Muscle force, perceived effort, & voluntary activation of the elbow flexors assessed with sensitive twitch interpolation in fibromyalgia (FM)

OBJECTIVE: To measure maximal voluntary strength and central
activation without fatigue, and to assess both peripheral and
central components of muscle fatigue of the elbow flexor
muscles, during exercise, in a group of patients with
fibromyalgia (FM) (n = 11). Results are compared with data
from control subjects (n = 36).

METHODS: Maximal voluntary
activation and strength of elbow flexors were quantified
using twitch interpolation during attempted maximal isometric
contractions both in unfatigued muscles and during fatigue
produced by 45 min of submaximal exercise.

RESULTS: Maximal
voluntary strength of the elbow flexors before and during
exercise was within the normal range. Central fatigue did not
develop to a greater extent in the patient group. No patient
had a decline in twitch amplitude during exercise below the
95% confidence limit for the decline in control subjects.
However, the increment in perceived effort (Borg Scale) was
abnormally large in 5 patients during the fatiguing exercise.

CONCLUSION: Neither poor motivation, reflex pain inhibition,
nor muscle contractile failure are important in the
pathogenesis of fatigue in patients with FM. However, the
subjective response to exercise is commonly excessive.

Miller TA, Allen GM, Gandevia SC

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