Modulation of pressure pain thresholds during & following isometric contraction in patients with fibromyalgia (FM) & in healthy controls

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This study aimed at evaluating the influence of submaximal

isometric contraction on pressure pain thresholds (PPTs) in 14

fibromyalgia (FM) patients and 14 healthy volunteers, before

and after skin hypoesthesia. PPTs were determined with

pressure algometry over m. quadriceps femoris before, during

and following an isometric contraction. Maximum voluntary

contraction (MVC) was assessed using a computerized

dynamometer. A contraction of 22% MVC on average was held

until exhaustion (max. 5 min) and PPTs were assessed every 30

sec.

A local anesthetic cream and a control cream were

applied following a double-blind design and PPTs were

reassessed. In healthy volunteers PPTs increased during

contraction (P < 0.001), then decreased after the end of

contraction (P < 0.001) but remained above precontraction

values during the 5 min of post-contraction assessments (P <

0.001). In FM patients PPTs decreased in the middle of the

contraction period (P < 0.05) and remained below

precontraction levels during the rest of the contraction

period (P < 0.05) and during the 5 min of post-contraction

assessment (immediately post-contraction NS; 2.5 min

post-contraction P < 0.01; 5 min post-contraction P < 0.05).

The normalized PPTs were significantly lower in patients than

in controls during contraction (start P < 0.01; middle P <

0.001; end P < 0.001) and at all times during post-contraction

assessments (P < 0.001). Anesthetic cream raised PPTs at rest

in controls (P < 0.01) but not in FM patients, and did not

influence contraction or post-contraction PPTs in either

group. Therefore, the increased pressure pain sensibility in

FM patients is more pronounced deep to the skin. The observed

decrease of PPTs during isometric contraction in FM patients

could be due to sensitization of mechanonociceptors caused by

muscle ischemia and/or dysfunction in pain modulation during

muscle contraction.

Kosek E, Ekholm J, Hansson P

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