Muscle strength, voluntary activation & cross-sectional muscle area in patients with fibromyalgia (FM)

The objectives were to determine whether the low muscle strength in
fibromyalgia is due to lack of exertion and to determine the
relation between strength and muscle area. Secondarily we
examined the voluntary muscle strength of the different
muscles of the leg. The twitch interpolation technique was
used to estimate the degree of central activation and the
'true' quadriceps muscle strength. Muscle cross-sectional area
was determined with magnetic resonance imaging (MRI). The
estimated 'true' muscle strength was 91 Nm (S.D. = 34 Nm) in
15 fibromyalgia patients 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 four bellies of the
quadriceps muscle was lower, being 1.56 Nm/cm2 (0.32 Nm/cm2)
in fibromyalgia patients compared with 2.11 Nm/cm2 (0.39
Nm/cm2) 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 could be observed in the strength of
the dorsal flexors of the ankle. In conclusion, a reduction of
the estimated 'true' quadriceps muscle strength per unit area
of about 35% was found in fibromyalgia patients.

Norregaard J, Bulow PM, Vestergaard-Poulsen P, Thomsen C,
Danneskiold-Samoe B

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