Relationships between Fibromyalgia Syndrome impact and muscle strength

A study, recently published in the journal Arthritis and Rheumatism, has found that more than half of Fibromyalgia Syndrome patients had significantly reduced knee muscle strength, but that muscle strength was not was not an indicator of how severe their Fibro was.

The aim of the study was to test the hypothesis that Fibromyalgia Syndrome (Fibro) patients with reduced lower extremity strength are more symptomatic and tender than Fibro patients with normal muscle strength.¹

For the study, a total of 840 Fibro patients and 122 healthy subjects were evaluated between 1998 and 2005.

All of the patients completed version 1 of the Fibromyalgia Impact Questionnaire (FIQ) and were assessed for tender points and knee muscle strength. All subjects underwent bilateral isokinetic knee muscle strength testing in flexion and extension.

Normative knee muscle strength values were calculated from the healthy subjects, and the Fibro patient group was divided in 2 groups: 1) patients with normal muscle strength and 2) patients with low muscle strength (2 SDs below normal). The clinical characteristics of these 2 groups were compared.

Significantly reduced knee muscle strength was found in 52% of the patients.¹

The researchers found that there were no clinically significant differences between patients with low versus normal muscle strength.¹

They also found that there were no clinically significant correlations between total FIQ score, tender point count, and muscle strength. Only 4.6% of the FIQ scores and 5.1% of the tender point counts could possibly be explained by muscle strength.¹

In conclusion:

"Significantly reduced knee muscle strength was found in more than half of the patients. Patients with subnormal muscle strength were not more symptomatic or tender than patients with normal muscle strength. There were no clinically significant correlations between FIQ, tender point count, and muscle strength; therefore, reduced knee muscle strength appears to be a common objective abnormality in [Fibromyalgia Syndrome] that is independent of measurements of disease activity. The implication of this finding in regard to the clinical assessment of [Fibromyalgia Syndrome] needs further study."

References:

1. Henriksen M, Lund H, Christensen R, Jespersen A, Dreyer L, Bennett RM, Danneskiold-Samsøe B, Bliddal H. Relationships between the fibromyalgia impact questionnaire, tender point count, and muscle strength in female patients with fibromyalgia: A cohort study. Arthritis Rheum. 2009 Jun 15;61(6):732-9.