients. A decrease in high energy phosphates is found in biopsies from painful muscle. The most characteristic morphological finding is the so called ragged red fibre, which is a finding that can been seen in mitochondrial disorders. The morphological and chemical findings are possibly a consequence of a long standing hypoxia. The possibility that activity in muscle sympathetic nerves is important for the development of chronic muscle pain is discussed.

Isometric muscle force was measured in 217 normal children aged 3.5-15 years. The standard error of a single determination made by the same observer was ca. 9% of the muscle force. When two measurements were made by different observers the standard error of the difference was estimated at ca. 17%. Reference values for isometric force are given for boys and girls separately. With regard to 7 of the 10 muscle groups tested the force was significantly greater in boys than in girls as early as at ca. 10 years of age. Age and weight were the most important predictors of muscle force.

Isometric muscle strength was measured in 63 women and 65 men, randomly selected, aged 17-70 years, using Penny & Giles' hand-held dynamometer. Eight muscle groups as well as the hand grip strength were tested bilaterally. The muscular endurance was measured as time to exhaustion in the abductors of the shoulder and the flexors of the hip. Reference values for muscle strength and muscular endurance are given in the age groups 17-18, 20-29, 30-39, 40-49, 50-59 and 60-70 years of age. The mean strength of females was about 65-70% of that of the men, but when the results were related to weight, the differences almost disappeared. Both men and women seem to have the greatest muscle strength at the age of about 17-18. The strength is rather constant up to the age of about 40 years, after which a discrete decline is seen up to about 60, from where the decline is more obvious. Muscular endurance showed great variability between individuals. However, no decrease in endurance was seen in older ages. For both sexes, lower reference limits of endurance, with the methods used, for arm abductors are suggested as being 3 minutes and for hip flexors, 90 seconds.

Adolescent patients with idiopathic scoliosis were treated with long-term electrical stimulation (30 Hz) at the posterior axillary line on the convex side of the curvature in order to correct the spinal deformity. The patients were also followed with muscle biopsies from the latissimus dorsi of the stimulated side taken before, after 3 and 6 months of electrical stimulation. There was a tendency for an increase in the percentage of type I and especially the type II C (undifferentiated) fibers after stimulation. The mean muscle fiber area and the fiber areas of the various fiber types did not change significantly. Histopathological findings were generally rare before as well as after 3 months of electrical stimulation, the only noticeable finding being a somewhat increased frequency of atrophic fibers in groups after 6 months of stimulation. In all studied patients the enzymatic activity of citrate synthase increased after 3 months and further in three studied patients after 6 months of stimulation. The present study gives some evidence of an adaptive process caused by electrical stimulation towards a more fatigue-resistant muscle.