Pressure and activity-related allodynia in delayed-onset muscle pain

Abstract

Objectives: Muscle pain from different activities was tested with the muscle pain expected to vary in ways that may clarify mechanisms of activity-induced exacerbation of myofascial pain.

Methods: Participants [N=20; 45% women; 23 y old (SD=2.09)] consented to participate in a 6 session protocol. Bilateral muscle pain ratings and pressure pain thresholds (PPTs) were collected before and for 4 days after lengthening (ie, eccentric) muscle contractions were completed with the nondominant elbow flexors to induce delayed-onset muscle pain. The muscle pain ratings were collected with the arms in several conditions (eg, resting, moving, and contracting in a static position) and PPTs were collected with the arms.

Results: In the ipsilateral arm, muscle pain ratings at rest and during activity significantly increased whereas PPTs significantly decreased after the eccentrics (ηs=0.17 to 0.54). The greatest increases in pain occurred during arm extension without applied load, in which there was more stretching but less force than isometrics. In the contralateral arm, neither muscle pain nor PPTs changed from baseline.

Discussion: These results resemble earlier electrophysiology studies showing differential sensitization across stimuli and support that increased depth of information about aggravating activities from clinical patients is needed.

Figure 1

Means and standard errors for the ratings of muscle pain intensity in the ipsilateral arm before and across 4 days after the eccentric contractions. Ratings at all time points increased from baseline when the ipsilateral arm was resting, flexing, and extending (p < .05). Ratings did not change significantly from baseline when the ipsilateral arm was maximally contracting in a isometric position.

Figure 2

Means and standard errors for the ratings of muscle pain unpleasantness in the ipsilateral arm before and across 4 days after the eccentric contractions. Ratings at all time points increased from baseline when the ipsilateral arm was extending (p < .05). Ratings at 1 to 4 days increased from baseline when the ipsilateral arm was resting, flexing, and maximally contracting in a static position (p < .05).

Figure 3

Means and standard errors for the pressure pain thresholds before and across 4 days after the eccentric contractions. Pressure pain thresholds at 1 to 3 days were significantly decreased from baseline for the ipsilateral arm. Pressure pain thresholds did not change significantly from baseline for the contralateral arm.