MUSCLE STRENGTH, VOLUNTARY ACTIVATION AND CROSS-SECTIONAL MUSCLE AREAIN PATIENTS WITH FIBROMYALGIA

The objectives were to determine whether the low muscle strength in fi bromyalgia is due to lack of exertion and to determine the relation be tween strength and muscle area. Secondarily we examined the voluntary muscle strength of the different muscles of the leg. The twitch interp olation technique was used to estimate the degree of central activatio n and the 'true' quadriceps muscle strength. Muscle cross-sectional ar ea was determined with magnetic resonance imaging (MRI). The estimated 'true' muscle strength was 91 Nm (S.D. = 34 Nm) in 15 fibromyalgia pa tients compared with 125 Nm (28 Nm) in 14 healthy controls (P < 0.02). The 'true' strength divided by the sum of the maximal areas of the fo ur bellies of the quadriceps muscle was lower, being 1.56Nm/cm(2) (0.3 2Nm/cm(2)) in fibromyalgia patients compared with 2.11Nm/cm(2) (0.39Nm /cm(2)) in the controls (P < 0.001). The voluntary muscle strength of the flexor muscles of the knee and of the plantar flexors of the ankle was markedly reduced in patients, but no significant differences coul d be observed in the strength of the dorsal flexors of the ankle. In c onclusion, a reduction of the estimated 'true' quadriceps muscle stren gth per unit area of about 35% was found in fibromyalgia patients.